1 Department of Pediatrics University of California School of Medicine Los Angeles, California 90024
The two major subpopulations of lymphocytes, T cells (thymus-dependent lymphocytes) and B cells (bursal equivalent or thymus-independent lymphocytes) have multiple roles in the immune system. In general, T cells are the functioning cells in the cellular immune system (delayed hypersensitivity, graft rejection, graft-versus hostreaction); and B cells, the precursors of plasma cells which form specific antibodies, are the functioning cells in the antibody immune system. It is now well recognized, however, that these cell types and immune systems usually do not function independently, but interact with one another in multiple ways and also with other, cells such as macrophages. For example, T cells may increase or suppress the production of antibodies by the B cell system, and macrophages may increase or suppress the response of T and B cells to antigens.