A noncanonical role for the engulfment gene ELMO1 in neutrophils that promotes inflammatory arthritis.

Rheumatoid arthritis is characterized by progressive joint inflammation and affects ~1% of the human population. We noted single-nucleotide polymorphisms (SNPs) in the apoptotic cell-engulfment genes ELMO1, DOCK2, and RAC1 linked to rheumatoid arthritis. As ELMO1 promotes cytoskeletal reorganization during engulfment, we hypothesized that ELMO1 loss would worsen inflammatory arthritis. Surprisingly, Elmo1-deficient mice showed reduced joint inflammation in acute and chronic arthritis models. Genetic and cell-biology studies revealed that ELMO1 associates with receptors linked to neutrophil function in arthritis and regulates activation and early neutrophil recruitment to the joints, without general inhibition of inflammatory responses. Further, neutrophils from the peripheral blood of human donors that carry the SNP in ELMO1 associated with arthritis display increased migratory capacity, whereas ELMO1 knockdown reduces human neutrophil migration to chemokines linked to arthritis. These data identify 'noncanonical' roles for ELMO1 as an important cytoplasmic regulator of specific neutrophil receptors and promoter of arthritis.

Splenectomy at early stage of autoimmune arthritis delayed inflammatory response and reduced joint deterioration in mice.

The spleen plays a role in innate and adaptive immunity, and autoimmune diseases like rheumatoid arthritis (RA). We investigated the effect of splenectomy in early and moderate stages of autoimmune arthritis in a mouse model. To induce recombinant human G1-induced arthritis (GIA), BALB/c mice were immunized intraperitoneally three times in 4-week intervals with the rhG1 antigen. Mice were splenectomized on day 7 (SPE1) or day 35 (SPE2) after the initiation of immunization; tested for clinical severity, joint radiological and histological changes, serum levels of inflammatory cytokines and autoantibodies, and rhG1-specific immune responses; and compared to those in control mice with spleen left intact. Circulating Tregs and T-helper subset ratios in the spleen and inguinal lymph nodes (LNs) were also examined using flow cytometry. The onset of severe inflammatory response was significantly delayed in SPE1 and SPE2 groups compared to control mice at early stages of GIA, which was associated with increased circulating Tregs. After the third immunization, as disease progressed, the severity scores were robustly increased in all mice. Nevertheless, in splenectomized mice, we observed reduced joint deterioration and cartilage damage, more Th2 cells in LNs, and reduced levels of pro-inflammatory cytokines and autoantibodies in their sera. Mesenteric LN cells of splenectomized mice exhibited weaker response in vitro against the rhG1 antigen compared to control mice spleen. In conclusion, splenectomy in the early stages of GIA delayed the inflammatory response, suggesting a protective effect against the development and progression of severe destructive arthritis.

TLR7 endogenous ligands remodel glycolytic macrophages and trigger skin-to-joint crosstalk in psoriatic arthritis.

Thirty percent of psoriasis patients develop psoriatic arthritis (PsA), nevertheless the mechanism remains unknown. Endogenous GU-rich miRNAs activate endosomal TLR7 that plays a critical role in autoimmune diseases. We found that endogenous TLR7 ligands, miR-29 and miR-Let7b, were markedly increased in PsA compared to osteoarthritis (OA) synovial fluid (SF)s. We showed that intradermal (i.d.) miR-Let7b injection promoted skin inflammation, which was characterized by amplified Th1 cells, CD68+ M1 macrophages, and transcriptional upregulation of glycolytic mediators, GLUT1, C-MYC, and HIF1α. Expansion of skin Th1 cells driven by miR-Let7b was also linked to elevated M1-associated IRFs. Interestingly, i.d. miR-Let7b administration exacerbated suboptimal joint inflammation along with metabolic reconfiguration of the PsA-like preclinical model. Moreover, TLR7 agonist, R837, potentiated metabolic reprogramming and expression of IL-1ß, IL-6, and IL-12 in murine macrophages, enabling myeloid-to-T-cell crosstalk. Consistently, treatment with glycolytic inhibitors, 2-DG and/or HIF1αi, reversed R837-induced metabolic remodeling and disrupted the TLR7-driven inflammatory phenotype in myeloid and lymphoid cells. Similar to miR-Let7b, R837 also differentiates progenitor cells into mature osteoclasts, primarily through RANKL induction. Taken together, this study indicates that TLR7-instigated metabolic rewiring of macrophages and their cross-regulation of T cells connects skin immunopathology to joint inflammation.

