CpG DNA Prevents Liver Injury and Shock-mediated Death by Modulating Expression of Interleukin-1 Receptor-associated Kinases

Abstract

Tumor necrosis factor-␣ (TNF-␣) produced by macrophages in response toThe innate immune response is initiated by recognition of evolutionarily conserved molecular motifs (pathogen-associated molecular patterns) found in a variety of microorganisms by pattern recognition receptors present in the host innate immune cells (1, 2). Among the pattern recognition receptors, Toll-like receptors (TLRs) 4 are the most extensively investigated. TLRs are a group of structurally related proteins that contain amino-terminal leucine-rich repeats that are responsible for binding to pathogen-associated molecular patterns, a transmembrane domain, and a carboxyl-terminal Toll/interleukin-1 receptor domain that is responsible for signaling. The TLR family now consists of at least 13 members (TLR1-TLR13) in the mouse and 11 members in humans. Among the different TLRs, TLR9 has been identified as a receptor for bacterial DNA, double-stranded viral DNA, and synthetic oligodeoxynucleotides containing an unmethylated CpG motif (CpG DNA) (3-5). Ligand (CpG DNA)-bound TLR9 recruits the adaptor molecule, myeloid differentiation factor 88 (MyD88), to its intracellular Toll/interleukin-1 receptor domain. MyD88 in turn recruits interleukin-1 receptor-associated kinase-4 (IRAK-4) and IRAK-1 to the TLR9/MyD88 signaling complex. IRAK-1 becomes rapidly phosphorylated by IRAK-4, leaves the receptor complex, and then associates with tumor necrosis factor-␣ receptor-associated factor 6 (TRAF6). Binding of TRAF6 to IRAK-1 ultimately results in activation of signaling cascades that lead to the activation of mitogen-associated protein kinases (MAPKs) and NF-B and subsequent expression of proinflammatory cytokines, chemokines, and oncogenes (6).The TLR-mediated production of proinflammatory mediators and cytokines by innate immune cells is necessary for efficient control of growth and dissemination of invading pathogens. However, uncontrolled, excessive, and prolonged activation of innate immunity can be detrimental to the host. To prevent such undesirable outcomes as septic shock-like syndrome and chronic inflammatory diseases, the innate immune system might employ regulatory mechanisms that ensure an

CpG ODN pretreatment attenuates concanavalin A-induced hepatitis in mice

“…Also, accumulating evidence suggests that NF-κB can regulate the network of inflammatory cytokines in hepatic injury induced by Con A [26,27]. Our data showed that CpG pretreatment prevented NF-κB DNA-binding activity, IκBα phosphorylation and the expression of proinflammatory cytokines including TNF-α and IFN-γ, which correlate with those showing CpG ODN-mediated protection from DNA/DGalN-induced liver injury and polymicrobial sepsis induced by the rat cecal ligation and puncture (CLP) model [10,28]. The attenuated activation of NF-κB in CpG ODN pretreated mice livers may contribute to the protective effects of CpG ODN on Con Ainduced hepatitis.…”

“…TNF-α was primarily released by activated T cells and Kuppfer cells in the livers of Con A treated mice. A previous study demonstrated that macrophages (both Kuppfer cells and RAW264.7) pretreated with CpG ODN became hyporesponsive to the following CpG ODN stimulation through modulating the expression of interleukin-1 receptor-associated kinases [10,24]. Our data suggest that CpG ODN pretreatment may function in vivo by inducing macrophage's hyporesponsiveness to Con A.…”

“…Moreover, the same CpG ODN can produce opposite effects in different model systems. For example, CpG ODN 1826 (5′-TCC ATG ACG TTC CTG ACG TT-3′) pretreatment protected mice from CpG DNA/DGalNinduced liver injury [10], but aggravated liver injury in a low dose Con A-induced hepatitis [17]. The CpG ODN used in our study had been showed to reduce the survival of mice in a LPS-induced lethal endotoxic shock model [11], which is significantly different from the Con Ainduced hepatitis model.…”

“…A recent study suggested that CpG ODN have a protective effect on the CpG ODN/D-GalN-induced hepatic injury [10]. However, the effects of CpG ODN on Con A-induced hepatitis are less known and need to be further investigated.…”

Molecular Basis for T Cell Response Induced by Altered Peptide Ligand of Type II Collagen

“…Transfection-Retroviral vectors expressing Myc-tagged Syk and Zap-70 as well as FLAG-tagged FcR␥ and TCR-were developed as previously described (14). Briefly, the coding region of each was amplified by PCR using murine spleen cDNA as a template and then inserted into a pIRES-hrGFPII (Stratagene, La Jolla, CA) vector.…”