Receptors for cold-insoluble globulin (plasma fibronectin) on human monocytes.

Abstract

This investigation focused on the role played by cold-insoluble globulin (CIg, plasma fibronectin) in monocyte function. Surface-bound CIg mediated a concentration-dependent of human blood monocytes to gelatin-coated surfaces. CIg also mediated the binding of gelatin-coated particles such as latex beads or tanned erythrocytes to surface-bound human monocytes. However, CIg did not mediate particle ingestion. Subfractionated CIg that was highly enriched in monomeric forms (zone II CIg, mol wt 190,000-235,000) was less effective than were fractions enriched in dimeric forms (zone I CIg, mol wt 450,000) in promoting monocyte attachment. Binding of CIg to a gelatin or plastic surface occurred in the absence of divalent cations, but monocyte attachment to CIg-coated surfaces required divalent cations, Mg++ being much more effective than Ca++. Cation-dependent cell attachment was reversible in that bound cells could be released by treatment with EDTA. Serum-mediated binding of monocytes to gelatin-coated plastic dishes was a result of its content of CIg because the binding activity was abolished by removal of CIg from serum, and could be restored by readdition of purified CIg. Treatment of monocytes with trypsin abolished subsequent cell attachment to CIg-gelatin surfaces or particles. Expression of certain other known monocyte membrane receptors (Fc and C3b) was markedly enhanced as a result of CIg-monocyte interaction. These several observations indicate that monocytes bear membrane receptors (termed receptor cold-insoluble globulin) for surface-bound CIg.

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

“…1). Fn also increased monocyte phagocytosis of EA in a dose-dependent fashion and increased monocyte rosettes with both EC3b and EA as described (7,8). In striking contrast, Fn affected none of these functions of neutrophils.…”

“…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.…”

“…Although some investigators have been able to demonstrate adherence of Fn-coated particles to PMN (27,28), in other systems, binding of PMN to Fn has not been observed (8). No investigators have been able to demonstrate that PMN will ingest particles opsonized solely by Fn.…”

Fibronectin stimulates macrophage uptake of low density lipoprotein-heparin-collagen complexes.

“…Consequently, lipoprotein-driven, cholesterol esterification measured in these cells was limited by the slow rate of lysosomal hydrolysis of endocytosed LDL. 1 Although it has been suggested that the interaction of Fn with glycosaminoglycans and collagen may have important biologic consequences in localizing monocyte-macrophages at sites of tissue injury and stimulating the uptake of tissue debris, 5 "" 8 it was not clear from our earlier studies if the enhanced uptake of LDL matrix complexes by macrophages was a consequence of simply insolubilizing LDL with matrix compo-nents or due to the presence of Fn in the model matrix. Integral to the latter phenomenon would be the interaction of lipoprotein matrix complexes with Fn.…”

The immunoreactivity, ligand, and cell binding characteristics of rheumatoid synovial fluid fibronectin

“…Known effects of fibronectin on the promotion of fibroblast and monocyte adherence and migration (1)(2)(3)(4) suggest that the high levels of fibronectin in rheumatoid arthritis (RA) synovial fluid (5-9) may influence the function of cells that compose the proliferated synovial lining. In addition, the opsonic activity of fibronectin that is displayed for denatured collagen and fibrin (1 0-1 2) may facilitate the clearance of these proteins from the inflamed joint.…”