Immunology Outline

1. Introduction to Immunity and Hematopoiesis

a. Lymphatic System
i. Drains all tissues and transport lymphocytes and Ag from the tissues to
organized lymph tissue (eg MALT, lymph nodes) where lymphocytes can
interact with foreign antigen
ii. Series of 1-way valves to ensure lymph only flows in 1 direction
iii. Lymph is not pumped; it moves via movement of muscles
iv. As blood circulates, the fluid component (plasma) seeps into surrounding
tissues via capillaries.
1. Most return to blood
2. Some (now called lymph) flow from c.t. into lymphatic vesicles and
empties into the L subclavian v
b. Lymphoid Organs
i. Primary Lymphoid Organs
1. Site of lymphocyte development and maturation (where immune cells
are born/developed)
a. Bone Marrow
i. Major site of hematopoiesis
ii. Site of B cell development and maturity
b. Thymus
i. Bilobed organ located above the heart
ii. Site of T cell development and selection
iii. Develops up until about point of puberty, then regresses
to fat
iv. DiGeorges Syndrome
1. Congenital birth defect where thymus fails to
develop
2. As a result, there is an absence of circulating T cells
and increased # of infections
ii. Secondary Lymphoid Organs
1. Environment where lymphocyte interacts with antigen (where immune
cells go to find work)
a. Lymph nodes (LN)
i. Encapsulated, bean shaped, contains network of
lymphocytes, macrophages, and dendritic cells
ii. 1st lymph tissue to encounter antigen
iii. As lymph from tissues percolate through LN, any Ags will
be trapped by phagocytic and dendritic cells
b. Spleen
i. Large, ovoid, situated in L abdominal cavity
ii. Composed of 2 major compartments
1. Red pulp
2. White pulp
a. Immune powerhouse of the spleen
b. Function: to trap antigens that get into the
blood
iii. Unlike LN, spleen is adapted to filtering blood and
trapping blood-borne antigens
iv. One can live w/o a spleen, but will be susceptible to
certain types of infection
1. Sickle cell pts can sometimes have functional
asplenia

c. Loose Clusters of Lymphoid Tissues

i. Not as structured as the spleen but still does a good job
ii. Mucosal Associated Lymphoid Tissue (MALT)
1. Appendix
2. Peyers patches
3. tonsils
iii. Cutaneous Associated Lymphoid Tissue (CALT)
c. Hematopoiesis
i. The formation and development of red and white blood cells from stem cells
ii. Begins in the yolk sac (as a fetus), then migrates to the fetal liver and spleen
iii. As gestation continues, the bone marrow becomes the major site of
hematopoiesis, and remains there during the lifetime of that individual
iv. Hematopoiesis initiates the bone marrow from pluripotent hematopoietic
stem cells (PHSC)
v. Pluripotent hematopoietic stem cells
1. Can self-renew
2. Does not proliferate very quickly
3. Resistant to radiation, but takes several weeks to make again
4. Are capable of developing into all cells of the blood lineage
5. Relatively rare population of cells representing only 1-2% of total bone
marrow
d. Clinical importance of stem cells
i. BM transplants
1. Must carefully match MHC to prevent graft rejection
ii. Graft vs. host disease (GVHD)
iii. Gene therapy
1. Used to treat Severe Combined Immunodeficiency (SCID)
a. No B cells or T cells are made
2. Used to treat adenosinedeaminase (ADA) deficiency
a. Replace the gene in HSCs (hematopoietic stem cells)
e. Cluster of Differentiation Antigens (CD markers)
i. Proteins present on the cell surface
ii. Most cell populations have unique CD markers (CD4, CD8)
iii. Some CD markers are shared (CD3)
iv. Recognized by monoclonal antibodies
f. CD Antigens
i. Used to determine lineage (where the cell comes from)
ii. Used to determine maturation (is it a progenitor cell or mature?)
iii. Used to determine activation (is it activated?)
iv. Common CD markers
1. CD4 (TH)
2. CD8 (TC)
3. CD3 (all T cells)
4. CD14 (macrophages)
5. CD16, CD56 (NK cells)
6. CD19, CD20, CD21 (all B cells)
7. CD34 (stem cells)
g. Immune System Cells
i. Lymphoid cells
1. There are 1010-1012 lymphocytes in the human body
2. Continuously circulate in the blood and lymph
3. Cannot be differentiated based on morphology
4. Nave cells
a. B/T cells that have not come in contact with antigens
b. Small (6um) lymphocytes (resting cells in G0)

c. When they contact an Ag, they progress from G 0 G1, then S,

G2, M, enlarge to 15um and eventually differentiate into memory
and effector cells
d. If they do not come in contact w/ their designated Ag, they will
eventually die
5. B cells
a. Born in the bone marrow
b. Develops and matures in the bone marrow
c. Develops into plasma cells and memory cells
i. Plasma cells secrete Ab
ii. Memory cells will react quickly on second response
d. Specifically recognize antigens
e. Membrane-bound Ig serves as receptor for antigen
f. All clonal progeny from a given B cell secrete Ab molecules with
the same Ag binding specificity
g. Main job: to secrete Ab
h. Help us against EXTRACELLULAR PATHOGENS
i. Can hit a bacteria/fungi on the outside of the cell
6. T cells
a. Born in the bone marrow
b. Develops and matures in the thymus
c. Specifically recognize antigens
d. Membrane receptors for Ag, similar to Ig (TCR=T cell receptor)
e. TCR only recognizes Ag in association with MHC (MHC has to
present Ag in order for T cells to receive the info)
f. 2 major subsets (2:1)
i. TH (CD4+) = Helper T cells have CD4+ marker
1. The 4 looks kind of like an H
2. Recognize antigen in association w/ class II MHC
(exogenous antigen)
3. Activated following recognition of Ag-class II MHC
on antigen presenting cells (APC)
4. Activated TH cells divide and give rise to clones of
effector cells which secrete various cytokines and
play a major role in B cell, and TC cell activation
5. TH1 activates TC and M
6. TH2 activates B cells
ii. TC (CD8+) = Cytotoxic T cells have CD8+ marker
1. CD8 it ate the cell
2. Recognize antigen in association with class I MHC
(endogenous antigens)
3. Activated following recognition with Ag-class I MHC
complex
4. Secretes few cytokines
5. Directly recognizes and kills target cells (virus
infected and intracellular bacteria)
7. Null Cells (NK cells)
a. Are not specific, but they come from the same cells as B and T
cells (lymphoid stem cells)
b. Has large granular lymphocytes
c. No B/T cell markers has CD16 and 56
d. No specific receptor for Ag (Ig/TCR) (nonspecific)
e. Cytotoxic activity against a wide array of tumors
i. Activation of NK cells leads to degranulation via perforin

ii. Apoptosis
1. FasL on the NK cell binds w/ Fas on the target cell
and induces the target cell to commit suicide
f. Responsible for killing viral infected and transformed cells
(ADCC)
g. NK cell killing
i. Kill cells that have decreased MHC Class I expression
ii. Have 2 types of receptors
1. Inhibitory recognizes MHC chains
a. All cells express MHC. If it doesnt, it either is
infect or is transformed so it no longer makes
it it needs to die
2. Stimulatory possibly recognizes(?) lectins
conserved among many pathogens
h. Chediak-Higashi (autosomal recessive) disease
i. No NK cells
ii. Increased incidence in lymphomas
ii. Mononuclear cells
1. Macrophages (M)
a. Monocytes are found in blood; macrophages are found in tissue
b. Develop in the BM & enter the blood where they differentiate
into mature monocytes
c. Monocytes circulate in blood for ~8hrs, then migrate into tissue
and differentiate into specific tissue macrophages
i. Alveolar macrophages lungs
ii. Histiocytes connective tissues
iii. Kupfer cells liver
iv. Mesangial cells kidney
v. Microglial cells Brain
d. Macrophage function: phagocytosis
i. Activity can be enhanced by TH cytokines
ii. Activated M are more efficient at eliminating pathogens
than resting M
iii. Activated M have:
1. Increased phagocytic activity
2. Increased ability to activate TH cells
3. Higher levels of Class II MHC on the cell surface
2. Granulocytes
a. Neutrophils
i. Granulated cytoplasm that stains w/ acidic and basic dyes
ii. Multi-lobed nucleus
iii. Formed in BM, released into blood, migrate 7-10hrs, then
home to the tissue where they have a 3day lifespan
iv. In response to infection, BM releases more neutrophils
(aka leukcytosis)
v. 1st type of cell at the site of infection
b. Eosinophils
i. Granulated cytoplasm stains w/ acidic dye (eosin)
ii. Bilobed nucleus
iii. Phagocytic, but less important than neutrophils
iv. Major role against parasites
v. Secretion of eosinophilic granules result in damage to the
parasite membrane
c. Basophils

i. Granulated cytoplasm that stains with basic dye

(methylene blue)
ii. Lobed nucleus, but nucleus is not visible d/t granules
iii. Non-phagocytic
1. Releases pharmacologically active substances
contained within granules
iv. Involved in allergy reactions
d. Mast Cells
i. Precursors formed in the BM during hematopoiesis and
released into the blood
ii. Do not differentiate until they leave the blood and enter
the tissue
iii. Involved in allergies
3. Dendritic Cells
a. Named because of long processes resembling dendrites of nerve
cells
b. Constitutively express high levels of class II MHC and B7, thus
better APCs than M and B cells
c. After capturing Ag in the tissues, it migrates into blood or lymph
and circulate to various lymphoid organs where they present Ag
to T cells
d. Can function as phagocytic cells
e. Tissue dendritic cells
i. Langerhans cells epidermis and mucous membranes
ii. Interstitial dendritic cells most organs
iii. Interdigitating T cell zones of secondary lymph tissue
and thymic medulla
iv. Circulating dendritic cells blood
v. Follicular dendritic cells exclusively located in follicles
of LN (B cell rich)
1. Dont express class II MHC
2. Dont function as APC for TH cell activation
3. Have many receptors for Ab/C3 and bind circulating
Ag-Ab complexes
4. Ag-Ab complexes can be retained on FDC
membranes for weeks to years
5. Role in formation of memory B cells.
2. Innate Immunity
a. The immune system has two types of immunity
i. Innate (native, natural)
1. What we have when we are born; is the same all our life
2. Nonspecific and rapid
3. Involves
a. Physical barriers
b. Phagocytosis
c. Complement system
d. Interferons
e. Lysozymes
4. Induces fever and inflammation
ii. Adaptive (acquired, specific)
1. What we acquire as we live; gets better as we get older
2. Specific and slow, then rapid
3. Is inducible
4. Involves

b.

c.

d.

e.

