The rat antigen-presenting lectin-like receptor complex influences innate immunity and development of infectious diseases.

Genetic variation in the antigen-presenting lectin-like receptor gene complex (APLEC) associates with autoimmunity and arthritis in rats and humans. We hypothesized that the encoded C-type lectin-like receptors might influence innate immunity and responses to infectious agents. To test this hypothesis, we compared in vivo and in vitro phenotypes in DA rats and APLEC-congenic rats. Survival rates following infection with Staphylococcus aureus and Herpes simplex virus differed significantly between the two strains. Likewise, differential delayed type hypersensitivity (DTH), an immunological reaction involving T lymphocytes and macrophages, was observed in response to provocation with the chemical oxazolone. Unstimulated bone marrow-derived macrophages from the two strains appeared to already have polarized activation states with different mRNA levels of CD163 and Dectin-1 receptors. Following stimulation with a panel of microbial agents, differences in induced mRNA and protein levels were shown for interleukin (IL)-6 and IL-10 following stimulation with lipopolysaccharide, mannan and beta-glucan. Expression levels of APLEC gene mRNAs also differed, and both strains had a notably dichotomous expression of the genes, with general downregulation of all four Dcir genes and upregulation of Mincle and Mcl. We suggest that human APLEC genes may similarly regulate infectious diseases, DTH and general macrophage activation status.

The impact of substance P signalling on the development of experimental staphylococcal sepsis and arthritis.

Substance P (SP), acting on the neurokinin-1 receptor (NK-1R), is a neuropeptide, involved in the inflammatory processes. It promotes vasodilatation and increases vasopermeability, thus ensuing extravasation and accumulation of leucocytes at sites of injury. The aim of this study was to assess the impact of SP signalling on the responses during staphylococcal infection and the accompanying arthritis. Three experiments were performed where NK-1R-/- mice and controls were intravenously infected with different doses of Staphylococcus aureus. Clinical assessment of arthritis was performed as well as histological analysis of bone and cartilage destruction in the joints. In addition, the impact of NK-1R mutation on bacterial load in the kidneys as well as the phagocytic capacity of blood leucocytes were studied. Mice lacking the NK-1R displayed significantly higher bacterial load in the kidneys and significantly more severe synovitis and cartilage/bone destruction than the controls when inoculated with 1.4 x 10(7) staphylococci. Infection with 3.5 x 10(8) CFU/mouse induced sepsis. Thus, 11 days after bacterial inoculation 15 of 19 mice in the NK-1R-/- group had died versus 8 of 15 in the control group. Phagocytosis test revealed that significantly fewer macrophages from NK-1R-/- mice were able to phagocytose S. aureus when compared with macrophages from congenic control mice. Blocking the biological responses to substance P via its receptor NK-1R results in a less efficient clearance of bacteria leading to more severe arthritic lesions in mice.

Histamine in rheumatoid arthritis.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by a persistent inflammation of the synovium, leading to the erosion of articular cartilage and bone. Synovial mast cells and their effector molecule, histamine, receive increased attention as mediators of joint inflammation. The aim of our study was to analyse levels of free histamine in serum and joint fluid of RA patients and to evaluate the potential inflammatogenic properties of histamine in vivo and in vitro. Histamine levels were measured by an ELISA in synovial fluid and sera of RA patients and of healthy controls. Histamine levels were also assessed in plasma of RA patients undergoing anti-TNF-alpha treatment. In the murine part of the study, histamine was injected intra-articularly in the knee joint of mice and the joints were subsequently analysed with respect to induction of inflammation. RA patients displayed significantly lower levels of histamine in circulation (0.93 +/- 0.16 ng/ml) compared with the healthy controls (1.89 +/- 0.45 ng/ml, P < 0.001). Locally, in synovial fluid the levels of histamine were even lower (0.37 +/- 0.16 ng/ml, P < 0.0006). Long-term anti-TNF-alpha treatment significantly increased circulating levels of histamine in RA patients. Our experiments on animals show that histamine on its own neither induces inflammation in the joint cavity nor influences the course of HMGB1 and peptidoglycan-induced joint inflammation. Based on our experimental and clinical studies we suggest that histamine lacks harmful properties in RA.

Riboflavin in innate and acquired immune responses.