Imaging of bone and joints in vivo: pathological osteoclastogenesis in arthritis.

Osteoimmunology highlights the reciprocal interactions between the skeletal and immune systems. Over the past two decades, many molecules that link the two have been identified, including cytokines, receptors and transcription factors, leading to successful translation of research into therapeutic approaches to autoimmune diseases such as rheumatoid arthritis. The development of an intravital imaging system using two-photon microscopy, combined with a variety of fluorescent probes and reporter mouse strains, has provided valuable insights into the real-time dynamics of osteoclasts and immune cells in the bone marrow. This technique is now applied to the synovial tissue of arthritic mice to investigate the pathogenesis of osteoimmune diseases and enables direct observation of complex biological phenomena in vivo. In addition, rapid progress in the next-generation sequencing technologies has provided important insights into the field of osteoimmunology through characterizing individual cells in the synovial microenvironment. Single-cell RNA sequencing (scRNA-seq) dissects cellular heterogeneity within a biological system and enables the identification of specific cells differentiating into mature osteoclasts within the previously defined 'osteoclast precursor-containing population'. In this review, we will explain the cellular interactions and cytokine milieu involved in inflammatory bone destruction and update how the novel technologies, such as scRNA-seq and intravital imaging, have contributed to better understand the pathogenesis of bone destruction in arthritis.

Apolipoprotein E Triggers Complement Activation in Joint Synovial Fluid of Rheumatoid Arthritis Patients by Binding C1q.

We identified apolipoprotein E (ApoE) as one of the proteins that are found in complex with complement component C4d in pooled synovial fluid of rheumatoid arthritis (RA) patients. Immobilized human ApoE activated both the classical and the alternative complement pathways. In contrast, ApoE in solution demonstrated an isoform-dependent inhibition of hemolysis and complement deposition at the level of sC5b-9. Using electron microscopy imaging, we confirmed that ApoE interacts differently with C1q depending on its context; surface-bound ApoE predominantly bound C1q globular heads, whereas ApoE in a solution favored the hinge/stalk region of C1q. As a model for the lipidated state of ApoE in lipoprotein particles, we incorporated ApoE into phosphatidylcholine/phosphatidylethanolamine liposomes and found that the presence of ApoE on liposomes increased deposition of C1q and C4b from serum when analyzed using flow cytometry. In addition, posttranslational modifications associated with RA, such as citrullination and oxidation, reduced C4b deposition, whereas carbamylation enhanced C4b deposition on immobilized ApoE. Posttranslational modification of ApoE did not alter C1q interaction but affected binding of complement inhibitors factor H and C4b-binding protein. This suggests that changed ability of C4b to deposit on modified ApoE may play an important role. Our data show that posttranslational modifications of ApoE alter its interactions with complement. Moreover, ApoE may play different roles in the body depending on its solubility, and in diseased states such as RA, deposited ApoE may induce local complement activation rather than exert its typical role of inhibition.

Hydrogen sulfide protects against IL-1ß-induced inflammation and mitochondrial dysfunction-related apoptosis in chondrocytes and ameliorates osteoarthritis.

