Non-specific suppression of delayed-type hypersensitivity by intrathymic injection of killed bacteria.

Previous intrathymic injection of 50 micrograms of killed BCG as well as killed Listeria in mice produced suppression of delayed-type hypersensitivity responsiveness induced with BCG cell walls (CW) or live Listeria. This finding was analysed in vitro by the macrophage migration inhibition test. Non-adherent spleen cells from mice that had been injected intrathymically with killed BCG or killed Listeria were tested for the ability to regulate the migration inhibition response of peritoneal exudate cells from BCG-CW immunized mice. No migration inhibition was observed, indicating that suppressor cells were induced in the spleen by intrathymic injection of killed BCG or killed Listeria. Suppressor cells were shown to be T cells since they were eliminated by treatment with anti-brain associated theta serum and complement. Thus intrathymic injection of bacteria induced antigen nonspecific suppressor T cells in the spleen.