title: T cell epitope characterization in tandemly repetitive Trypanosoma cruzi B13 protein.
abstract: Proteins containing tandemly repetitive sequences are present in several immunodominant protein antigens in pathogenic protozoan parasites. The tandemly repetitive Trypanosoma 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 B13 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 GQA were the major HLA contact residues. Among natural B13 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.
authors.affiliation: Laboratory of Immunology, Heart Institute (InCor), University of São Paulo School of Medicine, Av. Dr. Enéas de Carvalho Aguiar, 44, Bloco II, 9th andar, São Paulo, SP 05403-000, Brazil.
authors.forename: Lúcia C J
authors.initials: LC
authors.lastname: Abel
authors.forename: Leo K
authors.initials: LK
authors.lastname: Iwai
authors.forename: Wladia
authors.initials: W
authors.lastname: Viviani
authors.forename: Angelina M
authors.initials: AM
authors.lastname: Bilate
authors.forename: Kellen C
authors.initials: KC
authors.lastname: Faé
authors.forename: Renata C
authors.initials: RC
authors.lastname: Ferreira
authors.forename: Anna C
authors.initials: AC
authors.lastname: Goldberg
authors.forename: Luiz
authors.initials: L
authors.lastname: Juliano
authors.forename: Maria A
authors.initials: MA
authors.lastname: Juliano
authors.forename: Bárbara
authors.initials: B
authors.lastname: Ianni
authors.forename: Charles
authors.initials: C
authors.lastname: Mady
authors.forename: Arthur
authors.initials: A
authors.lastname: Gruber
authors.forename: Juergen
authors.initials: J
authors.lastname: Hammer
authors.forename: Francesco
authors.initials: F
authors.lastname: Sinigaglia
authors.forename: Jorge
authors.initials: J
authors.lastname: Kalil
authors.forename: Edecio
authors.initials: E
authors.lastname: Cunha-Neto
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D000953:Antigens, Protozoan / Q000737:chemistry / Q000276:immunology*; D014355:Chagas Disease / Q000276:immunology; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D006683:HLA-DQ Antigens / Q000235:genetics / Q000378:metabolism; D059848:HLA-DQ alpha-Chains; D015798:HLA-DR1 Antigen / Q000235:genetics / Q000378:metabolism; D015802:HLA-DR2 Antigen / Q000235:genetics / Q000378:metabolism; D006801:Humans; D016056:Immunodominant Epitopes; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000276:immunology*; D014349:Trypanosoma cruzi / Q000276:immunology*
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D018984:Epitopes, T-Lymphocyte; D006683:HLA-DQ Antigens; D059848:HLA-DQ alpha-Chains; C069050:HLA-DQA1 antigen; D015798:HLA-DR1 Antigen; D015802:HLA-DR2 Antigen; D016056:Immunodominant Epitopes; D015800:Protozoan Proteins