Trypanosoma musculi survival in the kidneys of chronically infected mice: kidney form ultrastructure, surface characteristics, and serological interactions.

After elimination of Trypanosoma musculi from the general circulation by the immune responses of infected mice, the animals are resistant to reinfection. Yet, parasites survive in the vasa recta of the kidneys for the life of these mice. These kidney forms (KF) actively reproduce in an environment that provides the necessary nutrients and appears to prevent their elimination from these capillaries by the hosts' immune responses. Comparative studies conducted with KF and the bloodstream forms (BSF) indicate that, although both forms appear to be similar morphologically at the ultrastructural level, they differ in their surface reactivities with lectins and tolerance to various pH and solute concentrations. Although antibodies are not detected on the surfaces of KF, urea levels approximating those in the vasa recta dissociate antibody from the surfaces of BSF. The data suggest that parasites found in the vasa recta of these chronically infected mice differ from the BSF and are protected from the humoral and cell-mediated immune responses of the murine hosts by the concentrated solutes present in these capillaries. The KF may be killed by these same immune effector mechanisms upon leaving the capillaries of the kidneys and, therefore, not be found in the general circulation of these chronically infected immune hosts.