a. Memory response
b. Antibodies
c. B and T cells
Professional phagocytes
i. Phagocytosis = cell eating
1. Extension of pseudopodia
2. Formation of phagosome
3. Fusion with lysosome to form phagolysosome
4. Digestion
5. exocytosis
ii. Cells that eat for a living
1. Neutrophils
a. Toll receptor
b. CR3, CR4 complement receptors
c. CD14 (LPS receptor)
d. F-met peptides receptor receptor for formal peptide on
bacteria; formal peptide is a formal group that is found on the
very first amino acids of bacterial proteins
2. Macrophages
a. Receptors
i. Toll receptor
ii. CR3, CR4 complement receptors
iii. CD14 (LPS receptor)
3. Eosinophils & basophils (to a lesser extent)
4. B cells can also be phagocytes
iii. Macrophages and neutrophils share some form of common receptor
1. LPS receptor (CD14) for gram bacteria
2. CR# = complement receptors one of the most important types of
receptors; is shared btwn neutrophils and macrophages
Opsonization
i. Phagocytes have membrane receptors for IgG and C3b
ii. Enhance phagocytosis up to 4,000-fold (increases binding efficiency of
phagocytes)
iii. IgG is the ONLY Ab that can do opsonization
Phagocytic Killing Mechanisms
i. Engulfment
1. Bug attaches to phagocyte and gets swallowed
2. Oxygen dependent killing
a. NADPH oxidase
i. Generates toxic oxygen radicals
ii. Deficiencies result in chronic granulomatous disease and
can be severe
b. Myeloperoxidase
i. Generates hypochlorite (bleach)
ii. Deficiencies are usually mild to asymptomatic
3. Oxygen independent killing (best by far)
a. Inducible nitric oxide synthetase (iNOS) generates nitric oxide
(NO) in both phagocytic cells and non-phagocytic cells
b. Cathepsin G, a neutral protease
c. Lactoferrin
d. Lysozyme
e. Defensins
f. Is like a BB gun/throwing rocks. Not that effective.
Cytokines secreted by macrophages

i. IL-1, TNF-, IL-6 are pro-inflammatory cytokines (promote inflammatory

response)
1. Can produce additional cytokines that can increase the response
2. Induction of acute-phase proteins (sometimes are complement
proteins, eg CRP)
ii. CXCL8 (IL8), IL-12 are essential to immune system in other ways
f. Activation of Macrophages induces inflammation
i. Phagocytosis production of cytokines recruit ment of neutrophils
diapedesis inflammation
g. Inflammation
i. Initial response to infection (innate)
ii. Recruitment of WBCs
iii. Rolling adhesion
1. Selectins
a. Vascular endothelium: P-selectin, E-selectin
b. Neutrophil: sialyl lewis carbohydrates on WBC
iv. Tight binding
1. Integrins
a. Vascular endothelium: ICAM-1
b. Neutrophils: LFA-1 and CR3
v. Diapedesis (transendothelial migration)
vi. Migration
h. Leukocyte Adhesion Deficiency
i. Rare autosomal disease
ii. Absence of CD18 (common B2 chain of integrins)
iii. Leukocytes cannot migrate from blood into tissues, neutrophila
iv. Omphalitis (infection/inflammation of umbilical cord)
v. Chronic recurrent bacteria infections
vi. No abscess or pus formation (WBC dwere not able to reach site of infection bc
they couldnt latch onto the wall and undergo diapedesis
i. Type I Interferons
i. Consists of interferon (INF-) and interferon (INF-)
1. INF- produced by leukocytes
2. INF- produced by fibroblasts
ii. Produced by the viral-infected cell & protects neighboring cells via IFN
receptors
iii. Functions:
1. Induce resistance to viral replication in all cells
a. Degrades mRNA inhibits protein synthesis
i. Shuts down cellular protein synthesis (NOT VIRAL
SPECIFIC) (INNATE!)
2. Increase MHC class I expression and antigen presentation in all cells
3. Activate NK cells to kill virus-infected cells
3. Complement
a. What is it?
i. A number of blood proteins produced by the liver, spleen, and macrophages
primarily. Originally discovered because of their ability, when activate, to lyse
antibody-coated RBCs
ii. Consists of proteins C1-9, factors B, D, P (properdin), and numerous inhibitors
of the pathway.
iii. Some factors are cleaved into proteolytic fragments such as C3 to C3a and
C3b
1. The b fragment is usually the larger fragment and have biological
activity

iv. Essentially, it is a cascading group of proteins.

b. 3 complement pathways
i. Classical
1. Requires antibodies in order to be activated
ii. Alternative
iii. Lectin
1. Set off by mannose residues
iv. When activated, they
1. Induce inflammation
2. Lyse certain infectious agents
3. Opsonize infectious agents
4. Clear immune complexes
c. Complement Activation
i. 3 different activators detect pathogens and activate C3
1. Convergence at C3 results in a membrane attack complex (MAC)
2. Larger proteins (b fragments for the most part) acquire enzyme activity
3. Smaller proteins (a fragments mainly) have biological activity and aka
anaphylatoxins
a. C3a & C5a can bind to mast cells and basophils w/o IgE and
cause them to degranulate
b. C3a, C4a, or C5a can all bind on to mas cell receptors and cause
degranulation with symptoms similar to allergies
ii. Lectin
1. Mannan binding lectin (binds to CHO on bacteria)
iii. Classical
1. Involves antibodies and antigens (immune complexes)
2. IgM and IgG activate classical. Think GM is a classic
3. Process
a. Begins with binding of pentameric IgM or 2 molecules of IgG
b. C1 is recruited to bind to the Ab
c. Once C1 binds, it brings other complementary molecules.
i. For each molecule that comes, it is cleaved into 2
fragments a fragment (binds to the complex) and b
fragment (floats away)
ii. C2 does the opposite C2a binds and C2b floats away
iii. C3 becomes a convertase (we want a lot of C3a and C3b)
iv. C5 finally binds, which activates the enzymatic activity
v. C5-C9 are the components that begins the MAC
(membrane attack complex) which forms a pore on the
surface membrane of the pathogen
iv. Alternate
1. Spontaneous lysis of C3; if it binds to bacteria, the pathway will be
initiated
d. So what is complement?
i. Complement effectors
1. Opsonization
a. Bacteria and other cells are delivered to phagocytes for
destruction in an efficient way
b. Molecules that aid this process = opsonins
i. IgG & complement C3b
c. Occurs via complement receptors
d. Enhances phagocytosis up to 4,000x more efficient
2. Clearance of immune complexes
a. Immune complexes (Ag & Ab complexes) are insoluble lattices

b. Immune complexes trigger inflammation and type III

hypersensitivity reactions
i. High level of C3b disrupts immune complexes making
them soluble
ii. C3b on immune complexes can bind to the C1 receptor on
RBCs and taken to the liver/spleen where they can be
removed by professional phagocytes
3. Anaphylatoxins
a. C3a and C5a split products diffuse away from the site of
complement activation
b. Can cause degranulation of mast cells and basophils without IgE
c. Results
i. Plays a major role in the inflammatory response
ii. C5a is a major chemotactic protein for inflammation
iii. Increase vascular permeability, stimulate phagocytosis
4. MAC
a. Pore-forming molecules C5-C9
b. Lyses the cell
c. Does not work for Gram + bacteria
d. Appears to be critical only for protection against Neisseria
infections
e. Deficiency in C5-C9 in Nesseria infections
e. What goes up must come down
i. Complement is a very important inflammatory mediator.
ii. After threat, needs to be turned off this is the job of complement inhibitors
4. Adaptive Immunity
a. When does adaptive immunity show up?
i. When physical barriers fail (eg cut in skin)
ii. When innate immunity is unable to clear infection (eg d/t stress, malnutrition)
iii. As a preventative step (eg artificial prevention, vaccination)
b. Adaptive immunity initiation does not start until about 5 days after the 1 st exposure.
It takes some time to get going, but once its seen the antigen, the next exposure
will have a faster response
c. Specificity
i. Characteristic of adaptive immunity; selectivity in response to antigen
interaction
ii. Is important because you want to have a specific interaction with one specific
antigen, not all antigens in the body
iii. Is generated via clonal selection
d. Memory
i. Created by T cells for future exposures to the same antigen; allows for a
faster response on subsequent exposures. The memory varies depending on
the antigen.
ii. Is important to protect the body and prevent the organism from coming back
e. Primary Response v. Secondary Response
i. IgM is always one of the 1st Ab at the scene (primary response)
ii. Next, there is a shift to IgG
iii. On the secondary response, there is a spike in IgG at the start of the
exposure
iv. **every time we see a spike in IgM, we know that it is a primary response for
that particular antigen**
f. Artificial active immunity
i. Made famous by Dr. Jenner and little James Phipps (cowpox story)
g. Artificial passive immunity

i. Eg would be taking an anti-venom/Ab to treat a snake bite. Theres not

enough time for the individual to make his own Ab by the time their
immune response begins, they may be dead. So, the Ab is given so that the
body can respond right away.
h. Cells of the adaptive immune response
i. Lymphocytes
1. Small lymphocytes
2. B lymphocytes attack outside the cells
a. Respond to large structures (hence would be outside of a cell)
3. T lymphocytes attack within the cells
a. Respond to small peptide (that would be located within a cell)
b. Cytotoxic T cells
c. Helper T cells
i. Clonal Selection
i. Necessary because there are a lot of antigens out there and you cant react
to all of them. There must be specificity/selectivity.
ii. Ramifications somewhere along the way in clonal selection, youll react to
yourself (autoimmunity). Body is supposed to filter out the antigens that are
self but sometimes it does not.
j. B cell receptors Immunoglobulins
i. B cell receptor (BCR)
1. Variable region is the reactor; what makes the specificity
2. Constant region is the base
k. What is an antibody?
i. Immunity conferring proteins
ii. Membrane bound or secreted
iii. Recognizes antigens (different from T cells which can only recognize a single
small peptide/protein)
1. Proteins, lipids, carbohydrates, nucleic acids, and chemical groups,
parts of macromolecules, capsules
iv. Aimed at extracellular microbes, toxins
v. Neutralizes microbes
vi. Target microbes for elimination (opsonization)
l. Cell-Mediated Immunity
i. Differ from Humoral (B cells)
ii. Membrane receptors only
iii. Aimed at intracellular pathogens
iv. Recognizes peptides displayed by MHC molecules on APC
1. Linear epitopes (small, little pieces)
5. The Humoral Immune System
a. Antibodies
i. Associated with humoral immunity protection of things that are
EXTRACELLULAR
ii. Found in the gamma globulin fraction of serum
iii. Antibody = an immunoglobulin
iv. Major line of defense against bacteria (extracellular pathogens)
1. Opsonization
2. Neutralization
a. Neutralization of toxin prevent them from binding to receptors
to cause symptoms
3. Antibody dependent cellular cytotoxicity (ADCC)
a. Cell mediated function
v. Basic structure
1. 2 identical heavy chains

2. 2 identical light chains

3. Heavy and light chains
a. Variable & constant regions
b. Disulfide bonds link the chains together
c. Light chains have 2 domains, 1V and 1 C
d. Heavy chains have 4-5 domains, 1V and 3-4 C
4. Variable region
a. Binds to the antigen
b. Allows for specificity
c. Aka Fab
d. Consists of a heavy chain and a light chain
5. Constant region
a. Determins the function
b. Aka FC
c. Determines: complement activation, opsonization, antibody
dependent cellular cytotoxicity, crossing placenta, etc
d. Determines isotype of Ab (IgG, IgM, IgA, IgE, IgD)
b. Antibody Gene Rearrangement
i. 5 heavy chain classes, 2 light chain classes
ii. Heavy & light chains are encoded by multiple gene segmetns
iii. Variable (V), diversity (D), and joining (J) segments compose the variable
region of the heavy chain while only V and J segments are used to generate
the light chains.
iv. Creates an incredible amount of diversity
c. Heavy Chain Rearrangement
i. Always start first. Once this is complete without any errors, then light chain
rearrangement will be initiated.
ii. Chain rearrangement refers to creating genetic variability of the VARIABLE
REGION of the chain.
iii. In every cell of our body, we have several V, D, and J regions in the DNA, but
it only gets rearranged or work in the heavy/light chains.
iv. Process
1. RAG (recombinating activating genes) RAG1 + RAG2; are the
location of these V, D, J segments
2. Recombinase, an enzyme only expressed in B/T cells, facilitates the
recombination
a. First it picks out a D and J section that it wants to join and lyses
out the rest.
b. DNA repair enzymes fuse the two sections together.
c. Recombinase then picks a V segment that it wants and lyses out
the rest.
d. Again, DNA repair enzyme fuses the sections together.
e. In the end, one will end with an DNA with gene sections in the
order of V, D, J, and C.
3. This undergoes transcription and translation, producing a protein which
is the heavy chain.
4. First constant region to follow the variable region is always C
5. Once heavy chain is made, it sits around and wait for the light chain so
it can complete its process of forming an Ab
6. The first Ab/Ig heavy chain to be made is IgM (for an initial infection)
d. Light Chain Rearrangement
i. Once heavy chains are rearranged properly, well get a light chain
rearrangement
ii. Light chains dont have D, just V & J

iii.
iv.
e. What
i.

f.

