title: Retinal Microglial Activation Following Topical Application of Intracellular Toll-Like Receptor Ligands.
abstract: OBJECTIVE
  We previously have reported that application of the intracellular toll-like receptor (TLR)-9 ligand CpG-ODN onto the injured corneal surface induces widespread inflammation within the eye, including the retina. We tested the hypothesis that topical application of two other intracellular TLR agonists, Poly I:C and R848, would cause retinal microglial activation and migration into the subretinal space.
  
  
  METHODS
  C57BL/6J wild-type and Cx3cr1gfp/+ mice were anesthetized and received central corneal abrasions followed by topical application of Poly I:C (TLR3 agonist), R848 (TLR7/8 agonist), or CpG-ODN (TLR9 agonist). Eyes were imaged in vivo by using spectral-domain optical coherence tomography to assess and quantify vitreous cells and retinal edema. Tissues were processed for whole-mount immunofluorescence staining or gene expression studies. Microglial activation was determined by morphologic changes, major histocompatibility complex (MHC) class II reactivity, and migration to the subretinal space. Expression of proinflammatory cytokine gene IL-6, IL-1β, IFN-γ, and MCP-1 in retinal tissues were analyzed.
  
  
  RESULTS
  At 24 hours, topical treatment with CpG-ODN and R848, but not Poly I:C, led to altered microglial morphology. One week after CpG-ODN and R848-treatment, eyes exhibited vitritis and mild inner retinal edema, increased number of subretinal Iba-1+ cells, and an increase in MHC II+ cells in the neural retina. Proinflammatory cytokine genes were upregulated after R848 treatment, whereas in the CpG-ODN group, only IL-1β and MCP-1 were significantly upregulated. Retinal microglial activation was not observed in the Poly I:C-treated group.
  
  
  CONCLUSIONS
  Topical application of CpG-ODN and R848, but not Poly I:C, to the damaged corneal surface can cause activation and migration of retinal microglia.
authors.affiliation: Department of Optometry and Vision Sciences University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Holly R
authors.initials: HR
authors.lastname: Chinnery
authors.affiliation: Department of Anatomy & Developmental Biology, School of Biomedical Sciences, Monash University, Victoria, Australia.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Naranjo Golborne
authors.affiliation: Department of Anatomy & Developmental Biology, School of Biomedical Sciences, Monash University, Victoria, Australia.
authors.forename: Cheng M
authors.initials: CM
authors.lastname: Leong
authors.affiliation: School of Molecular Sciences, Department of Biochemistry, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, Australia.
authors.forename: Weisan
authors.initials: W
authors.lastname: Chen
authors.affiliation: Lions Eye Institute and the Centre for Ophthalmology and Visual Sciences, University of Western Australia, Perth, Western Australia, Australia 5Section of Immunology and Infection, Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Ki.
authors.forename: John V
authors.initials: JV
authors.lastname: Forrester
authors.affiliation: Department of Anatomy & Developmental Biology, School of Biomedical Sciences, Monash University, Victoria, Australia.
authors.forename: Paul G
authors.initials: PG
authors.lastname: McMenamin
mesh_terms: D000287:Administration, Topical; D000818:Animals; D004195:Disease Models, Animal; D008024:Ligands; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017628:Microglia / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D012162:Retinal Degeneration / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000378:metabolism; D051217:Toll-Like Receptor 9 / Q000008:administration & dosage*; D041623:Tomography, Optical Coherence
chemical_list: D008024:Ligands; C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9