Immune Response in BALB/c Mice Following Immunization with Heat-killed Mycobacterium lepraemurium

BALB/c mice were immunized with 1 × 10⁷ heat-killed Mycobacterium lepraemurium (Mlm) via the hind foot pad. Four weeks later, the animals were infected with 1 × 10⁹ Mlm intraperitoneally. Skin test studies, using footpad swelling as a parameter, indicated the development of skin reactivity to Mlm and M. leprae cell extracts. Immunized animals that were infected showed positive reactions to both antigens by the second week. This persisted up to fourteen weeks, at which time, bacillary restriction was also observed in the spleens and livers. Non-immunized infected animals, on the other hand showed a decline in skin reactivity to the two antigens used, and also showed proliferation of Mlm in the two organs examined. Animals receiving heat-killed Mlm or sensitized splenocytes when challenged with 5 × 10³M. leprae via hind foot pad, did not show inhibition of the infecting agent, thus indicating a lack of cross-protection.