Rearrangement occurs just like in heavy chain

Once light chain is made, it gets escorted to the heavy chain
promotes diversity
Multiple germline gene segments can come together to give different levels
of diversity
ii. Combinatorial V-J, V-D-J joining gives specificity
iii. Random association of H and L chains
iv. Somatic hypermutation
v. P-nucleotide addition (Palindrome)
vi. N-nucleotide addition (randomly being put in by Tdt)
vii. TDT (terminal deoxynucleotidal transferase)
1. Adds random nucleotides in between the D and J chains on one end,
causing DNA polymerase to have to add the complementary
nucleotides to the other end. Makes the strands more random/diverse
viii. Allelic Exclusion
1. Even though cells are diploid, a given B cell will only express the
rearranged H chain genes from only 1 chromosome and the L chain
from only 1 chromosome
2. This ensures antigenic specificity
3. Eg: we get one H chain from each of our parents (H m and Hd). We also
get 2 L chains from each of our parents (m d m d). When we
rearrange the H chain gene, we will exclude one of the alleles. (Moms
v. Dads). When we rearrange the L chain gene, we will exclude 3 of
the alleles. Lets say the first lambda allele from mom didnt work out,
we have one more from dad that we can work on. If that one works,
then we will exclude the rest. If it does not work, then we would keep
going until one passes.
Immunoglobulin Classes (isotypes)
i. IgG
1. heavy chain
2. can participate in many immune functions including
a. opsonization
b. antibody dependent cellular cytotoxicity (ADCC)
c. activation of classical complement
d. only antibody that can cross the placenta
3. is the predominant antibody in the serum
4. is a high affinity antibody and predominates during the secondary
immune response
ii. IgM
1. heavy chain
2. predominant Ab made during the primary immune response
3. first Ab made in neonates
4. can activate the classical complement pathway
5. pentameric in serum
6. high avidity, low affinity
a. avidity = # of binding sites; affinity = how well it binds
7. monomeric IgM, part of the BCR
iii. IgA
1. heavy chain
2. predominant Ab in the secretions: mucosal surfaces, saliva, tears,
nasal fluids, sweat, colostrum and breast milk
3. in secretions present as a dimer
4. protected in secretion by secretory piece

a. binding of IgA to a poly Ig receptor helps it move through

epithelial cells
b. When it passes through the mucosa, it holds onto the receptor,
which becomes the secretory component of IgA. It acts like IgAs
body guard which protects it from enzymes in the mucosa
5. next highest avidity after IgM
iv. IgE

v.

g. B Cell
i.

ii.

h. B Cell
i.

ii.

i.

B Cell
i.

1. heavy chain
2. low levels in plasma
3. binds to mast cells and basophils
4. main Ig against parasites
5. Type I hypersensitivity reactions
IgD
1. heavy chain
2. Low levels in plasma
3. Mature B cells membrane bound
4. Antigen receptor on B cells
Development and Activation
Antigen independent stage
1. Occurs in the BM
2. Involves the development of B cells from hematopoietic stem cells
through a series of defined intermediates
3. Molecules that are expressed
a. Tdt occurs only during Ig heavy chain gene rearrangement
b. MHC II
c. CD19, CD20, CD21, CD40
i. CD40 plays an essential role in class switching
Antigen dependent stage
1. Occurs in the periphery
2. Involves the development of mature B cells to memory and plasma
cells
3. Nave resting B cell becomes an activated B cell
a. Once activated, the B cell will form memory B cells and plasma
cells.
b. Upon the next exposure to the pathogen, the memory B cell will
form plasma cells
c. Activation of B cell occurs in the periphery after it comes in
contact with an antigen
d. It is responsible for the generation of plasma and memory cells
Receptor / Pre B Cell Receptor
Pre B cell Receptor
1. M heavy chains
2. 5, VpreB
3. Lg and lg
B Cell Receptor
1. IgM or IgD
2. Ig and Ig
3. Immature IgM only
4. Mature IgM and mature IgD
Selection
Immature B cell in bone marrow undergoes selection to become mature
1. If it has no self-reaction migrates to periphery and becomes a
mature B cell

2. If it binds to multivalent self-antigen undergoes clonal deletion and

apoptosis
3. If it binds to soluble self-antigen migrates to periphery and becomes
an anergic B cell (nonreactive cell)
j. What occurs in germinal centers?
i. Germinal centers cen be found in lymph nodes & in spleen
ii. Only found where something is happening, not found in normal, healthy
lymph nodes or spleen
iii. What occurs
1. Class switching
2. Plasma cell or memory cell
3. Somatic hypermutation results in increased Ab affinity
k. B cell activation
i. T cell independent antigens
1. Stimulate B cells directly without T cell hehlp
2. Results in weaker Ab responses
3. IgM predominates as the Ab because there is no T cell help, no class
switching to different Ab isotopes
4. Higher avidity molecules induce crosslinking of BCRs on B cell surface
ii. T cell dependent antigens
1. Require T cell help
2. Results in stronger Ab responses
3. CD40/CD40L interaction is essential for class switching (Hyper IgM
syndrome)
4. Process:
a. B cell binds to antigen and undergoes a process similar to
phagocytosis. It breaks the antigen into small pieces and spits it
back on the cell surface with an MHC receptor to show/react with
a T cell.
b. TCR binds to B cells MHC with Ag presented
c. CD20 from T cell binds to a receptor on the B cell. CD40 from B
cell binds to CD40L from T cell
d. T cell releases cytokines to B cell
i. IL-4 promotes class switching to IgG and IgE
ii. IL-5 promotes class switching to IgA
e. B cell becomes activated and proliferates
5. Take note that signal transduction is an important step for B cell
activation.
a. Involves tyrosine kinase Syk, which contributes to the protein
cascade
i. If Syk was not inducible, it would cause
leukemia/lymphoma
b. CD19, CD20, CD21 function as corecptors, which lowers the # of
Ab the cell needs to get activated
6. 3 important events occur during this stage of development
a. Class switching
i. This is the hallmark of humoral immunity
ii. REQUIRES T cell help (CD40-CD40L)
iii. After communication with the TH cell, the B cell rearranges
the constant region
iv. Is a one way event (can only class switch once)
v. Does not affect variable domain (only the constant region
is changing)
vi. Occurs after a B cell has come in contact with an antigen

6. Major
a.

b.

c.

vii. Hyper-IgM Syndrome

1. X-linked failure to express CD40L on TH cells
2. As a result, IgM levels go up to 10 times the normal
3. Also, there will be a deficiency of IgG, IgA, and IgE
4. The body will fail to make germinal centers
5. Symptoms include recurrent respiratory infections
b. Plasma/memory cell formation
i. B cells have 2 choices after contact w/ Ag
1. Make plasma cells
a. Secrete buckets of Ab
2. Make memory cell
a. Hang out in the periphery and await arrival
of same pathogen
c. Affinity maturation
i. In the course of a humoral response, the avg affinity of
the Ab produced increases by 100-10,000 fold
ii. This is a result of somatic hypermutation & the Ag
selection of high affinity clones
1. Somatic mutation point mutations, deletions, or
insertion into the V, D, or J region of rearranged Ig
genes
a. Majority of mutations occur in the CDR (CD
receptor?)
2. Higher affinity Ab are positively selected, lower
affinity Ab are signaled to die by apoptosis
d. Note, these are also the highlights of germinal centers, which
probably mean they occur there
Histocompatibility Complex and Antigen Processing
The MHC
i. Genetic loci shared w/ every mammalian species
ii. Named for role in tissue transplantation (graft rejection)
1. In humans, its called the HLA (human lymphocyte antigens)
iii. MHC molecules expressed by an individual partly determines their response
to an Ag.
1. Thus, MHC plays a role in susceptibility to disease & autoimmunity
HLA Locus
i. 3 classes of HLA are found on chromosome 6
1. Class I (A, B, C) Cytotoxic T cells
2. Class II (DP, DQ, and DR) Helper T cells
3. Class III Non-Classical HLA
ii. Highly polymorphic
iii. Expression is co-dominant
1. Everything is getting expressed no repressed allele (all alleles from
both parents are expressed)
HLA Function
i. Bind antigenic peptides and present them to T cells
1. HLA Class I
a. Main role: present viral antigens to TC cells
b. Responsible for presentation of endogenous antigens (viral,
made within our cells)
c. Expressed on all nucleated cells (except sperm & neurons)
i. This is bc viruses can infect any nucleated cell
d. Highly polymorphic

i. Many types of alleles for each category, while a person

only has a maximum of 2 alleles
ii. 229 A alleles, 464 B alleles, and 111 C alleles
e. Composed of a 3-domain chain and 2 microglobulin (coded
outside of MHC)
i. 1 and 2 domains form an antigen binding cleft to bind
to short peptides approximately 8-10 aa in length
1. viral peptides that are larger than 8-10 aa are sent
through a proteasome prior to binding
ii. there is a hydrophobic transmembrane domain
iii. 2 microglobulin is REQUIRED for proper folding of the
molecule
1. It holds the HLA in the right conformation so the
binding cleft stays open
f. HLA Class I molecules are in the ER and pathogenic peptides are
in the cytoplasm. In order to get the HLA loaded, TAP1 and TAP2
are used
i. TAP = transporter of antigen processing; intermembrane
protein that acts as a tunnel to transport antigen to HLA
g. From the ER, HLA Class I and its antigen is moved to the cell
surface via vesicular transport through the golgi
2. HLA Class II
a. Main role: present bacterial antigens to TH cells
b. Responsible for presentation of exogenous antigens
(extracellular bacteria, made outside our cells)
c. Expressed on antigen presenting cells (APCs), including
macrophages, B cells, and dendritic cells
d. Highly polymorphic
e. Composed of an 2-domain chain and a 2-domain chain that
come together to form a cleft that binds peptides of ~12-15 aa
in length
i. There is a hydrophobic transmembrane region
ii. 1 and 1 combine to form the peptide binding cleft
(hotdog shape)
f. HLA Class II molecules are in the ER and the exogenous antigen
is taken into the cell via phagocytosis. For them to meet, the
vesicle transporting the HLA fuses with the vesicle with the
phagocytosed pathogen.
g. Before the pathogen antigen is reached, an invariant chain is
bound to the peptide binding groove to inhibit any unwanted
endogenous peptide binding.
ii. Antigen Processing
1. Process by which peptides get loaded into the HLA and presented to T C
or TH cells
2. Peptides come in 2 flavors:
a. Endogenous (intracellular pathogens, viruses) which bind to
Class I HLA
b. Exogenous (extracellular pathogens, extracellular bacteria)
which bind to Class II HLA
iii. HLA Susceptibility and Disease
1. Over 100 diseases have been linked to different HLA antigens

