Trypanosome variable surface antigens: studies using two-dimensional gel electrophoresis and monoclonal antibodies

Variable surface antigens of cloned populations of African trypanosomes were studied using 2-dimensional gel electrophoresis and monoclonal antibodies. Two-dimensional gel maps showed that the only major differences in protein profiles of the non-nuclear materials from different clones of solubilized trypanosomes were attributable to the variable surface antigens and that purification doesn't alter these molecules, at least with respect to charge and apparent m.w. Purified variable surface antigens were used as immunogens and a number of monoclonal antibodies were derived using cell-fusion technology. In radioimmunoassay, each of the monoclonal reagents was shown to be specific for the immunizing antigen, and in immunofluorescence tests using acetone-fixed trypanosomes, each bound specifically to the clone from which the antigens were purified. Only 20% of the monoclonal reagents bound to living trypanosomes, however, providing evidence for both exposed and nonexposed antigenic sites on the variable surface antigens. Those reagents derived to a single antigen bound to different nonoverlapping antigenic sites, which were on the protein portion of the molecules and not the carbohydrate moieties. The data show that monoclonal antibodies are ideal probes for studying localization of antigenic sites on the antigen molecules and for studying antigen synthesis, glycosylation, and architecture in relation to the cell surface. In addition, the finding of exposed and nonexposed antigenic sites on trypanosome variable antigens allows a possible explanation for the role of the antigens in pathogenesis of African trypanosomiasis.