Human and primate malarial sera inhibit Fc receptor-mediated phagocytosis

Sera obtained from humans in P. falciparum-endemic regions and from P. vivax-infected Saimiri sciureus were assayed for their ability to inhibit Fc receptor-mediated phagocytosis. Some sera of humans exposed to P. falciparum from The Gambia, Sudan, and Thailand inhibited ingestion via the Fc receptor by normal human monocytes. In addition, sera from infected monkeys and a high molecular weight fraction of infected monkey serum inhibited ingestion of EIgG by normal monkey spleen macrophages. Generally, inhibition was correlated with higher parasitemia and higher IFA titers.