2. HLA diseases appear to be inherited and do not follow simple

Mendelian genetics
3. The diseases are most often immunological; many are considered
autoimmune
a. Autoimmune diseases are more affected by women d/t
hormones on immune system
b. Majority of autoimmune diseases are associated w/ Class II HLA
i. For some reason those HLA types bind self peptides
with a higher affinity than foreign peptides
iv. Cytokine and Viral Regulation of HLA Expression
1. IFN- and TNF can increase the expression of Class II MHC by inducing
the formation of specific transcription factors that bind to promoters of
MHC genes
2. MHC expression is also increased, but more commonly decreased, by a
certain # of viruses (CMV, HBV, and adenovirus)
3. CMV proteins can bind to 2 to microglobulin preventing the proper
assembly of Class I MHC molecules
7. Cytokines
a. Overview
i. Chemical messengers of immune system
1. Low molecular weight proteins secreted by WBC (and other cell types)
in response to stimulus
ii. Cytokine is broad term for many small immune modulating proteins
1. Include: interferons, chemokines, interleukins
2. Chemokine: cytokine that functions in chemotaxis
a. Attract WBC to site of inflammation
b. Cytokine signaling: Overview
i. Bind to specific receptors on target cell
1. Activates signal transduction pathways
a. Ultimately alters gene expression
2. Bind receptors with high affinity
a. Picomolar concentrations can mediate biological effects
3. Act as autocrine, paracrine, or endocrine factors
4. Regulate intensity and duration of immune responses
a. Stimulating or inhibiting cellular:
i. Activation
ii. Proliferation
iii. Differentiation
c. Effects of Cytokine Signaling
i. Cytokines exhibit:
1. Pleiotropy
a. One cytokine can elicit multiple functions on multiple cells
2. Redundancy
a. Many different cytokines are able to elicit the same function on a
particular cell
3. Synergy
a. Two or more cytokines can work together to induce one function
on a cell
4. Antagonism
a. Cytokines can block each others effect on a particular cell
d. Interactions of Cytokine Signaling
i. Cytokine signaling plays a very important part in the immune system
ii. Specifically, IL-2 is VERY important for the production of T cells. Without it,
the activated TH cell cannot produce T cells, including TC cells and NK cells.

e. Cytokine Signaling Receptors

i. There are 4 types of cytokine receptors that receive the cytokine signal.
Without these receptors, the signal cannot be process and no cellular change
will occur.
ii. Receptors can share subunits
1. IL-2 and IL-4 share the gamma chain of IL-2R
a. IL-2 causes T- and B-cell proliferation
b. IL-4 causes B cells to make different antibodies
2. Mutations in chain of IL-2 R lead to SCID
f. Laundry List of Cytokines
i. Interferons
1. , , and
2. IFN- and IFN- are antiviral
a. IFN- used to treat HBV, HCV, HHV-8
b. IFN- used to treat multiple sclerosis
3. IFN- activates macrophages to stimulate intracellular killing and
inhibits TH2 response
a. IFN- used to treat chronic granulomatous disease
b. Pro-inflammatory cytokine, specifically made by CD4 TH1 cells
i. Eg: TB hangs out inside macrophages. If its living in
there, macrophages cant present it to B cells. CD4 T cells
will come along and see the helpless macrophage and
make interferon gamma. This will help kill the bacteria
inside the cell (intercellular bacterial infections)
ii. Interleukins
1. 1, 2, 3, 4, 5, 6, 7, 8, 10, 12
2. IL-1 & IL-6
a. Pro-inflammatory
i. Induce liver to make acute phase proteins
ii. Induce febrile response
3. IL-6
a. Stimulates hematopoiesis
b. Acts on plasma cells to drive Ab production
i. Can help w/ Ab switch to IgG (although IL-4 is more
important for this)
c. Clinical uses of IL-6 inhibitors
i. MRA (anti-IL-6 receptor) used to treat Rheumatoid arthritis
4. IL-2
a. Made by T cells
i. Autocrine regulation
b. Stimulates growth and differentiation of T cells (T H and CTL), B
cells, and NK cells
c. Clinical uses of IL-2
i. Monoclonal Ab
1. Directed toward alpha chain of the IL-2R blocks
IL-2 signaling
2. Increases success of organ transplants
3. Experimental treatment of leukemia and
melanomas
ii. Side effect: lots of risk of infections; heavily
immunosuppresses the pt.
5. IL-4 & IL-5
a. Made predominantly by TH2 cells
i. IL-4

b.

1. Promotes class switching from IgM to IgE and IgG

a. Inhibits IFN- production
ii. IL-5
1. Promotes class switching to IgA
a. TGF- is also required
2. Induces eosinophil development/differentiation
Clinical IL-4 inhibitors
i. Monoclonal Ab
1. Used to treat serious allergies

6. IL-10
a. Made predominantly by macrophages
b. Down-regulates pro-inflammatory cytokine production
c. Activates B cells
i. Promotes TH2 response
7. IL-12
a. Made predominantly by macrophages
b. Induces differentiation of TH cells to TH1 cells
i. Thought to be first cytokine responsible for stimulating
immune response
ii. Synergizes with IL-18 to induce IFN- from TH1 cellsS
iii. Tumor Necrosis Factor
1. TNF-
a. Was initially discovered as a cytokine with ability to kill tumor
cells
i. Alpha is made by macrophages, T cells, and fibroblasts
ii. Beta is made by activated T cells and B cells
b. Creation of TNF- will initiate a cascade of rxns that lead to
more cytokine production
2. Clinical uses of TNF- inhibitors
a. Monoclonal Ab to inhibit TNF-
i. Ends in -mab = monoclonal Ab = Ab against TNF-
b. Used to treat chronic inflammatory disease
i. Eg: Rheumatoid arthritis, Crohn, Psoriasis
c. Side effect of anti-TNF-
i. Increased susceptibility to disease
iv. Pyrogenic Cytokines
1. IL-1, IL-6, TNF-
2. Induces the hypothalamus to increase body temperature and
fat/muscle to mobilize protein and energy to create increased body
temperature
a. This decreases viral & bacterial replication, increase Ag
processing, and facilitates adaptive immune response
g. Chemokines
i. Attract leukocytes to site of inflammation
1. IL-8 (neutrophils)
a. Neutrophils look for IL-8 to know where to go; its the most
potent chemotracking component for neutrophils
2. RANTES (T cells/monocytes)
3. Eotaxin (eosinophils)
h. Hematopoietic Cytokines
i. Growth Factors (biological Wheaties)
1. IL-3 growth factor for wBC
2. IL-7 growth factor for lymphocytes (B/T cells)
ii. Colony stimulating factors (CSF)

1. GM-CSF: growth factor for hematopoietic stem cells and

granulocytes/monocytes
2. M-CSF (macrophage): essential for macrophage production
3. G-CSF (granulocyte): essential for neutrophils
4. Erythropoietin (EPO): growth factor for RBC
Cytokine

Secreted by:

Target cell or tissue

IL-1

Monocytes macrophages, B
cells dendritic cells,
endothelial cells

IL-2

TH1 cells

Activated TH cells and

CTLs

Proliferation, enhanced killing

IL-3

TH cells

Hematopoietic cells

Growth factor

IL-4

TH2 cells

B cells

Activation, class switching to IgE +

IgG

IL-5

TH2 cells

B cells

Activation, class switching to IgA

IL-6

Macrophages, TH2 cells

1.
2.
3.

1.
2.
3.

TH cells
Hepatocytes
hypothalamus

B cells
Hepatocytes
hypothalamus

Activity
4.
5.
6.

4.
5.
6.

Costimulatory
Acute phase protein induction
Fever

Differentiation into plasma

cells and Ab production
Acute phase protein induction
Fever

IL-7

Bone Marrow /thymic

stromal cells

B and T cell precursors

Differentiation

IL-8

Macrophages

Neutrophils

Chemotaxis

IL-10

Macrophages

Macrophages, TH cells

Down-regulation of pro-inflammatory
response

IL-12

Macrophage

TH cells

Promotes differentiation of TH cells

into TH1 cells

IFN- and
IFN-

Leukocytes and fibroblasts

Infected cells

Inhibits viral replication

IFN-

TH1

Macrophages

Activation

TNF-

Macrophages

Inflammatory cells

Induces cytokine secretion, cachexia

G-CSF

Macrophages and TH cells

Bone marrow
precursors

Granulocyte development

GM-CSF

Macrophages and TH cells

Bone marrow
precursors

Granulocyte and macrophage

development

8. Cell Mediated Immunity

a. T Cell Receptor (TCR)
i. The TCR differs from the BCR in 2 major ways
1. TCR is never secreted (always cell bound)
2. TCR must recognize antigen + MHC and NEVER free antigen
ii. Heterodimer composed of either or chains
1. Beta/delta chain is analogous to heavy chain
2. Alpha/gamma chain is analogous to light chain
iii. Resembles an Fab fragment (1 arm of an Ab molecule)
iv. Can ONLY bind to proteins/peptides
b. CD3
i. Signaling molecule for T cells (analogous to Ig and Ig on B cells)

ii. Composed of 5 proteins lodged in the membrane:

1. , , , and either homodimer or heterodimer
iii. non-covalently attached to TCR
iv. T cell activation and differentiation
v. Is often a molecule of focus for T-cell autoimmune disease and transplants
1. Interfering with CD3 will dampen T cell activation
c. TCR Gene Rearrangement
i. Occurs in a similar manner to Ig gene rearrangements in B cells
ii. () chain of TCR is like heavy chain of Ig
iii. () chain of TCR is like light chain of Ig
iv. Beta chain rearranges first. If no problems occur, then alpha chain will
rearrange
d. T Cell Development
i. T cell development and maturation occurs in the thymus
ii. Progenitor T cells are released from the bone marrow and migrate to the
thymus where they receive their thymic education
1. Positive selection
2. Negative selection
e. Thymus
i. Bilobed organ situated above the heart; divided into loboles
ii. Cortex
1. Immature lymphocytes
2. Selection occurs here
a. 5% of T cells pass and go on to become a T cell
3. Nurse cells (specialized epithelial cells)
iii. Medulla
1. Cells that survive selection
2. More mature thymocytes
iv. Pro-T cells leave the BM and cant recognize antigen
v. Undergo differentiation in the thymus
vi. Intimate association with thymic stromal cells required
1. Thymic epithelial cells, macrophages, and dendritic cells
vii. Thymic events
1. CD4-CD8a. When the T cell leaves the BM and first enters the thymus, it has
no markers
2. CD4+CD8+ (TCR+)
a. When they begin development in the thymus, they turn on all
expression so they have all the markers
3. CD4+CD8- (TCR+) or CD4-CD8+ (TCR+)
a. During selection, they become specialized. They downregulate
either CD4 or CD8, depending on the type of cell they will
become. (A mature T cell has EITHER CD4 or CD8, not both)
b. CD4 TH cell binds to Class II MHC exogenous antigen
i. CD4 stabilizes MHC II/TCR interaction
c. CD8 TC cell binds to Class I MHC endogenous antigen
i. CD8 stabilizes MHC I/TCR interaction
f. Selection
i. There are 2 forms of thymic selection:
1. Positive selection ensures that the TCRs expressed in a given
individual will bind to self MHC (essentially, to make sure that the TCRs
work)
a. T cell binds with low affinity to MHC + self protein pass
positive selection

g. T Cell
i.

ii.

iii.

