Differential expansion of T peripheral helper cells in early rheumatoid arthritis and osteoarthritis synovium.

OBJECTIVES: Programmed cell death protein 1 (PD-1)-expressing T cells are implicated in the pathogenesis of autoimmune inflammatory diseases such as rheumatoid arthritis. A subset of CXCR5- T cells, termed T peripheral helper (Tph) cells, which drive B cell differentiation, have been identified in ectopic lymphoid structures in established rheumatoid arthritis synovial tissue. Here, we aimed to characterise these in treatment-naïve, early rheumatoid arthritis to determine whether these cells accumulate prior to fully established disease. METHODS: Fresh dissociated tissue and peripheral blood mononuclear cell (PBMC) suspensions were stained with Zombie UV, followed by anti-CD45RO, PD-1, CD3, ICOS, CD8, CD4, CD20, CXCR5, TIGIT and CD38 antibodies prior to analysis. For histology, rheumatoid arthritis synovial sections were prepared for Opal multispectral immunofluorescence with anti-CD45RO, CD20, PD-1 and CXCR5 antibodies. Images were acquired on the Perkin Elmer Vectra V.3.0 imaging system and analysed using InForm Advanced Image Analysis software. RESULTS: Flow cytometry revealed T cell infiltration in the rheumatoid arthritis synovium with differential expression of PD-1, CD45RO, ICOS, TIGIT and CD38. We observed a higher frequency of PD1hiCXCR5- Tph in rheumatoid arthritis synovial tissue and PBMCs versus controls, and no significant difference in T follicular helper cell frequency. Microscopy identified a 10-fold increase of Tph cells in early rheumatoid arthritis synovial follicular and diffuse regions, and identified Tph adjacent to germinal centre B cells. CONCLUSIONS: These data demonstrate that PD-1hi Tph cells are present in early rheumatoid arthritis, but not osteoarthritis synovium, and therefore may provide a target for treatment of patients with early rheumatoid arthritis.

Nivolumab-induced synovitis is characterized by florid T cell infiltration and rapid resolution with synovial biopsy-guided therapy.

BACKGROUND: Immune checkpoint inhibitors (ICIs) are associated with rheumatic and musculoskeletal immune-related adverse events (irAEs) in 5%-20% of patients. Currently, patients refractory to corticosteroids and conventional disease-modifying antirheumatic drugs (cDMARD) are treated with biological DMARDs (bDMARDs) targeting tumor necrosis factor α (TNFα) and interleukin-6, although without a clear biological rationale. Synovial tissue (ST) biopsy presents a valuable opportunity to investigate irAE pathogenesis and appropriately stratify bDMARD use in refractory irAE patients. CASE PRESENTATION: We provide the first report of comparative, parallel ST and synovial fluid (SF) analyses of severe, cDMARD-refractory, seronegative polyarthritis, classified as a grade 3 irAE occurring in response to nivolumab treatment for metastatic squamous cell lung cancer, in comparison with ST and SF from patients with untreated rheumatoid arthritis (RA). We investigated immunohistochemical labeling of ST cytokine expression as a biological rationale for selecting therapy. Flow cytometric analysis of lymphocytes from ST, SF and blood collected before and after synovial biopsy-guided therapy, in comparison with RA, were evaluated for insights into the immunopathogenesis of irAE. Immunolabeling of ST demonstrated an excess of TNFα cytokine expression. Subsequent treatment with infliximab resulted in resolution of inflammatory symptoms and a significant reduction in C reactive protein levels. Flow cytometric analysis of synovial infiltrates indicated absence of programmed cell death protein-1 (PD-1) receptor positivity despite cessation of nivolumab approximately 200 days prior to the analyzes. CONCLUSIONS: A deeper understanding of the immunopathogenetic basis of immune activation in irAEs is required in order to select therapy that is likely to be the most effective. This is the first report investigating parallel blood, ST and SF in ICI-induced severe rheumatic irAE. Use of a bDMARD directed by the dominant inflammatory cytokine achieved resolution of synovitis while maintaining cancer remission.

