High mobility group box protein 1 in complex with lipopolysaccharide or IL-1 promotes an increased inflammatory phenotype in synovial fibroblasts

Inflammation can be infectious and/or sterile depending on the initiating event. The proinflammatory mediator High mobility group box protein 1 (HMGB1) is a nuclear protein released from cells during both sterile and infectious inflammation and once extracellular, initates and potentiates inflammation by inducing cytokine production and by recruiting inflammatory cells. Autoimmune diseases are characterised by chronic sterile inflammation leading to tissue destruction. HMGB1 has been implicated in the pathogenesis of several autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosis, multiple sclerosis and myositis. The involvement of HMGB1 in arthritis has been shown by overexpression of HMGB1 in RA synovial tissue and synovial fluid, by beneficial outcome of therapeutic HMGB1-blockade in several experimental arthritis models and by the induction of arthritis by intra-articular injection of recombinant HMGB1 into mice. In this thesis work I set out to investigate the potential role of HMGB1 in juvenile idiopathic arthritis (JIA), to further delineate mechanisms by which HMGB1 can contribute to arthritis pathogenesis and to study the means by which HMGB1 activity can be suppressed. I could report for the first time that HMGB1 levels were increased in synovial fluid as compared to plasma during JIA. HMGB1 levels in synovial fluid did not correlate to disease duration. In contrast, the recorded levels of IL-8 and S100 proteins were higher in synovial fluid during early phases of disease. This indicates a change in the inflammatory phenotype during the progression of JIA. High HMGB1 levels in synovial fluid correlated with early JIA onset, suggesting differences in immunopathogenesis between patient groups. I have also demonstrated that HMGB1 may form complexes with the exogenous TLR ligand LPS or the endogenous inflammatory mediators IL-1α and IL-1β, respectively. Compared to each mediator alone such complexes stimulated synovial fibroblasts from arthritis patients to enhanced production of cytokines and tissue degrading enzymes. This enhancement is mediated via the reciprocal receptor for each HMGB1-partner molecule. Since all the studied mediators are present in arthritic joint during inflammation, this is a potential mechanism through which HMGB1 enhances ongoing inflammation and destruction during rheumatic diseases. Finally, I have demonstrated that the proinflammatory activity of HMGB1 can be therapeutically targeted, either by inhibiting its active release by clinically approved anti-rheumatic drugs or by neutralization with a HMGB1-specific monoclonal antibody. Extracellular secretion of HMGB1 from LPS+IFN-γ stimulated human primary monocytes was inhibited by dexamethasone, chloroquine and gold sodium thiomalate in vitro as recorded using an ELISPOT assay. Therapeutic administration of an HMGB1-specific HMGB1 monoclonal antibody ameliorated arthritis in two separate experimental models. In conclusion, my thesis work has added to the growing evidence that HMGB1 is involved in the pathogenesis of arthritis, has revealed a potential mechanism for its proinflammatory function and has demonstrated a means by which HMGB1-mediated activities can be counteracted

Inflammatory pathways in spondyloarthritis

Spondyloarthritis is the second most common form of chronic inflammatory arthritis and a unique hallmark of the disease is pathologic new bone formation. Several cytokine pathways have been genetically associated with ankylosing spondylitis (AS), the prototypic subtype of SpA, and additional evidence from human and animal studies support a role of these pathways in the disease. TNF has a key role in SPA as blockade significantly reduces inflammation and destruction, however the treatment does not halt new bone formation. New insights into the TNF pathway were recently obtained from an animal model specifically overexpressing the transmembrane form of TNF. This model leads to axial and peripheral new bone formation which is not seen in soluble TNF overexpression models, indicating different pathogenic roles of soluble and transmembrane TNF in arthritis development. Besides TNF, the IL-23/IL-17 axis is emerging as an important inflammatory pathway in SpA, as a SNP in the IL-23R locus has been associated with developing AS, mice overexpressing IL-23 develop SpA-like features and IL-17 blockade has been shown to be efficacious for AS patients in a phase II trial. In this review, we focus on the cytokine pathways that have recently been genetically associated with SpA, i.e. TNF, IL-1, IL-6 and IL-23/IL-17. We review the current genetic, experimental and human in vivo data available and discuss how these different pathways are involved in the pathophysiology of SpA. Additionally, we discuss how these pathways relate to the pathogenic new bone formation in SpA. (C) 2013 Elsevier Ltd. All rights reserve

High Mobility Group Box Protein 1 (HMGB1)-Partner Molecule Complexes Enhance Cytokine Production by Signaling Through the Partner Molecule Receptor

The nuclear protein high mobility group box protein 1 (HMGB1) promotes inflammation upon extracellular release. HMGB1 induces proinflammatory cytokine production in macrophages via Toll-like receptor (TLR)-4 signaling in a redox-dependent fashion. Independent of its redox state and endogenous cytokine-inducing ability, HMGB1 can form highly immunostimulatory complexes by interaction with certain proinflammatory mediators. Such complexes have the ability to enhance the induced immune response up to 100-fold, compared with induction by the ligand alone. To clarify the mechanisms for these strong synergistic effects, we studied receptor requirements. Interleukin (IL)-6 production was assessed in supernatants from cultured peritoneal macrophages from mice each deficient in one of the HMGB1 receptors (receptor for advanced glycation end products [RAGE], TLR2 or TLR4) or from wild-type controls. The cultures were stimulated with the TLR4 ligand lipopolysaccaride (LPS), the TLR2 ligand Pam3CysSerLys4 (Pam3CSK4), noninflammatory HMGB1 or each TLR ligand in complex with noninflammatory HMGB1. The activity of the HMGB1-TLR ligand complexes relied on engagement of the same receptor as for the noncomplexed TLR ligand, since HMGB1-LPS complexes used TLR4 and HMGB1-Pam3CSK4 complexes used TLR2. Deletion of any of the intracellular adaptor molecules used by TLR2 (myeloid differentiation factor-88 [MyD88], TIR domain–containing adaptor protein [TIRAP]) or TLR4 (MyD88, TIRAP, TIR domain–containing adaptor-inducing interferon-β [TRIF], TRIF-related adaptor molecule [TRAM]) had similar effects on HMGB1 complex activation compared with noncomplexed LPS or Pam3CSK4. This result implies that the enhancing effects of HMGB1-partner molecule complexes are not regulated by the induction of additional signaling cascades. Elucidating HMGB1 receptor usage in processes where HMGB1 acts alone or in complex with other molecules is essential for the understanding of basic HMGB1 biology and for designing HMGB1-targeted therapies

Human type 1 innate lymphoid cells accumulate in inflamed mucosal tissues

Item does not contain fulltextInnate lymphoid cells (ILCs) are effectors of innate immunity and regulators of tissue modeling. Recently identified ILC populations have a cytokine expression pattern that resembles that of the helper T cell subsets T(H)2, T(H)17 and T(H)22. Here we describe a distinct ILC subset similar to T(H)1 cells, which we call 'ILC1'. ILC1 cells expressed the transcription factor T-bet and responded to interleukin 12 (IL-12) by producing interferon-gamma (IFN-gamma). ILC1 cells were distinct from natural killer (NK) cells as they lacked perforin, granzyme B and the NK cell markers CD56, CD16 and CD94, and could develop from RORgammat(+) ILC3 under the influence of IL-12. The frequency of the ILC1 subset was much higher in inflamed intestine of people with Crohn's disease, which indicated a role for these IFN-gamma-producing ILC1 cells in the pathogenesis of gut mucosal inflammation