Abstract
The binding of a complex containing self Ia and antigen (IAC) to T cells was investigated. Poly‐L (Tyr, Glu)‐poly‐DLAla—poly‐LLys [(T, G)‐A—L], bovine serum albumin, ovalbumin or fowl gamma‐globulin were used as antigen. The effect of this complex was investigated in three experimental systems: autoradiographic antigen binding, in vivo immunization, and in vitro radioactive suicide of helper T cells. Autoradiographic experiments have shown that antigen binding to T cell‐enriched spleen cells is a slow process with a half‐life period of 20 min. It was found that during this time, antigen which can bind to Lyt‐1^+^ T cells with much faster kinetics (half‐life period = 2 min), is liberated from adherent cells. This “processed” antigen was retained by anti‐Ia or lentil lectin affinity columns, and its binding to T cells was restricted by the I‐A subregion of H‐2. IAC was 100 to 1000‐fold more immunogenic in vivo than the same amount of untreated antigen. This immunogenicity could be removed on anti‐Ia columns, and was found to be under similar H‐2 restriction as was its binding to T cells. The functional T cells, to which IAC binds, were identified by radioactive antigen suicide. It was found that the IAC killed syngeneic but not allogeneic, helper T cells. For the binding of processed antigen, helper cells required metabolic energy and a nonspecific soluble factor of adherent cells. These data are interpreted to suggest that H‐2 restriction is directly determined by the interaction of the helper cell receptor with self Ia and foreign antigen. It also appears that the Ia‐containing antigen may be a potent, cell type‐directed immunogen.