Receptor-mediated phagocytosis of rat macrophages is regulated differentially for opsonized particles and non-opsonized particles containing beta-glucan

Experiments were conducted to test the hypothesis that opsonic and non-opso nic phagocytic capacities are differentially regulated by resting and wound -derived macrophages. Furthermore, the phagocytosis of non-opsonized zymosa n and beta -glucan particles was quantified to determine whether cells diff erentially regulate non-opsonic lectinophagocytosis in accordance with the carbohydrate composition of the ligand. In that regard, wound macrophages e xhibited profound differential regulation in lectinophagocytosis with a sev en-fold increase in phagocytosis of beta -glucan particles following overni ght culture but with a relatively modest increase in internalization of man nan-containing zymosan. Cultured peritoneal macrophages increased uptake of both particles similarly. Upon activation with interferon-gamma /lipopolys accharide (IFN-gamma /LPS), wound macrophages selectively suppressed beta - glucan ingestion, while phagocytosis of zymosan particles was unaffected. L ectinophagocytosis was decreased in activated peritoneal macrophages regard less of particle composition and was due in part to a nitric oxide-dependen t mechanism which was without a role in regulation of wound macrophage lect inophagocytosis. Overnight culture of wound macrophages suppressed their ca pacity for opsonic-dependent phagocytosis independently of activation, wher eas suppression of phagocytosis by peritoneal macrophages was activation-de pendent. Regulation of all three phagocytic pathways was achieved distinctl y by peritoneal and wound-derived macrophages, with changes found in the pe rcentage of resident peritoneal macrophages capable of phagocytosis, wherea s the phagocytic capacity of wound macrophages was primarily affected by th e number of particles ingested by individual cells. Taken together, these f indings demonstrate that the differential regulation of phagocytic pathways encompasses the nature of the phagocytic particle, the site from which mac rophages are obtained, their response to activating agents and the mechanis m through which the cell population alters its phagocytic potential.