Abstract: Objective To investigate the mechanism on BCG inducing protective immunity,and to seek for the component of BCG playing main role on it.Methods We determined the level of IL-12p40,IL-18,and IFN-γ secreted by peritoneal exudate cells(PEC) from the mice in response to the lysates or the culture filtrates of viable or killed M.bovis BCG strain.Results Viable BCG strain could activate macrophage to produce both IL-I 2p40 and IL-18.Their lysate and culture filtrate also showed the activity inducing lL-12p40.In contrast,killed BCG strain and heat-treated filtrate could not induce IL-12p40 and IL-18 pro ductions.However,the lysate of killed BCG strain exerted significant activity inducing IL-12p40.Conclusion It showed that some heat stable factors in the culture supernatant from viable BCG strain contribute to the cyto kine productions.

Key words: Tuberculosis, Immunity, BCG