Resistin, an adipokine with potent proinflammatory properties

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-alpha, 2) responding to TNF-alpha 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-kappaB inhibitor indicating the importance of NF-kappaB 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.

Staphylococcus aureus resists human defensins by production of staphylokinase, a novel bacterial evasion mechanism

Alpha-defensins are peptides secreted by polymorphonuclear cells and provide antimicrobial protection mediated by disruption of the integrity of bacterial cell walls. Staphylokinase is an exoprotein produced by Staphylococcus aureus, which activates host plasminogen. In this study, we analyzed the impact of interaction between alpha-defensins and staphylokinase on staphylococcal growth. We observed that staphylokinase induced extracellular release of alpha-defensins from polymorphonuclear cells. Moreover, a direct binding between alpha-defensins and staphylokinase was shown to result in a complex formation. The biological consequence of this interaction was an almost complete inhibition of the bactericidal effect of alpha-defensins. Notably, staphylokinase with blocked plasminogen binding site still retained its ability to neutralize the bactericidal effect of alpha-defensins. In contrast, a single mutation of a staphylokinase molecule at position 74, substituting lysine for alanine, resulted in a 50% reduction of its alpha-defensin-neutralizing properties. The bactericidal properties of alpha-defensins were tested in 19 S. aureus strains in vitro and in a murine model of S. aureus arthritis. Staphylococcal strains producing staphylokinase were protected against the bactericidal effect of alpha-defensins. When staphylokinase was added to staphylokinase-negative S. aureus cultures, it almost totally abrogated the effect of alpha-defensins. Finally, human neutrophil peptide 2 injected intra-articularly along with bacteria alleviated joint destruction. In this study, we report a new property of staphylokinase, its ability to induce secretion of defensins, to complex bind them and to neutralize their bactericidal effect. Staphylokinase production may therefore be responsible in vivo for defensin resistance during S. aureus infections.

High mobility group box chromosomal protein 1, a DNA binding cytokine, induces arthritis

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 microg or 5 microg 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 kappaB (NF-kappaB) 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-kappaB, 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-kappaB activation.

Leptin consumption in the inflamed joints of patients with rheumatoid arthritis

BACKGROUND

Leptin has been shown to participate in bone remodelling and leptin substitution reported to have a protective effect in experimental septic arthritis.

OBJECTIVE

To assess leptin levels in inflamed joints and plasma of patients with RA.

MATERIAL AND METHODS

Leptin concentrations were assessed in matched blood and synovial fluid samples from 76 patients with RA. Blood samples from 34 healthy subjects acted as additional controls. Results were analysed and correlated with duration and activity of RA, x ray changes, and treatment at time of sampling.

RESULTS

In patients with RA, leptin levels were significantly higher in plasma than in synovial fluid samples obtained simultaneously and higher than in control samples. Plasma and synovial fluid leptin levels correlated strongly. Locally in the joint, leptin levels were related to WBC count. Such a relation was not seen in the bloodstream. Leptin levels were not related to sex, age, or disease duration. Difference between leptin levels in plasma and synovial fluid was greater in non-erosive arthritis (5.1 (SEM 1.2) v 3.7 (0.9) ng/ml, p=0.006), than in patients with erosive joint disease (6.2 (1.0) v 5.4 (0.8) ng/ml, NS). Methotrexate treatment was associated with relatively high plasma leptin levels, while treatment with other DMARDs was associated with lower leptin levels than in patients receiving no DMARD treatment (p=0.0005).

CONCLUSIONS

Leptin production was significantly increased in patients with RA compared with healthy controls. Synovial fluid leptin levels were significantly lower than in matched plasma samples, suggesting an in situ consumption of this molecule.

