INDIVIDUALS FROM DIFFERENT POPULATIONS IDENTIFY MULTIPLE AND DIVERSE T-CELL DETERMINANTS ON MYCOBACTERIAL HSP70

The 70 kDa heat-shock protein (HSP) of Mycobacterium leprae stimulates both cellular and antibody responses in leprosy patients and subclini cally infected individuals despite partial homology with host HSP70. F urthermore, mycobacterial HSP70 can act as a carrier protein in unprim ed mice, suggesting the presence of widely shared T-cell determinants on this protein. In order to elucidate the frequency and genetic restr iction of these T-cell epitopes, we have undertaken a systematic analy sis of the proliferative responses to 20mer peptides encompassing the whole protein in different populations. Caucasian BCG vaccinees who re sponded to recombinant M. leprae HSP70 identified multiple scattered T -cell determinants, four of which were recognized by 60% of subjects i n association with a variety of HLA-DR haplotypes. When a group of Nep ali leprosy and tuberculosis patients were tested, significant differe nces in the pattern of peptide recognition were observed. The dominant peptides recognized by Caucasian subjects were infrequently reactive and other peptides were stimulatory, again in association with a varie ty of HLA-DR phenotypes. The C-terminal 70 residues of the M. leprae H SP70 are specific to M. leprae and sera from lepromatous leprosy patie nts bind to this region. However, few T-cell determinants were identif ied in these residues, indicating that this region is unhelpful as a d iagnostic tool for detecting M. leprae-specific T-cell responses. When compared with the equivalent regions of the human HSP70, the commonly recognized peptides showed significant differences in amino-acid sequ ence. When taken in conjunction with the failure of human HSP70 to sti mulate M. leprae HSP70-reactive T-cell clones (E. Adams et al., unpubl ished observations), this finding indicates that the human T-cell resp onse to this protein is largely directed at mycobacterial-specific det erminants. The presence of multiple T-cell epitopes on M. leprae HSP70 with varied patterns of HLA-DR association suggests that the whole pr otein is required for stimulating effective T-cell responses in geneti cally diverse populations.