title: C4b binding protein negatively regulates TLR1/2 response.
abstract: TLR2 associates with TLR1 and recognizes microbial lipoproteins. Pam3CSK4, a triacylated lipoprotein, is anchored to the extracellular domain of TLR1 and TLR2 and induces pro-inflammatory signals. Here we show that C4b binding protein (C4BP), which is a complement pathway inhibitor, is a TLR2-associated molecule. Immunoprecipitation assay using anti-TLR2 mAb shows that C4BP binds to TLR2. In C4BP-deficient mice, Pam3CSK4-induced IL-6 levels were increased compared with wild type mice. In C4BP-expressing cells, Pam3CSK4-induced IL-8 production was reduced depending on the C4BP expression levels. These results reveal the important role of C4BP in negative regulation of TLR1/2-dependent pro-inflammatory cytokine production. Furthermore, using a fluorescent conjugated Pam3CSK4, we show that C4BP blocks the binding of Pam3CSK4 to TLR1/2. Finally, we show that exogenous C4BP also inhibits Pam3CSK4-induced signaling leading to IL-8 production. Our results indicate C4BP binding to TLR2 and consequent neutralization of its activity otherwise inducing pro-inflammatory cytokine production. C4BP is a negative regulator of TLR1/2 activity.
authors: 1 Department of Microbiology and Immunology, Aichi Medical University School of Medicine, Aichi, Japan.
authors: Naoko
authors: N
authors: Morita
authors: 2 Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
authors: Ikuko
authors: I
authors: Yamai
authors: 3 Division of Hematology, Respiratory Medicine and Oncology, Department of Internal Medicine, Faculty of Medicine, Saga University, Saga, Japan.
authors: Koichiro
authors: K
authors: Takahashi
authors: 2 Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
authors: Yutaka
authors: Y
authors: Kusumoto
authors: 2 Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
authors: Takuma
authors: T
authors: Shibata
authors: 2 Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.|4 Research Institute, National Center for Global Health and Medicine, Tokyo, Japan.
authors: Toshihiko
authors: T
authors: Kobayashi
authors: 5 Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
authors: Mayumi I
authors: MI
authors: Nonaka
authors: 1 Department of Microbiology and Immunology, Aichi Medical University School of Medicine, Aichi, Japan.
authors: Isao
authors: I
authors: Ichimonji
authors: 1 Department of Microbiology and Immunology, Aichi Medical University School of Medicine, Aichi, Japan.
authors: Hidekazu
authors: H
authors: Takagi
authors: 2 Division of Innate Immunity, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
authors: Kensuke
authors: K
authors: Miyake
authors: 1 Department of Microbiology and Immunology, Aichi Medical University School of Medicine, Aichi, Japan.
authors: Sachiko A
authors: SA
authors: Takamura
mesh_terms: D000818:Animals; D001665:Binding Sites; D003167:Complement Activation; D050716:Complement C4b-Binding Protein / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D055666:Lipopeptides / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011485:Protein Binding; D015398:Signal Transduction; D051194:Toll-Like Receptor 1 / Q000378:metabolism*; D051195:Toll-Like Receptor 2 / Q000378:metabolism*
chemical_list: D050716:Complement C4b-Binding Protein; D015850:Interleukin-6; D016209:Interleukin-8; D055666:Lipopeptides; C508075:Pam(3)CSK(4) peptide; C493486:Tlr2 protein, mouse; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2
keywords: C4b binding protein; Pam3CSK4; TLR2; immune response; pro-inflammatory cytokine