RESUMO
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.
Assuntos
Antígenos de Protozoários/imunologia , Epitopos de Linfócito T/imunologia , Epitopos Imunodominantes , Proteínas de Protozoários/imunologia , Trypanosoma cruzi/imunologia , Sequência de Aminoácidos , Animais , Anticorpos Antiprotozoários/sangue , Antígenos de Protozoários/química , Doença de Chagas/imunologia , Antígenos HLA-DQ/genética , Antígenos HLA-DQ/metabolismo , Cadeias alfa de HLA-DQ , Antígeno HLA-DR1/genética , Antígeno HLA-DR1/metabolismo , Antígeno HLA-DR2/genética , Antígeno HLA-DR2/metabolismo , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Ligação Proteica , Proteínas de Protozoários/químicaRESUMO
We compared plasma tumor necrosis factor-alpha (TNF-alpha) levels among asymptomatic/"indeterminate" Chagas disease patients (ASY) and patients across the clinical spectrum of chronic Chagas disease cardiomyopathy (CCC). Idiopathic dilated cardiomyopathy (DCM) patients and normal controls (NC) were included as controls. ASY Chagas disease patients had significantly higher plasma TNF-alpha levels than NC. TNF-alpha levels among severe CCC patients with significant left ventricular (LV) dysfunction were similar to those of DCM patients, showing average 2-fold higher levels than CCC patients without LV dysfunction and ASY patients, and 8-fold higher levels than NC. In Chagas disease, chronic TNF-a production prior to heart failure may play a role in CCC progression.
Assuntos
Cardiomiopatia Dilatada/sangue , Doença de Chagas/sangue , Fator de Necrose Tumoral alfa/metabolismo , Adulto , Idoso , Idoso de 80 Anos ou mais , Estudos de Casos e Controles , Cardiomiopatia Chagásica/sangue , Doença Crônica , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Índice de Gravidade de Doença , Estatísticas não Paramétricas , Disfunção Ventricular Esquerda/sangueRESUMO
We compared plasma tumor necrosis factor-alpha (TNF-alpha) levels among asymptomatic/"indeterminate" Chagas disease patients (ASY) and patients across the clinical spectrum of chronic Chagas disease cardiomyopathy (CCC). Idiopathic dilated cardiomyopathy (DCM) patients and normal controls (NC) were included as controls. ASY Chagas disease patients had significantly higher plasma TNF-alpha levels than NC. TNF-alpha levels among severe CCC patients with significant left ventricular (LV) dysfunction were similar to those of DCM patients, showing average 2-fold higher levels than CCC patients without LV dysfunction and ASY patients, and 8-fold higher levels than NC. In Chagas disease, chronic TNF-a production prior to heart failure may play a role in CCC progression