Induction of immunoregulatory T cells by adjuvant

The effect of adjuvant on the generation of suppressor cells in the thymus was investigated. C57Bl/6 mice were injected i.p. with complete Freund's adjuvant (CFA), and the capacity of thymocytes and splenic T cells to suppress the in vitro generation of cytolytic T cells was studied. Suppressor thymocytes were detected within two days after CFA inoculation and preceded the appearance of suppressor T cells in the spleen by six days. Characterization of the suppressor thymocyte populations showed that they inhibited primary but not memory T cell responses in vitro. We suggest that the initial step in the regulation of the primary immune response by adjuvant is the generation of suppressor cells in the thymus. Thymic suppressors subsequently migrate to peripheral lymphoid tissue where they inhibit cytotoxic, but no helper, T cell function.