It is a great privilege to introduce this Cold Spring Harbor Symposium on quantitative biology on the subject of immune recognition. My predecessors in this role, Macfarlane Bumet (1967) and Niels Jerne (1976), had a profound effect on the development of ideas in our field, and many of the participants have made great contributions to our understanding of the subject of this symposium and are clearly more qualified than I to introduce it.

The first Cold Spring Harbor Symposium to consider the immune system was held in 1967 on the subject of antibodies. It marked the acceptance of the clonal selection theory as the central paradigm of immunology (Jerne 1967). That meeting also brought together sufficient data on antibody structure to promote the idea that immunoglobulins are encoded in two distinct types of gene segments, variable segments and constant segments, and that a genetic mechanism must exist to direct the association of these segments in antibodyproducing cells. Finally, it was becoming clear at the 1967 symposium that, although antibody molecules might be both the receptor on and the secreted product of single cells, the specificity of immune activation was distinct from the specificity of the antibodies themselves. Thus, the stage was set for the discovery over the succeeding years that lymphocytes were divided into two major populations, the B cells that bear antibody molecules as their surface receptor for antigen and secrete antibody molecules upon activation, and the T cells that mediate all other specific immune responses, including the activation of B cells to produce antibody.