Immunoconglutinin and suppression of an induced immune response by plasma from rats infected with Trypanosoma brucei rhodesiense.

Fresh plasma from rats infected with Trypanosoma brucei rhodesiense, incubated with splenic lymphocytes from rats previously immunized with sheep blood cells, suppressed the capacity of the splenic lymphocytes to produce antibody as was indicated by reductions in the numbers of hemolytic Jerne plaques produced by the treated cells. The effect was maximal in plasma samples drawn on the sixth to eighth day of infection when they contained elevated amounts of soluble immune complex, high titers of immunoconglutinin (IK), and reduced titers of lytic complement. We suggest that the active plasma may have affected the antibody-producing cells by one or both of two mechanisms. Soluble antigen-antibody complexes may have interacted with Fc receptors of activated lymphocytes to suppress antibody production. Alternatively, complement-fixing soluble immune complexes may have reacted with C3b receptors of the lymphocytes. These lymphocytes coated with the antigen for IK could then be injured by immunoconglutination.