OBJECTIVE AND DESIGN: Riboflavin, also known as vitamin B2, is a micronutrient with a key role in maintaining human health. It has also been shown to enhance host resistance to bacterial infections in mice. The aim of this study was to assess the role of vitamin B2 treatment in inflammatory conditions. SUBJECTS AND METHODS: Three models of inflammatory states were assessed. One of them encompasses neutrophil mediated but T cell/macrophage independent cutaneous inflammation. Another one is delayed type hypersensitivity reaction (DTH), a T cell/macrophage dependent but neutrophil independent inflammatory response. The third one is collagen- induced arthritis, having components from both of the above described reactions. Mice were treated with vitamin B2, administered by peritoneal injections, throughout the course of the experiments. RESULTS: The granulocyte dependent reaction to olive oil was significantly reduced in vitamin B2 treated mice. In contrast, DTH reactivity and collagen II arthritis were not affected by the treatment. CONCLUSION: Riboflavin administration affects neutrophil migration but does not alter acquired immune responsiveness.

Extracellular cytochrome c, a mitochondrial apoptosis-related protein, induces arthritis.

OBJECTIVES: The aim of the study was to assess the role of extracellular cytochrome c as an inducer of joint inflammation and to examine its levels in sera and synovial fluids of rheumatoid arthritis (RA) patients. METHODS: Mice were injected intra-articularly with different doses of cytochrome c and joints were evaluated histopathologically and immunohistochemically 3 and 10 days later. In addition, mouse spleen cells were stimulated with different concentrations of cytochrome c, followed by assessment of NF-kappaB activation and cytokine production. Sera and synovial fluid from RA patients and sera from healthy individuals were assessed with respect to cytochrome c levels by an enzyme-linked immunoassay technique. RESULTS: Histopathological signs of arthritis were evident in 75% of animals following intra-articular injection of cytochrome c. Synovitis was characterized by influx of Mac-1+ cells. In vivo depletion of neutrophils and monocytes led to abrogation of arthritis. Stimulation of mouse spleen cells in vitro with cytochrome c resulted in activation of NF-kappaB and release of proinflammatory cytokines and chemokines. Cytochrome c levels in RA patients' sera were significantly lower than in healthy controls. Further, cytochrome c levels in synovial fluid were significantly lower than in corresponding blood samples. CONCLUSIONS: Our findings demonstrate that extracellular cytochrome c displays direct proinflammatory properties mediated by activation of NF-kappaB and causing neutrophil and monocyte triggered inflammation. We hypothesize that decreased levels of cytochrome c in RA patients reflect consumption of this molecule in the synovial tissue, decreasing apoptosis and shifting the balance towards inflammation.

Topoisomerase II inhibitors, irrespective of their chemical composition, ameliorate experimental arthritis.

OBJECTIVE: Rheumatoid arthritis (RA) is an autoimmune disease, characterized by a chronic inflammation in the joints. The model of collagen-induced arthritis (CIA) has been extensively used to elucidate the pathogenic mechanisms relevant to human RA and is widely employed for the evaluation of potential anti-rheumatic agents. Etoposide and mitoxantrone are immunosuppressive drugs, both acting by inhibiting the topoisomerase II function. We have previously demonstrated an ameliorating effect of etoposide in CIA. The aims of this study were (1) to assess the optimal ameliorating dose of etoposide and (2) to ascertain that topoisomerase II inhibition, irrespective of the chemical composition of the drug, affects the course of autoimmunity. METHODS: Male DBA/1 mice were treated with 12.5 mg/kg body weight of etoposide five times, twice, once per week or once every second week. Mitoxantrone was administered as high dose (1 mg/kg body weight five times after immunization or after booster with collagen II) or low dose (3 microg/mouse, 5 days/week starting after collagen II immunization or after booster). RESULTS: Treatment with 12.5 mg/kg body weight five times or twice weekly with etoposide completely inhibited development of arthritis. Low-dose treatment with mitoxantrone after collagen II immunization or high-dose treatment after collagen II booster delayed the onset of arthritis. These results were observed clinically as well as histologically. In addition, serum levels of anti-collagen II antibodies were significantly lower in mice displaying less severe arthritis. CONCLUSION: Treatment of collagen-induced arthritis with topoisomerase II inhibitors ameliorates the development of disease.

Genistein as an anti-inflammatory agent.