Decreased levels of soluble receptor for advanced glycation end products in patients with rheumatoid arthritis indicating deficient inflammatory control

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily being expressed as a cell surface molecule and binding a variety of ligands. One of these ligands is high-mobility group box chromosomal protein 1, a potent proinflammatory cytokine, expression of which is increased in synovial tissue and in synovial fluid of rheumatoid arthritis (RA) patients. The interaction of high-mobility group box chromosomal protein 1 with cell-surface RAGE leads to an inflammatory response. In contrast, the presence of soluble RAGE (sRAGE) may abrogate cellular activation since the ligand is bound prior to interaction with the surface receptor. Our aim was to analyse to what extent sRAGE is present in patients with chronic joint inflammation (RA) as compared with patients with non-inflammatory joint disease and with healthy subjects, and to assess whether there is an association between sRAGE levels and disease characteristics. Matching samples of blood and synovial fluid were collected from 62 patients with RA with acute joint effusion. Blood from 45 healthy individuals, synovial fluid samples from 33 patients with non-inflammatory joint diseases and blood from six patients with non-inflammatory joint diseases were used for comparison. sRAGE levels were analysed using an ELISA.RA patients displayed significantly decreased blood levels of sRAGE (871 +/- 66 pg/ml, P < 0.0001) as compared with healthy controls (1290 +/- 78 pg/ml) and with patients with non-inflammatory joint disease (1569 +/- 168 pg/ml). Importantly, sRAGE levels in the synovial fluid of RA patients (379 +/- 36 pg/ml) were lower than in corresponding blood samples and correlated significantly with blood sRAGE. Interestingly, a significantly higher sRAGE level was found in synovial fluid of RA patients treated with methotrexate as compared with patients without disease-modifying anti-rheumatic treatment.We conclude that a decreased level of sRAGE in patients with RA might increase the propensity towards inflammation, whereas treatment with methotrexate counteracts this feature.

Human resistin is a systemic immune-derived proinflammatory cytokine targeting both leukocytes and adipocytes

The characteristics of human resistin (RETN) are unclear and controversial despite intensive adipose-focused research. Its transcriptional and functional similarity with the murine myeloid-specific and CCAAT/enhancer binding protein epsilon (Cebpe)-dependent gene, resistin-like gamma (Retnlg), is unexplored. We examined the human CEBPE-regulatory pathway by unbiased reference and custom gene expression assays. Real-time RT-PCR analysis demonstrated lack of both the transcriptional factor CEBPE and RETN expression in adipose and muscle cells. In contrast, primary myelocytic samples revealed a concerted CEBPE-RETN transcription that was significantly elevated in inflammatory synoviocytes relative to intact peripheral blood mononuclear cells (PBMC). Mouse Cebpe and Retnlg were predictably expressed in macrophages, whereas Retn was abundant in adipocytes. Quite the opposite, a low and inconsistent RETN transcription was seen in some human white adipose tissue (WAT) biopsies without any relationship to body mass index, insulin sensitivity, or fat depot. However, in these cases, RETN was co-detected with CEBPE and the leukocyte-specific marker, EMR1, indicating the presence of inflammatory cells and their possible resistin-mediated effect on adipocytes. Indeed, addition of human resistin to WAT in culture induced, like in PBMC, the inflammatory cytokines IL6, IL8 and TNF. Importantly, the expression of the adipose-specific markers CEBPA, FABP4 and SLC2A4 was unchanged, while the expected inhibitory effect was seen with TNF. Both cytokines increased the mRNA level of CCL2 and MMP3, which may further promote inflammation in WAT. Thus, the myeloid-restricted nature of CEBPE precludes the expression of RETN in human adipocytes which, however, are targeted by this innate immune-derived proinflammatory cytokine.

Outcomes of patients with systemic sclerosis-associated polyarthritis and myopathy treated with tocilizumab or abatacept: a EUSTAR observational study

OBJECTIVE

To evaluate the safety and effectiveness of tocilizumab and abatacept in systemic sclerosis (SSc)-polyarthritis or SSc-myopathy.

METHODS

20 patients with SSc with refractory polyarthritis and seven with refractory myopathy from the EUSTAR (EULAR Scleroderma Trials and Research) network were included: 15 patients received tocilizumab and 12 patients abatacept. All patients with SSc-myopathy received abatacept. Clinical and biological assessments were made at the start of treatment and at the last infusion.

RESULTS

After 5 months, tocilizumab induced a significant improvement in the 28-joint count Disease Activity Score and its components, with 10/15 patients achieving a EULAR good response. Treatment was stopped in two patients because of inefficacy. After 11 months' treatment of patients with abatacept, joint parameters improved significantly, with 6/11 patients fulfilling EULAR good-response criteria. Abatacept did not improve muscle outcome measures in SSc-myopathy. No significant change was seen for skin or lung fibrosis in the different groups. Both treatments were well tolerated.

