IL-6 Amplifies TLR Mediated Cytokine and Chemokine Production: Implications for the Pathogenesis of Rheumatic Inflammatory Diseases

Abstract

The role of Interleukin(IL)-6 in the pathogenesis of joint and systemic inflammation in rheumatoid arthritis (RA) and systemic juvenile idiopathic arthritis (s-JIA) has been clearly demonstrated. However, the mechanisms by which IL-6 contributes to the pathogenesis are not completely understood. This study investigates whether IL-6 affects, alone or upon toll like receptor (TLR) ligand stimulation, the production of inflammatory cytokines and chemokines in human peripheral blood mononuclear cells (PBMCs), synovial fluid mononuclear cells from JIA patients (SFMCs) and fibroblast-like synoviocytes from rheumatoid arthritis patients (RA synoviocytes) and signalling pathways involved. PBMCs were pre-treated with IL-6 and soluble IL-6 Receptor (sIL-6R). SFMCs and RA synoviocytes were pre-treated with IL-6/sIL-6R or sIL-6R, alone or in combination with Tocilizumab (TCZ). Cells were stimulated with LPS, S100A8-9, poly(I-C), CpG, Pam2CSK4, MDP, IL-1β. Treatment of PBMCs with IL-6 induced production of TNF-α, CXCL8, and CCL2, but not IL-1β. Addition of IL-6 to the same cells after stimulation with poly(I-C), CpG, Pam2CSK4, and MDP induced a significant increase in IL-1β and CXCL8, but not TNF-α production compared with TLR ligands alone. This enhanced production of IL-1β and CXCL8 paralleled increased p65 NF-κB activation. In contrast, addition of IL-6 to PBMCs stimulated with LPS or S100A8-9 (TLR-4 ligands) led to reduction of IL-1β, TNF-α and CXCL8 with reduced p65 NF-κB activation. IL-6/IL-1β co-stimulation increased CXCL8, CCL2 and IL-6 production. Addition of IL-6 to SFMCs stimulated with LPS or S100A8 increased CXCL8, CCL2 and IL-1β production. Treatment of RA synoviocytes with sIL-6R increased IL-6, CXCL8 and CCL2 production, with increased STAT3 and p65 NF-κB phosphorylation. Our results suggest that IL-6 amplifies TLR-induced inflammatory response. This effect may be relevant in the presence of high IL-6 and sIL-6R levels, such as in arthritic joints in the context of stimulation by endogenous TLR ligands.

A Heterozygous RAB27A Mutation Associated with Delayed Cytolytic Granule Polarization and Hemophagocytic Lymphohistiocytosis

“…This effect was seen in repeated experiments (Figure 2B) and suggested that over-expression of Rab27A p.A87P was able to diminish NK cell cytolytic capacity. Since it has recently been shown that the inflammatory environment may also contribute to decreased NK cell function (31), the experiment was repeated in the presence or absence of exogenous rIL-6 (37). As seen in Figure 2C, addition of IL-6 further decreased NK cell cytotoxicity when either WT or mutant Rab27A p.A87P was over-expressed.…”

Systemic inhibition of IL-6/Stat3 signalling protects against experimental osteoarthritis

“…This suggests that MR-16 might act through other pathways than Stat3 in the synovium tissue. Indeed, in RA synoviocytes, IL-6 can enhance p65 nuclear factor κB (NF-κB) activation and both Toll-like receptor ligand-induced inflammatory cytokine and chemokine production,35 which are known to be also involved in the genesis of OA synovitis 36…”

Macrophage Activation Syndrome: different mechanisms leading to a one clinical syndrome

“…When we looked at the stimulatory effect of IL-6, we showed that, in vitro, prolonged exposure of human macrophages to IL-6 leads to increased production of cytokines and chemokines, including Tumor Necrosis Factor-α (TNF-α) and (C-X-C Motif) Ligand 8 (CXCL-8), both at a basal level and upon stimulation with TLR ligands, suggesting a role for IL-6 in amplifying the inflammatory response [24]. In addition, we demonstrated that IL-6 amplifies TLR-induced inflammatory response also in cells originating from inflammatory site, such as synovial fluid mononuclear cells and fibroblast-like synoviocytes isolated from arthritides patients.…”

“…In addition, we demonstrated that IL-6 amplifies TLR-induced inflammatory response also in cells originating from inflammatory site, such as synovial fluid mononuclear cells and fibroblast-like synoviocytes isolated from arthritides patients. Indeed, treatments of these cells with IL-6 increased basal production of CXCL8, C-C motif chemokine ligand 2 (CCL2) and Interleukin-1β (IL-1β) following poly(I:C) and muramyl dipeptide stimulation [24]. …”