Monoclonal antibody to L3T4 blocks the function of T cells specific for class 2 major histocompatibility complex antigens.

The ability of antibody to Lyt-2 and to the newly described L3T4 antigen to block the functions of helper T cells with specificity for allogeneic class 1 or class 2 MHC subregion antigens was determined. Anti-Lyt-2 blocked both allohelp delivered by unprimed T cells and IL 2 production by primed T cells when the response was directed to class 1 MHC antigens, but had no effect when the response was directed to class 2 MHC or Mls antigens. Anti-L3T4 had reciprocal activity. A control reagent, anti-LFA-1, blocked all responses tested regardless of specificity. This and other reports provide strong evidence that L3T4 is the murine equivalent of the human T cell markers Leu 3/OKT4. The ability of antibodies directed against Lyt-2 and L3T4 to block T cell function in a fashion determined by the class of MHC antigen recognized by the T cell further supports the hypotheses that Lyt-2 and L3T4 molecule in the mouse and Leu-2 and Leu-3 molecules in the human are involved in the interaction of the T cell with class-specific determinants on MHC molecules.