Early lymphocyte trapping in malaria infections: a particulate antigen mediated phenomenon.

During the course of rodent malaria a marked decrease in the numbers of circulating lymphocytes within the peripheral blood occurred 2-4 days post-infection. Monocytes and polymorphs did not show the same degree of decline. For both avirulent Plasmodium yoelii and lethal Plasmodium berghei infections lymphocyte numbers returned to control levels by day 6-8 post-infection. While these levels were maintained until clearance of P. yoelii infection, a sustained and abnormal increase occurred during P. berghei infection. Early lymphocyte depletion was also observed following Babesia microti and Plasmodium vinckei petteri infections, and could be induced by freeze-thawed P. yoelii infected blood and its particulate, but not soluble, fraction. Corynebacterium parvum and sheep red blood cells had no depressant effect on peripheral blood lymphocyte counts. Cell trapping experiments indicated that peripheral blood lymphocytes were preferentially recruited to the spleen in the initial stages of infection. Cell surface marker tests showed that the major cell type involved was Thy-1.2+ T-lymphocytes.