Impairment of neutrophil migration to remote inflammatory site during lung histoplasmosis.

Histoplasma capsulatum (Hc) induces a pulmonary disease in which leukotrienes promote activation and recruitment of effectors cells. It is also well-recognized that leukotriene B4 (LTB4) and platelet-activating factor (PAF) induce leukocyte recruitment to inflammatory sites. We investigated the impact of pulmonary Hc infection on PMN migration to a remote inflammatory site.

Influenza virus H1N1 activates platelets through FcγRIIA signaling and thrombin generation.

Platelets play crucial functions in hemostasis and the prevention of bleeding. During H1N1 influenza A virus infection, platelets display activation markers. The platelet activation triggers during H1N1 infection remain elusive.

Cooperative role of endogenous leucotrienes and platelet-activating factor in ischaemia-reperfusion-mediated tissue injury.

Insufficient oxygen delivery to organs leads to tissue dysfunction and cell death. Reperfusion, although vital to organ survival, initiates an inflammatory response that may both aggravate local tissue injury and elicit remote organ damage. Polymorphonuclear neutrophil (PMN) trafficking to remote organs following ischaemia/reperfusion (I/R) is associated with the release of lipid mediators, including leucotriene (LT) B4 , cysteinyl-LTs (CysLTs) and platelet-activating factor (PAF).

Osteoblast retraction induced by adherent neutrophils promotes osteoclast bone resorption: implication for altered bone remodeling in chronic gout.

Bone destruction in chronic gout is correlated with deposits of monosodium urate (MSU) crystals. Bone with MSU tophi were histopathologically shown to have altered remodeling and cellular distribution. We investigated the impact of neutrophils in bone remodeling associated with MSU and demonstrated that neutrophils, through elastase localized at their surface, induced retraction of confluent osteoblasts (OBs) previously layered on calcified matrix.

Extra domain A of fibronectin primes leukotriene biosynthesis and stimulates neutrophil migration through activation of Toll-like receptor 4.

Objective: There is increasing evidence of a role for Toll-like receptors (TLRs) in inflammatory arthritis. The extra domain A (ED-A)-containing isoform of fibronectin is generated under pathologic conditions such as rheumatoid arthritis, and ED-A has been identified as an endogenous TLR-4 ligand. Leukotriene B4 (LTB4) and polymorphonuclear neutrophils (PMNs) play a critical role in murine models of inflammatory arthritis.

LTB4 increases nasal neutrophil activity and conditions neutrophils to exert antiviral effects.

Background: Leukotriene B4 (LTB4) recruits and activates neutrophils. Accordingly, this leukotriene is involved in innate defense actions.

Objective: To examine if nasal LTB4 can produce neutrophil activity and to explore whether or not LTB4 can condition neutrophils to exert virucidal effects in vitro and in vivo.

Toll-like receptor ligands induce polymorphonuclear leukocyte migration: key roles for leukotriene B4 and platelet-activating factor.

Activation of toll-like receptors (TLRs) and polymorphonuclear leukocyte (PMN) accumulation at infection sites are critical events of host defense. The involvement of leukotriene (LT) B(4) and platelet-activating factor (PAF) in TLR ligand-induced activation of inflammatory cell functions is essentially unknown. Using an in vitro model of human PMN migration through human endothelial cell monolayers, we demonstrate that prototypic ligands of TLR1/2, 2/6, 3, 4, 5, and 7/8 promote PMN migration, an effect markedly inhibited by 3 LTB(4) receptor antagonists (70-80% inhibition at 100 nM compared to vehicle-treated cells), 3 PAF receptor antagonists (20-50% inhibition at 10 nM), 3 LT biosynthesis inhibitors (75-85% inhibition at 100 nM), and 1 cytosolic phospholipase A(2)alpha (cPLA(2)alpha) inhibitor (90% inhibition at 1 microM).

Reprogramming of a subpopulation of human blood neutrophils by prolonged exposure to cytokines.

Essential cells of innate immunity, neutrophils are often considered to be a homogenous population of terminally differentiated cells. During inflammation, neutrophils are extravasated cells exposed to local factors that prolong their survival and activate their production of mediators implicated in disease progression. In this study, a phenotypically distinct subset of human neutrophils that appear after prolonged exposure to cytokines was characterized.

Involvement of endogenous leukotriene B4 and platelet-activating factor in polymorphonuclear leucocyte recruitment to dermal inflammatory sites in rats.

A critical role for leukotriene B(4) (LTB(4)) and/or platelet-activating factor (PAF) in regulating polymorphonuclear cell (PMN) trafficking to inflammatory sites has been reported in a number of experimental inflammatory models. In vitro, newly synthesized LTB(4) and PAF were shown to act in an autocrine/paracrine or intracrine fashion to enhance intracellular arachidonic acid availability and leukotriene biosynthesis. This suggested potentially cooperative effects of these lipid mediators in regulating PMN extravasation.

