Antigenic competition between two sequentially acting antigens. II.--The life-span and sensitivity to corticosteroids or to irradiation of T suppressor cells.

We have studied the immunosuppressive function of T cells using the antigenic competition system. A first antigen (inhibitory antigen) consisting of horse red blood cells is given as a primary or a secondary stimulus. This is followed 4 days later by a second antigen (test antigen) consisting of sheep red blood cells. Both antigens are given intraperitonealy. We have estimated the life-span of T suppressor cells by studying the time necessary for the abolition of antigenic competition after adult thymectomy. We find the response disappears after 6 weeks. The cortico- and radio-sensitivity of T suppressor cells were studied by the effect of hydrocortisone or of irradiation on antigenic competition. Lymphocytes from treated mice were transferred to compatible Nude mice whose ability to show antigenic competition was then studied. By these tichniques we have shown that T suppressor cells are not destroyed by hydrocortisone but their immunosuppressive function is merely temporarily inhibited during the time of high level of this hormone. Furthermore hydrocortisone only inhibits the T suppressor cells when the inhibitory antigen is given as a primary stimulus and shortly after the administration of the steroid. Irradiation on the other hand destroys or inactivates one out two or both cells with a suppressive activity (T suppressor cell and macrophage).