Opsonin-independent phagocytosis of periodate-treated sheep red blood cells by macrophages.

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Abstract
The opsonin-independent recognition of periodate-treated sheep red blood cells (P-SRBC) by macrophages was studied by observation of phagocytosis and the mechanism of the recognition was compared with those for other particles. Thioglycollate-elicited guinea pig peritoneal macrophages time-dependently ingested sheep red blood cells (SRBC) treated with periodate, as well as immunoglobulin G-coated sheep red blood cells (IgG-SRBC), zymosan (Z), serum-treated zymosan (STZ) and latex beads. Trypsinization of macrophages decreased the ingestion of P-SRBC to under 50% of the value of untreated cells and virtually abolished the ingestion of Z and STZ at a concentration that did not inhibit the phagocytosis of IgG-SRBC and latex beads. The decreased activities for P-SRBC recovered to 80% of the control value on incubation of the macrophages for 5h at 37.degree. C. The restoration of the ability to ingest P-SRBC following trypsin digestion was inhibited by cycloheximide and tunicamycin. Pretreatment of macrophages with ConA dose-dependently decreased ingestion of P-SRBC to under 50% of the original level, but did not decrease the internalization of IgG-SRBC and STZ. Rabbit anti-guinea pig peritoneal macrophage IgG abolished the ingestion of Z and caused marked and slight decreases of phagocytosis of IgG-SRBC and P-SRBC, respectively. These results indicated that the site of recognition of P-SRBC on the macrophage cell membrane could be composed of glycoproteins and is distinct from the receptors for C3b and Z. The role of plasma membrane components on macrophages in the action of opsonin-independent recognition is discussed in relation to the opsonin-mediated recognitions.