Trypanosoma musculi infection in B-cell-deficient mice.

The course of infection with Trypanosoma musculi was assessed in mice deprived of B-lymphocytes by administration, from birth, of rabbit antiserum to mouse immunoglobulin M (IgM). Initial control of parasitemia leading to the first crisis and establishment of the plateau phase was unaffected by lack of B-lymphocyte function, although multiplicative forms persisted throughout the infection in anti-IgM-treated mice, instead of disappearing after the first crisis as in intact mice. Elimination of trypanosomes after the second crisis was not observed in anti-IgM-treated mice, which maintained high numbers of parasites in the blood and peritoneal cavity, resulting in some mortality. A temporary reduction in parasitemia was achieved in anti-IgM-treated mice by transfusion of immune plasma. Immunodepression, as measured by splenic mitogen responsiveness, and splenomegaly were both observed in anti-IgM-treated as well as in intact mice, indicating that these features of murine trypanosomiasis are independent of B-lymphocyte function. Since in T. musculi infection parasitemia can be controlled initially but not eliminated in mice lacking B-cell function, the only crucial protection provided by antibody would appear to be in curing the infection after the second crisis.