CONCLUSIONS

In this observational study, tocilizumab and abatacept appeared to be safe and effective on joints, in patients with refractory SSc. No trend for any change of fibrotic lesions was seen but this may relate to the exposure time and inclusion criteria. Larger studies with longer follow-up are warranted to further determine the safety and effectiveness of these drugs in SSc.

Carbamylation-dependent activation of T cells: a novel mechanism in the pathogenesis of autoimmune arthritis

The posttranslational modification of proteins has the potential to generate neoepitopes that may subsequently trigger immune responses. The carbamylation of lysine residues to form homocitrulline may be a key mechanism triggering inflammatory responses. We evaluated the role of carbamylation in triggering immune responses and report a new role for this process in the induction of arthritis. Immunization of mice with homocitrulline-containing peptides induced chemotaxis, T cell activation, and Ab production. The mice also developed erosive arthritis following intra-articular injection of peptides derived from homocitrulline and citrulline. Adoptive transfer of T and B cells from homocitrulline-immunized mice into normal recipients induced arthritis, whereas systemic injection of homocitrulline-specific Abs or intra-articular injection of homocitrulline-Ab/citrulline-peptide mixture did not. Thus, the T cell response to homocitrulline-derived peptides, as well as the subsequent production of anti-homocitrulline Abs, is critical for the induction of autoimmune reactions against citrulline-derived peptides and provides a novel mechanism for the pathogenesis of arthritis.

Transcriptional signature of human pro-inflammatory TH17 cells identifies reduced IL10 gene expression in multiple sclerosis

We have previously reported the molecular signature of murine pathogenic T_H17 cells that induce experimental autoimmune encephalomyelitis (EAE) in animals. Here we show that human peripheral blood IFN-γ⁺IL-17⁺ (T_H1/17) and IFN-γ⁻IL-17⁺ (T_H17) CD4⁺ T cells display distinct transcriptional profiles in high-throughput transcription analyses. Compared to T_H17 cells, T_H1/17 cells have gene signatures with marked similarity to mouse pathogenic T_H17 cells. Assessing 15 representative signature genes in patients with multiple sclerosis, we find that T_H1/17 cells have elevated expression of CXCR3 and reduced expression of IFNG, CCL3, CLL4, GZMB, and IL10 compared to healthy controls. Moreover, higher expression of IL10 in T_H17 cells is found in clinically stable vs. active patients. Our results define the molecular signature of human pro-inflammatory T_H17 cells, which can be used to both identify pathogenic T_H17 cells and to measure the effect of treatment on T_H17 cells in human autoimmune diseases.

CD4⁺ T cells secreting interleukin-17 (T_H17) have diverse functions in modulating autoimmune diseases. Here the authors show via transcriptome analyses that a subset of human T_H 17 co-expressing interferon-γ (T_H1/17) has a molecular signature similar to “pathogenic” mouse T_H 17 but distinct from “non-pathogenic” mouse T_H 17.

Phenotypic and functional characterization of human CD25+ B cells

We demonstrate that humans have a phenotypically and functionally distinct subset of B lymphocytes that express the interleukin (IL)-2 receptor (IL-2R) alpha-chain, cluster of differentiation (CD) 25. We found that one-third of the circulating CD20+ B cells expressed CD25 and, using fluorescence-activated cell sorter (FACS) analysis, that these cells were significantly larger and more granulated than B cells not expressing CD25. The simultaneous expression of the other two subunits (CD122 and CD132) and the proliferative responses of cells expressing CD25 to IL-2 suggested that, in addition to CD25, functional IL-2 receptors were expressed on this cell population. CD25 expression on B cells was selectively up-regulated by Toll-like receptor 2 (TLR2), TLR4, and TLR9 ligands but not by a TLR3 ligand or Epstein-Barr virus (EBV) stimulation. Blockade of the nuclear factor (NF)-kappaB pathway completely abolished CD25 up-regulation by these B cells. Interestingly, CD25+ B cells expressed significantly higher levels of surface immunoglobulins but lacked the ability to secrete immunoglobulin (Ig), as compared with CD25- B cells. Furthermore, CD25+ B cells performed significantly better as antigen-presenting cells in allogeneic mixed lymphocyte reactions (MLR), which may be a result of their expression of high levels of the costimulatory molecules CD27 and CD80. Finally, blocking of CD25 on B cells led to an almost total abrogation of MLR. Our results indicate that CD25+ B cells have distinct phenotypic and functional properties, including the ability to contribute to antigen presentation, which is linked to their expression of CD25. Finally, the differential regulation of CD25 expression via selective TLR ligands suggests a role for CD25+ B cells in bridging innate and acquired immune responses.

