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 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.The process of phagocytosis by vertebrate phagocytes is markedly enhanced by humoral recognition factors called opsonins . Immune opsonins are antibody or complement proteins that interact with foreign antigens and with receptors on the surface of phagocytic cells (26, 36) . There also exist opsonins that enhance the uptake of colloidal material by macrophages of the reticuloendothelial system that are not immune proteins (34). One such nonimmune opsonin has been purified from rat (1,2,6,22) and human serum (4) and was originally designated a-2-macroglobulin on account of its electrophoretic mobility and size (2,22) . More recent studies have demonstrated that this nonimmune opsonin isolated from human serum is identical to cold-insoluble globulin (CIg) or fibronectin (5), a high molecular weight adhesive glycoprotein, a form of which is also found on the surface of many cell types (10,38) .Up until now, quantitation of the opsonic activity of CIg has depended largely on a liver slice assay utilizing radiolabeled,

Studies on the fibronectin receptors of human peripheral blood leukocytes. Morphologic and functional characterization.

“…There is evidence from a number of systems that monocytes and macrophages bind Fn at the plasma membrane (7)(8)(9)(10). It has been suggested (25) that fluidphase Fn will not bind to cells and that a conformational change in Fn, induced by binding to other molecules, is required for cell binding.…”

“…C 1, C4, C2, and C3 were then added sequentially as previously described (10). The concentration of C4 was limited to prevent interaction of EAC 14 with C3b receptors.…”

A 70-kDa amino-terminal fibronectin fragment supports gelatin binding to macrophages and decreases gelatinase activity

“…At sites of injury and during matrix remodeling fibronectin may serve as a coordinator between cells and the extracellular environment. For instance, the interaction between fibronectin and cells from the mononuclear phagocyte system affects chemotaxis, adherence, secretion, and phagocytosis [3][4][5][6][7][8]. We previously reported that association of macrophages with a 70-kDa amino-terminal fibronectin fragment and gelatin initiated a cellular response that induced 125 I-radiolabeled gelatin binding to the cells [1].…”

Opsonic activity of plasma fibronectin for Staphylococcus aureus by human alveolar macrophages: Inefficacy of trypsin-sensitive staphylococcal fibronectin receptor.

“…It was suggested that FN may be an opsonic regulator of macrophage function, by experiments using Kupffer cells (Saba and Jaffe 1980) and peritoneal macrophages (Gudewicz et al 1980). It seems likely that FN is relatively rich in the microenvironment of the human lung according to the present analysis of FN in bronchoalveolar lavage fluid using ELISA.…”