A role for β<sub>2</sub>integrins (CD11/CD18) in the regulation of cytokine gene expression of polymorphonuclear neutrophils during the inflammatory response

The in vivo contributions of CD18 integrin-dependent and -independent mechanisms in mediating the increases in lung neutrophil (polymorphonuclear leukocyte; PMN) sequestration and microvascular permeability are not well understood. We determined the time course of these responses to Gram-negative sepsis in the mouse lung and addressed the specific contributions of CD18 integrins and ICAM-1. PMN sequestration in the lung was assessed by morphometric analysis, and transalveolar PMN migration was assessed by bronchoalveolar lavage. Lung tissue PMN number increased by 6-fold within 1 h after i.p. Escherichia coli challenge; this value peaked at 3 h (7-fold above control) and decreased at 12 h (3.5-fold above control). PMN migration into the airspace was delayed; the value peaked at 6 h and remained elevated up to 12 h. Saturating concentrations of anti-CD18 and anti-ICAM-1 mAbs reduced lung tissue PMN sequestration and migration; however, peak responses at 3 and 6 h were inhibited by 40%, indicating that only a small component of PMN sequestration and migration was CD18 dependent at these times. In contrast to the time-dependent decreased role of CD18 integrins in mediating PMN sequestration and migration, CD18 and ICAM-1 blockade prevented the increase in lung microvascular permeability and edema formation at all times after E. coli challenge. Thus, Gram-negative sepsis engages CD18/ICAM-1-independent mechanisms capable of the time-dependent amplification of lung PMN sequestration and migration. The increased pulmonary microvascular permeability induced by E. coli is solely the result of engagement of CD18 integrins even when PMN accumulation and migration responses are significantly CD18 independent.

Section: Discussionmentioning

confidence: 69%

Differential Role of CD18 Integrins in Mediating Lung Neutrophil Sequestration and Increased Microvascular Permeability Induced byEscherichia coliin Mice

Gao

Sekosan

et al. 2001

“…Specifically, we found that primary macrophages and activated/differentiated monocytic cell lines exposed to fibrinogen up-regulate the expression of MIP-1␣, MIP-1␤, MIP-2, and MCP-1. Several prior reports had suggested that CD11b/CD18 contributes to fibrin(ogen)-stimulated NF-B activation and gene expression (20,21,29). To assess roles for the fibrinogen-binding CD18 integrins in macrophage chemokine secretion, we supplemented cultures with peptides and mAbs known to inhibit CD11b/ CD18-and CD11c/CD18-fibrinogen interactions (8 -12, 15, 20).…”

Section: Discussionmentioning

confidence: 99%

“…Several prior studies clearly established that cross-linking CD11b/CD18 or CD11c/CD18 can stimulate cellular activities (22, 29 -32), and some of those activities could also be stimulated by fibrinogen (22,29,30). However, the evidence that CD11b/CD18 mediates fibrinogen-stimulated signaling was less decisive.…”

Section: Discussionmentioning

confidence: 99%

Fibrinogen Stimulates Macrophage Chemokine Secretion Through Toll-Like Receptor 4

Smiley

King

Hancock

2001

874

583

Extravascular fibrin deposition is an early and persistent hallmark of inflammatory responses. Fibrin is generated from plasma-derived fibrinogen, which escapes the vasculature in response to endothelial cell retraction at sites of inflammation. Our ongoing efforts to define the physiologic functions of extravasated fibrin(ogen) have led to the discovery, reported here, that fibrinogen stimulates macrophage chemokine secretion. Differential mRNA expression analysis and RNase protection assays revealed that macrophage inflammatory protein-1α (MIP-1α), MIP-1β, MIP-2, and monocyte chemoattractant protein-1 are fibrinogen inducible in the RAW264.7 mouse macrophage-like cell line, and ELISA confirmed that both RAW264.7 cells and primary murine thioglycolate-elicited peritoneal macrophages up-regulate the secretion of monocyte chemoattractant protein-1 >100-fold upon exposure to fibrinogen. Human U937 and THP-1 precursor-1 (THP-1) monocytic cell lines also secreted chemokines in response to fibrinogen, upon activation with IFN-γ and differentiation with vitamin D3, respectively. LPS contamination could not account for our observations, as fibrinogen-induced chemokine secretion was sensitive to heat denaturation and was unaffected by the pharmacologic LPS antagonist polymyxin B. Nevertheless, fibrinogen- and LPS-induced chemokine secretion both apparently required expression of functional Toll-like receptor 4, as each was diminished in macrophages derived from C3H/HeJ mice. Thus, innate responses to fibrinogen and bacterial endotoxin may converge at the evolutionarily conserved Toll-like recognition molecules. Our data suggest that extravascular fibrin(ogen) induces macrophage chemokine expression, thereby promoting immune surveillance at sites of inflammation.

“…Fib has also been shown to activate platelets through the ␣ IIb ␤ 3 receptor (27) and is thought to play an important role in activating platelet aggregation and clot retraction. Neutrophil interactions with surface-bound Fib via ␤ 2 integrins results in a substantial increase in the production of IL-8 and IL-1␤, a response that is abrogated in CD18-deficient mice (28). However, the synergistic effect of Fib plus fMLP on neutrophils described here is independent of the ␤ 2 integrins because neutrophils from three patients with leukocyte adhesion deficiency, whose cells lack these receptors, exhibit responses to Fib plus fMLP that are normal (Table III).…”

Section: Discussionmentioning

confidence: 99%

Fibrinogen Induces IL-8 Synthesis in Human Neutrophils Stimulated with Formyl-Methionyl-Leucyl-Phenylalanine or Leukotriene B4

Kuhns

Nelson

Alvord

et al. 2001

Human exudative neutrophils have greatly increased stores of the neutrophil chemoattractant IL-8 compared with peripheral blood cells, but the mechanism for the increase is not defined. In this report, we show that treatment of peripheral blood neutrophils with the chemotactic peptide fMLP or with leukotriene B4 or fibrinogen results in little increase in the production of IL-8 by peripheral blood neutrophils. However, a chemotactically active dose of fMLP (5 × 10−9 M) or leukotriene B4 (1 × 10−7 M) in the presence of a physiological concentration (2 mg/ml) of fibrinogen results in a receptor-mediated, pertussis toxin-sensitive, synergistic 30-fold increase in IL-8 synthesis. The levels of IL-8 attained are comparable to those observed in exudative cells. Higher concentrations of fMLP (1 × 10−7 M) are associated with reduced IL-8 protein synthesis without IL-8 degradation, indicating a sensitive regulatory mechanism for IL-8 production. Treatment of neutrophils with fibrinogen and fMLP resulted in minimal changes in the steady state levels of mRNA for macrophage inflammatory protein-1α and -1β and monocyte chemoattractant protein-1. In contrast, in the presence of fibrinogen, the steady-state level of neutrophil IL-8 mRNA increased 8-fold with 5 × 10−9 M fMLP but was not decreased with 1 × 10−7 M fMLP, suggesting that neutrophils are specifically adapted to modulate neutrophil IL-8 synthesis through transcriptional and posttranscriptional mechanisms. The data indicate that fibrinogen can function not only as a substrate in the clotting cascade, but also as an important effector during the evolution of the innate immune response.