Geranylgeranyltransferase type I (GGTase-I) deficiency hyperactivates macrophages and induces erosive arthritis in mice

RHO family proteins are important for the function of inflammatory cells. They are modified with a 20-carbon geranylgeranyl lipid in a process catalyzed by protein geranylgeranyltransferase type I (GGTase-I). Geranylgeranylation is viewed as essential for the membrane targeting and activity of RHO proteins. Consequently, inhibiting GGTase-I to interfere with RHO protein activity has been proposed as a strategy to treat inflammatory disorders. However, here we show that mice lacking GGTase-I in macrophages develop severe joint inflammation resembling erosive rheumatoid arthritis. The disease was initiated by the GGTase-I-deficient macrophages and was transplantable and reversible in bone marrow transplantation experiments. The cells accumulated high levels of active GTP-bound RAC1, CDC42, and RHOA, and RAC1 remained associated with the plasma membrane. Moreover, GGTase-I deficiency activated p38 and NF-κB and increased the production of proinflammatory cytokines. The results challenge the view that geranylgeranylation is essential for the activity and localization of RHO family proteins and suggest that reduced geranylgeranylation in macrophages can initiate erosive arthritis.

Ethanol prevents development of destructive arthritis

Environmental factors are thought to play a major role in the development of rheumatoid arthritis. Because the use of ethanol is widespread, we assessed the role of ethanol intake on the propensity to develop chronic arthritis. Collagen type II-immunized mice were given water or water containing 10% (vol/vol) ethanol or its metabolite acetaldehyde. Their development of arthritis was assessed, as well as the impact of ethanol on leukocyte migration and activation of intracellular transcription factors. Mice exposed daily to this dose of ethanol did not display any liver toxicity, and the development of erosive arthritis was almost totally abrogated. In contrast, the antibody-mediated effector phase of collagen-induced arthritis was not influenced by ethanol exposure. Also, the major ethanol metabolite, acetaldehyde, prevented the development of arthritis. This antiinflammatory and antidestructive property of ethanol was mediated by (i) down-regulation of leukocyte migration and (ii) up-regulation of testosterone secretion, with the latter leading to decreased NF-kappaB activation. We conclude that low but persistent ethanol consumption delays the onset and halts the progression of collagen-induced arthritis by interaction with innate immune responsiveness.

Balance between survivin, a key member of the apoptosis inhibitor family, and its specific antibodies determines erosivity in rheumatoid arthritis

Rheumatoid arthritis (RA) is a highly heterogeneous disease with respect to its joint destructivity. The reasons underlying this heterogeneity are unknown. Deficient apoptosis in rheumatoid synovial tissue has been recently demonstrated. We have therefore decided to study the synovial expression of survivin, a key member of the apoptosis inhibitor family. The levels of survivin and antibodies against survivin were assessed by an ELISA in matched blood and synovial fluid samples collected from 131 RA patients. Results were related to joint erosivity at the time of sampling. Monocytes were transfected with survivin anti-sense oligonucleotides and were assessed for their ability to produce inflammatory cytokines. Survivin levels were significantly higher in patients with destructive disease as compared with in RA patients displaying a non-erosive disease. High survivin levels were an independent prognostic parameter for erosive RA. In contrast, high levels of antibodies against survivin were found in patients with non-erosive RA, and were negatively related to erosivity. Survivin levels in RA patients were influenced by treatment, being significantly lower among patients treated with disease-modifying anti-rheumatic drugs. Specific suppression of survivin mRNA resulted in downregulation of IL-6 production. We conclude that survivin determines the erosive course of RA, whereas survivin antibodies lead to a less aggressive course of the disease. These findings together with decreased survivin levels upon disease-modifying anti-rheumatic drug treatment, and the downregulation of inflammatory response using survivin anti-sense oligonucleotides, suggest that extracellular survivin expression mediates the erosive course of joint disease whereas autoimmune responses to the same molecule, manifested as survivin targeting antibodies, mediate protection.