The novel cytokine Metrnl/IL-41 is elevated in Psoriatic Arthritis synovium and inducible from both entheseal and synovial fibroblasts.

Meteorin-like(IL-41), is a novel cytokine that is thought to be immunoregulatory and is highly expressed in psoriatic skin. We investigated IL-41 protein expression in synovial tissue in RA(Rheumatoid Arthritis), PsA(Psoriatic Arthritis) and OA(Osteoarthritis) patients and evaluated IL-41 production from healthy enthesis samples, as the enthesis represent the primary inflammatory site in PsA. IL-41 was measured in synovial fluid from PsA, RA and OA patients. Synovial biopsies were stained for IL-41 by immunohistochemistry. IL-41 was highly expressed in the synovial fluid and synovial tissue of PsA patients (median = 7722 pg/ml) when compared to OA patients (median = 5044 pg/ml). We found that entheseal stromal cells were the dominant producer of IL-41 from the enthesis. Moreover, stromal derived IL-41, could be further induced by IL-17A/F and TNF. In conclusion, IL-41 is expressed in PsA synovium and is present and inducible at the enthesis. Its functional effect in psoriatic inflammation remains to be fully elucidated.

Triple DMARD treatment in early rheumatoid arthritis modulates synovial T cell activation and plasmablast/plasma cell differentiation pathways.

OBJECTIVES: This study sought to investigate the genome-wide transcriptional effects of a combination of disease modifying anti-rheumatic drugs (tDMARD; methotrexate, sulfasalazine and hydroxychloroquine) in synovial tissues obtained from early rheumatoid arthritis (RA) patients. While combination DMARD strategies have been investigated for clinical efficacy, very little data exists on the potential molecular mechanism of action. We hypothesized that tDMARD would impact multiple biological pathways, but the specific pathways were unknown. METHODS: Paired synovial biopsy samples from early RA patients before and after 6 months of tDMARD therapy were collected by arthroscopy (n = 19). These biopsies as well as those from subjects with normal synovium (n = 28) were profiled by total RNA sequencing. RESULTS: Large differences in gene expression between RA and control biopsies (over 5000 genes) were identified. Despite clinical efficacy, the expression of a restricted set of less than 300 genes was reversed after 6 months of treatment. Many genes remained elevated, even in patients who achieved low disease activity. Interestingly, tDMARD downregulated genes included those involved in T cell activation and signaling and plasmablast/plasma cell differentiation and function. CONCLUSIONS: We have identified transcriptomic signatures that characterize synovial tissue from RA patients with early disease. Analysis after 6 months of tDMARD treatment highlight consistent alterations in expression of genes related to T cell activation and plasmablast/plasma cell differentiation. These results provide novel insight into the biology of early RA and the mechanism of tDMARD action and may help identify novel drug targets to improve rates of treatment-induced disease remission.

Mucosal-associated invariant T cells are reduced and functionally immature in the peripheral blood of primary Sjögren's syndrome patients.

The frequencies, immunophenotype, and function of mucosal-associated invariant T (MAIT) cells were studied in patients with primary Sjögren syndrome (pSS) and healthy controls. MAIT cells were significantly decreased in the peripheral blood (PB) of patients with pSS. Vα7.2+ MAIT cells were detected in the salivary gland tissue from pSS patients, but not in controls, indicating that the reduction of MAIT cells in PB might be due to migration into the target tissue. Furthermore, the residual peripheral blood MAIT cells in pSS patients showed altered immunophenotype and function. While MAIT cells from controls were almost exclusively CD8+ and expressed an effector memory immunophenotype, in pSS patients they were enriched in CD4+ and naïve subpopulations. Consistently, the functional studies demonstrated that MAIT cells from pSS showed a lower level of activation with reduced expression of CD69 and CD154 (CD40L), and a lower production of TNF and IFN-γ. In summary, our findings demonstrate that MAIT cells were reduced and phenotypically and functionally altered in PB of pSS patients. The altered function of MAIT cells in target tissues from pSS patients may result in dysregulation of mucosal immunity leading to microbial damage of mucosal surfaces and subsequent initiation of autoimmune response.

