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. Although R-848 had minimal effects by itself, it strongly enhanced leukotriene B4 formation on subsequent stimulation by fMLP, platelet-activating factor, and the ionophore A23187. R-848 acted via TLR8 but not TLR7 as shown by the lack of effect of the TLR7-specific ligand imiquimod. Priming with R-848 also resulted in enhanced arachidonic acid release and platelet-activating factor formation following fMLP stimulation, as well as enhanced prostaglandin E2 synthesis following the addition of arachidonic acid. Western blot analysis demonstrated that R-848 induced the phosphorylation of the cytosolic phospholipase A2alpha, promoted 5-lipoxygenase translocation and potently stimulated the expression of the type 2 cyclooxygenase. Bafilomycin A1, an inhibitor of endosomal acidification, efficiently inhibited all R-848-induced effects. These studies demonstrate that TLR8 signaling strongly promotes inflammatory lipid mediator biosynthesis and provide novel insights on innate immune response to viral infections.
Hattermann
Kim
K
Centre de Recherche en Rhumatologie et Immunologie, Centre Hospitalier Universitaire de Quebec Research Center and Faculty of Medicine, Laval University, Québec, Canada.
Picard
Serge
S
Borgeat
Mathieu
M
Leclerc
Patrick
P
Pouliot
Marc
M
Borgeat
Pierre
P
D015232:Dinoprostone / Q000096:biosynthesis*; D006801:Humans; D007093:Imidazoles / Q000378:metabolism / Q000494:pharmacology*; D018836:Inflammation Mediators / Q000378:metabolism; D007975:Leukotriene B4 / Q000096:biosynthesis*; D009504:Neutrophils / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D010972:Platelet Activating Factor / Q000096:biosynthesis*; D012328:RNA Viruses / Q000276:immunology; D015398:Signal Transduction; D051199:Toll-Like Receptor 7 / Q000187:drug effects* / Q000378:metabolism; D051200:Toll-Like Receptor 8 / Q000187:drug effects* / Q000378:metabolism
D007093:Imidazoles; D018836:Inflammation Mediators; D010972:Platelet Activating Factor; C495348:TLR7 protein, human; C495349:TLR8 protein, human; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; D007975:Leukotriene B4; D015232:Dinoprostone; C402365:resiquimod