Mice chronically fed high-fat diet have increased mortality and disturbed immune response in sepsis

Background

Sepsis is a potentially deadly disease that often is caused by gram-positive bacteria, in particular Staphylococcus aureus (S. aureus). As there are few effective therapies for sepsis, increased basic knowledge about factors predisposing is needed.

Methodology/Principal Findings

The purpose of this study was to study the effect of Western diet on mortality induced by intravenous S. aureus inoculation and the immune functions before and after bacterial inoculation. Here we show that C57Bl/6 mice on high-fat diet (HFD) for 8 weeks, like genetically obese Ob/Ob mice on low-fat diet (LFD), have increased mortality during S. aureus-induced sepsis compared with LFD-fed C57Bl/6 controls. Bacterial load in the kidneys 5–7 days after inoculation was increased 10-fold in HFD-fed compared with LFD-fed mice. At that time, HFD-fed mice had increased serum levels and fat mRNA expression of the immune suppressing cytokines interleukin-1 receptor antagonist (IL-1Ra) and IL-10 compared with LFD-fed mice. In addition, HFD-fed mice had increased serum levels of the pro-inflammatory IL-1β. Also, HFD-fed mice with and without infection had increased levels of macrophages in fat. The proportion and function of phagocytosing granulocytes, and the production of reactive oxygen species (ROS) by peritoneal lavage cells were decreased in HFD-fed compared with LFD-fed mice.

Conclusions

Our findings imply that chronic HFD disturb several innate immune functions in mice, and impairs the ability to clear S. aureus and survive sepsis.

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.

Arthritogenic properties of double-stranded (viral) RNA

Viral infections often lead to arthralgias and overt arthritic states. The inflammatogenic compound of the viruses giving rise to such an outcome has to date not been identified. Because expression of dsRNA is a common feature of all viruses, we decided to analyze whether this property leads to the induction of arthritis. Histological signs of arthritis were evident already on day 3 following intra-articular administration of dsRNA. Arthritis was characterized by infiltration of macrophages into synovial tissue. It was not dependent on acquired immune responses because SCID mice also raised joint inflammation. NF-kappa B was activated upon in vitro exposure to dsRNA, indicating its role in the induction/progression of arthritis. Importantly, we found that dsRNA arthritis was triggered through IL-1R signaling because mice being deficient for this molecule were unable to develop joint inflammation. Although dsRNA is typically recognized by Toll-like receptor 3, Toll-like receptor 3 knockout mice developed arthritis, indicating that some other receptors are instrumental in the inducing of inflammation. Our results from in vitro experiments indicate that proinflammatory cytokines and chemokines stimulating monocyte influx were readily triggered in response to stimulation with dsRNA. These findings demonstrate that viral dsRNA is clearly arthritogenic. Importantly, macrophages and their products play an important role in the development of arthritis triggered by dsRNA.

The human immunomodulatory CD25+ B cell population belongs to the memory B cell pool

We have shown that human CD20(+)25(+) B cells display immunomodulatory properties. The aim of this study was to investigate if CD25(+) B cells are found within the CD27 memory B cell population, and to analyse pattern of their cytokine production. B cells isolated from healthy subjects, rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients were analysed regarding the frequency of CD25(+) B cells within certain B cell subsets. Purified CD25(+) B cells from healthy subject were used in vitro to evaluate their production of immunomodulatory cytokines. In healthy subjects the majority (60%) of memory B cells (CD20(+)27(+)) also co-expressed CD25 while only 10-20% of the naïve B cells (CD20(+)27(-)) and plasmablasts (CD20-27(+)) expressed CD25. In RA and SLE patients, we found that 51% and 48%, respectively, co-expressed CD25 in the memory population, whereas only 11% and 9% co-expressed CD25 in the naïve B cell population. Phenotypic analysis of the CD20(+)25(+)27(+) and CD20(+)25(+)27(-) cells using CD10, CD24, CD38, CD45, CD71, CD80, CD86, CD95, CD138, BAFF-R, TACI, IgA, IgD, IgG and IgM showed that CD20(+)25(+)27(+) B cells preferentially represent highly activated, Ig class switched memory B cells. Cytokine profile analysis showed that CD25(+) B cells secreted significantly higher levels of IL-10 versus CD25(-) B cells. In contrast, TGF-beta1 secretion was similar between the CD25(+) and CD25(-) sub-populations. In conclusion, CD20(+)25(+) B cells constitute a unique subpopulation preferentially occurring among CD20(+)27(+) memory B cells. We suggest that CD25 can be used as a marker for a memory B cell subset.

