RECOGNITION OF MYCOBACTERIUM-LEPRAE RECOMBINANT 18-KDA PROTEINS IN LEPROSY

An increasing number of Mycobacterium leprae genes have been cloned and sequenced (18). Several of these have been shown to belong to the family of heat-shock proteins, such as the M. leprae 65-kDa and 18-kDa antigens (8. 12), and are available through the World Heath Organization IMMLEP bank. Most of the M. leprae proteins exhibit immunologic crossreactivity at the antibody level with proteins from other mycobacteria. However, the determinant of the 18-kDa protein recognized by the monoclonal antibody L7.15 (2), later designated as L5, seemed to be species-specific for M. leprae (6) . Human T-cell recognition of the 18-kDa antigen was first reported using crude Escherichia coli lysates containing the antigen as the beta-galactosidase fusion protein; these preparations stimulated T-cell clones from M. leprae-vaccinated donors (6). When the 18-kDa beta-galactosidase (18K betagal) fusion protein was purified and used in proliferation assays with human peripheral blood mononuclear cells, there was a substantial antigen-specific response to beta-galactosidase which masked T-cell responses to the 18-kDa antigen itself (15). The 18-kDa gene was, therefore, recloned and expressed fused to a short leader sequence containing six consecutive asparagine residues (18K Asn) to reduce proteolysis; this protein stimulated T-cell proliferation in a high proportion of patients with the tuberculoid type of leprosy and in healthy contacts of leprosy patients (3). This 18-kDa gene, originally cloned in lambdagt11 (19) was found to contain only 70% of the whole 18-kDa gene as sequenced from a genomic M. leprae cosmid library (1). The full-length 18-kDa antigen (18K JDW) has now been cloned, purified and tested for B- and T-cell reactivity in mice ( 1, 4, 5, 7). The choice of expression systems in the presence or absence of beta-galactosidase (betagal) or a leader sequence and the method of purification may all affect the antigenic epitopes recognized by B and T cells to variable extents. In addition, epitopes recognized by the leprosy patients at both the B- and T-cell level may be different than those recognized by mice. We have, therefore, directly compared these three preparations of the M. leprae 18-kDa protein (I 8K Asn, 18K betagal and 18K JDW) for their immunological reactivity in patients with leprosy.