A key question in immunology concerns how sterile injury activates innate immunity to mediate damaging inflammation in the absence of foreign invaders. The discovery that HMGB1, a ubiquitous nuclear protein, mediates the activation of innate immune responses led directly to the understanding that HMGB1 plays a critical role at the intersection of the host inflammatory response to sterile and infectious threat. HMGB1 is actively released by stimulation of the innate immune system with exogenous pathogen-derived molecules and is passively released by ischemia or cell injury in the absence of invasion. Established molecular mechanisms of HMGB1 binding and signaling through TLR4 reveal signaling pathways that mediate cytokine release and tissue damage. Experimental strategies that selectively target HMGB1 and TLR4 effectively reverse and prevent activation of innate immunity and significantly attenuate damage in diverse models of sterile and infection-induced threat.

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HMGB1 Is a Therapeutic Target for Sterile Inflammation and Infection

High Mobility Group 1 protein (HMGB1) is a chromatin component that, when leaked out by necrotic cells, triggers inflammation. HMGB1 can also be secreted by activated monocytes and macrophages, and functions as a late mediator of inflammation. Secretion of a nuclear protein requires a tightly controlled relocation program. We show here that in all cells HMGB1 shuttles actively between the nucleus and cytoplasm. Monocytes and macrophages acetylate HMGB1 extensively upon activation with lipopolysaccharide; moreover, forced hyperacetylation of HMGB1 in resting macrophages causes its relocalization to the cytosol. Cytosolic HMGB1 is then concentrated by default into secretory lysosomes, and secreted when monocytic cells receive an appropriate second signal.

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Monocytic cells hyperacetylate chromatin protein HMGB1 to redirect it towards secretion

The immune system has evolved to respond not only to pathogens, but also to signals released from dying cells. Cell death through necrosis induces inflammation, whereas apoptotic cell death provides an important signal for tolerance induction. High mobility group box 1 (HMGB1) is a DNA-binding nuclear protein, released actively following cytokine stimulation as well as passively during cell death; it is the prototypic damage-associated molecular pattern (DAMP) molecule and has been implicated in several inflammatory disorders. HMGB1 can associate with other molecules, including TLR ligands and cytokines, and activates cells through the differential engagement of multiple surface receptors including TLR2, TLR4, and RAGE. RAGE is a multiligand receptor that binds structurally diverse molecules, including not only HMGB1, but also S100 family members and amyloid-β. RAGE activation has been implicated in sterile inflammation as well as in cancer, diabetes, and Alzheimer's disease. While HMGB1 through interacti...

HMGB1 and RAGE in inflammation and cancer.

of antibiotics, whether there was an explicit note in the medical chart in which the physician diagnosed a true bacteremia, and the Centers for Disease Control surveillance criteria for primary bloodstream infection. Agreement between same-strain bacteremia and each definition was examined, based on the assumption that most true infections should be the result of a single strain. The study sample consisted of 42 patients and 106 isolates. Nineteen of the 42 bacteremias (45%) were the same strain. Classification of bacteremias as same-strain correlated poorly with all three clinical assessments (range of percentage agreement, 50%-57%; range of kappa statistic, 0.01-0.15). There were both false-positive and false-negative errors. Patients with three or more positive blood cultures were more likely to have same-strain bacteremia than those with only two positive cultures (11/15 [73%] vs 8/27 [30%], P=.006). Pulsed-field gel electrophoresis was more discriminating than AP PCR (percentage agreement, 83%; kappa, 0.67). The authors concluded that molecular typing correlated poorly with clinical criteria for true bacteremia, suggesting either that true bacteremias are frequently the result of multiple strains or that the commonly used clinical criteria are not accurate for distinguishing contamination from true bacteremia. Vancomycin treatment of clinically defined coagulase-negative staphylococcal bacteremia may frequently be unnecessary. FROM: Seo SK, Venkataraman L, DeGirolami PC, Samore MH. Molecular typing of coagulase-negative staphylococci from blood cultures does not correlate with clinical criteria for true bacteremia. Am J Med 2000;109:697-704.