Protein prenylation restrains innate immunity by inhibiting Rac1 effector interactions

Rho family proteins are prenylated by geranylgeranyltransferase type I (GGTase-I), which normally target proteins to membranes for GTP-loading. However, conditional deletion of GGTase-I in mouse macrophages increases GTP-loading of Rho proteins, leading to enhanced inflammatory responses and severe rheumatoid arthritis. Here we show that heterozygous deletion of the Rho family gene Rac1, but not Rhoa and Cdc42, reverses inflammation and arthritis in GGTase-I-deficient mice. Non-prenylated Rac1 has a high affinity for the adaptor protein Ras GTPase-activating-like protein 1 (Iqgap1), which facilitates both GTP exchange and ubiquitination-mediated degradation of Rac1. Consistently, inactivating Iqgap1 normalizes Rac1 GTP-loading, and reduces inflammation and arthritis in GGTase-I-deficient mice, as well as prevents statins from increasing Rac1 GTP-loading and cytokine production in macrophages. We conclude that blocking prenylation stimulates Rac1 effector interactions and unleashes proinflammatory signaling. Our results thus suggest that prenylation normally restrains innate immune responses by preventing Rac1 effector interactions.

Macrophage specific deletion of GGTase-I, a prenylation enzyme, in mice induces inflammatory response and rheumatoid arthritis. Here the authors show that GGTase-I deficiency and the resulting reduction of RAC1 prenylation increase RAC1 interaction with the adaptor protein IQGAP1, leading to GTP-loading of RAC1 and enhanced proinflammatory cytokine production.

Role of resistin as a marker of inflammation in systemic lupus erythematosus

INTRODUCTION

Resistin is a cystein-rich secretory adipokine. It is proposed to have proinflammatory properties in humans. The aim of this study was to determine associations between serum levels of resistin and markers of inflammation and bone mineral density (BMD) in female patients with systemic lupus erythematosus (SLE).

METHODS

One hundred sixty-three female patients with SLE (20 to 82 years old) were examined in a cross-sectional study. Venous blood samples were analyzed for resistin, erythrocyte sedimentation rate (ESR), C-reactive protein, creatinine, fasting lipids, complements, tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, sIL-6R (soluble IL-6 receptor), ICTP (C-terminal telopeptide of type I collagen), and PINP (N-terminal propeptide of type I procollagen). Simple and multiple regression analyses as well as logistic regression analyses were performed. Resistin in serum was compared with 42 healthy female controls with respect to age.

RESULTS

Serum resistin levels in controls were similar to those of patients with SLE. Markers of inflammation and current dose of glucocorticosteroids correlated positively to resistin in serum. Markers of renal function, number of prevalent vertebral fractures, and BMD were also significantly associated with resistin. In a multiple regression model, ESR, creatinine, C3, current glucocorticosteroid dose, high-density lipoprotein, and BMD radius remained significantly associated with resistin. In logistic regression analyses with resistin as the independent variable, a significant association was found with ESR (normal or elevated) but not with S-creatinine or z score for hip and radius total.

CONCLUSION

Although resistin measurements did not differ between patients and controls, resistin was clearly associated with general inflammation, renal disease, treatment with glucocorticosteroids, and bone loss. We hypothesize that resistin has proinflammatory and disease-promoting properties in SLE. Further studies are needed to elucidate the mechanism behind these associations.