b. If it cant bind to MHC apoptosis

i. Occurs w/ double positive cells
c. Issues with + selection immunodeficiencies (no CD8/CD4 cells
no protection against pathogens)
2. Negative selection ensures that thymocytes bearing a high affinity for
self MHC or self Ag+self MHC are removed from the repertoire
(essentially, to make sure that the TCRs dont work TOO well)
a. T cell binds with low affinity or not at all to self MHC complete
maturation into single positive CD4 or CD8 T cells
b. T cell binds with high affinity to self apoptosis
c. Issues with selection auto-immune diseases (T cells will
begin to react with self)
Activation
T cells that have matured in the thymus leave and enter the periphery in
search of antigen
1. These T cells are considered nave until they come in contact with
antigen
T cells initially come in contact with antigen in secondary lymphoid tissue
(secondary lymphoid tissue (spleen, and lymph nodes) and tertiary lymphoid
tissue)
The interaction of TCR w/ antigen+MHC initiates activation, but other signals
are required

h. APCs
i. The only cells that can present antigens to T H cells
ii. Has to do w/ the co-stimulatory molecules present on APCs
1. A molecule called B7 is only constitutively expressed on dendritic cells
(IDC)
a. Dendritic cells are the only cells that activate nave T cells
b. Macrophages can only activate nave T cells when activated by
IFN-
c. B cells can activate nave T cells after contact with antigen
i. TH cell Activation
i. TH cell + APC exchange mutual activation signals
1. Cytokines
a. IL-4, IFN- from the TH cell activate B cells and macrophages
respectively
b. Macrophages secrete IL-1, IL-6, and TNF-
2. New cell surface markers
a. TH cell expressed IL-2R and secrete IL-2
b. Co-stimulatory molecules CD28 (TH) and B7 (B)
c. CTLA-4 (inhibitory molecule)
d. Adhesion molecules
3. DNA binding proteins that regulate the cell cycle
j. Signaling in T cells
i. Once the TCR/Ag+ MHC interaction occurs, signals are transduced through
the cell which result in activation
1. Phosphorylation of ITAMs on CD3
2. Recruitment of Zap-70 which becomes a tyrosine kinase (TK)
a. Zap-70 is one of the main tyrosine components; its docking on
the MHC-Ag-TCR complex initiates a lot of the T cell activation
changes
b. Expressed in both T and B cells

c. Usually if we see it in patients with leukemia, its a poor

prognosis
3. Increase in intracellular calcium
ii. Activation = changes in gene expression, functional changes, differentiation,
cell division, cytokine production
k. Superantigens
i. SAGs are viral or bacterial proteins that bind to particular V regions of TCR
and regions of MHC OUTSIDE of the peptide binding cleft (instead of where
it should bind the binding cleft)
1. This means less specificity and activation of numerous clones of T cells
2. Can cause problems like Toxic Shock Syndrome
ii. Comes in 2 flavors:
1. Endogenous
2. Exogenous
l. Cell Mediated Immunity (CMI)
i. Extracellular infectious agents are cleared by Ab, complement, and
phagocytes
ii. Intracellular infectious agents, all viruses and some bacteria, require an
entirely different line of defenses (CMI)
iii. With CMI, the goal is to destroy the intracellular gene by destroying the host
cell that harbors it
iv. Viruses always require CMI for effective clearance
v. Intracellular bacteria and parasites or fungi induce delayed type
hypersensitivity via TH1 and M activation
vi. Like humoral immunity, CMI requires TH cell help (TH1-IFN- and IL-2)
vii. Effector cells
1. CTL (cytotoxic T lymphocyte), CD8+
a. Class I MHC restricted and endogenous peptides
b. Clonal expansion of CTLs and full effector function requires IL-2
from an activated TH1 cell
c. Perforin
i. Membrane punching, pore forming molecule
d. Granzymes
i. Enzymes that damage the target cell
e. Cytokines
i. IFN- and TNF- are secreted by CTL
ii. Induce metabolic changes in target cells that lead to
apoptosis
f. Fas and FasL
i. CTLs express FasL and target cells express Fas
ii. Interaction between Fas and FasL causes apoptosis
m. T Cell Subsets and Interleukins
i. divided into 3 functional subsets based on the cytokines they secrete
ii. TH0
1. secrete IL-3, GM-CSF, IFN-, IL-2, IL-4, and IL-5
2. can differentiate into TH1 or TH2
iii. TH1 (Cell Mediated Immunity)
1. delayed type hypersensitivity helping the development of CD8 + TC cells
2. produces IFN-, IL-2, TNF-, IL-3 and GM-CSF
3. down regulates TH2 response via IFN-
iv. TH2 (Humoral Immunity)
1. help produce antibody
2. class switching
3. proliferates eosinophil and mast cell precursors

4. produces IL-4, IL-5, and IL-10

5. downregulates TH1 responses via IL-10
v. Function of TH subsets
1. Intracellular pathogens TH1 cells are made really contributes to
CMI
a. IFN- (activates macrophages), IL-2 (T cell proliferation and
activation) are made
2. Extracellular pathogens TH2 cells are made humoral immunity is
activated
a. IL-4, IL-5, IL-10 are made
n. Regulatory T cells
i. T regs
1. Committed to regulatory fate while in thymus
2. Requires TGF- for development
3. Prevents/limits the activation of T cells
a. Cytokines
b. Direct contract (killing)
i. Mechanism unknown
4. Deficiencies result in severe immune dysregulation and autoimmunity
ii. TH17
1. CD4+, RORT
a. Produces IL-17 and IL-17F which act on endothelial cells to
promote inflammation
b. IL-22 which acts on keratinocytes to increase defensins (skin
immunity)
2. Clearance of pathogens that are not adequately handled by the T H1 TH2
cells
3. Potent inducers of inflammation/autoimmunity
a. Psoriasis, rheumatoid arthritis, multiple sclerosis, IBD, and
asthma
b. Hyper IgE syndrome (Job syndrome)
o. Delayed Type Hypersensitivity Reaction (DTH)
i. Macrophages are often targets for infection with intracellular pathogens
1. Listeria
2. Mycobacterium
3. Toxoplasma
4. Leishmania
ii. The release of cytokines like IFN-, from TH1 (TDTH cells) activates
macrophages
iii. Activated macrophages kill any ingested organisms
iv. Activated macrophages also kill abnormal infected (transformed) cells
(nonspecifically)
v. Oxygen metabolites (H2O2 and O2-), nitric oxide, and TNF-
9. Ontogeny of an Immune Response
i. Dendritic cells
1. Dendritic cells is the term we give to immature IDCs
2. Interdigitating dendritic cells (IDC)
a. The only cells capable of activating nave T cells
3. Follicular dendritic cells
a. Do not express Class II MHC
b. Have long dendrites with C and AB receptors
c. Retain immune complexes and help in the formation of memory
and plasma cells
ii. Secondary lymphoid tissues

1. Where does the ag go when it enters the body?

a. Lymph Nodes
i. If the Ag penetrates the tissues, it will be cleared by the
draining lymph nodes
ii. Encapsulated lymphoid organs found throughout the
body, connected via lymphatics
iii. Ag check in, but they dont check out
iv. Separate compartments for B and T cells
v. Anatomy
1. Afferent lymphatics
2. Efferent lymphatics
3. Post capillary venules
4. Cortex
a. B cell area
b. Composed of primary follicles containing
small, resting B cells and follicular dendritic
cells (FDC?)
c. After challenge with Ag, the lymph node
forms secondary follicles with a corona of
concentrically packed resting B cells
surrounding a germinal center
d. Germinal centers consist of FDCs and
dividing B cells which can differentiate into
plasma cells and memory cells.
5. Paracortex
a. T cell area
b. Primarily T cells and IDC (increased Class II)
c. Neighbors to B cell area (good for activation)
6. Medulla
a. Plasma cells secreting antibody
b. Spleen
i. If the Ag enters the blood, it will be cleared by the spleen
ii. Large, encapsulated organ situated high in the L
abdominal cavity
iii. Not supplied by lymphatic vesicles
iv. Ag are carried in by the splenic artery
1. Blood borne antigens!
2. Splenic artery is a large end artery.
3. All white cells will eventually go through the spleen
no need to recruit nave white cells.
v. Separate compartments for B and T cells
vi. Anatomy
1. Red pulp location of venous sinuses
2. White pulp where PALS is located, surrounded by
the marginal zone
3. B cells
a. Found in the marginal zone (around the
white pulp)
b. Arranged in follicles
c. After Ag arrives, it can form secondary
follicles
4. T cells
a. Surround the artery in the periarteriorlar
lymphoid sheath (PALS) (white pulp)

c. Mucosal Associated Lymphoid Tissue (MALT)

i. If the Ag enters the GI or respiratory tract, they will be
cleared by the MALT
ii. Diffuse collections of lymphocytes, plasma cells, and
phagocytes
iii. Found in lung and intestine
iv. Tonsils, Peyers patches and appendix are more organized
v. Forms a separate secretory system in which plasma cells
secrete large amounts of IgA
vi. Mucosal immunity
1. Ag enters the Peyers patches across specialized
cells called M cells which are lying in the mucosa
a. These cells will take the Ag and deliver it to
MALT
2. After activation, lymphocytes enter lymph, go
through MLN (mesenteric lymph nodes) and
thoracic duct
a. They pass from the blood back into the
lamina propria and become IgA secreting
plasma cells
iii. The Response to Antigen
1. Pathogen in tissue
2. Pathogen gets taken up by dendritic cell
3. Dendritic cell enters afferent lymphatic
4. Immune cell activation
a. T cells are presented Ag
b. Effector lymphocyte results. (effector lymphocyte = T helper cell
that becomes TH1/TH2 makes cytokine OR TC cell that becomes
NK cell OR B cell that becomes plasma cell makes Ab)
5. T cell goes back into the blood and goes to site of infection
a. Recruited via inflammatory factors, eg neutrophils
iv. Lymphocyte Trafficking
1. Lymphocytes (B or T cells) must be able to continuously circulate
through the secondary lymphoid tissues in order to increase the
chances that they will come in contact with Ag
2. Once a lymphocyte recognizes Ag, w/I 24 hrs of Ag localizing in the LN,
Ag-specific lymphocytes are depleted from circulation.
a. They are all in the LN or spleen to be activated
3. The flow of B and T cells through the secondary lymphoid tissues is
directed by cell adhesion molecules (CAMs) and specialized
endothelial cells called high endothelial venules (HEVs)
a. Major CAM to know: Integrin (CD18)
i. Mediates tight binding to allow for binding between 2 cells
for diapedesis to occur
b. CAM
i. Selective gateways to the lymphoid organs
ii. Organize the traffic through the secondary lymphoid
tissue
iii. CAMs on the lymphocytes recognize CAMs on endothelial
cells
iv. Can be best observed via transmigration of activated or
memory lymphocytes (and neutrophils) through the blood
vessel walls into the tissues

v. Importance of CAMs
1. Demonstrated by leukocyte adhesion deficiency
(LAD)
a. Rare, autosomal recessive disease
b. Characterized by recurrent bacterial
infections and impaired wound healing
c. Leukocytes cant extravasate from blood
vessels into tissues leading to more frequent
and more severe bacterial infections
d. No pus or abscesses are found on the PT bc
the WBCs are unable to get to the site of
infection
e. One of the 1st signs of LAD = omphalitis
(infection of umbilical cord)
f. Another sign of LAD = very high WBC in
blood (signals keep being sent to BM to make
more cells bc cells arent reaching the
infection site)
c. Lymphocyte Homing
i. Nave lymphocytes specifically recirculate though
secondary lymphoid tissues by the recognition of high
endothelial venules (HEV) of the postcapillary venules
1. Nave cells have a special complementary receptor
to HEVs to let them know they are going through it.
v. Transmigration
1. Rolling
a. Selectins on the lymphocyte bind CD34 on the vascular
endothelium
2. Attachment
a. Above interaction activates 2 integrins
3. Arrest and adhesion
a. 2 integrins change conformation and bind very strongly to ICAM
molecules on the surface of the vascular endothelium
4. Transendothelial migration
10.Immunodeficiency Diseases
a. Primary immunodeficiencies
i. Inherited
ii. Autosomal recessive
1. Rare
2. Before 1950s, most patients died in childhood making it difficult to
pass the gene on
iii. X-linked Recessive
1. More common
2. Affects mostly men because they have only 1 copy of X
b. Development of Humoral Immunity in Infants
i. In fetal life, most humoral immunity is coming from maternal IgG
ii. Should the fetus get an infection, at some point, it can start making Ab on its
own
1. Best way to see if fetus was infected see if it has IgM (mothers IgM
cannot pass placenta)
2. We cant use IgG as an indicator of fetal infection because maternal
IgG can pass placenta
iii. After birth, infant starts building its own IgG.

