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

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Abstract
The present study demonstrates the ability of plasma fibronectin or cold-insoluble globulin (Clg) to promote the uptake of 125I-labeled, gelatin-coated latex beads (g-Ltx*) by monolayers of peritoneal macrophages (PM). The uptake of g-Ltx* by PM was enhanced by Clg 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 degrees C after particle uptake removed less than 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 greater than 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 Clg-dependent particle uptake. Phagocytosis of g-Ltx* by PM in the presence of Clg and heparin was confirmed by electron microscopy. Finally, g-Ltx* could also be effectively opsonized with Clg at 37 degrees C before their addition to the monolayers. These studies suggest that the recognition of g-Ltx* in the presence of Clg 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 Clg in the recognition and phagocytosis of gelatin-coated particles by phagocytic cells.