[The inhibitory mechanism responsible for antigenic competition in the mouse, upon successive injections of 2 different antigens: the immunosuppressive function of T cells].

Antigenic competition cannot be obtained in congenital athymic Nude mice, whatever the dose of inhibitor Ag used and the free interval between inhibitory Ag injections and the Ag test. On the other hand, competition is normal and even increased, in thymectomised, adult Swiss mice, used 10 to 30 days after thymectomy. In normal mice, the inhibitory mechanism induced by a first thymodependent antigen, may also occur with regard to certain thymo-independent antigens and thus act on the B cells. The antigens may also serve as inhibitory antigens for thymodependent antigens if the free interval between the two injections is small. Injection of hydrocortisone (25 mg/kg) or ALS a short time before the inhibitory antigens, suppresses competition. On the other hand, methotrexate is without effect. Thus the inhibitory TD mechanism does not require mitoses (methotrexate) and depends on corticosensitive T cells which are, no doubt, recirculated (Anti-lymphocyte serum) with a life span greater than 30 days (adult thymectomy). The previous results were obtained when two antigens were administered by intraperitoneal route and the PF cells sought in the spleen. The same experiment was carried out, injecting two antigens subcutaneously, in the same limb, and counting the PF cells in the appropriate lymph node; it shows the adjuvant effect exerted by the first antigen on the response with regard to the second antigen. On the other hand, inhibition is produced if the first antigen is injected intraperitoneally or into another limb. One may thus distinguish an inhibitory effect or an adjuvant effect depending on the experimental conditions. The inhibitory effect seems to be related to the T cells with an immunosuppressive function.