Objective. To examine the potential role of high mobility group box chromosomal protein 1 (HMGB-1) in the pathogenesis of arthritis.Methods. Mice were injected intraarticularly with 1 g or 5 g of HMGB-1. Joints were dissected on days 4, 7, and 28 after injection and were evaluated histopathologically and immunohistochemically. To investigate the importance of different white blood cell populations for the development of arthritis, in vivo cell depletion procedures were performed. In addition, spleen cells were cultured in the presence of HMGB-1, and nuclear factor B (NF-B) activation was detected by electrophoretic mobility shift assay.Results. Injection of recombinant HMGB-1 (rHMGB-1) into different mouse strains resulted in an overall frequency of arthritis in 80% of the animals. The inflammation was characterized by mild to moderate synovitis and lasted for at least 28 days. The majority of cells found in the inflamed synovium were Mac-1؉ macrophages, whereas only a few CD4؉ lymphocytes were detected. Pannus formation was observed in some cases 7 and 28 days after HMGB-1 injection. No significant differences were found with respect to incidence and severity of arthritis between mice depleted of monocytes, granulocytes, or lacking T/B lymphocytes. However, combined removal of monocytes and neutrophils resulted in a 43% lower incidence of arthritis. Mice rendered deficient in the interleukin-1 (IL-1) receptor did not develop inflammation upon challenge with HMGB-1. In vitro data corroborate this finding, showing that rHMGB-1 activated NF-B, a major pathway leading to IL-1 production. Conclusion. Our results indicate that HMGB-1 is not a mere expression of inflammatory responses, but on its own, it triggers joint inflammation by activating macrophages and inducing production of IL-1 via NF-B activation.High mobility group box chromosomal protein 1 (HMGB-1), named for its rapid mobility on electrophoresis gels, is a ubiquitous, nonhistone, chromatinassociated 215-amino acid protein with highly conserved amino acid sequence identity between rodents and humans (1-3). Nuclear HMGB-1 has been identified and studied for a long time as a DNA binding protein. It participates in maintenance of nucleosomal structure and stability and facilitates the binding of transcription factors to their cognate DNA sequences (4). HMGB-1 also has functions in DNA transcription, recombination (5,6), repair, cell replication, cell migration, and tumor growth (7,8).In contrast to its intranuclear role, extracellular HMGB-1 was recently shown to act as a cytokine mediating delayed endotoxin lethality (9) as well as acute lung injury in mice (10). Moreover, high levels of HMGB-1 have been detected in the blood of patients with sepsis (9) and in the synovial fluid of rheumatoid arthritis (RA) patients (11). Proinflammatory mediators, such as tumor necrosis factor ␣ (TNF␣) and interleukin-1 (IL-1), can dose-dependently induce the release of HMGB-1 from monocytes and macrophages

Objective. Receptor for advanced glycation end products (RAGE) is a cell surface molecule that binds a variety of ligands, including high mobility group box chromosomal protein 1 (HMGB-1), a potent proinflammatory cytokine. RAGE-ligand interaction leads to an inflammatory response. A truncated form of the receptor, soluble RAGE (sRAGE), has been suggested to function as a decoy abrogating cellular activation, but its endogenous activity is not fully understood. We undertook this study to assess the properties of sRAGE in vivo and in vitro and to analyze the role of sRAGE in HMGB-1-induced arthritis.Methods. Mice were injected intraarticularly with HMGB-1 and treated systemically with sRAGE prior to histologic joint evaluation. All animals were subjected to peritoneal lavage to assess the local effect of sRAGE treatment. For in vitro studies, mouse splenocytes were incubated with sRAGE followed by assessment of NF-B activation and cytokine production. The chemotactic properties of sRAGE were investigated using in vitro migration assay.Results. Soluble RAGE was determined to have proinflammatory properties since it gave rise to production of interleukin-6, tumor necrosis factor ␣, and macrophage inflammatory protein 2. This effect was triggered by interaction with leukocyte ␤2 integrin Mac-1 and was mediated via NF-B. Systemic treatment with sRAGE significantly down-regulated HMGB-1-triggered arthritis, but the observed effect was due to a deviation of the inflammatory response from the joint to the peritoneal cavity rather than a genuine antiinflammatory effect. Apart from its proinflammatory properties, sRAGE was proven to act as a chemotactic stimulus for neutrophils. Conclusion. We conclude that sRAGE interacts with Mac-1, thereby acting as an important proinflammatory and chemotactic molecule.The receptor for advanced glycation end products (RAGE) is a multiligand member of the immunoglobulin superfamily, being expressed as a cell surface molecule and playing a key role in diverse inflammatory processes (1). RAGE was first described as a receptor for "advanced glycation end products" (AGEs), the products of nonenzymatic glycation and oxidation of proteins and lipids that accumulate in the setting of diabetes (2). The receptor protein is composed of 3 immunoglobulin-like regions, a transmembrane domain, and a highly charged short cytosolic tail that is essential for intracellular signaling. The V domain in the extracellular part of the receptor protein is critical for ligand binding and interacts with a diverse class of ligands due to its ability to recognize 3-dimensional structures rather than specific amino acid sequences (3). Studies have shown that engagement of RAGE by its ligands results in a rapid and sustained cellular activation. Sustained receptor engagement leads to a positive feedback loop in which ligand-receptor interaction increases expression of the receptor itself on the cell surface (3). However, in normal tissues, RAGE is expressed at low levels (4).Soluble RAGE (sRAGE), a truncated form of...

Rapid bone destruction often leads to permanent joint dysfunction in patients with septic arthritis, which is mainly caused by Staphylococcus aureus ( S . aureus ). Staphylococcal cell wall components are known to induce joint inflammation and bone destruction. Here, we show that a single intra-articular injection of S . aureus lipoproteins (Lpps) into mouse knee joints induced chronic destructive macroscopic arthritis through TLR2. Arthritis was characterized by rapid infiltration of neutrophils and monocytes. The arthritogenic effect was mediated mainly by macrophages/monocytes and partially via TNF-α but not by neutrophils. Surprisingly, a S . aureus mutant lacking Lpp diacylglyceryl transferase ( lgt ) caused more severe joint inflammation, which coincided with higher bacterial loads of the lgt mutant in local joints than those of its parental strain. Coinjection of pathogenic S . aureus LS-1 with staphylococcal Lpps into mouse knee joints caused improved bacterial elimination and diminished bone erosion. The protective effect of the Lpps was mediated by their lipid moiety and was fully dependent on TLR2 and neutrophils. The blocking of CXCR2 on neutrophils resulted in total abrogation of the protective effect of the Lpps. Our data demonstrate that S . aureus Lpps elicit innate immune responses, resulting in a double-edged effect. On the one hand, staphylococcal Lpps boost septic arthritis. On the other hand, Lpps act as adjuvants and activate innate immunity, which could be useful for combating infections with multiple drug-resistant strains.

Thus, simultaneous systemic TNF inhibition and antibiotic therapy has beneficial effects on the outcome of S. aureus arthritis and sepsis in a mouse model, suggesting that the combination of a TNF inhibitor and antibiotics represents a novel therapeutic strategy for the treatment of staphylococcal infections.