Immunosuppression in bovine trypanosomiasis. The establishment of "memory" in cattle infected with T. congolense and the effect of post infection serum on in vitro (3H)-thymidine uptake by lymphocytes and on leucocyte migration.

Cattle infected with Trypanosoma congolense were intravenously immunized with Leptospira biflexa 15 days after trypanosomal infection. The primary immune response to L. biflexa was considerably reduced as compared to uninfected controls. The infected cattle mounted a secondary response when they were cured of trypanosomes by treatment with Berenil 25 days after infection and re-immunized 8 days later. The mean secondary response in these previously infected animals was lower tha, but not significantly different from that of the uninfected control animals. Serum collected 15, 20 and 25 days after infection was inhibitory to the migration of both autologous and isologous (control) peripheral blood leucocytes. The migration inhibitory activity was abolished by heating the serum at 56 degrees C for 30 minutes implying the involvement of a heat labile serum component(s). The same serum did not modify the mitogenic effect of PHA on autologous peripheral lymphocytes.