Lymphocyte function in experimental African trypanosomiasis. VI. Parasite-specific immunosuppression.

The ability of mice infected with African trypanosomes to produce antibodies to the surface antigen of the infecting trypanosome variant antigenic type upon primary and secondary exposure was examined. C57BL/10SnJ mice were infected initially with Trypanosoma rhodesiense clone LouTat 1.0. Surface antigen-specific antibody titers (IgM and IgG) to the infecting variant were measured throughout the course of infection; when the titers were sufficiently low, mice were reinfected with LouTat 1.0 trypanosomes and the antibody response was measured. Results demonstrate that mice in the early stage of infection exhibited transient suppression of antibody responses to LouTat 1.0 upon reexposure. In contrast, mice in the terminal phase of the disease were completely suppressed in their ability to mount a humoral response to LouTat 1.0. Trypanocidal chemotherapy of mice restored immunoresponsiveness in that treated mice responded with both IgM and IgG surface antigen-specific antibody to LouTat 1.0. The resulting antibody response, however, was more indicative of a primary humoral response to the parasites rather than a true secondary immune response.