Analysis and partial epitope mapping of human T cell responses to Trypanosoma cruzi cysteinyl proteinase

Human infection with Trypanosoma cruzi (Chagas' disease) is usually accompanied by humoral and cellular immune responses to GP57/51, a major antigen that was recently identified as a prominent cysteinyl proteinase (cruzipain). The PBMC responses of 11 chronic chagasic patients and the properties of anti-cruzipain T cell lines are reported herein. GP57/51, isolated from Y strain epimastigotes (n-cruzipain) or the recombinant protein expressed in E. coli (r-cruzipain), elicited proliferative responses of variable intensity from the patient's PBMC. T cell lines were then generated using each of these antigens. These lines, which always carried the CD4+ phenotype, were reciprocally stimulated by n-cruzipain or r-cruzipain, the responses to the former being usually stronger. The analysis of cytokine production suggested that Th1-like subsets dominate the patient's responses: IFN-gamma was consistently induced on stimulation with either n-cruzipain or r-cruzipain. In contrast, IL-4 was present in very small concentrations or was undetectable. We then sought to define T cell epitopes of cruzipain using synthetic peptides spanning portions of the central (catalytic) domain and COOH-terminal extension. From a panel of 11 peptides, only one 33 mer peptide (P214) elicited a strong proliferative response on anti-cruzipain T cell lines, the intensity being comparable to that induced by r-cruzipain. Conversely, T cell lines started with P214 were responsive to either n-cruzipain or r-cruzipain, the proliferative responses again being accompanied by IFN-gamma production, but not IL-4. Interestingly, P214 is located in a conserved region of the catalytic domain of cruzipain, hence may propitiate opportunities for cross-recognition of other members of the papain superfamily. Fine epitope mapping should reveal whether structurally similar regions of host thiol-cathepsins can be potential targets for cross-reactive T cell responses during chronic human infection.