Protective effects of specific antibodies in Trypanosoma cruzi infections.

The action of immune sera from animals with chronic Chagas disease on Trypanosoma cruzi bloodstream forms (Y and CL strains) was investigated. Y strain trypomastigotes were agglutinated by anti-CL or anti-Y immune sera and their infectivity was decreased when inoculated into normal mice. CL strain trypomastigotes, however, remained apparently unchanged, with neither agglutination nor decline of infectivity being observed after incubation with both immune sera. Sera from three patients with chronic Chagas disease clearly agglutinated and two of them decreased the infectivity of Y strain trypomastigotes. Passive transfer of immunity was achieved in mice that recieved anti-CL or anti-Y immune sera and that were challenged with Y strain parasites. These results suggest that humoral immunity participates in the protective immune response against T. cruzi and that bloodstream trypomastigotes represent a more suitable model for studies of antigenic variation in these infections.