MT021: IMMUNOLOGY & SEROLOGY

LESSON 2: ANTIGENS AND MHC

2ND SEMESTER | S.Y. 2021-2022 TRANSCRIBED BY: GILLIAN J. HERCE – L3
LECTURER: MR. JAN ETHAN LOVENDINO, RMT, MSPH

TOPIC ᵜ Immunogens must be at least 10,000 Daltons;

SUBTOPIC
SUB-SUB TOPIC most of the time the ones who are immunogenic
NOTES has molecular weight of 100,000 Daltons.
OUTLINE ᵜ There are immunogens that are small when it
‫؞‬ Antigen comes with their molecular weight but more
‫؞‬ Immunogens immunogenic than high molecular weight.
Notes:
‫؞‬ Immunogenicity ᵜ
Mas effective mas nakakahawa
º Factors that Affect Immunogenicity ᵜ
There are immunogens that are small but very
‫؞‬ Antigen-Host relationship
immunogenic
‫؞‬ Major Histocompatibility Complex º Ex. HIV
º Comparison of MHC Class I and Class
FOREIGNNESS
II
ᵜ How foreign the antigen to our self-antigen;
º Difference of MHC Class I and Class II
comparison to self-antigen
According to Function
ᵜ Our cell is capable of distinguishing self-antigen to
▪ How do CD8 Differentiate Self-
foreign antigen via receptors
Antigen to Antigen from the
ᵜ The more distant taxonomically the source of
Source
immunogen is from the host, the more successful
‫؞‬ MHC I Mechanism
it is as a stimulus
‫؞‬ MHC II Mechanism Notes:

ANTIGEN ᵜ
The more foreign it is, the more immunogenic
ᵜ A substance that reacts with an antibody or ᵜ
This can be distinguished via receptors
sensitized T cells but may not be able to evoke an º APC (Antigen-presenting cell);
immune response in the first place Dendritic cell is the best APC –
ᵜ Non-self-antigens/Immunogens – evoke an because it has many receptors
immune response CHEMICAL COMPOSITION AND MOLECULAR
ᵜ Self-antigen – Antigens present into your body; will COMPLEXITY
not elicit immune response. However, in instance, ᵜ What are the components of immunogen that
we have developed immune response against our makes it effective/complex as immunogen?
own antigen, results into disorder called ᵜ Proteins are the most immunogenic; if the nature
AUTOIMMUNE DISEASE of antigens is protein, they are the most
Notes: immunogenic.
ᵜ Can be foreign or innate ᵜ Proteins have different structure such as Primary,
ᵜ Self/non-self Secondary, Tertiary, Quaternary
ᵜ Non-self nagkakaroon ng reaction or elicit ᵜ Most immunogenic among macromolecules like
response. Given that’s its foreign, magrereact carbohydrates, nucleic acids, and lipids.
ang body ᵜ Carbohydrates, Lipids, Nucleic Acids are not
ᵜ Self-antigen ex: Surface of RBC may antigen immunogenic, they need another macromolecule
º Since may antigen ofc may antibody to combined with to elicit immune response.
ᵜ Self has no elicit response bcs the body is Notes/ Side notes:

familiar with it ᵜ
Carbohydrate, lipids, nucleic acid need
another macromolecule to combined with to
IMMUNOGENS
elicit immune response
ᵜ Macromolecules capable of triggering an º Binds with another macromolecule/
adaptive immune response by inducing the
malaking molecular weight na antigen
formation of antibodies or sensitized T cells in an
para maging effective sinda
immunocompetent host. ᵜ Example of glycoprotein/glycolipids: blood
ᵜ Immunogens are antigens that elicit immune
groups
response º Rh is glycoproteins
ᵜ All immunogens are all antigens but not all º Blood groups are glycolipid in nature
antigens are immunogens
Notes: *These are from the body, not foreign
ᵜ T cell and B cell activated if may antigen which that’s why there’s no response.
makes the adaptive immune system triggered. THE ABILITY TO BE PROCESSED AND PRESENTED WITH MHC
B cell will produce antibodies. MOLECULES
ᵜ All immunogens are all antigens but not all ᵜ How effective to be processed by antigen
antigens are immunogens presenting cells (APCs)
º Self-antigen doesn’t trigger the ᵜ Most important factor for a substance to elicit an
adaptive or elicit response kasi nga immune response, it must be subjected to antigen
kilala sila processing via APCs
Notes:
IMMUNOGENICITY ᵜ
Meaning: madedetect yan ng cells.
ᵜ Ability of an immunogen to stimulate a host ᵜ
Ex. Dendritic cell, pag naprocess na ng DC and
response may mapresent na siyang antigen sa T cell.
ᵜ How effective the ability of immunogen to elicit an Magccreate ng another T cell that activates B
immune response cell to create plasma and memory cell.
FACTORS THAT AFFECT IMMUNOGENICITY Because of this mageelicit na ng immune
MACROMOLECULAR SIZE response
ᵜ General rule: “the higher molecular weight, the ADJUVANT
more immunogenic”
 MT021: IMMUNOLOGY & SEROLOGY
LESSON 2: ANTIGENS AND MHC
2ND SEMESTER | S.Y. 2021-2022 TRANSCRIBED BY: GILLIAN J. HERCE – L3
LECTURER: MR. JAN ETHAN LOVENDINO, RMT, MSPH

