Suppression of antigraft immunity by preimmunization. II. Characterization of the suppressor cells.

Immunization of mice with irradiated (20 Gy) or non-irradiated allogeneic spleen cells i.v. induces delayed-type hypersensitivity (DTH)-reactive T cells, as well as suppressor T cells, against histocompatibility antigens. The suppressor T cells are unable to suppress the induction and functional activity of the simultaneously activated DTH-reactive T cells. However, the suppressor T cells do suppress the generation of DTH-reactive T cells after subsequent s.c. immunization of the same mice, and after transfer into secondary recipients. Systemic transfer of suppressor T cells is effective the first few days after their induction, and affects the afferent limb of the DTH response. The population of suppressor T cells, which is essential for the systemic transfer of suppression, appeared to be Lyt-1+2+. Splenectomy experiments showed that the spleen is not essential for induction of the suppressor T cells. The precursors of the suppressor T cells belong to the pool of recirculating T lymphocytes; they are insensitive to adult thymectomy and can be depleted by antithymocyte serum treatment.