OBJECTIVE AND DESIGN: The aim of this study was to investigate the impact of the isoflavone genistein on in vivo cell-mediated responses. In addition, we wanted to study the influence of genistein on collagen induced arthritis (CIA) in mice. METHODS: Delayed type hypersensitivity reaction (DTH) to oxazolone and the inflammatory response to olive oil were measured in mice treated with genistein. In addition, the impact of genistein treatment on disease progression and outcome of collagen induced arthritis (CIA) was examined. RESULTS: The DTH reaction to oxazolone and the granulocyte-mediated response were significantly suppressed in genistein-treated as compared to control mice. Also, genistein treatment led to decreased levels of oxazolone-specific antibodies. Histologically, mice exposed to genistein and immunized with collagen II displayed somewhat lower degree of inflammation and joint destruction. In addition, serum levels of autoantibodies to collagen II were significantly lower following genistein-treatment in immunized mice. CONCLUSION: We conclude that genistein exerts evident anti-inflammatory properties affecting granulocytes, monocytes, and lymphocytes.

Impact of topoisomerase II inhibition on cytokine and chemokine production.

OBJECTIVE AND DESIGN: In systemic inflammatory diseases such as rheumatoid arthritis, cytokines and chemokines are deeply involved in the development of the disease manifestations. Etoposide is a cytostatic drug, known to deplete the monocyte population in mice and rabbits. We have recently shown that suboptimal doses have a disease-ameliorating effect in collagen II induced arthritis in the absence of monocyte depletion. Anti-arthritic properties parallelled with almost total eradication of production of specific collagen II antibodies. The aim of the present study was to investigate ex vivo and in vitro the function of the mononuclear cells and their production of B cell stimulating cytokines following exposure to etoposide, a topoisomerase II inhibitor. MATERIALS AND METHODS: Spleen cells from mice treated during four weeks with etoposide were cultured and the supernatants were analyzed with respect to content of TNF and IL-6. In addition, cells from the murine macrophage cell clone IC-21 were exposed to etoposide and the production of IL-6, using a bioassay, and the production of TNF, MIP-1alpha, RANTES, and IL-1beta, using sandwich ELISAs, was determined. RESULTS: Spleen cells from etoposide-treated mice secreted lower amounts of IL-6 and TNF as compared to the control animals. In addition, in vitro etoposide-exposed macrophages showed reduced capacity to produce TNF, IL-6 and MIP-1alpha. CONCLUSION: Our results indicate that inhibition of topoisomerase II downregulated the function of monocytes. Owing to its immunoregulatory properties, use of etoposide is suggested in treatment of chronic inflammatory diseases.

Total abrogation of collagen II-induced arthritis and the B cell response to type II collagen using suboptimal doses of a topoisomerase II antagonist.

BACKGROUND: Collagen-induced arthritis (CIA) is the most commonly used model of rheumatoid arthritis (RA). In both CIA and RA there is an increase in the cellular content of the synovium, this being dominated by macrophages. OBJECTIVE: To assess the impact of etoposide, a topoisomerase II antagonist known to induce monocyte apoptosis, on the development of CIA. METHODS: Mice were primed and booster immunised against collagen II (CII). One group of mice was treated with etoposide two days before CII immunisation and then on four consecutive days weekly until the end of the experiment. The second group of mice was injected with etoposide on four consecutive days a week starting 40 days after CII priming. The third group of mice were controls receiving phosphate buffered saline (PBS). The mice were examined for development of arthritis, numbers of circulating leucocytes, serum CII antibody, and cytokine concentrations. RESULTS: None of the mice given etoposide before CII immunisation developed arthritis. Serum concentrations of anti-CII antibodies were undetectable in these mice, whereas they displayed significantly increased concentrations of interferon gamma and interleukin 6. In addition, the CII specific B cell responses in the draining lymph nodes were highly suppressed. Also, mice treated with etoposide at the onset of clinical arthritis showed reduced frequency of their disease by 50%. CONCLUSION: There was a striking disease alleviating impact of topoisomerase II antagonist on the course of CII-induced arthritis.

Model systems: modeling human staphylococcal arthritis and sepsis in the mouse.

The staphylococci have been recognized as serious pathogens for over a century and are the etiological agent of a variety of diseases ranging from mild cutaneous infections to often fatal forms of septic arthritis, endocarditis, toxic shock syndrome and sepsis. Despite intensive efforts to halt their spread, they remain the most common cause of community- and nosocomially acquired bacteremia. Murine models of Staphylocococus aureus-mediated arthritis and sepsis exist and are being used to gain a better understanding of the host-bacterium relationship as well to develop better methods of prevention and treatment.

