Toxoplasma gondii surface antigen-1 in sera of HIV-infected patients as an indicator of reactivated toxoplasmosis

Abstract

The major surface antigen from the proliferative form of Toxoplasma gondii (P-30 or SAG-1) was chosen as a target for exploration of Toxoplasma gondii reactivation in sera from immunocompromised patients. Samples were obtained from 37 HIV-infected subjects with lymphocyte levels of CD4+ <200/mm3. The prevalence of IgG antibodies to Toxoplasma gondii was 64.9 %. Ten patients had clinical symptoms of reactivated toxoplasmosis; eight of these had Toxoplasma encephalitis. The SAG-1 epitopes were found as circulating antigen in five cases with an immunocapture enzyme immunoassay (EIA). The EIA was improved with an IgG1 monoclonal antibody to SAG-1 and a streptavidinbiotin amplification. The sensitivity, specificity and positive predictive value were 30, 92 and 60 %, respectively. The SAG-1 levels were compared with different biological parameters such as HIV p24 antigen, β2 microglobulin, CD4+ cell count and IgG antibodies to Toxoplasma gondii. The levels of SAG-1 in these patients were significantly higher than those in the 75 healthy control persons with or without a chronic Toxoplasma gondii infection. Therefore, SAG-1 may be involved as a marker of reactivated toxoplasmosis in HIV-infected patients. © 1995 Springer-Verlag.