1. It receives some maternal IgA if mother breastfeeds

iv. Infant vaccinations do not begin in the first year
1. Infant is still carrying some of the mothers Ab vaccinations would not
protect child from future pathogen exposures
2. Must wait until after 12 months when maternal Abs are gone and infant
has its own Ab
c. Types of Immunodeficiencies
i. Defects in phagocytic cell function
1. Phagocytic Deficiencies
a. Phagocytosis = a primary means for the removal of extracellular
bacteria from the body.
b. Defects reveal an inability to clear infections
c. Can result from a reduction in the numbers of phagocytic cells or
form a reduction in their function
d. In each case, the hallmarks are recurrent bacterial or fungal
infections
i. Range from mild skin infections to life threatening
systemic infections
ii. Frequent infections with S. aureus, S. pneumoniae, E. coli,
Pseudomonas, Candida, Aspergillus
2. Chronic Granulomatous Disease (CGD)
a. Mutation in one of 4 genes for NADPH Oxidase
i. Deficiency of NADPH oxidase failure to generate O2
radicals
b. X-linked
c. Symptoms:
i. Severe and recurrent infections with catalase positive
organisms
1. Staphylococcus, Klebsiella, Serratia, Candida,
Pseudomonas, and Aspergillus
ii. Infections, if unresolved, lead to the formation of
granulomas
d. Dx: Use the NBT test
i. Nitroblue Tetrazolium Reduction (NBT)
1. Used to look for presence of NADPH oxidase
2. Take some cells and incubate them in Nitroblue
Tetrazolium
a. If there is NADPH oxidase NBT is used and
cell converts to a blue color (POSITIVE TEST,
NEGATIVE FOR DISEASE)
b. If there is no NADPH oxidase cannot
convert NBT and cell stays a yellow color
(NEGATIVE TEST, POSITIVE FOR DISEASE)
e. Tx: Abx & IFN-
i. BM transplant is controversial but can cure CGD
3. Leukocyte Adhesion Deficiency (LAD)
a. Rare autosomal recessive
b. Absence of CD18 (common 2 chain of integrins)
c. Leukocytes cannot migrate
d. Symptoms
i. Omphalitis
ii. Chronic recurrent bacterial infections
iii. No abscess or puss formation

iv. Patients suffer w/ recurrent pyogenic infections, impaired

wound healing and severe gum inflammation
e. Dx: CBC reveals leukocytosis and flow cytometry can determine
the presence or absence of cell adhesion molecules
f. Tx: bone marrow transplant (Tx of choice), Abx, IFN-
4. Chediak-Higashi
a. Rare, autosomal recessive disorder
b. Affects the synthesis and maintenance of storage granules in
many cell types, including neutrophils, melanocytes, monocytes,
NK cells
c. Phagocytosed material is not delivered to the lysosomes
because of a fusion defect
i. Granules cant be moved; they just accumulate within the
cell, causing the cell to swell
d. Symptoms
i. Recurrent bacterial infections
ii. No NK activity increased incidence of lymphomas
iii. Chemotactic & degranulation defects
iv. Partial albinism bc melanocytes are affected
e. Dx:
i. Labs routine blood smear
1. Results will reveal giant granules and neutropenia
f. Tx: bone marrow transplant (BMT) and high doses of gamma
globulins
5. G6PD deficiency
a. Defect: deficiency of essential enzyme in hexose monophosphate shunt
b. Symptoms: same as CGD w/ associated anemia (need G6PD to
get to NADPH oxidase)
6. MPO deficiency
a. Defect: granule enzyme deficiency
b. Symptoms: Mild or none (usually asymptomatic)
7. Job Syndrome
a. Defect:
i. TH1 cells cant make IFN-
1. No IFN-, cant shut down TH2 lots of TH2
problems excessive IgE and allergies
ii. PMNs dont respond to chemotactic stimuli (PMN = ?)
b. Symptoms
i. Coarse facies
ii. Cold abscesses
iii. Retained primary teeth
iv. Increased IgE
v. eczema
ii. Defects in complement
1. Manifest similar to phagocytic deficiencies and Ab deficiencies
2. Major sequelae associated with complement deficiencies
a. Defects in opsonization
b. Defects in lytic activity
c. Defects in clearing of immune complexes
i. C prevents immune complexes from forming
ii. C aids in the clearing of immune complexes
3. C3 deficiency
a. Most severe of the complement defects

i. Defects in opsonization, chemotaxis, clearance of immune

complexes and lysis
b. Increased susceptibility and severity of pyogenic bacteria
c. Dx: Clinically presents at an early age with severe infections
from encapsulated bacteria
d. Tx: Abx
4. MAC deficiency
a. C5-C8 (MAC) deficiency
b. Pts have increased susceptibility and severity of infections with
the genus Neisseria
c. Neisseria species (N. gonorrhoeae and N. meningitidis) are
particularly susceptible to complement mediated destruction
d. MAC deficiencies present later in life are associated with less
morbidity and mortality
e. Tx: 3rd and 4th generation cephalosporins
5. Hereditary Angioedema (HAE)
a. Autosomal dominant, affects 1:1000
b. C1inh deficiency
c. Leads to uncontrolled activation of the classical pathway
d. Overproduction of C2, which is extremely vasoactive, leads to
accumulation of fluid and swelling (edema)
e. Over use of C1, C4, C2; edema at mucosa surfaces
f. Usually noticeable after trauma
g. Swelling in esophagus or GI can be fatal
h. Treated with commercial C1inh or fresh frozen plasma
i. Androgens like stanozolol suppress the symptoms of HAE
6. Deficiencies of Complement
a. Classical pathway
i. Defect: C1q, C1r, C1s, C4, C2
ii. Symptoms: increased immune complex diseases,
increased infections with pyogenic bacteria
b. Alternative pathway
i. Defect: Factor B, properdin
ii. Symptoms: increased Neisserial infections
c. Both pathways
i. Defect: C3
ii. Symptoms: recurrent bacterial infections, immune
complex disease
iii. Defect: C5, C6, C7, C8
iv. Symptoms: recurrent meningococcal & gonococcal
infections
iii. Defects in B cell development or function
1. Usually characterized by recurrent bacterial infections w/ normal
immunity to virus and fungal parasites
2. Most common infections include Staphylococcus and Streptococcus
because Ab is critical for the opsonization and clearance of these
organisms
a. X-linked agammaglobulinemia
i. Mutation in a tyrosine kinase (Brutons tyrosine kinase,
btk) important in a development of pre-B cells to mature B
cells
1. ONLY HUMORAL DEFECT WITH NO B CELLS
ii. Pts have difficulty with encapsulated bacteria like H.
influenzae, S. pneumoniae, S. pyogenes, and S. aureus

b.

c.

d.

e.

and increased severity of viral infections that affect the

gut (enteroviruses)
iii. Symptoms:
1. Decrease Ig in all classes
2. No circulating B cells
3. Pre-B cells in bone marrow are normal, normal CMI
iv. Usually appears around 6 months of age and 80% present
w/ pneumonia and other sinopulmonary infections
v. Tx: IV injections of gamma globulin & Abx as needed
X-linked hyper IgM (defect in class switching)
i. Mutation in CD40L on T cells
ii. CD40L is necessary for T cell Communication with B cells
and the formation of specific Ab, therefore there is no
class switching (to Abs other than IgM) and no germinal
centers formed
iii. Increased levels of IgM
1. No IgA, IgG, or IgE
iv. Symptoms: Pts usu have recurrent bacterial infections and
severe diarrhea
v. Tx: monthly gamma globulin injections and Abx as
needed
Selective IgA deficiency
i. Most common of the Immunodeficiency diseases (1:800)
ii. Gene componenet not known
iii. In some patients, we can detect anti-IgA; in others the
IgA+ B cells dont differentiate into plasma cells
iv. Symptoms: Pts can be asymptomatic to presenting w/ an
increased incidence of respiratory tract infections,
infections at mucosal surface
v. Tx: Abx are needed. (NOT IVIG)
Common variable hypogammaglobulinemia
i. Aka late onset agammaglobulinemia
ii. Heterogenous disease
iii. Associated w/ increased incidence of autoimmunity
iv. Occurs in late teens, early 20s
v. Ig levels decrease with age
vi. Inadequate T cell:Bcell signaling so that B cells cant
differentiate into plasma cells
vii. B cells can be found in the periphery, low Ig levels
viii. Symptoms:
1. Pts present w/ recurrent bacterial infections
2. B cells present in blood
3. Ig levels decrease over time
4. Increased autoimmunity
ix. Tx: IV gamma globulin and Abx
Hypogammaglobulinemia of infancy
i. Aka Transient hypogammaglobulinemia of infancy, aka
early onset agammaglobulinemia
ii. Delayed onset of normal IgG synthesis, usually seen in the
5th to 6th month of life
iii. Usually resolves by 2-6 years of age
iv. Symptoms: Pts usually have recurrent respiratory
infections; infections with pyogenic bactiera
v. Tx: Abx & gamma globulin replacement

iv. Defects in T cell development or function

1. Because T cells orchestrate the immune response, T cell deficiencies
can affect both the humoral and cell mediated responses
2. Much more severe than the previously discussed disorders
3. Patients usually have increased incidence of fungal and viral pathogens
a. DiGeorges Syndrome
i. Autosomal dominant mutation
ii. Reflects a failure of the 3rd and 4th pharyngeal pouches to
develop between weeks 10-12 of gestation (development
of aortic arch of heart)
iii. Symptoms:
1. Absence of a thymus
2. Cardiovascular anomalies
3. Characteristic facial features
4. Recurrent infections w/ intracellular pathogens,
Candida (Chronic mucocutaneous candidiasis), and
viruses
iv. Tx: fetal thymic transplants and bone marrow transplants
b. Bare Lymphocyte Syndrome aka MHC deficiency
i. MHC Class I deficiency
1. Defect: failure of TAP 1 molecules to transport
peptides to ER
2. Clinicals
a. CD8+ T cells decrease; CD4+ T cells are
normal
b. Recurrent viral infections
c. Normal DTH (Delayed Type Hypersensitivity?)
d. Normal Ab
ii. MHC Class II Deficiency
1. Autosomal recessive mutation
2. Presentation similar to DiGeorges (SCID)
3. Defect:
a. Failure of MHC Class II expression TH cells
cant develop
b. Defects in transcription factors
4. Clinical:
a. Deficient in CD4 cells
b. No GVHD (graft v. host disease? =??)
c. Decreased in Igs
d. Observed as SCID
5. Tx: BMT
v. Combined B and T cell deficiencies
1. Usually comprises of both the humoral and cell mediated arms of the
immune system
2. Pts are susceptible to any type of pathogen, even those in low
virulence
a. Severe Combined Immunodeficiency disease (SCID)
i. Mutations in RAG 1/2 , ADA (adenosine deaminase), and
PNP (purine nucleotide phosphatase) are autosomal
recessive whereas mutations in the IL-2R chain (shared
by several cytokines) are X-linked
ii. Defect:
1. Defect in common of IL-2 receptor (present in
receptors for IL-4, 7, 9, 15)