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Nasal Carriage as a Source of Staphylococcus aureus Bacteremia

The adipokine resistin is suggested to be an important link between obesity and insulin resistance. In the present study, we assessed the impact of resistin as inflammatogenic cytokine in the setting of arthritis. In vitro experiments on human PBMC were performed to assess cytokine response and transcription pathways of resistin-induced inflammation. Proinflammatory properties of resistin were evaluated in animal model by intra-articular injection of resistin followed by histological evaluation of the joint. Levels of resistin were assessed by ELISA in 74 paired blood and synovial fluid samples of patients with rheumatoid arthritis. Results were compared with the control group comprised blood samples from 34 healthy individuals and 21 synovial fluids from patients with noninflammatory joint diseases. We now show that resistin displays potent proinflammatory properties by 1) strongly up-regulating IL-6 and TNF-α, 2) responding to TNF-α challenge, 3) enhancing its own activity by a positive feedback, and finally 4) inducing arthritis when injected into healthy mouse joints. Proinflammatory properties of resistin were abrogated by NF-κB inhibitor indicating the importance of NF-κB signaling pathway for resistin-induced inflammation. Resistin is also shown to specifically accumulate in the inflamed joints of patients with rheumatoid arthritis and its levels correlate with other markers of inflammation. Our results indicate that resistin is a new and important member of the cytokine family with potent regulatory functions. Importantly, the identified properties of resistin make it a novel and interesting therapeutic target in chronic inflammatory diseases such as rheumatoid arthritis.

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Resistin, an adipokine with potent proinflammatory properties

To the Editor: 

High mobility group box 1 (HMGB1) chromosomal protein, an endogenous molecule with multiple intra- and extracellular effects, is also defined as a novel proinflammatory cytokine, proved to contribute to the pathogenesis of several rheumatic diseases1. Evidence grows showing that HMGB1 plays a role as an important endogenous mediator of arthritis. Significantly elevated levels of HMGB1 are reported in the sera and synovial fluid of patients with rheumatoid arthritis (RA) as compared to patients with osteoarthritis2. Levels of HMGB1 are increased in the synovial tissues of animals and humans with joint inflammation3. HMGB1 mediates the development of arthritis when applied into the joints of naive mice4 and treatment strategies directed against HMGB1 attenuate progression in collagen-induced arthritis1. In RA, characterized by chronic autoimmune destructive joint inflammation, extensive production of proinflammatory cytokines is known to mediate tissue damage.

HMGB1, either released actively from myeloid and dendritic cells or passively during local cell death in the joint, could sustain chronic synovitis by several mechanisms including an augmentation of production of several proinflammatory mediators such as interleukin 1 (IL-1), tumor necrosis factor-α (TNF-α), and IL-6, all known to be important in the pathogenesis of arthritis5.

In a cross-sectional study, we investigated the relationship between concentrations of HMGB1 and proinflammatory cytokines and disease characteristics in a cohort6 of 81 postmenopausal patients with RA. The … 

Address correspondence to Dr. R. Pullerits, The Sahlgrenska Academy, University of Gothenburg, Department of Rheumatology and Inflammation Research, Guldhedsgatan 10A, 41346, Gothenburg, Sweden. E-mail: rille.pullerits{at}rheuma.gu.se

https://www.jrheum.org/content/jrheum/38/7/1523.2.full.pdf

Serum levels of HMGB1 in postmenopausal patients with rheumatoid arthritis: associations with proinflammatory cytokines, acute-phase reactants, and clinical disease characteristics.

Objective. The aim of the study was to prospectively investigate the effects of HRT on serum soluble receptor for advanced glycation end product (sRAGE) levels in RA patients and to determine whether sRAGE production is related to bone/cartilage metabolism. Methods. Eighty-eight post-menopausal RA patients were randomized to receive vitamin D3 and calcium supplementation with or without HRT (oestradiol plus noretisterone acetate). The levels of total sRAGE in sera were measured before, 1 and 2 years after treatment initiation. Potential associations between sRAGE levels, bone/cartilage metabolic markers and BMD were investigated. Results. Patients receiving HRT displayed significantly decreased levels of serum sRAGE at 1 and 2 years as compared with levels at study entry. The increase in serum oestradiol was associated with the decline in sRAGE levels. Importantly, sRAGE levels at baseline significantly correlated with bone/cartilage turnover markers including C-terminal propeptide of type I procollagen, carboxyterminal telopeptide of type I collagen and cartilage oligomeric matrix protein, and the decrease of sRAGE levels paralleled with diminished concentration of these molecules. BMD in hip and femoral neck and progression of Larsen score at 1 year were associated with baseline sRAGE levels. The decline in sRAGE levels significantly correlated with an increase in total BMD following 2 years of treatment in patients receiving HRT but not in the control group. Conclusion. Our findings suggest that HRT decreases the levels of endogenous sRAGE in post-menopausal RA patients implicating its role in sRAGE regulation. In addition, serum sRAGE was associated with BMD and markers of bone/cartilage metabolism. These data suggest that sRAGE is involved directly or indirectly in bone metabolism. Trial registration. Current Controlled Trials, ISRCTN46523456, http://www.controlled-trials.com/isrctn/search.html?srch¼ISRCTN46523456

