Fibronectin-Mediated Uptake of Gelatin-Coated Latex Particles by Peritoneal Macrophages

The present study demonstrates the ability of plasma fibronectin or cold-insoluble globulin (CIg) to promote the uptake of125I-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 75%. Pretreatment of PM monolayers with inhibitors of glycolysis effectively reduced the CIg-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 by PM was energy dependent and required intact intracellular cytoskeleton elements. Thus, PM monolayers provide a suitable system for further studies on the function of CIg in the recognition and phagocytosis of gelatin-coated particles by phagocytic cells.