The inflammatory environment and excessive chondrocyte apoptosis have been demonstrated to play crucial roles in the onset of osteoarthritis (OA). Hydrogen sulfide (H2 S), a gaseous signalling molecule, exerts an inhibitory effect on inflammation and apoptosis in several degenerative diseases. However, the protective effect of H2 S against OA has not been fully clarified, and its underlying mechanism should be examined further. In the current study, the role of endogenous H2 S in the pathogenesis of OA and its protective effects on interleukin (IL)-1ß-induced chondrocytes were identified. Our data revealed decreased H2 S expression in both human degenerative OA cartilage tissue and IL-1ß-induced chondrocytes. Pretreatment with the H2 S donor sodium hydrosulfide (NaHS) dramatically attenuated IL-1ß-induced overproduction of inflammatory cytokines and improved the balance between anabolic and catabolic chondrocyte capacities, and these effects were dependent on PI3K/AKT pathway-mediated inhibition of nuclear factor kappa B (NF-κB). Moreover, mitochondrial dysfunction-related apoptosis was significantly reversed by NaHS in IL-1ß-stimulated chondrocytes. Mechanistically, NaHS partially suppressed IL-1ß-induced phosphorylation of the mitogen-activated protein kinase (MAPK) cascades. Furthermore, in the destabilization of the medial meniscus mouse model, OA progression was ameliorated by NaHS administration. Taken together, these results suggest that H2 S may antagonize IL-1ß-induced inflammation and mitochondrial dysfunction-related apoptosis via selective suppression of the PI3K/Akt/NF-κB and MAPK signalling pathways, respectively, in chondrocytes and may be a potential therapeutic agent for the treatment of OA.

CD300a contributes to the resolution of articular inflammation triggered by MSU crystals by controlling neutrophil apoptosis.

Gout is an inflammatory disease triggered by deposition of monosodium urate (MSU) crystals in the joints, resulting in high neutrophil influx and pain. Here, we studied the role of the inhibitory receptor CD300a in the resolution process in a murine model of gout. We found increased CD300a expression on neutrophils emigrated to the joint. When compared to WT mice, CD300a-/- mice had persistent neutrophil influx till 24 hr after MSU injection. This was associated with increased concentration of IL-1ß and greater tissue damage in the joints of CD300a-/- mice. There was an increase in the percentage of apoptotic neutrophils in the synovial lavage of WT mice, as compared to CD300a-/- mice. This difference was reflected in the decline of efferocytic events in the synovial cavity of CD300a-/- mice 24 hr after MSU injection. A CD300a agonistic antibody was shown, for the first time, to increase apoptosis of human neutrophils, and this was associated with cleavage of caspase-8. In conclusion, our results reveal an important role of CD300a in the control of leucocyte infiltration, IL-1ß production and caspase-8 cleavage in neutrophils, contributing to the resolution of inflammation triggered by MSU injection.

Current insights and future prospects for the pathogenesis and treatment for rheumatoid arthritis.

Genetic, environmental, and epigenetic factors simultaneously or serially contribute to immune cells and resident joint tissue cell abnormalities, invariably leading to joint destruction. Understanding the immune cell dysfunction in earlier years has brought forward life-changing therapeutics to patients with rheumatoid arthritis (RA). Further advances in the understanding of the immune and joint tissue-resident cell signaling and metabolic defects should produce additional tools to treat people with RA and foretell those who will respond to each biological or small drug. This review presents the latest evidence on RA pathogenesis and outlines the prospects for achieving precision medicine.

Chikungunya Virus Evades Antiviral CD8+ T Cell Responses To Establish Persistent Infection in Joint-Associated Tissues.