Role of macrophages in Staphylococcus aureus-induced arthritis and sepsis.

OBJECTIVE: A model of hematogenously induced Staphylococcus aureus arthritis was used to analyze the role of macrophages in this highly destructive condition. In this model, the majority of cells in the cartilage-synovial junction that participate in the destructive process are macrophages. METHODS: To assess the role of monocytes/macrophages in staphylococcal arthritis, mice were inoculated with S aureus or given phosphate buffered saline as control. Mice were rendered monocytopenic by administration of etoposide, a drug that selectively depletes the monocyte/macrophage population. RESULTS: Throughout the course of infection, the etoposide-treated mice exhibited a significantly less severe arthritis than the control animals. These data were confirmed by histopathologic analysis of the joints. The down-regulation of development of arthritis was accompanied by decreased serum levels of the proinflammatory cytokines tumor necrosis factor alpha and interleukin-6. In contrast, infection-triggered mortality was increased in the etoposide-treated mice as compared with the control animals. Notably, the monocytopenic mice exhibited elevated bacterial burden in the blood and kidneys on days 3 and 7 after inoculation with staphylococci. CONCLUSION: This study indicates a dual role of mononuclear phagocytes in the pathogenesis of S aureus-induced infection. On the one hand, absence of macrophages leads to a favorable outcome concerning the severity of arthritic lesions, but on the other hand, the clearance of bacteria by monocytes/macrophages is decreased, resulting in poor survival.

The major role of macrophages and their product tumor necrosis factor alpha in the induction of arthritis triggered by bacterial DNA containing CpG motifs.

OBJECTIVE: To understand the mechanisms of arthritis triggered by CpG-containing oligonucleotides (ODN). METHODS: Following the induction of CpG ODN-triggered arthritis in mice, we analyzed the impact of depletion of immune cells, including neutrophils, natural killer (NK) cells, and monocyte/macrophages, on the arthritis, as well as the impact in SCID mice lacking T and B cells. In addition, tumor necrosis factor alpha (TNFalpha) knockout mice were studied, and intraarticular administration of p65 antisense to nuclear factor kappaB (NF-kappaB) was used to examine effects in CpG ODN-triggered arthritis. Cytokine messenger RNA expression in synovial tissue was evaluated by in situ hybridization. RESULTS: The presence of macrophages was mandatory for the mediation of arthritis triggered by CpG ODN, whereas the absence of neutrophils, NK cells, T cells, and B cells was of minor importance in this regard. The proinflammatory cytokines TNFalpha, interleukin-1beta, and interleukin-12, which originate from macrophages, were frequently found in the inflamed joints, and TNFalpha was confirmed to be an important mediator in the development of arthritis, since the incidence and severity of joint inflammation were markedly reduced in TNFalpha knockout mice. NF-kappaB exerted an important regulatory role in the development of CpG ODN-mediated arthritis, since local administration of antisense to the p65 subunit of NF-kappaB diminished the incidence of inflammation by 50%. CONCLUSION: Macrophages and their products play an important role in the development of arthritis triggered by bacterial DNA containing CpG motifs.

Role of neutrophil leukocytes in cutaneous infection caused by Staphylococcus aureus.

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.

Role of selectins in experimental Staphylococcus aureus-induced arthritis.

The selectin family of adhesion molecules mediates the initial attachment of leukocytes to venular endothelial cells at sites of tissue injury and inflammation. To assess the role of selectin family in Staphylococcus aureus-triggered septic arthritis, we used several approaches. First, treatment with fucoidin, a carbohydrate molecule capable of binding to and blocking selectin functions, was used. In addition, we used P-selectin gene-targeted mice as well as mice pretreated with monoclonal antibody blocking L-selectin function. The P-selectin-deficient and fucoidin-treated animals initially exhibited a less severe septic arthritis both clinically and histopathologically. In the later stages of the disease no significant differences with respect to arthritis were evident. Pretreatment with L-selectin blocking antibody did not influence the severity of arthritis. High numbers of staphylococci were recovered from the kidneys of selectin-deficient mice, indicating a less efficient clearance of bacteria. Our results demonstrate a dual role for selectins in S. aureus-induced arthritis: on the one hand, blockade of these selectins leads to less severe arthritic lesions in the initial stage of the disease; on the other, delayed recruitment of phagocytes decreases the clearance of bacteria.

