Role of antibody and complement in the control of Encephalitozoon cuniculi infections by rabbit macrophages.

The capacity of mononuclear peritoneal macrophages to phagocytose Encephalitozoon cuniculi was tested in vitro. Normal rabbit serum or cell culture medium had little effect on the rate of removal of organisms by rabbit peritoneal macrophages. Treatment with immune rabbit serum or immune rabbit immunoglobulin G significantly (P less than 0.001) increased phagocytosis of E. cuniculi. Guinea pig complement was found to significantly (P less than 0.001) enhance the phagocytosis of antibody-treated E. cuniculi. With few exceptions, induced (peritoneal exudate) macrophages were no more effective than unstimulated (resident) macrophages in the phagocytosis of E. cuniculi. Secondary lysosomes labeled with ferritin were seen fusing with phagosomes containing immune rabbit serum-treated parasites. Phagosome-lysosome fusion was not observed when parasites were treated with either normal rabbit serum or culture medium. The results of the present study suggest a role for antibody enhancement of phagocytosis and intracellular killing as a mechanism of resistance to encephalitozoonosis in rabbits.