2. X-linked
3. Adenosine deaminase deficiency
4. Rag1 or Rag2 gene nonsense mutations
iii. Clinical
1. Chronic diarrhea
2. Skin, mouth, throat lesions
3. Opportunistic infections
4. Recurrent infections with bacteria, fungi, and
viruses
5. Circulating LC
6. Cells unresponsive to mitogens
7. Total absence of B and T cells
iv. Tx: BMT, gene therapy
b. Wiskott-Aldrich Syndrome
i. Complex X-linked disorder
ii. Mutation in leukosialin (CD43), which is responsible for
actin filament assembly and cytoskeletal rearrangement
necessary for T cell signaling
iii. Severity increases with age and usually results in fatal
infections or lymphoid malignancy
iv. Clinical
1. Decreased response to bacterial polysaccharides
2. Decreased IgM
3. Gradual decrease in HMI and CMI
v. Triad of symptoms
1. Thrombocytopenia (decrease of platelets)
2. Eczema
a. Eczema + low platelets bleeding problems
3. Immunodeficiency
vi. Tx: IVIG & corticosteroids
1. BMT are preferred if matched donor can be found
2. Surveillance for malignancy is also important
c. Ataxia-Telangiectasia
i. Autosomal recessive disease
ii. Mutation in a cell cycle kinase
iii. Ataxia = difficulty maintaining balance
iv. Telangiectasia = broken capillaries (sclera of eye)
v. Immune findings:
1. IgA and sometimes IgE deficient
2. CMI defects are variable
3. Ataxia
4. telangiectasia
vi. Relationship between immune deficiency and other
manifestations of Ataxia are unknown
vii. Tx: no specific treatment is available; Ab have helped
prolong life in many AT patients.
11.Vaccinations
a. Definition: to induce a protective immune response against an infectious agent
without causing harm to the patient (falls under artificial immunization)
b. Memory: induce antibodies and activated T cells to protect host from future
infection
c. Types of Vaccines
i. Killed/inactivated
1. Eg: influenza, rabies, Salk polio (IPV)
2. Chemically treated with formalin

3. Physically treated with heat or irradiation

4. Advantage:
a. Safe can no longer cause disease in any way, shape, or form
5. Disadvantage:
a. Need large amounts
b. Not as strong of an immune response compared to live vaccine
ii. Live attenuated
1. Eg: measles, mumps, rubella, Sabin polio (OPV), BCG, rotavirus
2. Genetic mutations
3. Grow in non-human animal hosts
a. Eg: chicken eggs
4. Advantage:
a. Capable of replication
b. Reach the anatomical site
i. Allows vaccinated person to produce Ab at the site where
they will be potentially infected
1. Respiratory mucosa focus site for flu vaccine
2. GI tract mucosa focus site for rotavirus vaccine
c. Strongly immunogenic
5. Disadvantage
a. Can revert back to virulent form
b. Contraindicated for immunodeficient population
iii. Subunit
1. Utilizes an antigenic portion of the organism (use the portion that will
produce an immune response)
a. Toxoids: inactivated toxins
i. Tetanus, diptheria, acellular pertussis (toxoid + fimbriae)
vaccines
b. Surface antigen: outer surface protein
i. Heptatitis B
2. Capsule: comprised of polysaccharides
a. Polysaccharides on their own are not very immunogenic
i. Thus, conjugate vaccines are made, which include the
polysaccharide and a protein. This makes it very
immunogenic.
b. Haemophilus influenzae type b HiB, conjugate vaccine
i. Haemohilus influenzae can cause otitis media &
meningitis
c. Meningococcal
i. Meningococcal polysaccharide vaccine (MPSV4): >55
years old
ii. Meningococcal conjugation vaccine (MCV4): <55years old
d. Pneumococcal
i. Pneumococcal polysaccharide vaccine (PPSV23) all adults
>65 years old and those 19 or order with risk factors
ii. Pneumococcal conjugate vaccine (PCV13) all children <5
years old and all with high risk factors
e. As people get older, their immune response decreases. Their
body cannot responds to strong vaccines, so they should not be
taking the conjugate vaccine.
d. Adjuvants
i. A substance bound to the antigen to illicit a stronger immune response
1. Freunds complete adjuvant: lab research only; not for human use
2. Alum: aluminum hydroxide: human use

e. Route of Vaccine Delivery

i. Oral
1. Polio (not used in USA)
2. Rotavirus
ii. Intranasal
1. Influenza
iii. Oral & intranasal route stimulates a mucosal immune response & mimics
route of infection; live, attenuated vaccines used
iv. Subcutaneous injectable
v. Intramuscular injectable
f. Herd Immunity
i. When the majority of the population has immunity and thus protects the
minority of the population that is not immune
ii. When the number of vaccinated individuals decreases, those who are not
vaccinated are not as protected and are more susceptible to getting sick,
allowing for multiple strains of the pathogen to evolve. This defeats the
purpose of a vaccine and the people who are vaccinated are not that
protected either.
12.Hypersensitivity
a. Failure of the immune system
b. Reactions that are unwarranted and harmful to the host
c. The immune response itself is responsible for induction of disease
d. Requires sensitization and is antigen specific
e. Classified by Gell and Coombs
i. Type I immediate hypersensitivity effector: IgE
ii. Type II cytotoxic hypersensitivity effectors: IgG and IgM
1. IgG and IgM are in tissues
iii. Type III immune complexes hypersensitivity effectors: IgG and IgM
1. IgG and IgM are bound in immune complexes and are trapped in
tissues
iv. Type IV delayed hypersensitivity effectors: T cells (40-72 hours)
f. Basic characteristics of hypersensitivity
i. First contact w/ allergen produces no symptoms, but the individual becomes
sensitized
ii. Re-exposure to the same antigen (allergen) elicits a reaction
1. Reaction is highly specific
iii. Re-exposure to the same allergen may increase and sometimes decrease the
severity of the reaction
g. Type I Hypersensitivity
i. Reaction
1. Induced by certain types of Ag (allergens) and has all the hallmarks of
a normal immune response
ii. What distinguishes a Type I HS rxn from a normal immune response?
1. The secretion of IgE from plasma cells
a. IgE binds to a high affinity Fc receptor on the surface of tissue
mast cells and blood basophils
b. IgE-coated-mast cells/basophils are said to be sensitized
c. Future exposure to the same allergen crosslinks the mIgE on
sensitized mast cells/basophils and causes the degranulation of
these cells, resulting in the release of pharmacologically active
mediators.
iii. IgE
1. In normal individuals, serum IgE range is 0.1-0.4g/ml

2. In severely allergic individuals, serum IgE range is rarely greater than 1

g/ml
3. life of IgE is only 2-3 days, unless it is bound to a F C receptor on a
mast cell or basophil in which it is stable for weeks to months
iv. Mast Cells (and Basophils)
1. Mucosa and epithelial surfaces lining body surfaces
2. Mast cells and basophils basically have the same function but are
present in different places
a. Mast cells = tissues
b. Basophils = blood
3. All vascularized tissue (excluding CNS and retina)
4. Contain granules with pre-formed (primary immediate)
pharmacologically active mediators
5. Once the FC receptor has been cross-linked, degranulation occurs in
seconds
v. Allergens
1. The majority of humans mount significant IgE responses only as a
defense against parasites
2. After an individual is exposed to a parasite, the serum IgE levels
increase and remain at high levels until the parasite is cleared
3. Atopic persons have a genetic defect affecting the regulation of the
IgE response
a. This allows non-parasitic antigens to stimulate inappropriate IgE
production leading to tissue-damaging Type I HS reactions
4. Most allergic IgE responses occur on mucous membrane surfaces in
response to allergens that enter the body by inhalation or ingestion
5. Common allergens
a. Generally small proteins
b. Usually present in dried up particles
c. Rehydrate upon inhalation and get presented by APCs to T H cells
d. Leads to development of TH2 response and increased IgE
vi. Primary Mediators
1. Primary (or immediate) rxns are the direct result of IgE crosslinking and
degranulation
2. Pre-stored in the granules and effects are immediate but short lived
a. Histamine**
i. Binds to histamine receptors (H1, H2, H3)
ii. Binds to H1 on nearby smooth muscle cells and
endothelial cells lining blood vessels
1. Induces vascular permeability and eventually
causes inflammation
iii. Smooth muscle contraction
1. Constricts airways
2. Increases secretion of mucous
b. Heparin anticoagulant
c. Eosinophil chemotactic factor A chemotactic

d.
e.
f.
g.

TNF-
Proteases
Degradative enzymes
Inflammatory mediators
i. ECF (eosinophil chemotactic factor)

1. Late stage asthma

ii. NCF (neutrophil chemotactic factor)
iii. Both are released in granules as well. Recruit eosinophil
and neutrophil. Can cause lots of damage
iv. Are found in the later stages of these diseases. They
recruit cells and activate them. In the absence of ab, they
will damage the tissue
vii. Secondary (late) Mediators
1. IL-4
2. Platelet activating factor (PAF)
a. Chemotactic for leukocytes
b. Activates neutrophils, eosinophils, and platelets
3. Prostaglandins & leukotrienes also come into action
a. Similar activity to histamines, but they do it better
b. Their response is a little more pronounced/problematic
c. Leads to extensive respiratory tissue damage
d. Prostaglandin D2, E2, F2 increased smooth muscle
contraction & vascular permeability
e. Leukotriene C4, D4, E4 (lipoxygenase pathway) increased
smooth muscle contraction & permeability
f. Leukotriene B4 chemotactic for neutrophils
4. Effects are felt after the primary, but are more potent and longer
lasting
viii. Consequences of Type I Mediators
1. Mast cell/basophil
a. Biogenic amines & lipid mediators (eg PAF, PGD 2) vascular
leakage & bronchoconstriction & intestinal hypermotility
b. Cytokines, lipid mediators, enzymes inflammation & tissue
damage
2. Eosinophil
a. Cationic granule proteins killing of parasite and host cells
b. Enzymes killing of parasite and host cells & tissue remodeling
h. Systemic v. Organ Specific Anaphylaxis
i. Systemic Anaphylaxis
1. Occurs when allergens enter the blood
2. Widespread activation of mast cells
3. Increased vascular permeability
4. Widespread constriction of smooth muscle
5. Fluid leaving the blood leads to a rapid drop in blood pressure and
anaphylactic shock
6. Many organ systems are damaged because they are functionally
impaired
7. Mortality usually associated with asphyxiation d/t airway constriction
and epiglottal swelling
8. Allergens
a. Most common = PCN
b. Insect stings
c. Peanuts & brazil nuts
9. Tx = rapid administration of epinephrine
a. Stimulates reformation of tight junctions
b. Reduces permeability
c. Prevents fluid loss from blood
d. Decreases swelling
e. Increases blood pressure

i.

j.

