Shedding of tumor necrosis factor receptors by activated human neutrophils.

Abstract

SummaryThe capacity of human neutrophils (PMN) to bind tumor necrosis factor (TNF) was rapidly lost when the cells were incubated in suspension with agents that can stimulate their migratory and secretory responses . Both physiological (poly)peptides (FMLP, C5a, CSF-GM) and pharmacologic agonists (PMN, calcium ionophore A23187) induced the loss ofTNF receptors (TNF-R) from the cell surface. Half-maximal loss in TNF-R ensued after only ti2 min with 10 -7 M FMLP at 37°C, and required only 10-9 M FMLP during a 30-min exposure . However, there were no such changes even with prolonged exposure of PMN to FMLP at 4°or 16°C. Scatchard analysis revealed loss of TNF-binding sites without change in their affinity (Kd -0.4 nM) as measured at incompletely modulating concentrations of FMLP, C5a, PMA, or A23187. The binding of antiTNF-R mAbs to PMN decreased in parallel, providing independent evidence for the loss of TNF-R from the cell surface. At the same time, soluble TNF-R appeared in the medium of stimulated PMN . This inference was based on the PMN-and FMLP-dependent generation of a nonsedimentable activity that could inhibit the binding of TNF to fresh human PMN or to mouse macrophages, and the ability of mAbs specific for human TNF-R to abolish inhibition by PMN-conditioned medium of binding of TNF to mouse macrophages. Soluble TNF-R activity was associated with a protein of Mr -28,000 by ligand blot analysis of cell-free supernatants of FMLP-treated PMN . Thus, some portion of the FMLP-induced loss of TNF-R from human PMN is due to shedding of TNF-R . Shedding was unaffectedby inhibitors of serine and thiol proteases and could not be induced with phosphatidylinositol-specific phospholipase C. Loss of TNF-R from PMN first stimulated by other agents may decrease their responsiveness to TNF. TNF-R shed by PMN may be one source of the TNF-binding proteins found in body fluids, and may blunt the actions of the cytokine on other cells.

Elevation of plasma-soluble tumour necrosis factor receptors (TNF-R) in sarcoidosis

“…The soluble forms originating from the extramembranous portion of the TNF-RI (sTNF-RI) and TNF-RII (sTNF-RII) can be found in the culture supernatants of lymphocytes, monocytes and neutrophils [15,[19][20][21] and biological fluids [22,23]. The elevation of sTNF-R in serum/plasma and biological fluids reflecting a variety of inflammatory disorders has been shown in several diseases [24][25][26][27][28][29][30][31].…”

TNF-Induced Shedding of TNF Receptors in Human Polymorphonuclear Leukocytes: Role of the 55-kDa TNF Receptor and Involvement of a Membrane-Bound and Non-Matrix Metalloproteinase

“…It is well established that the surface expression of both receptors decreases considerably when PMN are exposed to TNF and various agents including FMLP, the tumor promoter PMA, the Ca 2ϩ ionofore A23187, endotoxin, and GM-CSF (11)(12)(13). The decrease in receptor expression occurs via a process known as shedding, whereby the extracellular portion of the receptors is proteolytically cleaved and released in a soluble form that maintains the ability to bind TNF (11,14). With TNF, receptor down-modulation has been shown to occur via internalization of TNF-R55 and shedding of TNF-R75 (14).…”

“…Because PMN rapidly and extensively release their TNF receptors after adherence or exposure to various agonists (11)(12)(13), it has been suggested that these cells might be a significant source of increased circulating TNF receptors observed in physiologic and pathologic conditions such as exercise (19), experimental endotoxemia (20), a clinical model of postoperative sepsis (21), and high-dose TNF in isolated limb perfusion (22). In light of these observations, the comprehension of the mechanisms that regulate shedding in PMN might provide the basis for experimental approaches aimed at modulating systemic responses to TNF.…”

TNFR2 expression on non-bone marrow-derived cells is crucial for lipopolysaccharide-induced septic shock and downregulation of soluble TNFR2 level in serum

“…18 Similar to TNF, elevated levels of soluble TNFR2 (sTNFR2) in serum or other body fluids has been recognized as a predictor of pathological conditions, such as sepsis, infections, hepatitis, organ fibrosis, cancer development and other inflammatory diseases. 19,20 In vitro experiments demonstrated that sTNFR2 can be rapidly shed from activated BM-derived cells, such as neutrophils and cultured mononuclear cells, upon TNF, lipopolysaccharide (LPS) or IL-10 stimulation.…”