Further characterization of immunological unresponsiveness induced in mice by ultraviolet radiation. II. Studies on the origin and activity of ultraviolet-induced suppressor lymphocytes.

We are studying the development and mode of action of suppressor T cells induced by ultraviolet (UV) radiation, which prevent the rejection of syngeneic UV-induced tumors. Suppressor cells were induced in C3H mice by exposure to FS40 sunlamps for 1 hr, three times per week for 3 months. Neither thymectomy nor splenectomy prior to UV irradiation prevented the development of these suppressor T cells in other lymphoid tissues. The UV-induced suppressor cells functioned when injected s.c. with mixtures of normal lymphocytes and tumor cells in a Winn-type assay in immunodeficient recipients. When UV T cells were mixed with syngeneic UV-induced tumor cells they did not increase the incidence or growth rate of the tumors relative to tumor cells alone, suggesting that the suppressor cells function by interacting with normal lymphocytes and not by directly stimulating tumor growth. Although the suppressor cells were effective in vivo when injected i.v. or when injected locally with normal lymphocytes, they did not suppress cytotoxic effector lymphocytes in a short-term 51Cr release assay in vitro.