title: ST2 negatively regulates TLR2 signaling, but is not required for bacterial lipoprotein-induced tolerance.
abstract: Activation of TLR signaling is critical for host innate immunity against bacterial infection. Previous studies reported that the ST2 receptor, a member of the Toll/IL-1 receptor superfamily, functions as a negative regulator of TLR4 signaling and maintains LPS tolerance. However, it is undetermined whether ST2 negatively regulates TLR2 signaling and furthermore, whether a TLR2 agonist, bacterial lipoprotein (BLP)-induced tolerance is dependent on ST2. In this study, we show that BLP stimulation-induced production of proinflammatory cytokines and immunocomplex formation of TLR2-MyD88 and MyD88-IL-1R-associated kinase (IRAK) were significantly enhanced in ST2-deficient macrophages compared with those in wild-type controls. Furthermore, overexpression of ST2 dose-dependently attenuated BLP-induced NF-kappaB activation, suggesting a negative regulatory role of ST2 in TLR2 signaling. A moderate but significantly attenuated production of TNF-alpha and IL-6 on a second BLP stimulation was observed in BLP-pretreated, ST2-deficient macrophages, which is associated with substantially reduced IRAK-1 protein expression and downregulated TLR2-MyD88 and MyD88-IRAK immunocomplex formation. ST2-deficient mice, when pretreated with a nonlethal dose of BLP, benefitted from an improved survival against a subsequent lethal BLP challenge, indicating BLP tolerance develops in the absence of the ST2 receptor. Taken together, our results demonstrate that ST2 acts as a negative regulator of TLR2 signaling, but is not required for BLP-induced tolerance.
authors.affiliation: Department of Academic Surgery, University College Cork/National University of Ireland, Cork University Hospital, Cork, Ireland.
authors.forename: Jinghua
authors.initials: J
authors.lastname: Liu
authors.forename: Julliette M
authors.initials: JM
authors.lastname: Buckley
authors.forename: H Paul
authors.initials: HP
authors.lastname: Redmond
authors.forename: Jiang Huai
authors.initials: JH
authors.lastname: Wang
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology*; D002478:Cells, Cultured; D015536:Down-Regulation / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007108:Immune Tolerance / Q000235:genetics; D000072179:Interleukin-1 Receptor-Like 1 Protein; D008074:Lipoproteins / Q000502:physiology*; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D018123:Receptors, Interleukin / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D051195:Toll-Like Receptor 2 / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; C486189:Il1rl1 protein, mouse; D000072179:Interleukin-1 Receptor-Like 1 Protein; D008074:Lipoproteins; D018123:Receptors, Interleukin; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2