Toll‐like receptor ligands induce polymorphonuclear leukocyte migration: key roles for leukotriene B 4 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 α (cPLA 2 α) inhibitor (90% inhibition at 1 μM). Accordingly, selected TLR ligands caused Ser505‐phosphorylation of cPLA 2 α 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 α inhibitor. Finally, LTB 4 and PAF receptor antagonists inhibited (up to ~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.—Lefebvre, J. S., Marleau, S., Milot, V., Lévesque, T., Picard, S., Flamand, N., Borgeat, P. Toll‐like receptor ligands induce polymorphonuclear leukocyte migration: key roles for leukotriene B 4 and platelet‐activating factor. FASEB J . 24, 637–647 (2010). www.fasebj.org