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes explosive epidemics of a febrile illness characterized by debilitating arthralgia and arthritis that can endure for months to years following infection. In mouse models, CHIKV persists in joint tissues for weeks to months and is associated with chronic synovitis. Using a recombinant CHIKV strain encoding a CD8+ T cell receptor epitope from ovalbumin, as well as a viral peptide-specific major histocompatibility complex class I tetramer, we interrogated CD8+ T cell responses during CHIKV infection. Epitope-specific CD8+ T cells, which were reduced in Batf3-/- and Wdfy4-/- mice with known defects in antigen cross-presentation, accumulated in joint tissue and the spleen. Antigen-specific ex vivo restimulation assays and in vivo killing assays demonstrated that CD8+ T cells produce cytokine and have cytolytic activity. Despite the induction of a virus-specific CD8+ T cell response, the CHIKV burden in joint-associated tissues and the spleen were equivalent in wild-type (WT) and CD8α-/- mice during both the acute and the chronic phases of infection. In comparison, CD8+ T cells were essential for the control of acute and chronic lymphocytic choriomeningitis virus infection in the joint and spleen. Moreover, adoptive transfer of virus-specific effector CD8+ T cells or immunization with a vaccine that induces virus-specific effector CD8+ T cells prior to infection enhanced the clearance of CHIKV infection in the spleen but had a minimal impact on CHIKV infection in the joint. Collectively, these data suggest that CHIKV establishes and maintains a persistent infection in joint-associated tissue in part by evading CD8+ T cell immunity.IMPORTANCE CHIKV is a reemerging mosquito-transmitted virus that in the last decade has spread into Europe, Asia, the Pacific Region, and the Americas. Joint pain, swelling, and stiffness can endure for months to years after CHIKV infection, and epidemics have a severe economic impact. Elucidating the mechanisms by which CHIKV subverts antiviral immunity to establish and maintain a persistent infection may lead to the development of new therapeutic strategies against chronic CHIKV disease. In this study, we found that CHIKV establishes and maintains a persistent infection in joint-associated tissue in part by evading antiviral CD8+ T cell immunity. Thus, immunomodulatory therapies that improve CD8+ T cell immune surveillance and clearance of CHIKV infection could be a strategy for mitigating chronic CHIKV disease.

Citrullinated inter-alpha-trypsin inhibitor heavy chain 4 in arthritic joints and its potential effect in the neutrophil migration.

The citrullinated inter-alpha-trypsin inhibitor heavy chain 4 (cit-ITIH4) was identified as its blood level was associated with the arthritis score in peptide glucose-6-phosphate-isomerase-induced arthritis (pGIA) mice and the disease activity in patients with rheumatoid arthritis (RA). This study aimed to clarify its citrullination pathway and function as related to neutrophils. In pGIA-afflicted joints, ITIH4 and cit-ITIH4 levels were examined by immunohistochemistry (IHC), immunoprecipitation (IP) and Western blotting (WB), while peptidylarginine deiminase (PAD) expression was measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), IHC and immunofluorescent methods. The pGIA mice received anti-lymphocyte antigen 6 complex locus G6D (Ly6G) antibodies to deplete neutrophils and the expression of cit-ITIH4 was investigated by WB. The amounts of ITIH4 and cit-ITIH4 in synovial fluid (SF) from RA and osteoarthritis (OA) patients were examined by I.P. and W.B. Recombinant ITIH4 and cit-ITIH4 were incubated with sera from healthy volunteers before its chemotactic ability and C5a level were evaluated using Boyden's chamber assay and enzyme-linked immunosorbent assay (ELISA). During peak arthritic phase, ITIH4 and cit-ITIH4 were increased in joints while PAD4 was over-expressed, especially in the infiltrating neutrophils of pGIA mice. Levels of cit-ITIH4 in plasma and joints significantly decreased upon neutrophil depletion. ITIH4 was specifically citrullinated in SF from RA patients compared with OA patients. Native ITIH4 inhibited neutrophilic migration and decreased C5a levels, while cit-ITIH4 increased its migration and C5a levels significantly. Cit-ITIH4 is generated mainly in inflamed joints by neutrophils via PAD4. Citrullination of ITIH4 may change its function to up-regulate neutrophilic migration by activating the complement cascade, exacerbating arthritis.

Crossing the boundaries: IL-23 and its role in linking inflammation of the skin, gut and joints.

Several lines of evidence point towards the central role of IL-23 as a crucial inflammatory mediator in the pathogenesis of SpA-a group of inflammatory arthritic diseases whose symptoms span the skin, gastrointestinal tract and joints. While therapeutic blockade of IL-23 proved successful in the treatment of IBD, psoriatic skin disease and peripheral SpA, it failed in patients suffering from SpA with predominantly axial involvement. Here we review state-of-the-art discoveries on IL-23 signalling pathways across target tissues involved in SpA. We discuss the discrepancies in resident IL-23-responding cells and their downstream activities across skin, gut and joint that shape the unique immunological landscape of SpA.

