Determinants of T cell reactivity to the Mycobacterium leprae GroES homologue

The 10-kDa protein Ag of Mycobacterium leprae, a human GroES hsp10 cognate, is a major T cell Ag in human leprosy infection. We investigated the mechanism for T cell responsiveness to this Ag according to the trimolecular interaction between T cell, peptide, and Ag-presenting element. This research was accomplished by mapping T cell epitopes in leprosy patients and correlating these responses with peptide-MHC binding affinities. We found that the majority of tuberculoid leprosy patients responded to peptides corresponding to residues 25-39 and 28-42. Truncation analysis of these peptides mapped the exact epitope to be within the overlapping region comprising residues 28-39. Responsiveness was correlated with the HLA-DRB5*0101 allele, which bound the peptides with moderate affinity. This allele is linked to HLA-DR2, which is associated with the resistant form of leprosy. Therefore, T cell responsiveness in tuberculoid leprosy may be mediated by the ability of HLA-DRB5*0101 to bind and present peptides of the immunodominant 10-kDa Ag.