T-cell recognition of peptides from the Mycobacterium leprae 35 kDa protein in Thai leprosy patients, healthy contacts, and non-contacts.

The objective of the study was to identify Mycobacterium leprae-specific immunogenic peptides for the development of a skin test reagent. Such a reagent is required for the detection of M. leprae infection and possibly for the diagnosis of patients with active leprosy. For this purpose, we analyzed the in vitro responses of human peripheral blood mononuclear cell (PBMCs) to peptides from the 35 kDa protein of M. leprae. This protein is of interest since it has no homologue within the Mycobacterium tuberculosis complex, although it has a homologue in Mycobacterium avium. The subjects enrolled in the study were paucibacillary (PB) and multibacillary (MB) leprosy patients, healthy contacts, and non-contacts. Seventy-three PB and 124 MB leprosy patients were recruited from four leprosy clinics in Thailand. Fifty-seven healthy contacts were household contacts. Twenty non-leprosy contacts had no family history of or exposure to leprosy. PBMCs from individuals were tested for stimulation with 12 overlapping peptides from the M. leprae 35 kDa protein using the lymphocyte proliferation assay. These peptides were located in four areas containing three to six residues which were distinct for the M. leprae product in comparison to that from M. avium. Four peptides (p60-76, p132-151, p206-224 and p267-286), which were the most permissive from each region and recognized by non-contacts with significantly lower frequencies than other subject groups, were identified. From this preliminary result, we conclude that these four peptides were likely to be M. leprae-specific.