The efficacy of a cell-mediated reaction in the disposal of M. leprae in human skin.

The inability of lepromatous leprosy patients to mount a cellular immune response against Mycobacterium leprae antigens is not understood. The extensive intracellular replication of bacilli in the phagocytes and the relative paucity of T lymphocytes in the lesions suggest that these patients might be incapable of generating normal delayed type hypersensitivity responses in their skin. In order to elucidate this problem we evaluated the patient's response to local antigen administration. Our observations suggest that the majority of lepromatous patients can respond normally to intradermal injections of a soluble antigen such as purified protein derivative of tuberculin. The underlying lepromatous lesions do not inhibit mononuclear cell infiltration or differentiation. Moreover, the generation of a cellular immune response in the lesions appears to modify the lepromatous lesion to a lesion resembling the tuberculoid type. This process involves local T cells recruitment, granuloma formation and a reduction in the bacterial load at the antigen responsive site.