Trypanosoma cruzi metacyclic trypomastigotes: neutralization by the stage-specific monoclonal antibody 1G7 and immunogenicity of 90 kD surface antigen.

In this study we have investigated the ability of the stage-specific monoclonal antibody (MoAb) 1G7 to neutralize the infectivity of Trypanosoma cruzi metacyclic trypomastigotes (Tulahuen strain). Mice inoculated with metacyclics pre-incubated with 1G7 or the corresponding Fab fragments were found to develop greatly reduced parasitaemias compared with control animals. Similar results were obtained when mice received 1G7 (0.5 mg/mouse) before challenge with metacyclics. The 90 kD surface protein recognized by MoAb 1G7 was affinity purified and analysed for its immunogenic properties. Immunization of mice with 90 kD antigen induced antibodies that reacted with the native metacyclic surface antigen. The purified antigen was also capable of specifically stimulating the 'in-vitro' proliferation of 90 kD-primed T-cells. Furthermore, in a preliminary experiment in which mice were immunized with the purified polypeptide and challenged with Tulahuen metacyclics, low parasitaemia levels were observed in 60% of animals as opposed to non-immunized controls. The iodinated 90 kD antigen, which has previously been shown to be ubiquitous among T. cruzi strains, was precipitated by different immune sera including various chagasic sera.