Abstract

The serologic activity of a cationic fraction (denoted CEF6) of Schistosoma mansoni soluble egg antigen was compared in an ELISA with that of the unpurified soluble egg antigen for the ability to detect human infections and for the prediction of chemotherapeutic success in patients followed up to 5 years post-treatment with oxamniquine. The cationic fraction correctly identified 100% of 20 patients as infected with S. mansoni; moreover, 50% (10 of 20) seroconverted to negative by 2 years post-treatment and 100% of 15 patients tested were negative 5 years post-treatment. In general, the cationic fraction was superior to the unpurified soluble egg antigen for the detection of infection and for the prediction of chemotherapeutic success. The cationic fraction also exhibited greater immunologic specificity over the unpurified soluble egg antigen in that the latter exhibited higher titers than the former to antibodies against heterologous parasite antigens (Fasciola hepatica, Clonorchis sinensis, Paragonimus westermani adult worms; Trichinella spiralis larvae). Moreover, rabbit antisera raised against egg antigens isolated from the precipitation formed when fresh S. mansoni eggs are incubated with S. mansoni infection of immunization sera (known as circumoval precipitin reactions or COP) reacted strongly with the cationic fraction in ELISA. In addition, antiserum to the cationic fraction as well as antisera against either of the two antigenic components of this fraction, known as antigens α1 and θ1, all give positive COP reactions when incubated with fresh S. mansoni eggs. This suggests that the cationic fraction antigens are a subcomponent of the COP reaction, a phenomenon which has been used as a highly sensitive and specific serological assay for the detection of S. mansoni infections.