T-Cell Recognition of Mycobacterial GroES Peptides in Thai Leprosy Patients and Contacts

Leprosy research has predominantly been concerned with the dichotomy between immunological events in tuberculoid leprosy and lepromatous leprosy. Thus, distinct cytokine-secreting profiles have been reported for cloned CD4 and CD8 T cells (30), and lepromatous leprosy patients were found to respond to some purified antigens while remaining anergic to whole mycobacterial extracts (21, 26, 34). Analysis of the specificity of “split anergy” at the level of individual antigenic determinants showed skewing of T-cell responses toward Mycobacterium tuberculosis-specific epitopes, accompanied by relative anergy to the cross-reactive common mycobacterial peptides (13). However, consistent differences in either the specificities or phenotypes of T cells between the sensitized healthy contacts and tuberculoid leprosy patients have so far not been revealed. Previous studies of HLA associations reported the association of tuberculoid leprosy with DR2 in India (18, 37), Japan (11, 23), Thailand (31), and Korea (16); with DR3 in Venezuela and Surinam (36); or with DQ1 (11, 23, 31). On the basis of molecular modelling, the presence of arginine (R) and absence of negatively charged amino acids at positions 13 or 70–71 in pocket 4 of the DRB1 alleles (e.g., DR15) has been associated with susceptibility to tuberculoid leprosy (40), but the molecular source of the corresponding peptide specificity has not been identified. Proteins with a molecular mass of 10 to 12 kDa from Mycobacterium leprae (10) and M. tuberculosis (22) were originally found to carry separate species-specific epitopes identified with monoclonal antibodies. Their sequence analysis showed 90% identity between M. leprae and M. tuberculosis and 44% homology with the GroES heat shock protein of Escherichia coli (1, 20, 33), and the protein was localized to the cell wall and cytosol of M. leprae (29). The protein induced strong DTH and Th1 cytokine production, and limiting cell dilution analysis showed a high frequency of responding T cells from blood or from lepromin-induced Mitsuda reactions (17, 19, 35), but it also reacted with human “suppressor” T-cell clones (27) and was reported either to suppress (32) or to induce (9) DTH responses in lepromatous leprosy patients. This study was performed at the level of individual peptide determinants, with additional emphasis on the analysis of HLA class II genetic associations. Using a comprehensive set of GroES peptides of the M. leprae and M. tuberculosis sequences, the aim of this study has been to identify any differences in the proliferation of blood mononuclear cells between paucibacillary or multibacillary leprosy patients and healthy leprosy contacts or medical staff in Thailand. Possible HLA associations were ascertained on the basis of typing for HLA-DR and -DQ alleles and by peptide binding to purified DR molecules.