Expression profiling in spondyloarthropathy synovial biopsies highlights changes in expression of inflammatory genes in conjunction with tissue remodelling genes.

BACKGROUND: In the spondyloarthropathies, the underlying molecular and cellular pathways driving disease are poorly understood. By undertaking a study in knee synovial biopsies from spondyloarthropathy (SpA) and ankylosing spondylitis (AS) patients we aimed to elucidate dysregulated genes and pathways. METHODS: RNA was extracted from six SpA, two AS, three osteoarthritis (OA) and four normal control knee synovial biopsies. Whole genome expression profiling was undertaken using the Illumina DASL system, which assays 24000 cDNA probes. Differentially expressed candidate genes were then validated using quantitative PCR and immunohistochemistry. RESULTS: Four hundred and sixteen differentially expressed genes were identified that clearly delineated between AS/SpA and control groups. Pathway analysis showed altered gene-expression in oxidoreductase activity, B-cell associated, matrix catabolic, and metabolic pathways. Altered "myogene" profiling was also identified. The inflammatory mediator, MMP3, was strongly upregulated (5-fold) in AS/SpA samples and the Wnt pathway inhibitors DKK3 (2.7-fold) and Kremen1 (1.5-fold) were downregulated. CONCLUSIONS: Altered expression profiling in SpA and AS samples demonstrates that disease pathogenesis is associated with both systemic inflammation as well as local tissue alterations that may underlie tissue damaging modelling and remodelling outcomes. This supports the hypothesis that initial systemic inflammation in spondyloarthropathies transfers to and persists in the local joint environment, and might subsequently mediate changes in genes directly involved in the destructive tissue remodelling.

Enrichment of circulating interleukin-17-secreting interleukin-23 receptor-positive γ/δ T cells in patients with active ankylosing spondylitis.

OBJECTIVE: Ankylosing spondylitis (AS) is a common inflammatory arthritis affecting primarily the axial skeleton. IL23R is genetically associated with AS. This study was undertaken to investigate and characterize the role of interleukin-23 (IL-23) signaling in AS pathogenesis. METHODS: The study population consisted of patients with active AS (n = 17), patients with psoriatic arthritis (n = 8), patients with rheumatoid arthritis, (n = 9), and healthy subjects (n = 20). IL-23 receptor (IL-23R) expression in T cells was determined in each subject group, and expression levels were compared. RESULTS: The proportion of IL-23R-expressing T cells in the periphery was 2-fold higher in AS patients than in healthy controls, specifically driven by a 3-fold increase in IL-23R-positive γ/δ T cells in AS patients. The proportions of CD4+ and CD8+ cells that were positive for IL-17 were unchanged. This increased IL-23R expression on γ/δ T cells was also associated with enhanced IL-17 secretion, with no observable IL-17 production from IL-23R-negative γ/δ T cells in AS patients. Furthermore, γ/δ T cells from AS patients were heavily skewed toward IL-17 production in response to stimulation with IL-23 and/or anti-CD3/CD28. CONCLUSION: Recently, mouse models have shown IL-17-secreting γ/δ T cells to be pathogenic in infection and autoimmunity. Our data provide the first description of a potentially pathogenic role of these cells in a human autoimmune disease. Since IL-23 is a maturation and growth factor for IL-17-producing cells, increased IL-23R expression may regulate the function of this putative pathogenic γ/δ T cell population.

TWEAK and Fn14 expression in the pathogenesis of joint inflammation and bone erosion in rheumatoid arthritis.

