The regulation of T cell growth: requirements for the activation and replication of antigen-specific interleukin 2 producing T cells.

The antigenic requirements for stimulating the production of interleukin 2 (IL2) and the growth of IL2 producing T cells was evaluated using antigen-(Keyhole limpet hemocyanin) specific F1 T helper cell lines. The results demonstrate that both the induction and growth of these cells requires specific antigen and antigen-presenting cells of the correct I-A type. Evidence is presented that argues that soluble macrophage derived factors released as a result of T cell-macrophage interaction are insufficient, even in the presence of antigen, to promote growth of IL2 producing cells. We thus conclude that the direct interaction of IL2 producing cells with an antigen presenting cell is obligatory for activation and growth. These results suggest that T cell proliferation, and as a consequence the magnitude of T cell mediated immune responses, is limited by the availability of "approximately" presented antigen to IL2 producing T cells. The requirement for antigen presenting cells in antigen-driven responses is in contrast with mitogen-induced T cell activation, in which soluble factors can substitute for the accessory cells.