Toll-like receptor 4 (TLR4) and interferon-gamma (IFN-r) are required for HMGB1-induced TNF release from macrophages. (34.18)

Abstract High mobility group box 1 (HMGB1) has been implicated as a cytokine mediator in the pathogenesis of inflammatory diseases (Yang et al. BBA, 2009). To study mechanisms of HMGB1 action, we produced mammalian HMGB1, devoid of bacterial products, and examined receptor signaling for HMGB1 mediated macrophage cytokine release. HMGB1 induced significant TNF release in macrophages from TLR2 KO, RAGE KO and wild type (WT) mice (n = 4-5 experiments). HMGB1 induced TNF release was completely abolished in TLR4 KO macrophages as compared to WT. Interestingly, we observed that HMGB1 induced TNF mRNA expression, but not TNF protein release, from TLR4 KO mouse macrophages. Pre-treatment of TLR4 KO macrophages with IFN-r restored HMGB1-induced TNF protein release. Thus, our results indicate that TLR4 is required for HMGB1-mediated cytokine release from macrophages, and that IFN-r can restore HMGB1-induced TNF release in TLR4 KO macrophages. (supported in part by grant from NIH, NIGMS, to KJT).