Murine malaria: immune complexes inhibit Fc receptor-mediated phagocytosis

Immune complexes have been partially purified from the serum of Plasmodium berghei-infected mice by ultracentrifugation on 10 to 40% linear sucrose gradients, by precipitation with polyethylene glycol, and by gel filtration through Sephacryl S-300. The complexes contain gamma 1, gamma 2a, gamma 2b, and gamma 3 subclasses of mouse immunoglobulin G in differing amounts, as well as malarial antigen. Complexes isolated by all three methods inhibit Fc receptor-mediated phagocytosis by normal mouse peritoneal macrophages but do not inhibit attachment to the Fc receptor or to the C3 receptor or the ingestion of latex particles. The phagocytosis-inhibiting activity of the immune complexes can be partially removed by prior incubation with protein A-Sepharose CL-4B. Splenic macrophages, isolated from P. berghei-infected mice, may be already coated with immune complexes in vivo. Attachment of mouse erythrocytes sensitized with immunoglobulin G to these macrophages is greatly enhanced during malaria, but ingestion is not. These results suggest that immune complexes modulate the immune response to malaria by inhibiting immune phagocytosis and perhaps by interfering with other effector mechanisms. Further understanding of the influence of immune complexes and the antigens involved in these complexes may be useful in vaccine development and prophylaxis.