title: IL-33 signaling is essential to attenuate viral-induced encephalitis development by downregulating iNOS expression in the central nervous system.
abstract: Viral encephalitis is a common cause of lethal infections in humans, and several different viruses are documented to be responsible. Rocio virus is a flavivirus that causes a severe lethal encephalitis syndrome in humans and also mice, providing an interesting model to study the CNS compartmentalized immune response. Interleukin 33 (IL-33), a member of the IL-1 family, is an immunomodulatory cytokine that is highly expressed in the CNS. However, the role of IL-33 on viral encephalitis remains unclear. Therefore, we aimed to explore how the IL-33/ST2 axis regulates the local immune response during Rocio virus infection.
  
  
  
  Wild-type (WT), ST2 (ST2(-/-)), and nitric oxide synthase-deficient mice (iNOS(-/-)) and Stat6 (Stat6(-/-))-deficient mice were infected with different concentrations of the Rocio virus by intraperitoneal route, the cytokine mRNA level in CNS was analyzed by qPCR, and cellular immunophenotyping was performed on infected mice by the flow cytometry of isolated CNS mononuclear cells.
  
  
  
  We have shown that the mRNA expression of IL-33 and ST2 receptors is increased in the CNS of Rocio virus-infected WT mice and that ST2(-/-) mice showed increased susceptibility to infection. ST2 deficiency was correlated with increased tissue pathology, cellular infiltration, and tumor necrosis factor alpha (TNF-α) and interferon-gamma (IFN-γ) mRNA levels and higher viral load in the CNS, compared with wild-type mice. The increased Th1 cytokine levels released in the CNS acted on infiltrating macrophages, as evidenced by flow cytometry characterization of cellular infiltrates, inducing the expression of iNOS, contributing to brain injury. Moreover, iNOS(-/-) mice were more resistant to Rocio virus encephalitis, presenting a lower clinical score and reduced mortality rate, despite the increased tissue pathology.
  
  
  
  We provide evidences of a specific role for IL-33 receptor signaling in nitric oxide induction through local IFN-γ modulation, suggesting that nitric oxide overproduction might have an important role in the progression of experimental viral encephalitis.
authors.affiliation: Department of Virology and Experimental Therapy LAVITE, Oswaldo Cruz Foundation - FIOCRUZ, Institute Aggeu Magalhães IAM, Av. Professor Moraes Rego, s/n, Recife, PE, 50740-465, Brazil. rafael.franca@cpqam.fiocruz.br.
authors.forename: Rafael F O
authors.initials: RF
authors.lastname: Franca
authors.affiliation: Program of Basic and Applied Immunology, University of São Paulo, Ribeirao Preto, SP, 14049-900, Brazil.
authors.forename: Renata S
authors.initials: RS
authors.lastname: Costa
authors.affiliation: Program of Basic and Applied Immunology, University of São Paulo, Ribeirao Preto, SP, 14049-900, Brazil.
authors.forename: Jaqueline R
authors.initials: JR
authors.lastname: Silva
authors.affiliation: Program of Basic and Applied Immunology, University of São Paulo, Ribeirao Preto, SP, 14049-900, Brazil.
authors.forename: Raphael S
authors.initials: RS
authors.lastname: Peres
authors.affiliation: Department of Virology and Experimental Therapy LAVITE, Oswaldo Cruz Foundation - FIOCRUZ, Institute Aggeu Magalhães IAM, Av. Professor Moraes Rego, s/n, Recife, PE, 50740-465, Brazil.
authors.forename: Leila R
authors.initials: LR
authors.lastname: Mendonça
authors.affiliation: Program of Basic and Applied Immunology, University of São Paulo, Ribeirao Preto, SP, 14049-900, Brazil.
authors.forename: David F
authors.initials: DF
authors.lastname: Colón
authors.affiliation: Department of Pharmacology, Ribeirão Preto School of Medicine, University of São Paulo, Ribeirão Preto, SP, 14049-900, Brazil.
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Alves-Filho
authors.affiliation: Department of Pharmacology, Ribeirão Preto School of Medicine, University of São Paulo, Ribeirão Preto, SP, 14049-900, Brazil. fdqcunha@fmrp.uspbr.
authors.forename: Fernando Q
authors.initials: FQ
authors.lastname: Cunha
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D002490:Central Nervous System / Q000276:immunology / Q000473:pathology / Q000821:virology; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000235:genetics; D018792:Encephalitis, Viral / Q000473:pathology*; D005260:Female; D018178:Flaviviridae Infections / Q000473:pathology; D005434:Flow Cytometry; D000072179:Interleukin-1 Receptor-Like 1 Protein / Q000172:deficiency / Q000235:genetics; D000067596:Interleukin-33 / Q000235:genetics / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D050800:STAT6 Transcription Factor / Q000172:deficiency / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology
chemical_list: D000943:Antigens, Differentiation; D016207:Cytokines; C486189:Il1rl1 protein, mouse; C506535:Il33 protein, mouse; D000072179:Interleukin-1 Receptor-Like 1 Protein; D000067596:Interleukin-33; D012333:RNA, Messenger; D050800:STAT6 Transcription Factor; C494100:Stat6 protein, mouse; C036763:monocyte-macrophage differentiation antigen; D052247:Nitric Oxide Synthase Type II
keywords: Experimental viral encephalitis; Flavivirus; Interleukin 33; Nitric oxide; ST2 receptor