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The decrease of soluble RAGE levels in rheumatoid arthritis patients following hormone replacement therapy is associated with increased bone mineral density and diminished bone/cartilage turnover: a randomized controlled trial

Objectives. The receptor for advanced glycation end products (RAGE) is expressed by many cells in joints of rheumatoid arthritis (RA) patients and interacts with a variety of pro-inflammatory ligands that are enriched in inflamed joint. The RAGE-ligand interaction leads to a sustained inflammatory response. Also, secreted form of the receptor, called soluble RAGE (sRAGE), the levels of which are decreased in RA patients, modulates inflammatory responses. We sought to determine whether RA patients display increased occurrence of autoantibodies against RAGE and whether such an autoantibody production is related to disease characteristics. Methods. Matching samples of blood and synovial fluid were collected from 50 patients with RA with acute joint effusion. Blood from 43 healthy individuals and synovial fluid samples from 32 patients with non-inflammatory joint diseases were used for comparison. Anti-RAGE antibody levels were analysed using an ELISA. Results. RA patients displayed significantly higher blood and synovial fluid levels of anti-RAGE antibodies, both of IgG as well as of IgM class as compared with healthy controls and with patients with non-inflammatory joint diseases. Patients with seropositive RA had significantly less IgG antibodies in their synovial fluid as compared to seronegative patients. Furthermore, the presence of IgG class of anti-RAGE antibodies locally in the joint was found to be related to less aggressive, i.e. non-erosive disease. Conclusion. These results suggest that RAGE-specific B cell response protect patients with RA from destructive course of the disease.

Synovial fluid expression of autoantibodies specific for RAGE relates to less erosive course of rheumatoid arthritis

The rationale of the study was to evaluate the efficacy of infliximab (IFX) treatment in patients with ankylosing spondylitis (AS) and to determine whether IFX dose reduction and interval extension sustains the treatment effect. Nineteen patients were included and treated with IFX 5 mg/kg every 6 weeks for 56 weeks. All patients concomitantly received MTX with median dose 7.5 mg/weekly. During the second year, the IFX dose was reduced to 3 mg/kg every 8 weeks. Eighteen patients completed the 1-year and 15 patients the 2-year trial. The ≥50% improvement at week 16 from baseline of BASDAI was achieved in 16/19 (84%) patients. Significant reductions in BASDAI, BASFI, and BASMI scores, decrease in ESR and CRP, and improvement in SF-36 were observed at weeks 16 and 56. The MRI-defined inflammatory changes in the sacroiliac joints disappeared in 10/15 patients (67%) already at 16 weeks. IFX treatment effect was sustained throughout the second year after IFX dose reduction and interval extension. We conclude that IFX treatment is effective in well-established active AS and a dose reduction sustains the treatment effect. These observations are of clinical importance and open the opportunity to reduce the drug costs.

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Infliximab Dose Reduction Sustains the Clinical Treatment Effect in Active HLAB27 Positive Ankylosing Spondylitis: A Two-Year Pilot Study

Introduction
TNFα and high mobility group box chromosomal protein 1 (HMGB1) are two potent proinflammatory cytokines implicated as important mediators of arthritis. Increased levels of these cytokines are found in the joints of rheumatoid arthritis patients, and the cytokines trigger arthritis when applied into the joints of naive mice. HMGB1 is actively released from immune cells in response to TNFα; once released, HMGB1 in turn induces production of several proinflammatory cytokines – including IL-6 and TNFα – by macrophages. Whether HMGB1-induced arthritis is mediated via the TNFα pathway, however, is unknown. The purpose of the present study was to investigate whether the arthritis-inducing effect of HMGB1 is dependent on TNFα expression in vivo and to assess whether TNFα deficiency affects a proinflammatory cytokine response to HMGB1 in vitro.

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Rille Pullerits

Papers

Serum levels of HMGB1 in postmenopausal patients with rheumatoid arthritis: associations with proinflammatory cytokines, acute-phase reactants, and clinical disease characteristics.

The decrease of soluble RAGE levels in rheumatoid arthritis patients following hormone replacement therapy is associated with increased bone mineral density and diminished bone/cartilage turnover: a randomized controlled trial

Synovial fluid expression of autoantibodies specific for RAGE relates to less erosive course of rheumatoid arthritis

Infliximab Dose Reduction Sustains the Clinical Treatment Effect in Active HLAB27 Positive Ankylosing Spondylitis: A Two-Year Pilot Study

Induction of arthritis by high mobility group box chromosomal protein 1 is independent of tumour necrosis factor signalling