Human T-cell clones recognize a major M. leprae protein antigen expressed in E. coli

Abstract

Leprosy is a chronic infectious disease caused by Mycobacterium leprae. As with other intracellular parasites, protective immunity is dependent on T cells and cell-mediated immunity¹. In animal models, immunization with killed armadillo-derived M. leprae elicits strong T-cell responses, delayed-type hypersensitivity and protection against viable challenge^2–5. We have recently shown that killed M. leprae can induce delayed-type hypersensitivity in healthy human volunteers⁶. Identification of the M. leprae antigens that are recognized by T cells and may be involved in protection has been hampered by the inability to cultivate the organism in vitro and by difficulties in antigen purification from limited quantities of armadillo-derived bacillus. Because genes for the major protein antigens of M. leprae as seen by mouse monoclonal antibodies have been isolated^7,8, it has become possible to test whether these individual antigens are recognized by T cells. We screened crude λ gtll phage lysates of Escherichia coli containing individual M. leprae antigens using M. leprae-specific T-cell clones isolated from M. leprae-vaccinated volunteers. Using this method, we find that nearly half of the M. leprae-specific T-cell clones are stimulated to proliferate by lysates containing an epitope of a M. leprae protein of relative molecular mass 18,000 (18K).