Potential therapeutic compounds from traditional Chinese medicine targeting endoplasmic reticulum stress to alleviate rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease which affects about 0.5-1% of people with symptoms that significantly impact a sufferer's lifestyle. The cells involved in propagating RA tend to display pro-inflammatory and cancer-like characteristics. Medical drug treatment is currently the main avenue of RA therapy. However, drug options are limited due to severe side effects, high costs, insufficient disease retardation in a majority of patients, and therapeutic effects possibly subsiding over time. Thus there is a need for new drug therapies. Endoplasmic reticulum (ER) stress, a condition due to accumulation of misfolded proteins in the ER, and subsequent cellular responses have been found to be involved in cancer and inflammatory pathologies, including RA. ER stress protein markers and their modulation have therefore been suggested as therapeutic targets, such as GRP78 and CHOP, among others. Some current RA therapeutic drugs have been found to have ER stress-modulating properties. Traditional Chinese Medicines (TCMs) frequently use natural products that affect multiple body and cellular targets, and several medicines and/or their isolated compounds have been found to also have ER stress-modulating capabilities, including TCMs used in RA treatment by Chinese Medicine practitioners. This review encourages, in light of the available information, the study of these RA-treating, ER stress-modulating TCMs as potential new pharmaceutical drugs for use in clinical RA therapy, along with providing a list of other ER stress-modulating TCMs utilized in treatment of cancers, inflammatory diseases and other diseases, that have potential use in RA treatment given similar ER stress-modulating capacity.

Liver X receptors conserve the therapeutic target potential for the treatment of rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic multi-system autoimmune disease with extremely complex pathogenesis. Significantly altered lipid paradox related to the inflammatory burden is reported in RA patients, inducing 50% higher cardiovascular risks. Recent studies have also demonstrated that lipid metabolism can regulate many functions of immune cells in which metabolic pathways have altered. The nuclear liver X receptors (LXRs), including LXRα and LXRß, play a central role in regulating lipid homeostasis and inflammatory responses. Undoubtedly, LXRs have been considered as an attractive therapeutic target for the treatment of RA. However, there are some contradictory effects of LXRs agonists observed in previous animal studies where both pro-inflammatory role and anti-inflammatory role were revealed for LXRs activation in RA. Therefore, in addition to updating the knowledge of LXRs as the prominent regulators of lipid homeostasis, the purpose of this review is to summarize the effects of LXRs agonists in RA-associated immune cells, to explore the underlying reasons for the contradictory therapeutic effects of LXRs agonists observed in RA animal models, and to discuss future strategy for the treatment of RA with LXRs modulators.

Pathological mechanism of joint destruction in haemophilic arthropathy.

Haemophilic arthropathy (HA), caused by intra-articular haemorrhage, is one of the most common complications in patients with haemophilia. Factor replacement therapy provides missing coagulation factors to prevent children with haemophilia from joint bleeding and decreases their risk for HA. However, haemophilia patients in developing countries are still suffering from HA due to insufficient replacement therapy. Symptoms such as pain and activity limitations caused by HA seriously affect the functional abilities and quality of life of patients with HA, causing a high disability rate in the haemophilia cohort. The pathological mechanism of HA is complicated because the whole pathological mainly involves hypertrophic synovitis, osteopenia, cartilage and bone destruction, and these pathological changes occur in parallel and interact with each other. Inflammation plays an important role in the whole complex pathological process, and iron, cytokines, growth factors and other factors are involved. This review summarizes the pathological mechanism of HA to provide background for clinical and basic research.

Specific Increase in Joint Neutrophil Extracellular Traps and Its Relation to Interleukin 6 in Autoimmune Arthritis.