Characterization of prostaglandin E2 generation through the cyclooxygenase (COX)-2 pathway in human neutrophils.

In the present study, we characterized the generation of prostaglandin (PG)E2 in human neutrophils. We found that the Ca2+-dependent type IV cytosolic phospholipase A2 (cPLA2) was pivotally involved in the COX-2-mediated generation of PGE2 in response to a calcium ionophore, as determined by the use of selected PLA2 inhibitors. PGE2 biosynthesis elicited by bacterial-derived peptides or by phagocytic stimuli acting on cell surface receptors also showed to be dependent on cPLA2 activity.

Leukotriene B4 triggers the in vitro and in vivo release of potent antimicrobial agents.

Leukotriene B(4) (LTB(4)) is a bioactive lipid derived from the metabolism of arachidonic acid. Mainly produced by polymorphonuclear leukocytes (PMN) and macrophages, LTB(4) triggers several functional responses important in host defense, including the secretion of lysosomal enzymes, the activation of NADPH oxidase activity, NO formation, and phagocytosis. We report that LTB(4), but not structural analogs thereof, stimulates primed human PMN to release molecules having potent antimicrobial activities.

The Toll-like receptor 7/8-ligand resiquimod (R-848) primes human neutrophils for leukotriene B4, prostaglandin E2 and platelet-activating factor biosynthesis.

Toll-like receptors (TLR) recognize pathogen-associated molecular patterns and play important roles in the innate immune system. While single-stranded viral RNA is the natural ligand of TLR7/TLR8, the imidazoquinoline resiquimod (R-848) is recognized as a potent synthetic agonist of TLR7/TLR8. We investigated the effects of TLR7/8 activation on lipid mediator production in polymorphonuclear leukocytes exposed to R-848.

Inhibition of platelet-activating factor biosynthesis by adenosine and histamine in human neutrophils: involvement of cPLA2alpha and reversal by lyso-PAF.

Leukotrienes (LT) and platelet-activating factor (PAF) are important lipid mediators of inflammation. We and others reported previously that autacoids such as adenosine, histamine, prostaglandin E2, and beta-adrenergic agents inhibit LT biosynthesis in activated human polymorphonuclear leukocytes (PMN). In this study, we demonstrate that CGS-21680 (a selective agonist of the adenosine A2A receptor) and histamine also potently inhibit PAF biosynthesis in agonist [formyl Met-Leu-Phe (fMLP)]- and thapsigargin-activated human PMN.

Differential expression of adenosine receptors in human neutrophils: up-regulation by specific Th1 cytokines and lipopolysaccharide.

Four types of adenosine receptors have been identified in different tissues and cell types, namely, A1, A2A, A2B, and A3 receptors. We report that A2AR but not A2BR mRNA in freshly isolated polymorphonuclear neutrophils (PMN) is maximally up-regulated after 4 h stimulation with lipopolysaccharide (LPS) or tumor necrosis factor alpha (TNF-alpha) and to a lesser extent, with interleukin (IL)-1beta. These effects were maintained up to 21 h.

Arachidonic acid regulates the translocation of 5-lipoxygenase to the nuclear membranes in human neutrophils.

Elevation of the intracellular cAMP concentration in agonist-activated human neutrophils (PMN) leads to the concomitant inhibitions of arachidonic acid (AA) release, 5-lipoxygenase (5-LO) translocation, and leukotriene (LT) biosynthesis. We report herein that exogenous AA completely prevents cAMP-dependent inhibition of 5-LO translocation and LT biosynthesis in agonist-activated PMN. Moreover, the group IVA phospholipase A2 inhibitor pyrrophenone and the MEK inhibitor U-0126 inhibited AA release and 5-LO translocation in activated PMN, and these effects were also prevented by exogenous AA, demonstrating a functional link between AA release and 5-LO translocation.

5-Lipoxygenase-activating protein homodimer in human neutrophils: evidence for a role in leukotriene biosynthesis.

FLAP (5-lipoxygenase-activating protein) is a nuclear transmembrane protein involved in the biosynthesis of LTs (leukotrienes) and other 5-LO (5-lipoxygenase) products. However, little is known about its mechanism of action. In the present study, using cross-linkers, we demonstrate that FLAP is present as a monomer and a homodimer in human PMN (polymorphonuclear cells).

Potentiation of neutrophil cyclooxygenase-2 by adenosine: an early anti-inflammatory signal.

Neutrophils, which are often the first to migrate at inflamed sites, can generate leukotriene B(4) from the 5-lipoxygenase pathway and prostaglandin E(2) through the inducible cyclooxygenase-2 pathway. Adenosine, an endogenous autacoid with several anti-inflammatory properties, blocks the synthesis of leukotriene B(4) while it potentiates the cyclooxygenase-2 pathway in fMLP-treated neutrophils, following activation of the A(2A) receptor. Using the murine air pouch model of inflammation, we observed that inflammatory leukocytes from mice lacking the A(2A) receptor have less cyclooxygenase-2 induction than wild-type animals.

