Lymphocyte receptors for autoantigens, autologous serum inhibits self-recognition.

IMMUNE reactions are triggered by the recognition of an immunogen by specific lymphocytes. Autoimmune reactions are evoked when lymphocytes recognize autologous antigens and react against them. The absence of reactivity against self-antigens in normal organisms is attributed either to the lack of self-recognizing lymphocytes1 or to a regulatory mechanism which prevents potentially self-reactive lymphocytes from producing autoimmune reactions. The results of previous studies in our laboratory seemed incompatible with the first hypothesis, which is based on the absence of cells recognizing self-antigens. We demonstrated that lymphocytes from normal adult rats can be readily sensitized in vitro against syngeneic embryonic fibroblasts2 as well as against syngeneic adult thymus reticulum cells3. In both cases the autoimmune reactions were induced in cell culture and the effector phase was measured either in vitro by assaying cell mediated cytolysis, or in vivo by the graft versus host (GvH) reaction4. These studies thus indicate that cells capable of reacting against self-antigens do exist in a normal population of lymphocytes. Two questions then arise. First, can one demonstrate that such lymphocytes do in fact possess specific receptors for self-antigens? Second, what prevents in vivo immune reactions against self-antigens?