Serodiagnosis of acute toxoplasmosis using a recombinant form of the dense granule antigen GRA6 in an enzyme-linked immunosorbent assay.

We developed an indirect enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of acute toxoplasmosis that used the recombinant granule antigen GRA6-GST as diagnostic antigen for the detection of IgG antibodies to Toxoplasma gondii in human sera. A total of 431 sera obtained from 336 patients with acute and chronic toxoplasmosis and from patients who were not infected with T. gondii were tested. Sera from patients with acute T. gondii infection, chronic infection, and no infection showed different absorbance values. For discrimination between the presence and the absence of acute toxoplasmosis the assay reached a specificity of 99.6%. Only one of the sera without significant anti-T. gondii. IgM antibodies showed a positive reaction to rGRA6-GST. The assay showed good intra- and interassay reproducibility (CV 6%/14%). We included a glutathione S-transferase (GST)-IgG enzyme immunoassay as a control assay in this study. Only 7 (4%) of 159 random sample sera reacted positively with GST.