The effect of site-specific monoclonal antibodies directed to toxic shock syndrome toxin-1 in experimental Staphylococcus aureus arthritis.

Staphylococcus aureus produces a large number of potential virulence factors, among these the superantigen toxic shock syndrome toxin-1 (TSST-1). We have recently demonstrated that TSST-1 is involved in the pathogenesis of septic arthritis. Recent data show that the TSST-1 molecule is composed of two distinct domains, one proposed to interact with T cell receptor (TCR) and one with the MHC class II. The aim of this study was to assess if interaction between TSST-1-specific MoAbs directed to sites on the MHC and/or TCR Vbeta affects the development of experimental S. aureus-induced arthritis. For that purpose we used a panel of seven MoAbs, which were injected intraperitoneally before and after inoculation with a TSST-1-producing S. aureus strain. Administration of antibodies did not affect the development of arthritis, suggesting inefficacy of such a procedure in neutralization of exotoxin-mediated disease manifestations.

Protection against Staphylococcus aureus sepsis by vaccination with recombinant staphylococcal enterotoxin A devoid of superantigenicity.

Staphylococcal exotoxins are virulence determinants in Staphylococcus aureus arthritis and septicemia. To assess the utility of enterotoxins as vaccine candidates for these diseases, a genetically modified staphylococcal enterotoxin A (SEA) that lacks superantigenic properties was used. Mice immunized with recombinant (r) SEA had significantly longer survival than control immunized mice and lost significantly less weight than the controls. Transfer of SEA-specific antibodies to naive mice resulted in good protection against death in staphylococcal sepsis. In vitro proliferative responses to SEA by naive lymphocytes were almost totally abolished on incubation with serum from rSEA but not with control antigen-immunized mice. These results suggest that immunization with rSEA devoid of superantigenic properties provides good protection against S. aureus sepsis. In addition, the data indicate that the protection is at least in part mediated by SEA neutralizing antibodies.

Intra-articularly localized bacterial DNA containing CpG motifs induces arthritis.

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.

Integrin-associated protein (IAP)-deficient mice are less susceptible to developing Staphylococcus aureus-induced arthritis.

The integrin-associated protein (IAP) has been shown to function in a signaling complex with beta3 integrins, influencing the migration of phagocytic cells into inflamed tissues. We have previously shown that gene-targeted mice deficient for IAP succumbed to peritonitis when inoculated with gram-negative bacteria. The aim of this study was to assess the role of IAP in our recently established model of haematogenously induced Staphylococcus aureus septicaemia and arthritis. In this model, neutrophils play a crucial role in the early phase of the infection. Mice lacking IAP and congenic controls were intravenously inoculated with S. aureus LS-1. The IAP-/- mice were resistant to developing clinical signs of arthritis compared with their IAP-expressing littermates. The clinical findings were corroborated by histopathological evaluation indicating that the IAP-/- mice had less cartilage and bone destruction in the joints. We believe that a delayed migration of leukocytes into the joints of mice lacking IAP expression leads to decreased susceptibility to develop S. aureus-induced arthritis.

Granulocyte-macrophage colony-stimulating factor in Staphylococcus aureus-induced arthritis.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokine that is able to increase not only the production of phagocytic cells but also their efficacy with respect to, e.g., bactericidal properties. In this study, we wanted to analyze the impact of GM-CSF on experimental Staphylococcus aureus-induced arthritis. For that purpose, mice were administered GM-CSF before and after bacterial inoculation. Although there was an increase in the total number of leukocytes as well as in the granulocyte fraction, there was no favorable effect on the severity of arthritis or on survival rates. There were no obvious differences between the GM-CSF-pretreated animals and controls with regard to growth of staphylococci in joints and kidneys 4 days after the bacterial inoculation. In contrast, mice that had been pretreated with GM-CSF prior to bacterial inoculation showed approximately four times lower numbers of bacteria in their blood 24 h later. These results, along with those of our previous studies, suggest that on the one hand the granulocyte is the main protective cell during the course of S. aureus infection but that on the other hand, upregulation of granulocyte-macrophage production will not exert any additional protective effects with respect to tissue injury.

Role of neutrophils in experimental septicemia and septic arthritis induced by Staphylococcus aureus.

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 x 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 x 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.