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Survival of Trypanosoma musculi in the kidneys of chronically infected mice: kidney form reproduction and immunological reactions.

Trypanosoma musculi are detected in the blood of the mouse host within 3-5 days after infection. Peak parasitemia is reached within 10 days and parasites persist at a plateau level for 2-3 wk. There are no intracellular stages and the flagellates are eliminated from the peripheral blood within 4 wk. However, trypanosomes persist in the vasa recta of the kidneys and may be present for the life of the host. Infection provides lifelong resistance to reinfection. Kidney forms (KF) of T. musculi were isolated and studied to define their morphology, reproductive activity, and serological reactivity. Dividing epimastigotes and trypomastigote stages were present in kidneys. Multinucleate and rosette forms were common. Measurements of the coefficient of variation of the KF confirmed that the trypanosomes were actively reproducing. Direct immunofluorescence reactions with rabbit antimouse IgG + IgA + IgM detected antibodies on bloodstream forms (BSF) but not on the KF. However, indirect immunofluorescence tests using antisera collected from mice during early and late phases of the infections showed that KF were capable of reacting with antibodies. The reproductive activity displayed by the KF appears to be responsible for the continuous replacement of the trypanosomes that are killed by the immune responses of the resistant mice when they leave the vasa recta. Solute concentrations of the blood within the vasa recta appear to prevent antibodies from complexing with surface antigens of the parasites. These capillaries provide nutrients that allow the trypanosomes to reproduce and persist unaffected by the host immune responses.