INTRODUCTION: TNF-like weak inducer of apoptosis (TWEAK) has been proposed as a mediator of inflammation and bone erosion in rheumatoid arthritis (RA). This study aimed to investigate TWEAK and TWEAK receptor (Fn14) expression in synovial tissue from patients with active and inactive rheumatoid arthritis (RA), osteoarthritis (OA) and normal controls and assess soluble (s)TWEAK levels in the synovial fluids from patients with active RA and OA. Effects of sTWEAK on osteoclasts and osteoblasts were investigated in vitro. METHODS: TWEAK and Fn14 expression were detected in synovial tissues by immunohistochemistry (IHC). Selected tissues were dual labelled with antibodies specific for TWEAK and lineage-selective cell surface markers CD68, Tryptase G, CD22 and CD38. TWEAK mRNA expression was examined in human peripheral blood mononuclear cells (PBMC) sorted on the basis of their expression of CD22. sTWEAK was detected in synovial fluid from OA and RA patients by ELISA. The effect of sTWEAK on PBMC and RAW 264.7 osteoclastogenesis was examined. The effect of sTWEAK on cell surface receptor activator of NF Kappa B Ligand (RANKL) expression by human osteoblasts was determined by flow cytometry. RESULTS: TWEAK and Fn14 expression were significantly higher in synovial tissue from all patient groups compared to the synovial tissue from control subjects (P < 0.05). TWEAK was significantly higher in active compared with inactive RA tissues (P < 0.05). TWEAK expression co-localised with a subset of CD38+ plasma cells and with CD22+ B-lymphocytes in RA tissues. Abundant TWEAK mRNA expression was detected in normal human CD22+ B cells. Higher levels of sTWEAK were observed in synovial fluids isolated from active RA compared with OA patients. sTWEAK did not stimulate osteoclast formation directly from PBMC, however, sTWEAK induced the surface expression of RANKL by human immature, STRO-1+ osteoblasts. CONCLUSIONS: The expression of TWEAK by CD22+ B cells and CD38+ plasma cells in RA synovium represents a novel potential pathogenic pathway. High levels of sTWEAK in active RA synovial fluid and of TWEAK and Fn14 in active RA tissue, together with the effect of TWEAK to induce osteoblastic RANKL expression, is consistent with TWEAK/Fn14 signalling being important in the pathogenesis of inflammation and bone erosion in RA.

Ramipril retards development of aortic valve stenosis in a rabbit model: mechanistic considerations.

BACKGROUND AND PURPOSE: Aortic valve stenosis (AVS) is associated with significant cardiovascular morbidity and mortality. To date, no therapeutic modality has been shown to be effective in retarding AVS progression. We evaluated the effect of angiotensin-converting enzyme inhibition with ramipril on disease progression in a recently developed rabbit model of AVS. EXPERIMENTAL APPROACH: The effects of 8 weeks of treatment with either vitamin D2 at 25,000 IU for 4 days a week alone or in combination with ramipril (0.5 mg·kg⁻¹) on aortic valve structure and function were examined in New Zealand white rabbits. Echocardiographic aortic valve backscatter (AV(BS)) and aortic valve:outflow tract flow velocity ratio were utilized to quantify changes in valve structure and function. KEY RESULTS: Treatment with ramipril significantly reduced AV(BS) and improved aortic valve :outflow tract flow velocity ratio. The intravalvular content of the pro-oxidant thioredoxin-interacting protein was decreased significantly with ramipril treatment. Endothelial function, as measured by asymmetric dimethylarginine concentrations and vascular responses to ACh, was improved significantly with ramipril treatment. CONCLUSIONS AND IMPLICATIONS: Ramipril retards the development of AVS, reduces valvular thioredoxin-interacting protein accumulation and limits endothelial dysfunction in this animal model. These findings provide important insights into the mechanisms of AVS development and an impetus for future human studies of AVS retardation using an angiotensin-converting enzyme inhibitor.

Apoptosis in the rheumatoid arthritis synovial membrane: modulation by disease-modifying anti-rheumatic drug treatment.

