Roles of macrophage Fc and C3b receptors in phagocytosis of immunologically coated Cryptococcus neoformans.

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Abstract
The roles of macrophage Fc and C3b [b fragment of complement component 3] receptors in the cell''s interaction with encapsulated C. neoformans were studied. The effects of a lymphokine that enhances macrophage complement receptor function, the effects of ingestion of soluble immune complexes and the effects of corticosteroid treatment upon the ability of macrophages to phagocytize cryptococci via these receptors were defined. Neither uncoated nor C3-coated cryptococci were phagocytized; IgG-coated cryptococci were avidly phagocytized by mouse peritoneal macrophages. Treatment of macrophages with the lymphokine enabled them to ingest C3-coated cryptococci. Prior ingestion of soluble immune complexes severely compromised macrophages'' ability to phagocytize cryptococci via their Fc receptors but did not affect their ability to ingest cryptococci via their complement receptors. Corticosteroid treatment severely impaired the ability of macrophages to respond to the lymphokine. Based upon these experimental observations, a model for normal host defense mechanisms against disease due to C. neoformans was constructed.