Inhibition of helper function with anti-Lyt-2 or anti-L3T4 monoclonal antibodies depending on stimulating antigens.

The role of L3T4+ and Lyt-2+ cells in the induction of cytotoxic T cells (CTL) after stimulation with trinitrobenzene sulfonate (TNBS)-treated syngeneic cells, or with cells differing for the entire major histocompatibility complex or for class I molecules alone was investigated using anti-L3T4 and anti-Lyt-2 monoclonal antibodies (mAb). Anti-L3T4 mAb inhibited both induction of CTL and interleukin 2 (IL2) production by T cells stimulated with allogeneic (class I + class II differences) or by TNBS-treated syngeneic cells. In the same culture conditions, anti-Lyt-2 mAb inhibited CTL induction but had no effect on IL2 production. By contrast, only anti-Lyt-2 mAb inhibited both CTL induction and IL2 production when T cells were stimulated by allogeneic cells differing only for class I antigens. Anti-L3T4 mAb had no inhibitory effect in this situation. These results indicate that two helper pathways can be activated, depending on the type of T cell stimulation: one, implicating L3T4+ cells, is used when stimulation involves class I and class II alloantigens or hapten on syngeneic cells; the other, involving Lyt-2+ T cells, is preferentially stimulated when responding and stimulating cells differ only for class I major histocompatibility complex antigen.