Neutrophils and their extracellular traps have been shown to play an important role in the pathogenesis of rheumatoid arthritis (RA), but the detailed mechanisms in joints are still unclear, and their regulation remains to be solved. Here, we explored neutrophil extracellular trap (NET)osis in experimental models of arthritis and further investigated the effects of interleukin-6 (IL-6) inhibition in neutrophils and NETosis. In skins of peptide GPI-induced arthritis (pGIA), citrullinated protein was detected as well as citrullinated histone expression in immunized skin but this was not specific to pGIA. Citrullinated histone expression in pGIA joints was specific to pGIA and was merged with neutrophil elastase, suggesting NETosis. Neutrophils in joints tend to upregulate IL-6 receptors when compared with bone marrow neutrophils. Administration of mouse anti-IL-6 receptor antibodies in pGIA suppressed arthritis in association with a decrease in neutrophil infiltration and NETosis in joints. In the plasma of RA patients, citrullinated protein was significantly reduced after tocilizumab treatment. Our results suggest that IL-6 enhances neutrophil chemotaxis and NETosis in inflammatory joints and could be the source of citrullinated proteins.

The immunosuppressive functions of two novel tick serpins, HlSerpin-a and HlSerpin-b, from Haemaphysalis longicornis.

Serpins are evolutionarily conserved serine protease inhibitors that are widely distributed in animals, plants and microbes. In this study, we reported the cloning and functional characterizations of two novel serpin genes, HlSerpin-a and HlSerpin-b, from the hard tick Haemaphysalis longicornis of China. Recombinant HlSerpin-a and HlSerpin-b displayed protease inhibitory activities against multiple mammalian proteases. Similar to other tick serpins, HlSerpin-a and HlSerpin-b suppressed the expression of inflammatory cytokines such as TNF-α, interleukin (IL)-6 and IL-1ß from lipopolysaccharide-stimulated mouse bone-marrow-derived macrophages (BMDMs) or mouse bone-marrow-derived dendritic cells (BMDCs). The minimum active region (reaction centre loop) of HlSerpin-a, named SA-RCL, showed similar biological activities as HlSerpin-a in the protease inhibition and immune suppression assays. The immunosuppressive activities of full-length HlSerpin-a and SA-RCL are impaired in Cathepsin G or Cathepsin B knockout mouse macrophages, suggesting that the immunomodulation functions of SA and SA-RCL are dependent on their protease inhibitory activity. Finally, we showed that both full-length HlSerpins and SA-RCL can relieve the joint swelling and inflammatory response in collagen-induced mouse arthritis models. These results suggested that HlSerpin-a and HlSerpin-b are two functional arthropod serpins, and the minimal reactive peptide SA-RCL is a potential candidate for drug development against inflammatory diseases.

Theacrine alleviates chronic inflammation by enhancing TGF-ß-mediated shifts via TGF-ß/SMAD pathway in Freund's incomplete adjuvant-induced rats.

Rheumatoid arthritis is a chronic and systemic autoimmune disease, which affects approximately 1% of the adult population worldwide. The present study investigated the therapeutic effect of theacrine (TC) on arthritis and its mechanisms in Freund's incomplete adjuvant (FIA)-induced SD rats. Rats were randomly divided into 5 groups: i) healthy control; ii) model; iii) positive control with methotrexate (MTX); iv) treatment with 12.5 mg/kg TC; and v) treatment with 25.0 mg/kg TC. The apparent scores, including changes in body weights, degree of paw swelling and arthritis indicators, were analyzed to evaluate the anti-chronic inflammatory effect of TC. The levels of interleukin (IL)-6 and transforming growth factor-ß (TGF-ß) in serum were measured by enzyme-linked immunosorbent assay. The protein and RNA expression levels of the critical factors in rats were measured to elucidate the mechanisms responsible for chronic inflammation and to verify molecular indexes of chronic inflammatory conditions. TC notably suppressed the severity of FIA-induced rat by attenuating the apparent scores, animal weight and inflammatory indexes in the 25 mg/kg TC group compared with the FIA rat model. Furthermore, TC significantly decreased the levels of IL-6 and increased the levels of TGF-ß. Histopathological examinations indicated that TC rescued the synovial hyperplasia and inflammatory cell infiltration in joint tissues. In addition, TC enhanced TGF-ß-mediated shifts in inflammatory marker expression in joint tissue. Overall, the present study demonstrated that TC exerted a superior anti-arthritic effect via the suppression of IL-6 and the activation of TGF-ß by the TGF-ß/SMAD pathway.