ᵜ Substance administered with an immunogen that ▪ Locus B

increases the immune response in order to ▪ Locus C
provide immunity to a particular disease. º MHC CLASS II
ᵜ To strengthen immunogenicity of immunogen to ▪ DP gene
elicit immune response. ▪ DQ gene
Notes:
▪ DR gene
ᵜ Best na ginagamitan ng adjuvant: vaccine • Each gene has different
ᵜ Increases immune response in order to locus
provide immunity through memory º MHC CLASS III
ANTIGEN-HOST RELATIONSHIP ▪ All nucleated cells contain
AUTOANTIGENS surface protein (antigen) that
ᵜ Self-antigen the belongs to the host elicit immune response
ᵜ Under normal circumstances; they do not elicit
immune response
ᵜ If for instance it elicited immune response
(Autoantigens) to our antibodies AUTOIMMUNE
DISORDERS
Notes:
ᵜ
Self-antigens ex. RBCs
ᵜ
Response to autoantigens -> autoimmune
disease
ALLOANGTIGENS MHC CLASS I
ᵜ Antigens from family of the same species, but ᵜ Expressed on all nucleated cells
capable of eliciting immune response to you. ᵜ Highest express of MHC class I are found on
Notes: Lymphocytes and myeloid cells.
ᵜ
Best example: organ transplantation, blood ᵜ Not detectable or low expression on liver cells.
transfusion That’s why HLA typing isn’t done on liver for
º Rejection transplantation.
HETEROANTIGENS ᵜ Lowest concentration is Locus C
ᵜ Antigens from a different specie like animals, ᵜ Locus A and B are significant in HLA typing
plants, microorganism. MHC CLASS II
ᵜ Heterophile Antigen ᵜ MHC Class I and II are involved in antigen
º They are heteroantigen, however their recognition and are expressed on the surface of
structure is identical or similar on the the cell.
antigens that can be seen on humans. ᵜ Found on lymphocytes, macrophages, activated
º Capable of inducing CROSS IMMUNITY. T lymphocytes and other antigen-presenting
º Ex. Human Blood Group (Blood type A/B) cells.
Notes:
ᵜ Dendritic cell has highest expression on MHC
ᵜ Although similar in structure it can still elicit a class II because they are the most effective
reaction antigen presenting cell.
ᵜ Capable of inducing cross immunity Notes:
ᵜ Ex. Type B, pag naka come in contact ka with ᵜ Not used for liver transplantation coz not
another microorganism na similar sa structure detectable sa test
kang type B, magkakaresponse ka man ᵜ MHC Class II is found in lympho, macro,
giraray dawa dae ka naka come in contact activated T lymphocyte and other APCs
with Type B directly since similar si structure. ᵜ Class I usually self-antigen, and Class II foreign
ᵜ If type A ka automatically may antibodies ka antigen ang nadedetect
for type B COMPARISON OF MHC CLASS I AND CLASS II
ᵜ Even though there’s no direct exposure to type
B, we still have antibodies against type B bcs Class I Class II
we were still exposed to a microorganism with Loci HLA-A, B, & C HLA-DN, -DO, -DP, -
similar structure to type B – cross immunity DQ & -DR
ᵜ It says that antigen present in blood on human Distribution Most nucleated B lymphocytes,
(A/B) are similar or related to bacterial cells macrophages, other
polysaccharide. antigen-presenting
ᵜ When we are infant, we develop antibodies cells, activated T
against the opposite blood type and has lymphocytes
something to do with exposure to heterophile Function To present To present
antigens. endogenous endogenous antigen
ᵜ For instance, the antibody produced is against antigen to to T helper
that of opposite blood type. It will elicit immune cytotoxic T lymphocytes
response. lymphocytes
Remember:
MAJOR HISTOCOMPATIBILITY COMPLEX ᵜ A, B, C for Class I
HUMAN LEUKOCYTE ANTIGENS ᵜ D- Class II (add N, O, P, Q, R on D)
ᵜ HLA genes are found on short arm of the
DIFFERENCE OF MHC CLASS I AND CLASS II
chromosomes 6. MHC are divided into three:
ACCORDING TO FUNCTION
º MHC CLASS I Notes:
▪ Locus A
 MT021: IMMUNOLOGY & SEROLOGY
LESSON 2: ANTIGENS AND MHC
2ND SEMESTER | S.Y. 2021-2022 TRANSCRIBED BY: GILLIAN J. HERCE – L3
LECTURER: MR. JAN ETHAN LOVENDINO, RMT, MSPH

