Modulation of the immune response by a methanol-insoluble fraction of attenuated tubercle bacilli (BCG). I. Primary and secondary responses to sheep red blood cells and T2 phage.

Studies were continued on the mode of action of a methanol-insoluble moiety (methanol-extraction residue) of attenuated tubercle bacilli which enhances the immune response. We analysed the effects of treatment with this material on the primary and secondary immune responses of mice to two antigens, sheep red blood cells and T phage. Pretreatment with methanol-extraction residue enhanced the primary response to sheep red blood cells, accelerating the formation of both 19S and 7S plaqueforming cells and of circulating haemagglutinins, and prolonging high levels of 19S and 7S plaque-forming cells. Methanol-extraction residue delayed the secondary response to sheep red blood cells when administered between primary and secondary immunization. Methanolextraction residue administration subsequent to immunization did not affect an ongoing primary response to this antigen. Administration of methanol-extraction residue before primary immunization with T phage, or between primary and secondary immunizations, enhanced both the primary and secondary circulating antibody responses to this antigen. The findings are discussed in relation to possible sites of action of methanol-extraction residue.