Immunity to Mycobacterium leprae infections in mice stimulated by M. leprae, BCG, and graft-versus-host reactions.

Infections of mice with Mycobacterium leprae in one rear foot pad immunized them against a second infection in the other rear foot pad. Purified bacilli harvested from the first infection also produced immuniy when injection into the foot pads of previously uninfected mice. Injections of BCG afforded similar protection, but had no adjuvant effect on M. leprae. M. duvali, a cultivable mycobacterium that is reported to be more closely related antigenically to M. leprae than BCG is, provided much less protection against M. leprae challenge than BCG did. Moreover, when M. duvali was mixed with BCG, it was not any more effective than BCG alone. Graft-versus-host reactions, induced by injections of parental spleen cells into F1 hybrids, provided no protection against M. tuberculosis and M. marinum challenge. They gave moderate protection against M. leprae in one experiment but not in another with a different schedule. Allogenic spleen cells had a protective effect when injected locally into the infected foot pad. The effect produced by these injections of spleen cells was a delay in the appearance of bacterial growth; however, there was no decrease in the rate of logarithmic growth when it did appear and no reduction in the eventual plateau level.