Fibronectin-mediated uptake of gelatin--coated latex particles by peritoneal macrophages

ABSTRACT The present study demonstrates the ability of plasma fibronectin or cold-insoluble globulin (CIg) to promote the uptake of ' 25 1-labeled, gelatin-coated latex beads (g-Ltx*) by monolayers of peritoneal macrophages (PM). The uptake of g-Ltx * by PM was enhanced by CIg in a concentration-dependent fashion and required the presence of heparin (10 U/ml) as an obligatory cofactor for maximal particle uptake. Treatment of PM monolayers with trypsin (1 mg/ml) for 15 min at 37 °C after particle uptake removed <15 % of the radioactivity incorporated by the monolayers. However, a similar trypsin treatment of the monolayers before the addition of latex particles depressed Clg-dependent uptake by>75 %. Pretreatment of PM monolayers with inhibitors of glycolysis effectively reduced the Clg-dependent uptake of latex. Similarly, pretreatment of monolayers with either inhibitors of protein synthesis or agents that disrupt cytoskeletal elements also significantly depressed CIg-dependent particle uptake. Phagocytosis of g-Ltx * by PM in the presence of CIg and heparin was confirmed by electron microscopy. Finally, g-Ltx * could also be effectively opsonized with CIg at 37°C before their addition to the monolayers. These studies suggest that the recognition of g-Ltx * in the presence of CIg required cell surface protein(s) and that subsequent phagocytosis of these particles b