T cell epitope characterization in tandemly repetitive Trypanosoma cruzi B13 protein

Proteins containing tandemly repetitive sequences are present in several immunodominant protein antigens in pathogenic protozoan parasites. the tandemly repetitive Ttypanosoma cruzi B13 protein is recognized by IgG antibodies from 98% of Chagas' disease patients. Little is known about the molecular mechanisms that lead to the immunodominance of the repeated sequences, and there is limited information on T cell epitopes in such repetitive antigens. We finely characterized the T cell recognition of the tandemly repetitive, degenerate B13 protein by T cell lines, clones and PBMC from Chagas' disease cardiomyopathy (CCC), asymptomatic T cruzi infected (ASY) and non-infected individuals (N). PBMC proliferative responses to recombinant B 13 protein were restricted to individuals bearing HLA-DQA1*0501 (DQ7),-DR1, and -DR2; B13 peptides bound to the same HLA molecules in binding assays. the HLA-DQ7-restricted minimal T cell epitope [FGQAAAG(D/E)KP] was identified with an overlapping combinatorial peptide library including all B13 sequence variants in T cruzi Y strain B13 protein; the underlined small residues (G) under barQ (A) under bar were the major HLA contact residues. Among natural B 13 15-mer variant peptides, molecular modeling showed that several variant positions were solvent (TCR)-exposed, and substitutions at exposed positions abolished recognition. While natural B13 variant peptide S15.9 seems to be the immunodominant epitope for Chagas' disease patients, S15.4 was preferentially recognized by CCC rather than ASY patients, which may be pathogenically relevant. This is the first thorough characterization of T cell epitopes of a tandemly repetitive protozoan antigen and may suggest a role for T cell help in the immunodominance of protozoan repetitive antigens. (c) 2005 Elsevier SAS. All rights reserved.Univ São Paulo, Sch Med, Immunol Lab, Inst Heart,InCor, BR-05403000 São Paulo, BrazilUniv São Paulo, Sch Med, Gen Cardiopathies Div, Inst Heart,InCor, BR-05403000 São Paulo, BrazilUniv São Paulo, Sch Med, Div Clin Immunol & Allergy, Dept Med, BR-05403000 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biophys, São Paulo, BrazilBioxell, Milan, ItalyUniv São Paulo, Fac Vet Med & Zoothechny, Dept Pathol, BR-05508 São Paulo, BrazilUniv São Paulo, Inst Chem, Dept Biochem, BR-05508 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biophys, São Paulo, BrazilWeb of Scienc