OBJECTIVES: RA is characterized at the synovial tissue level by synovial lining hyperplasia, angiogenesis and mononuclear cell infiltrates. A failure of apoptotic pathways may explain these pathological changes in RA synovial tissue. This study aims to demonstrate the presence of initiators and inhibitors of apoptosis in RA synovial tissue and the effect of treatment with DMARDs on apoptotic pathways in RA. METHODS: Synovial biopsy specimens were obtained at arthroscopy from 16 RA patients before and at 3- or 6-month intervals after commencing treatment with a DMARD. Apoptosis (by the terminal deoxynucleotidyl transferase mediated dUTP nick end labelling method and polyADP-ribose polymerase staining), proteins regulating apoptosis [Fas, FADD-like IL1b converting enzyme inhibitory protein (FLIP), Bcl-2, Survivin and X-linked inhibitor of apoptosis protein (XIAP)] and the presence of activated caspases (caspases 3 and 8) were detected by immunohistochemistry and quantified using image analysis and semiquantitative techniques. RESULTS: Fifteen patients responded to treatment, with an ACR response of > or =20%, 13 achieving an ACR response of > or =50% and 3 achieving an ACR remission. There was a significant reduction in SM macrophages and memory T cells, with an increase in fibroblast-like synovial lining cells following DMARD treatment. Apoptosis was not detected in the inflamed synovial tissue of RA patients before starting treatment, despite evidence of caspase activation, but was detectable after successful treatment with DMARDs. Inhibitors of activated caspases (FLIP, Survivin and XIAP) were detected in RA synovial tissue and were down-modulated with successful DMARD treatment. CONCLUSIONS: Apoptotic pathways are defective in RA synovial tissue from patients with active disease, despite the presence of activated caspases, possibly due to the abundant expression of inhibitors of the caspase pathway in RA synovial tissue. DMARD treatment can modulate apoptosis in the RA SM, which may lead to restoration of the SM architecture towards that of normal synovial tissue.

Elevated expression of caspase-3 inhibitors, survivin and xIAP correlates with low levels of apoptosis in active rheumatoid synovium.

INTRODUCTION: Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a tumour necrosis factor (TNF) family member capable of inducing apoptosis in many cell types. METHODS: Using immunohistochemistry, terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL) and real-time PCR we investigated the expression of TRAIL, TRAIL receptors and several key molecules of the intracellular apoptotic pathway in human synovial tissues from various types of arthritis and normal controls. Synovial tissues from patients with active rheumatoid arthritis (RA), inactive RA, osteoarthritis (OA) or spondyloarthritis (SpA) and normal individuals were studied. RESULTS: Significantly higher levels of TRAIL, TRAIL R1, TRAIL R2 and TRAIL R4 were observed in synovial tissues from patients with active RA compared with normal controls (p < 0.05). TRAIL, TRAIL R1 and TRAIL R4 were expressed by many of the cells expressing CD68 (macrophages). Lower levels of TUNEL but higher levels of cleaved caspase-3 staining were detected in tissue from active RA compared with inactive RA patients (p < 0.05). Higher levels of survivin and x-linked inhibitor of apoptosis protein (xIAP) were expressed in active RA synovial tissues compared with inactive RA observed at both the protein and mRNA levels. CONCLUSIONS: This study indicates that the induction of apoptosis in active RA synovial tissues is inhibited despite stimulation of the intracellular pathway(s) that lead to apoptosis. This inhibition of apoptosis was observed downstream of caspase-3 and may involve the caspase-3 inhibitors, survivin and xIAP.

Vitamin D(2) supplementation induces the development of aortic stenosis in rabbits: interactions with endothelial function and thioredoxin-interacting protein.

