Avaliação do antígeno SAG2a recombinante de Toxoplasma gondii como um potencial marcador diagnóstico para Toxoplasmose humana aguda

Abstract

Recombinant proteins have been used for the serological diagnosis of Toxoplasma gondii infection to differentiate between the acute and chronic phases of toxoplasmosis. In this study, we evaluated the reactivity of IgG and IgG1 antibodies by immunoassays in acute and chronic phase sera from patients with toxoplasmosis against two recombinant antigens cloned and expressed in E. coli, SAG2A (full recombinant molecule) and SAG2A(DELTA) (truncated recombinant molecule deleted from the epitope recognized by A4D12 mAb). The performance of both recombinant antigens was compared with the soluble Toxoplasma antigen (STAg). Results demonstrated a higher IgG reactivity in acute sera with both STAg and SAG2A than in chronic phase sera and this difference was more evident for IgG1 antibodies to SAG2A antigen. Low reactivity to SAG2A(DELTA) antigen was found in human sera from acute or chronic phases. A high sensitivity (95%) and specificity (100%) was found for the indirect ELISA-IgGSAG2A. ELISA-IgG1-SAG2A sensitivity was analyzed separately for acute or chronic phase, showing values significantly higher for acute (90%) than for chronic (67%) phases. ELISA-IgG avidity using STAG was better for charactering sera with high avidity, while the ELISA-IgG1 using SAG2A was the best for this purpose. In conclusion, ELISA-IgG1-SAG2A may be a potential diagnostic tool to characterize the acute phase T. gondii infection. This is the first time that recombinat SAG2A antigen has been proposed as a molecular marker and the epitope recognized by the A4D12 mAb showed to be critical and valuable for application in diagnostic procedures.