Immune mechanisms in C57B1 mice genetically resistant to Trypanosoma congolense infection. II. Aspects of the humoral response.

Some aspects of the humoral response in trypanotolerant C57B1 mice and susceptible A/J mice were investigated to determine the possible basis of trypanotolerance. When the hepatic uptake of 75Se-labelled T. congolense by infected mice was measured as an index of antibody production, it was found that only C57B1 mice could remove circulating labelled parasites, this ability persisting for several weeks after infection. Estimation of the immunoglobulin concentrations in both strains of mice showed that C57B1 mice developed a pronounced IgM response during the first parasitaemic wave, while A/J mice did not. Over the same period the IgM concentrations in C57B1 mice initially fell, but recovered at the time of peak parasitaemia. In contrast, A/J mice showed a continual fall in total IgG concentrations in the circulation until death 10 days after infection. Finally, it was shown that during the initial rising parasitaemia, the plaque forming cell responses of both strains of mice to sheep red blood cells were normal indicating that neither strain of mice was immunosuppressed. Also, A/J mice vaccinated with irradiated T. brucei on day 4 and C57B1 mice vaccinated either on day 4 or day 60 of a T. congolense infection were able to mount an effective immune response to the vaccine, as judged by the hepatic uptake of radiolabelled parasites. All of the results indicate that the trypanotolerance of C57B1 mice depends, at least in part, on their more efficient antibody response.