Characterization of an immunodominant antigenic epitope from Trypanosoma cruzi as a biomarker of chronic Chagas' disease pathology.

Nowadays, the techniques available for chronic Chagas' disease diagnosis are very sensitive; however, they do not allow discrimination of the patient's clinical stages of the disease. The present paper describes that three out of the five different repeats contained in the Trypanosoma cruzi TcCA-2 membrane protein (3972-FGQAAAGDKPPP, 6303-FGQAAAGDKPAP, and 3973-FGQAAAGDKPSL) are recognized with high sensitivity (>90%) by sera from chronic Chagas' disease patients and that they are not recognized by sera from patients in the acute phase of the disease. A total of 133 serum samples from chagasic patients and 50 serum samples from healthy donors were tested. In addition, sera from 15 patients with different autoimmune diseases, 43 serum samples from patients suffering an infectious disease other than Chagas' disease, and 38 serum samples from patients with nonchagasic cardiac disorders were also included in this study. The residue 3973 peptide shows a specificity of >98%, as it is not recognized by individuals with autoimmune and inflammatory processes or by patients with a nonchagasic cardiomyopathy. Remarkably, the levels of antibody against the 3973 epitope detected by the sera from Chagas' disease patients in the symptomatic chronic phase, involving cardiac or digestive alterations, are higher than those detected by the sera from Chagas' disease patients in the indeterminate phase of the disease. It is suggested that the diagnostic technique described could also be used to indicate the degree of pathology. The amino acids F, Q, and DKP located in the peptide at positions 1, 3, and 8 to 10, respectively, are essential to conform to the immunodominant antigenic epitope.