Lymphocyte subsets and activation.

The biology of lymphocytes is regulated by a large and seemi& growing number of soluble and cell-associated species. A current list includes: interleukins IL l-7, interferons, antigen and perhaps CD4 and cytokines derived from non-lymphoid tissues such as neuropepride, steroid and admnergic hormones. The quality and quantity of regulators present in the B cell milieu during an immunologic insult determine the ultimate character of the immune response, including the immunoglobulin isotype expressed and memory cells generated, and also the absolute numbers of antibody-secreting daughter cells and thus the absolute amount of antibody prcxiuced. The B cell faces a formidable task in sensing, transducing and integmnng information carried by this multitude of species. The past year has seen important progress in research in several areas pertaining to immune regulation. This commentary discusses progress made in four specilic area% (1) Characterization of T helper cell subsets, their products, and their role in the immune response; (2) the molecular T cell help; (3) structure and function of the T cell antigen receptor signal transducer (CD3) complex, and (4) molecular bases of signal transduction by IL receptors. Much of the information discussed is incorporated in Fig. 1.