Activation of the adhesive capacity of CR3 on neutrophils by endotoxin: dependence on lipopolysaccharide binding protein and CD14.

Abstract

SummaryTumor necrosis factor a, granulocyte colony-stimulating factor, granulocyte/macrophage colonystimulating factor, and formyl peptide were each found to cause a twofold increase in expression of CD14 on the surface of polymorphonuclear leukocytes (PMN). Upregulation of CD14 was complete by 20 min and thus appeared to result from expression of preformed stores ofprotein . The CD14 on the surface ofPMN was shown to serve two biological functions. It bound particles coated with complexes oflipopolysaccharide (LPS) and LPS binding protein (LBP). This binding activity was enhanced by agonists that upregulated CD14 expression and may serve in the clearance of Gram-negative bacteria opsonized with LBP. Interaction of CD14 with LPS in the presence of LBP or serum also caused a dramatic, transient increase in the adhesive activity of CR3 (CD11b/CD18) on PMN . Enhanced activity of CR3 and other members of the CD11/CD18 family underlies many of the known physiological responses ofPMN to LPS and may be a central feature of the in vivo responses of PMN to endotoxin. BacterialLPS(endotoxin) is known to have profound physiological effects on PMN both in vivo and in vitro. Animals respond to intravenous LPS with a rapid fall in the number of circulating PMN and a concomitant accumulation ofPMN in the lungs (1) . Isolated PMN respond to LPS with increased adhesion to protein-coated surfaces (2), enhanced ability to mount an oxidative burst (3), and enhanced microbicidal powers (4) . Many of these responses to LPS appear to depend at least in part on enhanced function of the three members of the CD11/CD18 family of adhesion-promoting receptors (LFA1, CR3, and p150,95, also known as the 02 or leukocyte integrins) on the surface of PMN . Adhesion of PMN to endothelium requires the participation ofCDII/CD18 molecules (5-7), and blockade ofCD18 with mAbs prevents accumulation ofPMN in the lungs ofendotoxin-treated animals (8) . Adhesion ofPMN to protein-coated glass (5), enhanced oxidative burst in response to soluble agonists (9), and microbicidal activity (5) are also dependent on increased CD11/CD18 function. Here, we directly measure the effect of LPS on the adhesive function ofCR3 (CD11b/CD18) and describe a dramatic enhancement of its adhesive activity by complexes of LPS with proteins from the serum.Recent studies have described a novel mechanism by which mononuclear cells may respond to LPS (10, 11) . LPS is first bound by the serum protein LPS binding protein (LBP)l, and the resulting LPS-LBP complex is then recognized by CD14, a 55-kD glycoprotein that is strongly expressed on monocytes and macrophages. LBP and CD14 serve two physiological roles. These proteins act as opsonin and opsonic receptor, respectively, to promote the phagocytic uptake of bacteria or LPS-coated particles by macrophages (12). They also dramatically enhance the ability of mononuclear cells to synthesize TNF in response to endotoxin . Addition of LBP speeds the synthesis of TNF and enables a response to doses of LPS 100-fold lower than are otherwi...

Lipopolysaccharide-induced expression of cell surface receptors and cell activation of neutrophils and monocytes in whole human blood

“…Some investigators claim that CD14 is expressed in polymorphonuclear neutrophils, although to a lesser extent in monocytes (18), and a positive modulation of CD14 expression on neutrophils by LPS has been reported (20). FACS analysis of the present data showed that the levels of CD14 on unstimulated neutrophils were marginal or absent and, in agreement with Wright et al (21), not affected by LPS stimulation. This absence of significant amounts of CD14 is also indirectly supported by results of an earlier study (22), in which only R-form LPS preparations elicited oxidative responses in isolated neutrophils, while the S-form LPS was virtually inactive.…”

The IFN-inducible nucleoprotein IFI 16 is expressed in cells of the monocyte lineage, but is rapidly and markedly down-regulated in other myeloid precursor populations

“…3B). Some mature neutrophils are also known to express CD14 [30][31][32], however, we have previously shown that IFI 16 is not expressed in these cells [12]. Our two-color cytofluorographic studies were all performed with relatively immature cell populations (e.g., day 7 G-CSF colonies with few mature neutrophils) and we therefore did not see a subpopulation of CD14 ϩ IFI 16 Ϫ neutrophils.…”

β2 Integrins Are Involved in Cytokine Responses to Whole Gram-Positive Bacteria

“…CR3 can also bind to LBP (19), and, in the presence of serum and LPS, associate transiently with surface CD14 on the plane of the neutrophil membrane (20). CR4, also a ␤ 2 integrin, is made up by CD18/CD11c and may be involved in transducing LPS signals in the absence of serum (21).…”