Heterogeneity of Trichomonas vaginalis and discrimination among trichomonal isolates and subpopulations with sera of patients and experimentally infected mice.

The antibody response in trichomoniasis patients was examined with a variety of methodologies including enzyme-linked immunosorbent assays, indirect immunofluorescence, immunoblotting, and radioimmunoprecipitation-electrophoresis-autoradiography. Based on enzyme-linked immunosorbent assay recognition of trichomonal isolates, sera from patients with trichomoniasis were categorized into reactive class I (IA, IB, and IC) and nonreactive class II sera. A diminished ability to precipitate antibody-binding trichomonad membrane proteins by the whole cell radioimmunoprecipitation assay was noted from class IA to class II sera. The antigenic distinctions among various Trichomonas vaginalis isolates appeared due to high-molecular-weight protein antigens detected by class IA sera in a whole cell radioimmunoprecipitation assay. The heterogeneity in antigenic patterns was confirmed among the isolates with sera from experimental animals. Also, live T. vaginalis cells appear to have only a few of the entire repertoire of major immunogenic surface proteins accessible to antibody binding. Immunoblotting demonstrated that the high-molecular-weight proteins responsible for trichomonal isolate heterogeneity are present in all isolates. The data suggest that trichomonads of a given isolate express only a subset of internally synthesized protein antigens on their surface. Importantly, the presence of these protein antigens on T. vaginalis membranes correlated with antibody production in subcutaneously challenged mice. Finally, indirect immunofluorescence studies with highly reactive, pooled sera from either patients or mice revealed a subpopulation of nonstaining trichomonads. These data support the view that heterogeneity among T. vaginalis is dependent upon the surface disposition of highly immunogenic protein antigens. Strategies may now be developed not only for studying potential vaccine reagents, but also for examining possible antigenic phenotypic variations in this experimental model.