Activity of human blood leukocytes against Toxoplasma gondii.

Previous reports on the ability of Toxoplasma gondii to multiply within human mononuclear phagocytes have supported the concept that the phagocytes may protect Toxoplasma from antibody and act as a transport mechanism for dissemination of the organism throughout the body. However, after phagocytosis of viable Toxoplasma, greater than 80% of freshly isolated human peripheral blood monocytes and 50% of polymorphonuclear leukocytes rapidly destroyed these intracellular organisms. Virtually no replication of Toxoplasma occurred within these cells, as determined by microscopic examination and by uptake of [3H]uracil. These results suggested that circulating phagocytes from humans restrict rather than facilitate the initial dissemination of Toxoplasma.