Resistin is stored in neutrophil granules being released upon challenge with inflammatory stimuli

We have recently shown that resistin is a key mediator of arthritis accumulating in the inflamed joints and exerting its pro-inflammatory properties independently of TNFalpha. Here we evaluate neutrophils as a cellular source of resistin. Human neutrophils were subjected to subcellular fractionation where the presence of resistin was assessed using western blot, ELISA, and mass spectrometry. Presence of resistin on the neutrophil surface was visualized by flow cytometry. More than 95% of the neutrophils in circulation and in synovial fluid express resistin on their surface. Stimulation of mature neutrophils with fMLF induced release of resistin into supernatants and increased expression of resistin on the surface. Resistin is mobilized simultaneously with lactoferrin, a protein found in specific granules, and with granule-stored CR3/CD11b. Subcellular fractionation of human neutrophils demonstrated the presence of resistin in azurophilic and in specific granules. Here we show that neutrophils have two pools of resistin, the major one exists in specific granules, and the second on their cell membrane. Release of resistin from the neutrophil granules probably serves the main source of resistin at the site of inflammation.

Smoking and nicotine exposure delay development of collagen-induced arthritis in mice

Introduction

Recent epidemiologic studies have implicated smoking as an environmental risk factor for the development of rheumatoid arthritis (RA). The aim of the present study is the evaluation of the role of cigarette smoke (CS) in the pathogenesis of collagen-induced arthritis in mice.

Methods

DBA/1 mice exposed to CS for 16 weeks (n = 25) and mice exposed to nicotine in drinking water (n = 10) were immunized with collagen type II (CII). Severity of arthritis was evaluated clinically and morphologically and compared with control mice (n = 35). Intensity of inflammation was evaluated by serum IL-6 and TNF-α levels. Additionally, antibody response to CII (anti-CII) and citrullinated peptides (aCCP) was measured.

Results

Clinical evaluation of arthritis showed a delayed onset of arthritis in CS-exposed mice compared with non-smoking controls (P < 0.05). Histologic index and weight changes were comparable between the groups; however, smoking mice presented less weight loss during the acute phase of the disease and gained weight significantly faster in the recovery phase (P < 0.05). Similar results were obtained in the mice exposed to nicotine. Nicotine also showed a direct anti-inflammatory effect diminishing IL-6 production by stimulated splenocytes in vitro (P < 0.001). Additionally, smoking mice had lower levels of aCCP and anti-CII antibodies compared with non-smoking (P < 0.05).

Conclusions

Neither smoking nor nicotine exposure aggravates development of CII-induced arthritis in mouse model. Moreover, CS exposure was associated with a lower level of anti-CII antibodies, providing a possible explanation for a delay of arthritis onset in this group.

Resistin in serum is associated with higher levels of IL-1Ra in post-menopausal women with rheumatoid arthritis

OBJECTIVES

The aim of this study was to investigate associations between serum levels of resistin, an adipokine and markers of inflammation, bone metabolism, plasma lipids and kidney function in post-menopausal RA patients and to evaluate if HRT during 2 yrs affected resistin levels.

METHODS

Eighty-eight women were randomly allocated to receive HRT, vitamin D(3) and calcium or vitamin D(3) and calcium alone. Serum levels of resistin, IL-1beta, IL-1 receptor antagonist (IL-1Ra), IL-6, IL-6 soluble receptor, TNF-alpha were measured by ELISA, markers of bone metabolism, carboxyterminal cross-linked telopeptide of type I collagen (ICTP) and carboxyterminal propeptide of type I procollagen by RIA, ESR, CRP, Hb, creatinine and lipids by standard laboratory techniques, BMD and total lean mass (TLM) by DXA and joint destruction by Larsen score. Resistin was also measured in 42 healthy control women.

RESULTS

There was no difference in resistin concentration between patients and healthy controls. Resistin was significantly correlated with IL-1Ra, CRP, TNF-alpha, ICTP, glucocorticosteroids and Larsen score and inversely with BMD, hip and with TLM. In multiple regression analysis, IL-1Ra, TLM and use of corticosteroids remained determinants of resistin. Patients treated with HRT displayed significant increase in resistin compared with controls in the first but not the second year.

