Vitronectin (S protein) augments the functional activity of monocyte receptors for IgG and complement C3b

Abstract

An arginine-glycine-aspartic acid sequence (RGD in the single letter code for amino acids) is present in the cell attachment site of both vitronectin and fibronectin. Inasmuch as fibronectin and synthetic peptides containing RGD enhance ingestion of opsonized particles by monocytes, we investigated the effects of vitronectin on phagocytosis by monocytes of sheep erythrocytes bearing IgG (EA) or complement C3b (EC3b). Peripheral blood monocytes were isolated by countercurrent elutriation and allowed to adhere to slides that had been coated with either vitronectin or fibronectin. Next, EA or EC3b were incubated with the adherent monocytes, and phagocytosis was subsequently quantified. Vitronectin caused the same dose dependent increase in phagocytosis as fibronectin. The augmentation of phagocytosis of EA induced by vitronectin could be inhibited by the F(ab')2 fragments of anti- vitronectin IgG but not by preimmune F(ab')2. The maximum phagocytosis of EA induced by vitronectin could not be enhanced by the addition of fibronectin, suggesting that vitronectin and fibronectin act on the same population of monocytes and that the two proteins stimulate the same mechanism through which the enhanced phagocytosis is mediated. Fibronectin and vitronectin caused a tenfold increase in the attachment of EC3b to monocytes, but phagocytosis was augmented minimally. These studies demonstrate that vitronectin modulates interactions between monocytes and opsonized particles.

Vitronectin in liver disorders: Biochemical and immunohistochemical studies

“…They were also localized continuously around inflammatory cells such as macrophages, neutrophils and lymphocytes that infiltrated into these regions, around sinusoidal endothelial cells, Ito cells and hepatocytes and in intercellular spaces among these cells. Parker, Frame and Elstad (38) reported that VN modulates interactions between inflammatory cells and opsonized particles. The results of our study support these findings.…”

Vitronectin (S protein) is associated with platelets

“…The proteins were transferred to nitrocellulose paper (Towbin et al, 1979). and the paper was incubated with TBS-milk at RT (Parker et al 1988). After 30 min the paper was washed with TBS.…”

“…Recently. vitronectin was shown to augment the activity of monocyte receptors for IgG and complement C3b (Parker et al 1988). and increased expression of vitronectin receptors appears to correlate with differentiation of monocytes into macrophages (Charo et al,198 7).…”

S‐Protein Is Synthesized by Human Monocytes and Macrophages in Vitro

“…Both fibronectin and S-protein belong to a family of adhesive proteins which share an Arg-Gly-Asp amino acid sequence in the cell attachment site [37]. The platelet receptor gpIIb-IIIa for Arg-Gly-Asp [36] is also present on monocytes [5,8] and may be the S-protein receptor on these cells [32]. The phagocytes may thus produce their own adhesion molecules, which bind to cellular receptors and take part in the attachmetit and also enhance the Fc and C3b receptor activities [32] of the cells in the tissues.…”

“…The platelet receptor gpIIb-IIIa for Arg-Gly-Asp [36] is also present on monocytes [5,8] and may be the S-protein receptor on these cells [32]. The phagocytes may thus produce their own adhesion molecules, which bind to cellular receptors and take part in the attachmetit and also enhance the Fc and C3b receptor activities [32] of the cells in the tissues. These functions, together with the capacity of S-protein to inhibit the lytic effect of the phagocyte complement components and its possible involvement in the regulation of macrophage-derived coagulation factors, demonstrate that synthesis of S-protein by mononuclear phagocytes may be of great biological importance in the local tissue environment.…”