Unmethylated CpG motifs are often found in bacterial DNA, and exert immunostimulatory effects on hematopoietic cells. Bacteria produce severe joint inflammation in septic and reactive arthritides; bacterial DNA may be involved in this process. We injected bacterial DNA originating from Escherichia coli and Staphylococcus aureus and oligonucleotides containing CpG directly into the knee joints of mice of different strains. Arthritis was seen by histopathology within 2 hours and lasted for at least 14 days. Unmethylated CpG motifs were responsible for this induction of arthritis, as oligonucleotides containing these motifs produced the arthritis. The arthritis was characterized by an influx of monocytic, Mac-1+ cells and by a lack of T lymphocytes. Depletion of monocytes resulted in abrogation of the synovial inflammation. Tumor necrosis factor (TNF)-alpha, a cytokine produced by cells of the monocyte/macrophage lineage, is an important mediator of this disease, as expression of mRNA for TNF-alpha was evident in the inflamed joints, and the CpG-mediated inflammation was abrogated in mice genetically unable to produce this cytokine. These findings demonstrate that bacterial DNA containing unmethylated CpG motifs induces arthritis, and indicate an important pathogenic role for bacterial DNA in septic arthritis.

We conclude that genistein exerts evident anti-inflammatory properties affecting granulocytes, monocytes, and lymphocytes.

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

Despite the high prevalence of cutaneous infections, little is known about the role of host immune responsiveness during Staphylococcus aureus dermatitis. We have recently described a murine model of infectious dermatitis induced by superantigen-producing S. aureus. To assess the role of neutrophils in staphylococcal dermatitis, mice were given granulocyte-depleting monoclonal antibody prior to and on several occasions following intracutaneous inoculation with staphylococci. The granulocyte-depleted mice that had been intradermally inoculated with S. aureus developed crusted ulcerations which tended not to heal, whereas animals injected with control monoclonal antibody displayed only minor and transient skin lesions. The finding of severe ulcerations in neutropenic mice correlated with a significantly higher burden of bacteria in the blood and skin during the early phase of the infection. Importantly, while mice with an intact granulocyte population showed only limited skin infection, bacteremia occurred in the great majority of the neutrophil-depleted animals. As a consequence, the latter individuals exhibited significantly increased levels of the proinflammatory cytokine interleukin-6 and specific antibodies to staphylococcal cell wall components and toxic shock syndrome toxin-1 in the serum. Our data point to a crucial protective role of granulocytes in S. aureus dermatitis.Neutrophils are host immune defense cells that are among the first to migrate into the skin in response to invading pathogens. These cells respond to chemotactic signals present at the site of infection. Among the roles played by neutrophils in inflammatory and immune responses are phagocytosis and killing of bacteria via the generation of reactive oxygen intermediates and the release of lytic enzymes stored in granules. In a recently described model of infectious dermatitis induced by the toxic shock syndrome toxin-1 (TSST-1)-producing Staphylococcus aureus strain LS-1 (12), healthy mice inoculated with high doses of staphylococci (10 8 CFU) displayed clinical and histopathological signs of local infection and inflammation within 48 h but lacked clinical or bacteriological signs of sepsis. The aim of this study was to evaluate the role of neutrophils in the induction, progression, and outcome of infectious dermatitis induced by intradermal injection of TSST-1-producing S. aureus. Our results show that depletion of neutrophil granulocytes both increases the severity of the skin lesion and gives rise to generalized infection, including bacteremia. These data demonstrate a crucial protective role for neutrophil granulocytes in S. aureus dermatitis. MATERIALS AND METHODSMice. Male BALB/c mice, 5 to 6 weeks old, were purchased from B&K Universal AB (Sollentuna, Sweden). They were housed in the animal facility of the Department of Rheumatology, University of Göteborg, under standard conditions of light and temperature and fed standard laboratory chow and water ad libitum.Bacterial strain. The BALB/c mice were inoculated intracutaneously with S....

We have previously described a murine model of hematogenously induced Staphylococcus aureus sepsis and arthritis. In this model, large numbers of granulocytes can be observed both in the circulation and locally in the inflamed synovium within 24 h after bacterial inoculation. To assess the role of neutrophils in this severe infection, mice were given granulocyte-depleting monoclonal antibody RB6-8C5 before being inoculated with S. aureus. All the control mice survived their intravenous injection with 3 ؋ 10 7 CFU of S. aureus, whereas all the mice given RB6-8C5 antibody died of sepsis within 2 to 3 days. Even when the inoculum size was reduced sixfold (i.e., 6 ؋ 10 6 CFU/mouse), 50% of the RB6-8C5-treated animals died within 6 days. The RB6-8C5-treated mice had a significantly higher burden of bacteria in their blood and kidneys 24 and 48 h after bacterial inoculation. In addition, when a suboptimal dose of bacteria was administered, the neutrophil-depleted animals displayed a higher frequency of arthritis than did the controls. The granulocyte-depleted animals exhibited increased levels of the proinflammatory cytokines tumor necrosis factor alpha, interleukin-6, and gamma interferon, reflecting the severity of their disease. This is the first direct demonstration of neutrophils playing a crucial protective role in the early phase of S. aureus infection.