ᵜ Class I – to present endogenous antigen to Perforins - perforate the cells

Granzymes- an enzyme that kills the cell
cytotoxic T lymphocyte/ CD8
*sisirain ang cell thru perforins then ipapasok ang
º Antigen from ourselves to CD8 granzymes
lymphocytes
º Presents pathogens that attacks cells *Self-antigen is endogenous, same with virus since
on the inside. intracellular man sinda nagmumultiply.
º CD8 is a killer cell but if class 1 MHC II MECHANISM
presents our self-antigen to cd8, cd8
will treat is as normal bcs it can
identify it as our own antigen
ᵜ Class II – to present exogenous antigen to T
helper lymphocytes/ CD4
º Mostly bacterial kasi ang antigens na
pinepresent, coming from the outside
º Always foreign
º Doesn’t present self-antigen
º CD4 activates macrophage and B cells
kaya associate and CD4 sa class II
HOW DO CD8 DIFFERENTIATE SELF-ANTIGEN TO
ANTIGEN FROM THE SOURCE
ᵜ Has something to do with the receptor of CD8,
CD8 receptor are patterned knowing what
antigen is presented
Notes: Notes:
ᵜ Since same origin of genetic material, hindi sila ᵜ Has 2 criteria to consider
nag eelicit ng immune response. Since same º Antigen na pinepresent kay MHC class
ng pinagmulan 2 is foreign
MHC I MECHANISM º It blocks endoplasmic or endogenous
protein - Invariant chain - blocks endo
protein
ᵜ Endogenous antigen may attach to MHC class
2 tapos ma insert si invariant chain para iblock
si attcahment kang endo protein
ᵜ Once naka attach na si invariant chain,
maluwas na sinda sa RER, then mapunta sa
golgi complex
ᵜ During this time invariant chain will be
degraded
º Bcs kung san naka bind si IC duman
supposedly ma attach si foreign
antigen. Nagbind siya duman
temporarily para ireserve si slot sa
foreign instead na magbind si endo
Notes:
º Madedegrade na din siya coz dae
ᵜ Protein (self-antigen) will undergo proteosome naman makaka pass thru duman si
for degradation endo protein/antigen since endo
ᵜ Proteosome will transport it sa ER with the protein can only enter through RER
help of TAP which is transport protein ᵜ Once degraded there will be clip fragment
Side note: ᵜ MHC class 2 with clip fragment will wait for
May MHC talaga sa laog kang RER, magbbind na lang
foreign antigen
si antigen duman
ᵜ Once na may pumasok na na foreign antigen
ᵜ Yang green MHC class I
ᵜ via phagocytos, pupunta na sa taas si golgi
Pag nagbind na si antigen sa MHC class I,
complex
maduman na sa golgi complex
ᵜ Then matatanggal yung clip fragment kasi
ᵜ GC transport it to the surface, then magwwait
papasok na si foreign antigen sa MHC class 2
sa CD8 ᵜ If may nagbind na na antigen, ready na
ᵜ May CD8 sa labas ng cell na nagaact as a
pumunta sa surface
guard-- para icheck if self-antigen yung
ᵜ Then ma contact na siya sa CD4, once naka
nakuha niya.
ᵜ contact na si exogenous antigen it will now
If maconfirm na self-antigen, papabyaan lang
elicit immune response,
siya ng CD8 since self nga siya
ᵜ Then CD4 T cell will release cytokines to
ᵜ Bakit CD8 ang yaon? Bcs capable siya of
stimulate B cells, plasma cells and memory
directly killing the cell, by the induction of
cells.
apoptosis due to the release of perforins and
º Other effect of cytokines,
granzymes
Side note: magmmumultiply ng magmmultiply si
Same process if ever virus si antigen na present. T cells, more cytokines then more cells
Pero ang difference si CD8 ma produce siya ning
perforins and granzymes --> apoptosis
 MT021: IMMUNOLOGY & SEROLOGY
LESSON 2: ANTIGENS AND MHC
2ND SEMESTER | S.Y. 2021-2022 TRANSCRIBED BY: GILLIAN J. HERCE – L3
LECTURER: MR. JAN ETHAN LOVENDINO, RMT, MSPH

mentioned kaya mas effective mag

elicit ng immune response
º Plasma cells-release antibodies
º Memory cells-familiarize/ remember
with the antigen
º T helper cell will activate B cell then
produce antibodies, then stimulate
production of other T cells and
activate others cells
Side note:
ᵜ There's possibility na not only CD4
ang nasa surface. If ever si CD8 ang
maka come in contact,
automatically ikikill to kang CD8