IMMUNOGENICITY OF THE RECOMBINANT SAPA PROTEIN OF TRYPANOSOMA-CRUZI FOR MICE

The humoral and cellular immune responses induced by the recombinant S APA (shed acute phase antigen) of Trypanosoma cruzi were studied in mi ce and correlated with the immunologic control of parasitemia. The imm unizing schedule used consisted of 2 weekly injections of 50 mu g glut athione-S-transferase (GST)-SAPA in Freund's adjuvant. Specific alpha aGST-SAPA antibodies were detected by enzyme-linked immunosorbent assa y 1 wk after each antigen dose, the concentration of antibodies after tile second injection being 30-fold higher than after the first. Immed iate- (ITH) and delayed-type hypersensitivity (DTH) reactions were obs erved as footpad swelling after injecting 50 mu g GST-SAPA in preimmun ized mice as compared to naive controls. Adoptive transfer experiments indicated that these cutaneous reactions were mediated by lymphoid ce lls and not by serum. Both humoral and cellular responses were specifi c for the GST-SAPA antigen and did not cross-react with either the GST or the recombinant GST-1 T. cruzi antigen. Immunized mice that had de veloped high levels of antibody and DTH reaction to GST-SAPA were able to control the level of parasitemia after challenge with 10(3) blood trypomastigotes. The levels of parasitemia obtained were lowered to ab out 1/3 (P < 0.05) and mortality at day 60 was reduced from 67 to 25% (P = 0.085). Comparison of this immunizing method with other schedules involving more injections or higher antigen doses indicates that cont rol of parasitemia can be obtained with low amounts of antigen and see ms to be associated with the development of DTH.