ii. Organ specific anaphylaxis

1. Occurs when allergens effect target organs
2. Most commonly effected are the respiratory, GI and connective tissues
3. Urticaria/Hives
a. Allergens that activate mast cells in the skin
b. Most common cause = insect bites
c. Can get hives from food allergies if the allergen gets carried
through the blood
4. Atopic dermatitis (eczema)
a. Chronic itching w/ skin rash, eruptions
b. Hx of increased IgE and allergies
Type II v. Type III Hypersensitivity
i. Type II = IgG and IgM bind directly to some kind of tissue, causing damage to
that tissue directly
ii. Type III = IgG and IgM make immune complexes that get trapped in tissue,
causing damage to the tissue indirectly
Type II Hypersensitivity
i. Ab mediated HS against our own cells or receptors or membranes
ii. Mediated by IgG or IgM
iii. Ab against tissue Ag
iv. Causes
1. Local complement activation
2. Influx of leukocytes
3. Tissue destruction via ADCC, degranulation and oxygen radicals
v. Examples
1. Cytotoxic
a. Direct lysis of RBC
i. Drugs
ii. Transfusion rxns
iii. Erythroblastosis fetalis
1. Rh- mother giving birth to an Rh+ fetus
a. Transport of maternal IgG specific for Rh
across the placenta
b. Not much of a problem during 1st pregnancy
because mothers immune system will not
encounter the fetal RBCs until the time of
birth
c. Problem in subsequent pregnancies
d. T-dependent response generating IgG
e. RhoGam (human, anti-RhD IgG) (Rx to take)
at 28 weeks and w/I 24 hours after birth
f. Also given to any Rh- woman following
termination of pregnancy
iv. Graft rejection
2. Non-cytotoxic
a. The cell or tissue is altered in function
i. Graves Disease (hyperthyroidism)
1. IgG autoantibodies are formed against the TSH
receptor
2. Ab bind to the TSH receptor and stimulat the
unregulated production of thyroid hormones
3. Thus, there was a change in tissue function and not
lysing of blood cells.
ii. Myasthenia Gravis

k. Type III Hypersensitivity

i. Caused by high levels of circulating immune complexes (IgG or IgM)
ii. Systemic, rather than organ specific damage
iii. Circulating immune complexes overwhelm the immune systems ability to
remove them
iv. Deposit in various tissues (skin, glomeruli, blood vessels, synovium, and
lungs) and activate complement
v. Neutrophils try to remove the complexes and this results in degranulation and
tissue damage
vi. Classical examples
1. Lupus
a. Deposit in skin butterfly rash
2. Serum sickness
a. Many of the classic treatments for infectious diseases has been
to generate antiserum in horses and administer to pts as
immediate treatment
b. 7-10 days following administration of horse serum, pt would get
chills, fever, vasculitis, and occasional glomerulonephritis
c. D/t horse serum forming complexes with human Ab
d. Today:
i. Anti-venom
ii. Streptokinase (for MI)
iii. Large doses of PCN (most common)
3. Arthus Reaction
a. If antigen is injected beneath the skin, it can form immune
complexes w/ Ab that have diffused from the blood into the c.t.
b. Complement gets activated and an inflammatory response
ensues
c. Appears as localized areas of redness & swelling
l. Type IV Hypersensitivity
i. Only HS reaction that is T cell mediated
ii. Rxns typically take 24-48 hrs
iii. Non-harmful components (pentadecacatechol from poison ivy) complex with
proteins in the skin & get taken up by APCs and presented to T cells (DTH
REPONSE)
iv. TH1 response develops, resulting in activation of macrophages via IFN-
resulting in an inflammatory response that is unwarranted
v. Classic examples:
1. Contact dermatitis
2. TB skin test
13.Diagnostic Principles in Immunology
a. Microscopy
i. Purpose
1. Initial detection of microbes
a. Bacterial cells, fungal elements, parasites (eggs, larvae, or adult
forms), viral inclusion present in infected cells
2. Preliminary or definitive identification of microbes
ii. General microscopic methods used
1. Brightfield (light) microscopy
a. Light passes from bottom of sample
b. Total magnification = objective x ocular lens
i. Objective (10-fold) x oil immersion ocular (100-fold) =
1,000x magnification
c. Shows most bacteria, not viruses

i. Used for many specimens

1. Parasites & eggs (10-40x(
2. Gram-stain of bacteria *** (100x ocular)
3. Blood smears (40-100x)
2. Darkfield microscopy
a. Same as brightfield, but uses scattered light
i. Causes specimen to be brightly illuminated
ii. Used for thin bacteria (spirochetes)
1. Treponema pallidum, Borrelia, Leptospira spp.
2. Used for diagnosing syphilis
3. Phase-contrast microscopy
a. Not really used anymore
b. Shows internal details of microbes
i. Creates 3D image
4. Fluorescent microscopy
a. Organisms stained w/ fluorescent dyes
b. Brightly illuminated against background
i. Different colors
c. Used for looking at Ab
5. Electron microscopy
a. Used for very small organisms
i. Viral particles can be seen
ii. Transmission (TEM)
1. Electrons pass directly through specimen
iii. Scanning (SEM)
1. Electrons bounce off surface for 3D picture
b. Gold standard for diagnosis certain diseases, such as rotavirus
c. Very expensive and time consuming so not used often
b. Examination Methods
i. Clinical specimens or suspensions
ii. Direct examination
1. Wet mount
a. Looking for parasites (or fungus) floating around, never bacteria
(too small)
2. KOH prep to dissolve background material
a. Looking for parasites & fungi; will dissolve bacterial cells, virally
infected cells, etc
3. Contrasting dye
a. Lactophenol cotton blue, iodine, India ink
iii. Differential stains
1. Gram stain for bacteria (and some yeast)
a. ***most important stain in microbiology***
2. Wright-Giemsa stain for blood parasites
3. Iron hematoxylin for protozoan parasites
4. Acid-Fast Stains for TB
a. Auramine-rhodamine (fluorescent stain) for TB
c. Types of Culture Media
i. Enriched nonselective media
1. Blood, chocolate agar
ii. Selective media
1. Thioglycolate broth anaerobes
2. Sabouraud dextrose agar fungi
3. MacConkey agar GNR, lactose-fermentation (differential)
iii. Differential media
1. Mannitol salt agar S. aureus

2. Lowenstein-Jensen medium mycobacteria

iv. Specialized media
1. Buffered charcoal yeast extract (BCYE) agar Legionella
2. Thiosulfate citrate bile salts sucrose (TCBS) agar - Vibrios
d. Molecular Techniques
i. DNA probes
1. Detect, locate, quantify specific nucleic acid sequences in clinical
specimens
a. DNA-specific probes tagged w/ fluorescent or radioactive
compounds
i. Currently used to diagnose
1. Chlamydia trachomatis
2. Neisseria gonorrhoeae
3. Gardnerella, Trichomonas
4. Candida, TB
5. CMV, HCV, HIV, and HPV
a. CMV = cytomegalovirus. Big deal in AIDS pts
and most common neonatal infection
ii. Also used to diagnose cancer and type HLA
ii. PCR
1. Amplification of DNA
a. RT-PCR for RNA
b. Real time RT-PCR for HIV
2. More sensitive than DNA probes
a. Can detect small sample size
3. Mainly used for viruses
a. HIV, HSV, HPV, Hantavirus
b. Also antibiotic resistance
i. MRSA
4. Restriction Fragment Length Polymorphism (RFLP)
a. DNA fragments patterns when DNA cleaved by restriction
enzymes
i. Recognize and cleave specific sequences
1. Distinguish HSV-1 from HSV-2
2. Identify spread of pathogens between pts
a. Salmonella spp.
iii. Western Blot
1. Used to identify specific protein in mixture
a. Separated on polyacrylamide in presence of SDS
b. Proteins transferred to membrane
i. AB used for detection
1. Conjugated to
a. Enzymes
b. Radioactivity
c. Chemiluminescent
2. This is THE DEFINITIVE TEST to confirm diagnosis of HIV
3. Densitometry
a. Can detect changes in [protein]
i. More qualitative than quantitative
1. Can just say whether or not its there, not really
how much is there.
4. Microarrays
a. Can test/screen for large number of organisms (>10,000)
i. DNA, RNA, or Ab probes spotted onto chip
ii. Sample added

1. DNA, RNA, protein binds to chip

2. Bound sample detected via chemiluminescence
b. People pay for these types of things to find out their
polymorphisms
i. To see if they are at risk for any diseases
ii. To find out what they can pass on to their children
e. Serological techniques
i. Precipitation rxns
1. Interaction btwn Ab and soluble Ag forms visible precipitate
a. Forms lattice that develops into visible precipitate
i. Develops slowly and depends on valency of Ab and Ag
ii. Ab must be bivalent (can attach to 2 Ag)
iii. Ag must be bi-poly valent
b. Cause Type III hypersensitivity rxns
2. Soluble proteins become insoluble
a. Immune complexes
3. Precipitation Rxns in fluids
a. Constant amount of Ab w/ increasing Ag
i. Excess Ag or ab interferes w/ precipitation
ii. Can detect Ab made during bacterial infection
1. Serum from pt diluted in series of test tubes ans
suspect bacteria added
2. Test tube showing visible agglutination will reflect
serum titer
a. Eg: 1/640 is positive. Next dilution 1/1280
is negative. So, serum Ab titer is 640
ii. Agglutination rxns
1. Interaction btwn Ab and particulate Ag forms visible clumping
a. Similar in principle to precipitation rxns
2. Excess Ab inhibits agglutination rxns
a. Same as precipitation rnx
3. Particles settle out of suspension
a. clumping
4. RBCs and latex beads most commonly used
a. RBC rxns used to
i. Define ABO blood groups
ii. Diagnose EBV
b. Latex beads used to
i. Diagnose CSF infections (Meningococci, Cryptococcosis)
5. Types of agglutination rxns
a. Hemagglutination
i. Blood type groups
1. A, B, AB, and O
2. RBCs placed on slide and anti-A and anti-B serum
used to type
a. Agglutination w/ A = Type A
b. Agglutination w/ B = Type B
c. Agglutination w/ A and B = Type AB
d. No agglutination = Type O
ii. Anti-Rh can also be used
1. Anti-D
b. Bacterial agglutination
c. Diagnostic techniques
i. Monospot test
iii. Serology

1. Looks for Ag or Ab to pathogens in blood (serum)

a. Can determine the course of infection
i. IgM good indicator of recent primary infection
2. Titers
a. Pt [Ab] reported as titer
i. Titer is inverse of greatest dilution (lowest []) of pt serum
that retains activity
1. Dilution of 1:64 = titer of 64
3. Ab derivation
a. Some serological assays need specific Abs to detect pathogens
b. Polyclonal Abs derived from many B cell clones
i. Most antigens have multiple epitopes (can bind to
different parts of same antigen)
1. Resulting serum contains mixture of Abs, each
specific for 1 epitope
c. Monoclonal Abs derived from one B cell clone
i. Specific for single epitope (bind to only one part of
antigen)
ii. Not feasible to isolate clones from humans
1. 1975 Kohler and Milstein developed method for
producing Mab by fusing myeloma cell w/ plasma
cell to form hybridoma
a. Hybridoma clone makes 1 Ab with 1 epitope
i. Single epitope; may not detect
different pathogenic strains
iv. ELISA
1. Enzyme-Linked Immunosorbent Assay
2. Detects Ag or Ab in samples
a. Enzyme linked to an ab
b. Substrate used for color development
3. Most often used serologic test
4. Used for infections by looking for Ag in blood
v. Flow cytometry
1. Uses fluorochrome labeled Abs
a. Separates FITC v. rhodamine stained subpopulations of cells
i. Now can routinely analyze up to 5 colors
1. Up to 18
b. Individual cell populations can be studied
i. Used to type HLA
ii. Cancer detection
iii. Immune disorder screening
2. Analysis
a. Data presented as histogram or dot plot
i. Differential analysis of cell surface markers
1. WBC expression of CD4 and CD8
ii. Bottom left box = double negative. Nothing should be
there
iii. Top right box = double positive. Nothing should be there
iv. Anything to the R of the vertical line is POSITIVE to the X
axis
v. Anything to the TOP of the horizontal line is POSITIVE to
the Y axis