Significance of Lyt phenotypes: Lyt2 antibodies block activities of T cells that recognize class 1 major histocompatibility complex antigens regardless of their function.

The effect of anti-Lyt2 on the generation of helper T-cell function and on cytotoxic effects specific for subregions of the major histocompatibility complex (MHC) was determined. The addition of anti-Lyt2 without complement to in vitro cultures blocked the generation of allogeneic MHC-induced help and lymphokine production and cytotoxic effects when the response was directed against allogeneic class 1 MHC antigens (K and D gene products of the mouse H-2 complex) but had no effect when these responses were specific for class 2 MHC antigens (I region gene products). Anti-Lyt2 failed to block the response of help induced to allogeneic mixed lymphocyte-stimulating determinants or the production of lymphokines by T cells specific for class 1 MHC antigens when concanavalin A lectin was used to induce activity. These and earlier results indicate that the ability of anti-Lyt2 antisera to block function is correlated with T cell specificity for class 1 MHC antigens not with the functional activity of the cells.