Suppression of BCG cell wall-induced delayed-type hypersensitivity by BCG pre-treatment. II. Induction of suppressor T cells by heat-killed BCG injection.

Previous intravenous (i.v.) injection of heat-killed Bacillus Calmette-Guérin (BCG) in mice produced a suppression of delayed-type hypersensitivity (DTH) induced with oil-treated BCG cell walls. This phenomenon was analysed by the macrophage migration inhibition (MI) test in which non-adherent spleen cells from mice which had been injected with heat-killed BCG (K-Non-ad. cells) were mixed with peritoneal exudate cells from BCG cell wall-immunized mice (effector-PEC). The test showed that the K-Non-ad. cells suppressed the MI activity in the effector-PEC, which indicated that the suppressor cells were induced in the spleen by the heat-killed BCG injections. Moreover, the suppressive effect of the K-Non-ad. cells disappeared after treatment with anti-brain associated theta serum (BA theta) and guinea-pig complement, and operated across the H-2 barrier. The suppressor cells inhibited the production or release of the migration inhibition factor from the BCG cell wall-sensitized cells in the presence of the specific antigen, purified protein derivatives (PPD). It was concluded that the injections of heat-killed BCG produced antigen non-specific suppressor T cells in DTH suppression.