The role of CD8 T cells in controlling Mycobacterium tuberculosis infections in mice was confirmed by comparing the levels of growth of the organism in control, major histocompatibility complex: class Ii knockout, and athymic mice and by transferring T-cell populations into athymic mice. By using donor mice which were incapable of making gamma interferon (IFN-gamma), it was shown that IFN-gamma production was essential for CD8 cell mediation of protective immunity against M. tuberculosis.