CONCLUSIONS

Resistin was associated with increased inflammation, particularly by the acute-phase reactant IL-1Ra antagonizing IL-1beta, joint destruction, glucocorticosteroids and with reduced BMD and TLM. These findings suggest resistin being a significant mediator in the inflammatory process in RA. Further studies examining the mechanisms behind the relation between resistin and IL-1Ra are encouraged. HRT does not seem to have important long-term effect on resistin.

Human synovial lubricin expresses sialyl Lewis x determinant and has L-selectin ligand activity

Lubricin (or proteoglycan 4 (PRG4)) is an abundant mucin-like glycoprotein in synovial fluid (SF) and a major component responsible for joint lubrication. In this study, it was shown that O-linked core 2 oligosaccharides (Galβ1-3(GlcNAcβ1-6)GalNAcα1-Thr/Ser) on lubricin isolated from rheumatoid arthritis SF contained both sulfate and fucose residues, and SF lubricin was capable of binding to recombinant L-selectin in a glycosylation-dependent manner. Using resting human polymorphonuclear granulocytes (PMN) from peripheral blood, confocal microscopy showed that lubricin coated circulating PMN and that it partly co-localized with L-selectin expressed by these cells. In agreement with this, activation-induced shedding of L-selectin also mediated decreased lubricin binding to PMN. It was also found that PMN recruited to inflamed synovial area and fluid in rheumatoid arthritis patients kept a coat of lubricin. These observations suggest that lubricin is able to bind to PMN via an L-selectin-dependent and -independent manner and may play a role in PMN-mediated inflammation.

Survivin is an essential mediator of arthritis interacting with urokinase signalling

Proto-oncogene survivin has recently been identified as a prognostic marker distinguishing patients with destructive rheumatoid arthritis (RA). In the present material of 132 RA patients and 82 controls, the levels of survivin correlated to urokinase (uPA) (r= 0.46), a plasminogen activator over-expressed in inflamed joints and known to exhibit potent arthritogenic properties. Here we evaluate the functional relationship between these proteins using primary synovial fibroblasts and leucocytes of RA patients, human monocytic (THP-1) and fibroblast (MRC-5) cell lines. Using inhibitors of intracellular signalling, we show that uPA and survivin share common transduction pathways in synovial fibroblasts being dependent on the activity of tyrosine kinases, phosphatidylinositide 3 kinase and mitogen effector kinase. Moreover, uPA production is significantly reduced in fibroblasts if survivin synthesis has been silenced by siRNA. Importantly, silencing of survivin in fibroblasts prevented their invasive growth in knee joints of severe combined immune deficient mice. Interaction of uPA with receptor up-regulates survivin expression in leucocytes. In turn, survivin is required for the up-regulation of uPA receptor on the cell surface. These findings indicate that survivin is an essential mediator of arthritogenic properties of uPA regulating its synthesis in synovial fibroblasts and uPAR expression in leucocytes. Close correlation between survivin and uPA levels in patients with RA supports the importance of this connection for the pathogenesis of arthritis.

Fatal outcome of bacteraemic patients caused by infection with staphylokinase-deficient Staphylococcus aureus strains

Staphylokinase (SAK) is a plasminogen-activator protein produced by Staphylococcus aureus. SAK production was evaluated in vitro in S. aureus isolates from the bloodstream of patients with lethal (n = 56) and non-lethal (n = 57) bacteraemia and from anterior nares of healthy subjects (n = 48). Most isolates (93/161) produced SAK, and 68 % of SAK-producing isolates expressed both surface-bound and secreted types of SAK. SAK production was significantly less common among isolates from patients with lethal bacteraemia (39 %) than isolates from patients with non-lethal bacteraemia (68 %) or nasal carriage isolates (67 %) (P < 0.01). After adjusting for infection with methicillin-resistant S. aureus and APACHE II score, patients infected with SAK-deficient isolates were 4.3 times more likely to have lethal bacteraemia than patients whose infecting isolate produced high levels of SAK (> or =5 microg ml(-1)), suggesting that in vitro SAK production was inversely associated with clinical outcome among patients with S. aureus bacteraemia. The high frequency of SAK production in nasal isolates and in cases with uncomplicated bacteraemia suggests that SAK may be one of the adaptive mechanisms of S. aureus symbiosis with the host.