Leukotriene B4 protects latently infected mice against murine cytomegalovirus reactivation following allogeneic transplantation.

Human CMV is often associated with transplant rejection and opportunistic infections such as pneumonia in immunosuppressed patients. Current anti-CMV therapies, although effective, show relatively high toxicity, which seriously limits their long-term use. In this study, we provide evidence that leukotriene B(4) (LTB(4)) plays an important role in the fight against murine CMV (MCMV) infection in vivo.

Release of anti-HIV mediators after administration of leukotriene B4 to humans.

Background: CD8(+) T cells can control human immunodeficiency virus (HIV) through the lysis of infected cells and the release of soluble mediators, such as macrophage inflammatory protein (MIP)-1 beta, which prevent entry of HIV and/or inhibit HIV replication. Because neutrophils represent a major source of alpha-defensins and, to a lesser extent, MIP-1 beta, we determined whether leukotriene B(4) (LTB(4)), a potent neutrophil agonist, would trigger the release of these 2 anti-HIV peptides.

Methods: Plasma samples from HIV-uninfected subjects receiving intravenous bolus of LTB(4) were analyzed for alpha-defensins and MIP-1 beta levels by use of enzyme-linked immunosorbent assay.

Histamine-induced inhibition of leukotriene biosynthesis in human neutrophils: involvement of the H2 receptor and cAMP.

1. Histamine is generally regarded as a pro-inflammatory mediator in diseases such as allergy and asthma. A growing number of studies, however, suggest that this autacoid is also involved in the downregulation of human polymorphonuclear leukocyte (PMN) functions and inflammatory responses through activation of the Gs-coupled histamine H(2) receptor.

Urinary metabolites of leukotriene B4 in the human subject.

Leukotriene B4 (LTB4) is a potent chemoattractant for neutrophils and is thought to play a role in a variety of inflammatory responses in humans. The metabolism of LTB4 in vitro is complex with several competing pathways of biotransformation, but metabolism in vivo, especially for normal human subjects, is poorly understood. As part of a Phase I Clinical Trial of human tolerance to LTB4, four human subjects were injected with 150 nmol/kg LTB4 with one additional subject as placebo control.

Crystal-induced neutrophil activation: VIII. Immediate production of prostaglandin E2 mediated by constitutive cyclooxygenase 2 in human neutrophils stimulated by urate crystals.

Objective: To evaluate the impact of monosodium urate monohydrate (MSUM) crystals on the synthesis of prostaglandin E(2) (PGE(2)) by human neutrophils, and to examine some of the mechanisms underlying these responses.

Methods: The amount of PGE(2) released in the supernatants of stimulated human neutrophils was evaluated by enzyme immunoassay, and expression of cyclooxygenase 2 (COX-2) was monitored by immunoblot on cell lysates, as well as by cytofluorometry of buffy-coat cells.

Results: We observed that MSUM crystals rapidly stimulated the synthesis of PGE(2), with levels peaking at 1 hour.

Arachidonic acid activates phospholipase D in human neutrophils; essential role of endogenous leukotriene B4 and inhibition by adenosine A2A receptor engagement.

We report in human neutrophils (PMN) that phospholipase D (PLD) was stimulated by micromolar concentrations of arachidonic acid (AA) and nanomolar concentrations of leukotriene B(4) (LTB(4)), and eicosapentaenoic acid was inactive. The stimulatory effect of AA occurred only when adenosine was eliminated from PMN suspensions or when PMN were incubated with adenosine A(2A) receptor antagonists. The mechanism of AA-induced PLD activation was investigated.

Glucuronidation of arachidonic and linoleic acid metabolites by human UDP-glucuronosyltransferases.

Arachidonic acids (AA) and linoleic acids (LAs) are metabolized, in several tissues, to hydroxylated metabolites that are important mediators of many physiological and pathophysiological processes. The conjugation of leukotriene B4 (LTB4), 5-hydroxyeicosatetraenoic acid (HETE), 12-HETE, 15-HETE, and 13-hydroxyoctadecadienoic acid (HODE) by the human UDP-glucuronosyltransferase (UGT) enzymes was investigated. All substrates tested were efficiently conjugated by human liver microsomes to polar derivatives containing the glucuronyl moiety as assessed by mass spectrometry.

Adenosine up-regulates cyclooxygenase-2 in human granulocytes: impact on the balance of eicosanoid generation.

Polymorphonuclear neutrophils (granulocytes; PMNs) are often the first blood cells to migrate toward inflammatory lesions to perform host defense functions. PMNs respond to specific stimuli by releasing several factors and generate lipid mediators of inflammation from the 5-lipoxygenase and the inducible cyclooxygenase (COX)-2 pathways. In view of adenosine's anti-inflammatory properties and suppressive impact on the 5-lipoxygenase pathway, we addressed in this study the impact of this autacoid on the COX-2 pathway.