Immunoreactivity of the recombinant Rop2196–561 with a collection of sera from humans infected with T. gondii and other pathogens. The sera were divided into groups according to IgG IIF and IgA and IgM ISAGA or IIF with absorbed IgG sera. Groups A (n = 35), B (n = 21), C (n = 5), D (n = 16), and E (n = 26) are defined in Materials and Methods. All sera were tested by ELISA sensitized with 3 μg of Rop2196–561/ml. Bound antibodies were developed with horseradish peroxidase-labeled goat anti-human IgG (G), IgA (A), and IgM (M) and the chromogenic substrate. The relative absorbance is the mean absorbance value of test sera divided by the mean absorbance value of sera from negative controls (n = 5). The sera were used at an optimal dilution of 1:200 for IgG detection, with a cutoff value of 1.9, and an optimal dilution of 1:50 for IgA and IgM detection, with cutoff values of 1.8 (A) and 1.7 (M).