Understanding of the pathophysiology of aortic valve stenosis (AVS) and finding potentially effective treatments are impeded by the lack of suitable AVS animal models. A previous study demonstrated the development of AVS in rabbits with vitamin D(2) and cholesterol supplementation without any hemodynamic changes in the cholesterol supplemented group alone. The current study aimed to determine whether AVS develops in an animal model with vitamin D(2) supplementation alone, and to explore pathophysiological mechanisms underlying this process. The effects of 8 weeks' treatment with vitamin D(2) alone (n=8) at 25,000 IU/4 days weekly on aortic valve structure and function were examined in male New Zealand white rabbits. Echocardiographic aortic valve backscatter (AV(BS)), transvalvular velocity, and transvalvular pressure gradient were utilized to quantitate changes in valve structure and function. Valvular histology/immunochemistry and function were examined after 8 weeks. Changes in valves were compared with those in endothelial function and in valvular measurement of thioredoxin-interacting protein (TXNIP), a marker/mediator of reactive oxygen species-induced oxidative stress. Vitamin D(2) treated rabbits developed AVS with increased AV(BS) (17.6+/-1.4 dB vs 6.7+/-0.8 dB, P<0.0001), increased transvalvular velocity and transvalvular pressure gradient (both P<0.01 via 2-way ANOVA) compared to the control group. There was associated valve calcification, lipid deposition and macrophage infiltration. Endothelial function was markedly impaired, and intravalvular TXNIP concentration increased. In this model, vitamin D(2) induces the development of AVS with histological features similar to those of early AVS in humans and associated endothelial dysfunction/redox stress. AVS development may result from the loss of nitric oxide suppression of TXNIP expression.

Modulation of RANKL and osteoprotegerin expression in synovial tissue from patients with rheumatoid arthritis in response to disease-modifying antirheumatic drug treatment and correlation with radiologic outcome.

OBJECTIVE: To demonstrate the effect of treatment with disease-modifying agents on the expression of osteoprotegerin (OPG) and RANKL in the synovial tissue from rheumatoid arthritis (RA) patients and to correlate these changes with radiologic damage measured on sequential radiographs of the hands and feet. METHODS: Synovial biopsy specimens were obtained at arthroscopy from 25 patients with active RA (16 of whom had a disease duration <12 months) before and at 3-6-month intervals after starting treatment with a disease-modifying agent. Immunohistologic analysis was performed using monoclonal antibodies to detect OPG and RANKL expression, with staining quantitated using computer-assisted image analysis and semiquantitative analysis techniques. Serial radiographs of the hands and feet were analyzed independently by 2 radiologists and a rheumatologist using the van der Heide modification of the Sharp scoring method. RESULTS: Thirteen patients achieved a low disease state as defined by a disease activity score <2.6 while 19 patients achieved an American College of Rheumatology response >20% after disease-modifying antirheumatic drug (DMARD) treatment. Successful DMARD treatment resulted in an increase in OPG expression and a decrease in RANKL expression at the synovial tissue level, which correlated with a reduction in erosion scores measured on annual radiographs of the hands and feet. CONCLUSION: Successful treatment-induced modulation of OPG and RANKL expression at the synovial tissue level, resulting in a reduction in the RANKL:OPG ratio, is likely to have a significant impact on osteoclast formation and joint damage in patients with active RA.

Serum macrophage inhibitory cytokine 1 in rheumatoid arthritis: a potential marker of erosive joint destruction.

