title: Microglia recognize double-stranded RNA via TLR3.
abstract: Microglia are CNS resident innate immune cells of myeloid origin that become activated and produce innate proinflammatory molecules upon encountering bacteria or viruses. TLRs are a phylogenetically conserved diverse family of sensors for pathogen-associated molecular patterns that drive innate immune responses. We have recently shown that mice deficient in TLR3 (TLR3(-/-) mice) are resistant to lethal encephalitis and have reduced microglial activation after infection with West Nile virus, a retrovirus that produces dsRNA. We wished to determine whether microglia recognize dsRNA through the TLR3 pathway. In vitro, murine wild-type primary cultured microglia responded to synthetic dsRNA polyinosinic-polycytidylic acid (poly(I:C)) by increasing TLR3 and IFN-beta mRNA and by morphologic activation. Furthermore, wild-type microglia dose dependently secreted TNF-alpha and IL-6 after poly(I:C) challenge, whereas TLR3(-/-) microglia produced diminished cytokines. Activation of MAPK occurred in a time-dependent fashion following poly(I:C) treatment of wild-type microglia, but happened with delayed kinetics in TLR3(-/-) microglia. As an in vivo model of encephalitis, wild-type or TLR3(-/-) mice were injected intracerebroventricularly with poly(I:C) or LPS, and microglial activation was assessed by cell surface marker or phospho-MAPK immunofluorescence. After intracerebroventricular injection of poly(I:C), microgliosis was clearly evident in wild-type mice but was nearly absent in TLR3(-/-) animals. When taken together, our results demonstrate that microglia recognize dsRNA through TLR3 and associated signaling molecules and suggest that these cells are key sensors of dsRNA-producing viruses that may invade the CNS.
authors.affiliation: Section of Immunobiology, Yale University School of Medicine, 300 Cedar Street, New Haven, CT 06520, USA.
authors.forename: Terrence
authors.initials: T
authors.lastname: Town
authors.forename: David
authors.initials: D
authors.lastname: Jeng
authors.forename: Lena
authors.initials: L
authors.lastname: Alexopoulou
authors.forename: Jun
authors.initials: J
authors.lastname: Tan
authors.forename: Richard A
authors.initials: RA
authors.lastname: Flavell
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D020672:I-kappa B Proteins / Q000378:metabolism; D018836:Inflammation Mediators / Q000378:metabolism; D007275:Injections, Intravenous; D016899:Interferon-beta / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011070:Poly I-C / Q000008:administration & dosage / Q000276:immunology; D012330:RNA, Double-Stranded / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics; D051196:Toll-Like Receptor 3 / Q000172:deficiency / Q000235:genetics / Q000276:immunology*
chemical_list: D016207:Cytokines; C083487:I kappa B beta protein; D020672:I-kappa B Proteins; D018836:Inflammation Mediators; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D051196:Toll-Like Receptor 3; D016899:Interferon-beta; D020928:Mitogen-Activated Protein Kinases; D011070:Poly I-C