The immunomodulatory role of PDEs inhibitors in immune cells: therapeutic implication in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by inflammatory synovitis and progressive joint. Although the etiology is extremely complex, overwhelming evidence suggests that dysregulation or imbalance of the immune system plays a central role in disease pathogenesis. The bone loss and joint destruction are immunological insults mediated by infiltration and abnormal activation of various immune cells. Since pharmacological inhibition of cyclic nucleotide phosphodiesterases (PDEs), which degrade cyclic AMP and cyclic GMP, can regulate the activity of multiple immune cells, which are considered as a potential strategy for treating RA. Therefore, this review attempted to summarize the modulating effects of PDEs on immune cells and described the molecular underpinnings and potential clinical application of PDEs inhibitors for RA.

Role of different Th17 and Treg downstream signalling pathways in the pathogenesis of Staphylococcus aureus infection induced septic arthritis in mice.

Septic arthritis is a condition of bone disorder caused predominantly by Staphylococcus aureus. Following the bacterial entry activated immune cells specially macrophages and dendritic cells release pro-inflammatory mediators such as IL-6, TNF-α, IL-1ß etc., which not only create an inflammatory microenvironment but also play crucial roles in the proliferation of different CD+ T cell subsets. Among them, Th17 and Tregs are of major concern in recent times because of their potential roles in regulating the ongoing inflammation in many diseases including experimental arthritis. But the downstream signalling mechanism of these cells in regulating the severity of inflammation in case of septic arthritis is not known yet. So, here we have established a murine model of S. aureus induced septic arthritis and kept the animal upto 15 days post-infection. To examine the signalling mechanism, Th17 and Treg cells were isolated from blood, spleen and synovial joints of control and infected mice and observed the expression of JNK, NFκB and RANKL in the lysate of isolated Th17 and Tregs. We have also estimated the levels of serum IL-21 and TGF-ß. NFκB, JNK and RANKL expression was found to be higher at 3 and 15 days post-infection along with serum IL-21 levels. On the other hand, maximum TGF-ß level was observed at 9 days post-infection along with increased Treg population. In conclusion it was hypothesized that bone resorption is related with downstream signalling pathways of Th17 cells, which stimulate osteoclast generation via NFκB/JNK-RANKL axis and helps in the persistence of the disease.

CSF-1 in Inflammatory and Arthritic Pain Development.

Pain is one of the most debilitating symptoms in many diseases for which there is inadequate management and understanding. CSF-1, also known as M-CSF, acts via its receptor (CSF-1R, c-Fms) to regulate the development of the monocyte/macrophage lineage and to act locally in tissues to control macrophage numbers and function. It has been implicated in the control of neuropathic pain via a central action on microglia. We report in this study that systemic administration of a neutralizing anti-CSF-1R or CSF-1 mAb inhibits the development of inflammatory pain induced by zymosan, GM-CSF, and TNF in mice. This approach also prevented but did not ameliorate the development of arthritic pain and optimal disease driven by the three stimuli in mice, suggesting that CSF-1 may only be relevant when the driving inflammatory insults in tissues are acute and/or periodic. Systemic CSF-1 administration rapidly induced pain and enhanced the arthritis in an inflamed mouse joint, albeit via a different pathway(s) from that used by systemic GM-CSF and TNF. It is concluded that CSF-1 can function peripherally during the generation of inflammatory pain and hence may be a target for such pain and associated disease, including when the clinically important cytokines, TNF and GM-CSF, are involved. Our findings have ramifications for the selection and design of anti-CSF-1R/CSF-1 trials.