OBJECTIVE: The transforming growth factor beta superfamily member macrophage inhibitory cytokine 1 (MIC-1) is expressed upon macrophage activation, regulated by the p53 pathway, and linked to clinical events in atherosclerosis and cancer. Since rheumatoid arthritis (RA) shares similar etiopathologic mechanisms with the above diseases, we sought to determine the clinical utility of determining MIC-1 serum levels and MIC-1 genotype in the management of RA. METHODS: Ninety-one RA patients were recruited. Serum was collected from 83 of these patients and synovial biopsy samples were collected from the remaining 8 patients. Of the 83 patients from whom serum was collected, 61 were treated on an outpatient basis (defined as having nonsevere disease), and 22 patients went on to undergo hemopoietic stem cell transplantation (HSCT) (defined as having severe disease). RESULTS: Serum levels of MIC-1 were higher in RA patients and reflected disease severity independently of classic disease markers. MIC-1 was detected in rheumatoid synovial specimens, and allelic variation of MIC-1 was associated with earlier erosive disease and severe treatment-resistant chronic RA. Additionally, algorithms including serum and/or allelic variation in MIC-1 predicted response to HSCT, the presence of severe disease, and joint erosions. CONCLUSION: Determination of serum levels of MIC-1 and MIC-1 genotype may be clinically useful in the management of RA as well as in selection of patients for HSCT, since they predict disease course and response to therapy. The data indicate a potential role for MIC-1 in RA pathogenesis. These results warrant larger prospective studies to fully delineate and confirm a role for MIC-1 genotyping and serum estimation in patient selection for HSCT and in the management of RA.

Variability of RANKL and osteoprotegerin staining in synovial tissue from patients with active rheumatoid arthritis: quantification using color video image analysis.

OBJECTIVE: To assess the interpatient, interbiopsy, and intrabiopsy variability of receptor activator of nuclear factor kB ligand (RANKL) and osteoprotegerin (OPG) immunostaining within synovial tissue from rheumatoid knee joints with active synovitis, using digital image analysis. METHODS: Synovial biopsy specimens were obtained from patients with rheumatoid arthritis (RA) and active synovitis. Immunohistologic analysis was performed on frozen synovial tissue biopsy specimens from 6 patients using a monoclonal antibody (Mab) to detect RANKL (626) or OPG (805 or 8051). Patients with a minimum of 4 synovial biopsies were included in the study. Sections were evaluated by computer assisted image analysis to assess between-patient, between-biopsy, and intra-biopsy variability of OPG and RANKL protein expression. The study was designed to deliberately maximize the variability. RESULTS: Computerized image analysis of staining with Mab to RANKL and OPG revealed variance for each antibody across the 3 components of the total variability. CONCLUSION: Our study shows that variability in synovial immunostaining of RANKL and OPG protein is a significant and complex problem. We discuss methods to reduce this variability and suggest that the auspices of OMERACT may be employed to advance the study of synovium in collaborative international studies.

Receptor activator NF kappaB ligand (RANKL) and osteoprotegerin (OPG) protein expression in periodontitis.

OBJECTIVES AND BACKGROUND: This study investigated the expression of key mediators that regulate differentiation of osteoclasts, receptor activator of nuclear factor kappaB ligand (RANKL), and its natural inhibitor, osteoprotegerin (OPG), in periodontitis. We aimed to compare the levels of the RANKL and OPG in the granulomatous tissue adjacent to areas of alveolar bone loss from patients with periodontitis to that present in tissue from patients without periodontitis. In addition, we aimed to determine the types of cells expressing these factors in these tissues and to demonstrate the expression of the osteoclastic markers, RANK and tartrate-resistant acid phosphatase (TRAP), in periodontitis. MATERIALS AND METHODS: Frozen biopsy specimens were analysed using specific monoclonal antibodies and were evaluated by semiquantitative analysis and digital image analysis to compare levels of RANKL and OPG protein expression. Double labelling of frozen sections with antibodies to different cell lineage specific markers was used to determine the types of cells expressing these proteins. In situ hybridization was used to detect cells expressing RANK mRNA. RESULTS: Semiquantitative image analysis demonstrated that significantly higher levels of RANKL protein (P < 0.05) were expressed in the periodontitis tissue. Conversely, OPG protein was significantly lower (P < 0.05) in the periodontitis tissues. RANKL protein was associated with lymphocytes and macrophages. OPG protein was associated with endothelial cells in both tissues. Many leukocytes expressing RANK mRNA and TRAP were observed in periodontitis tissues. CONCLUSION: The change in the levels of these key regulators of osteoclast differentiation may play a major role in the bone loss seen in periodontitis.