Interferon-gamma depresses binding of ligand by C3b and C3bi receptors on cultured human monocytes, an effect reversed by fibronectin.

Abstract

Receptors for C3 bind ligand and generate intracellular signals that lead to the engulfment of C3-coated particles. Recent experiments suggest that both the binding and the subsequent signal transduction activities of C3 receptors can be regulated. Cultured human monocytes (MO) 1 express receptors for C3b (CR1) and C3bi (CR3) that bind ligand-coated particles but do not signal the cell to initiate phagocytosis. After stimulation of the MO with PMA (1), or after interaction of the MO with surfaces coated with fibronectin (Fn, reference 2), CR1 and CR3 readily generate signals leading to phagocytosis. Thus PMA and Fn regulate the signaling capacity of CR1 and CR3 in these cells. In polymorphonuclear leukocytes, both the binding and the signaling activities are coordinately regulated. Brief (15 min) stimulation with PMA increases binding and signaling activities of CR 1 and CR3, but prolonged (60 min) incubation with PMA eliminates both binding and signaling (3). Since the PMA-mediated decline in the binding capacity of CR1 and CR3 is not accompanied by a loss of cell surface receptors, it appears that PMA regulates the binding and signaling activities of existing cell surface receptors.In this report, we show that treatment of human monocytes and MO with recombinant IFN-~, causes CR1 and CR3 to lose the ability to bind ligand. IFN-"),-treated cells express normal levels of cell surface CRI and CR3 as measured with anti-receptor antibodies, and the inhibition of ligand binding by CR 1 and CR3 is reversed in minutes by interaction of the phagocytes with Fn-coated surfaces. Therefore, cultivation with IFN-~, causes a reversible change in the nature of these receptors, which prevents them from interacting with ligand.

The distinct leukocyte integrins of mouse spleen dendritic cells as identified with new hamster monoclonal antibodies.

“…The function of leukocyte integrins is regulated not merely by expression at the cell surface but by exposure to stimuli like PMA (20,21) and other more physiologic ligands (38,39). Also, the known ligands ofthe integrins, ICAM-1 and ICAM-2, are regulated at the level of expression but again by cytokines (40).…”

Cytokines in context.

“…Whether endothelial cells respond to TGF-~ by proliferating to form tubes resembling capillaries, or cease to grow, likewise depends on the nature of the extracellular matrix (Madri et al, 1990). Pretreatment of monocytes with IFN-7 depresses the binding capacity of their receptors for complement component C3bi (comprised of the CDllb/CD18/32 family integrins), but this effect is promptly reversed when the cells are plated on fibronectin (Wright et al, 1986).…”

RhoG is required for both FcγR- and CR3-mediated phagocytosis

“…Before commencement of the phagocytosis assays, cells were incubated for 1 hour at 37˚C with serum-free DMEM plus 10 mM Hepes (Invitrogen). For CR3-mediated phagocytosis, macrophages were pre-activated for 30 minutes with 100 ng/ml phorbol 12-myristate 13-acetate (Caron et al, 2000;Wright et al, 1986). All cells were challenged with opsonised RBCs for 20 minutes at 37˚C and then processed for immunofluorescence.…”