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 LTB4 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 mu M). Accordingly, selected TLR ligands caused Ser-505- phosphorylation of cPLA(2)alpha and measurable LTB4 and PAF biosynthesis in the transmigration assay. As negative controls, interleukin-8- and formyl-methionylleucyl-phenylalanine-elicited migration in vitro was not inhibited either by an LTB4 receptor antagonist or by the cPLA(2)alpha inhibitor. Finally, LTB4 and PAF receptor antagonists inhibited (up to similar 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 LTB4 and PAF biosynthesis in PMN migration elicited by TLR ligands.-Lefebvre, J. S., Marleau, S., Milot, V., Levesque, 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