This article is protected by copyright. All rights reserved. “
“Activation of Toll-like receptors (TLRs) triggers rapid inflammatory cytokine production in various cell types. The exogenous product of growth-arrest-specific gene 6 (Gas6) and Protein S (ProS) inhibit the TLR-triggered inflammatory responses through the activation of Tyro3, Axl and Mer (TAM) receptors. However, regulation of the Gas6/ProS-TAM system remains largely unknown. In the current study, mouse macrophages are shown to constitutively express Gas6 and

ProS, which synergistically suppress the basal and TLR-triggered production of inflammatory cytokines, including those of tumour necrosis factor-α, interleukin-6 and interleukin-1β, by the macrophages in an autocrine manner. Notably, TLR signalling markedly decreases LBH589 ic50 Gas6 and ProS expression in macrophages through the activation of the nuclear factor-κB. Further,

the down-regulation of Gas6 and ProS by TLR signalling facilitates the TLR-mediated inflammatory cytokine see more production in mouse macrophages. These results describe a self-regulatory mechanism of TLR signalling through the suppression of Gas6 and ProS expression. Toll-like receptors (TLRs) are crucial triggers of innate immunity through the recognition of pathogen-associated molecular patterns.1 To date, 11 distinct TLRs have been found in humans, and 13 in mice.2 The ligands of most TLRs have been identified.3 For example, TLR4 recognizes the lipopolysaccharides (LPS) of Gram-negative bacteria;4 TLR3 recognizes the double-stranded RNA (dsRNA) produced by many viruses during replication, and is also activated by a synthetic dsRNA analogue, polyinosinic-polycytidylic acid [poly(I:C)],5 and TLR9 can be activated by CpG DNA motifs of both bacteria and viruses.6 Activation

of TLR triggers two signalling pathways:3 the MyD88-dependent (D) pathway, which uses the adaptor molecule MyD88, leading to the activation of the nuclear factor-κB HAS1 (NF-κB) and mitogen-activated protein kinases (MAPKs); and the MyD88-independent (I) pathway through the recruitment of Toll/interleukin-1 receptor domain-containing adaptor inducing interferon-β, resulting in the activation of NF-κB and interferon-regulating factor-3 (IRF3). With the exception of TLR3 and TLR4, all other TLRs trigger immune response exclusively through the D pathway. TLR3 signals exclusively through the I pathway,7 whereas TLR4 initiates both the D and I pathways.8 The TLR pathway-mediated activation of NF-κB and MAPKs induces the production of numerous pro-inflammatory cytokines including interleukin-1β (IL-1β), IL-6 and tumour necrosis factor-α (TNF-α). The I pathway-mediated IRF3 activation leads to the induction of type 1 interferons (IFN-α and IFN-β).