Immune responses of trypanoresistant and trypanosusceptible cattle after cyclic infection with Trypanosoma congolense.

To study the mechanisms by which certain West African taurine cattle are able to resist trypanosomiasis, the disease course and several immune parameters were examined in eleven Baoulé and five Zebu cattle after infection with tsetse-transmitted T. congolense (clone 1180 of stock Serengeti/71/STIB/212). All animals showed a similar onset of parasitemia but subsequently a continuum of disease was observed ranging from four Baoulé which were mildly susceptible (controlled parasitemia by week 10 post-infection and had little anemia) to two Baoulé and two Zebu which were highly susceptible (unable to control parasitemia, severe anemia leading to death or drug treatment in extremis). The remaining five Baoulé and three Zebu showed intermediate susceptibility. Although the most resistant animals were of the Baoulé breed, there was a spectrum of susceptibility which crossed the two breeds. Neutralizing antibody to metacyclic trypanosome antigens was detectable by day 18 in four of the mildly susceptible and three of the highly susceptible individuals but such antibodies were delayed in the remaining one severely susceptible animal. Neutralizing antibodies to antigenic variants of the first peak of blood trypanosomes were of significantly higher titre and appeared earlier in the four mildly susceptible as opposed to the highly susceptible animals. No differences in lymphocyte in vitro mitogen responses were observed in these animals except shortly before death in those severely affected. In vitro lymphocyte responses to allogeneic cells did appear to correlate with disease severity, in that animals with mild disease showed little immunosuppression of this response whilst in severely affected individuals the response was almost ablated.