Immune phagocytosis of Plasmodium yoelii-infected erythrocytes by macrophages and eosinophils.

Unstimulated peritoneal cells from C57Bl mice were allowed to phagocytose in vitro different mixtures of Percoll-separated parasitized and non-parasitized erythrocytes (PE and NPE) from the blood of mice infected with Plasmodium yoelii in the presence of immune and normal serum. Immune serum caused a significant enhancement of phagocytosis, and both the number of PE adhering to and/or ingested by 100 macrophages and the number of the latter cells engaged in phagocytosis was increased. The effect of immune serum was more marked when the ratio of PE/macrophages was 5--40/1, but was less at a ratio of 80/1, when considerable phagocytosis of PE occurred in the presence of normal serum. From 83--100% of the phagocytosed cells were parasitized erythrocytes, even when the ratio of PE/NPE was as low as 1/15. In the system used, macrophages were unable to discriminate between non-parasitized erythrocytes from infected mice and normal erythrocytes. Eosinophils were also observed to engage in phagocytosis of parasitized erythrocytes. Their activity was entirely dependent on immune serum and was never directed against non-parasitized red blood cells.