Toll‐like receptor ligands induce polymorphonuclear leukocyte migration: key roles for leukotriene B₄and platelet‐activating factor

Abstract

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). Accordingly, selected TLR ligands caused Ser-505-phosphorylation of cPLA(2)alpha and measurable LTB(4) and PAF biosynthesis in the transmigration assay. As negative controls, interleukin-8- and formyl-methionyl-leucyl-phenylalanine-elicited migration in vitro was not inhibited either by an LTB(4) receptor antagonist or by the cPLA(2)alpha inhibitor. Finally, LTB(4) and PAF receptor antagonists inhibited (up to approximately 65% at optimal doses) TLR ligand-induced PMN infiltration in the mouse air-pouch model. These studies unravel the critical involvement of de novo LTB(4) and PAF biosynthesis in PMN migration elicited by TLR ligands.

Understanding the Mechanisms Controlling Leishmania amazonensis Infection In Vitro: The Role of LTB4 Derived From Human Neutrophils

“…Previous studies have shown an association between TLR signaling and lipid mediators [16, 37]. Our results further indicate that this interaction may lead to NFkB activation, possibly through TLR2, and LTB 4 production.…”

“…Signaling through LTB 4 induces leukocyte accumulation [13], microbial ingestion [14], and killing [15]. LTB 4 also plays a critical role in human neutrophil migration induced by Toll-like receptor (TLR) stimulation [16]. TLR ligands prime LTB 4 production and neutrophil migration [17], and the LTB 4 receptor, B leukotriene receptor 1 (BLT1), is responsible for mediating these effects [18].…”

Cissampelos sympodialis (Menispermaceae): A Novel Phytotherapic Weapon Against Allergic Diseases?

“…Corroborating this hypothesis was the observation that prophylactic treatment of experimental animals (rats) with AFL also showed inhibition of neutrophil migration into the intraperitoneal cavity induced by carrageenan (Batista-Lima et al, 2001). The migration of neutrophils into the peritoneal cavity of rats induced by carrageenan is dependent on the release of eicosanoids and chemotactic agents such as leukotriene B4 and/or IL-8, respectively, produced by mast cells and/or resident macrophages (Lefebvre et al, 2010, Nakagome & Nagata, 2011. Taken together the results support the hypothesis that AFL treatment is modulating cytokines as well as antiinflammatory mediator effects.…”

State of the art papers HLA-DR expression, cytokines and bioactive lipids in sepsis

“…On the other hand, failure to produce adequate amounts of inflammation-resolving and tissue repair factors at the most appropriate time and stage of sepsis may prove to be fatal. In this context, it is noteworthy that TLRs regulate free radical generation as well as macrophage and leukocyte function and modulate eicosanoid synthesis, and thus play a critical role in inflammation and the immune response [8–10]. It is likely that initial excess stimulation of TLRs leads to exaggerated production of free radicals, pro-inflammatory eicosanoids and cytokines that produce the initial hyperinflammatory response which if followed by exacerbated negative feedback control could lead to progressive development of immunosuppression seen in sepsis.…”