A RECOMBINANT PROTEIN-BASED ON THE TRYPANOSOMA-CRUZI METACYCLIC TRYPOMASTIGOTE 82-KILODALTON ANTIGEN THAT INDUCES AN EFFECTIVE IMMUNE-RESPONSE TO ACUTE INFECTION

To further investigate the immunological properties of the stage-speci fic 82-kDa glycoprotein (gp82) of Trypanosoma cruzi metacyclic trypoma stigotes, previously shown to induce antigen-specific humoral and T-ce ll responses in mice, we performed a series of experiments with recomb inant proteins containing sequences of gp82 fused to glutathione S-tra nsferase. Of five fusion proteins tested, only J18b and J18b1, the car boxy-proximal peptides containing amino acids 224 to 516 and 303 to 51 6, respectively, were recognized by monoclonal antibody 3F6 as well as by various anti-T. cruzi antisera and, when administered to mice, wer e capable of eliciting antibodies directed to the native gp82. The ami no-terminal peptide and other carboxy-terminal recombinant proteins la cking the central domain of gp82 (amino acids 224 to 356), which is ex posed on the surface of live metacyclic forms, did not display any of these properties. Spleen cells derived from mice immunized with any of the five recombinant proteins proliferated in vitro in the presence o f native gp82, J18b was the most stimulatory, whereas J18b3, the pepti de containing amino acids 408 to 516, elicited the weakest response, W hen BALB/c mice immunized with J18b antigen plus Al(OH)(3) as adjuvant were challenged with 10(5) metacyclic trypomastigotes, 85% of them re sisted acute infection, in comparison with control mice that received glutathione S-transferase plus adjuvant. Antibodies induced by J18b pr otein lacked agglutinating or complement-dependent lytic activity and failed to neutralize parasite infectivity, On the other hand, CD4+ T c ells from the spleens of J18b-immunized mice displayed an intense prol iferative activity upon stimulation with 1.25 mu g of native gp82 per ml, which resulted in increased production of gamma interferon, a cyto kine associated with resistance to T. cruzi infection.