Alterations in the distribution and proliferative responses of rhesus monkey peripheral blood and spleen cells during malaria (Plasmodium knowlesi) infection.

Rhesus monkeys are used frequently as animal models in malaria research, but few studies have evaluated lymphocyte functions in these animals after experimental infections with the primate malarial parasite Plasmodium knowlesi. In this study, the distribution and mitogen responses of mononuclear cells in the peripheral blood and spleens of 16 P. knowlesi-infected rhesus monkeys were followed. All animals included in the study developed acute infections and were bled out with parasitemias of more than 50%. With progression of the infection, alterations in the peripheral blood mononuclear cells were observed, including decreases in the percentage of T cells (measured by E rosette formation) and the total numbers of E and EAC rosette-forming cells per cubic millimeter. In addition, peripheral blood mononuclear cells displayed reduced responses to mitogen stimulation with phytohemagglutinin, concanavalin A, and pokeweed mitogen. Peripheral blood mononuclear cells from infected animals showed similar reductions in mitogen responses when cultured in media containing 15% autologous pre- or postinfection plasma. The mitogen responses of spleen cells did not appear to be affected, but a significant reduction in the proportion of splenic T cells was observed. These lymphocyte changes in P. knowlesi-infected rhesus monkeys are similar to those reported for mice with acute rodent malaria and for humans with chronic Plasmodium falciparum infections.