Toxoplasmosis in Singapore.

The present paper reports research done in the following areas in the Parasitology Unit of the Department of Microbiology, National University of Singapore: determination of anti-Toxoplasma gondii antibodies in different IgG subclasses; immunoblot analysis of the antibody response to T. gondii and identification of key reactive epitopes; production and characterization of monoclonal antibodies to T. gondii; and the development of an IgM capture ELISA. IgG1 is the dominant subclass involved in the humoral response to T. gondii. IgG3 and IgG4 may be produced at low but significant levels. IgG2 production was not apparent. Immunoblot analysis of the positive sera revealed that the major antigens recognized by IgG and IgM antibodies were of MW 22, 35 and 67 kDa. Many of the bands observed in blots with positive sera were also present in blots with negative sera. The 22 kDa band was seen in majority of positive sera and was generally absent in negative sera. Anti-Toxoplasma sera also revealed IgA antibodies. Immunoblot analysis of the antigen revealed a 14 kDa band that reacted with all IgA positive sera. From a panel of monoclonals produced against T. gondii, one monoclonal, 5F3 (A) was selected for development of a monoclonal based IgM capture ELISA for detection of antibodies to 22 kDa and 41 kDa epitopes of T. gondii.