Lorraine Yeo

Cytokine mRNA profiling identifies B cells as a major source of RANKL in rheumatoid arthritis

Objectives In rheumatoid arthritis (RA), a complex cytokine network drives chronic inflammation and joint destruction. So far, few attempts have been made to identify the cellular sources of individual cytokines systematically. Therefore, the primary objective of this study was systematically to assess the cytokine messenger RNA expression profiles in the five largest cell populations in the synovial fluid and peripheral blood of RA patients. To reflect the in vivo situation as closely as possible, the cells were neither cultured nor stimulated ex vivo. Methods Inflammatory cells from 12 RA patients were sorted into CD4 and CD8 T cells, B cells, macrophages and neutrophils. mRNA expression for 41 cytokines was determined by real-time PCR using microfluidic cards. Receptor activator nuclear factor kappa B ligand (RANKL) (TNFSF11) expression by B cells was further confirmed by flow cytometry and by immunofluorescence staining of frozen sections of synovial tissue from patients with RA. Results The detection of cytokines characteristic for T cells and myeloid cells in the expected populations validated this methodology. Beyond the expected cytokine patterns, novel observations were made. Striking among these was the high expression of mRNA for RANKL in B cells from synovial fluid. This observation was validated at the protein level in synovial tissue and fluid. Conclusions RANKL, the key cytokine driving bone destruction by osteoclast activation, is produced by synovial B cells in RA. This observation is of importance for our understanding of the role of B cells in RA and their therapeutic targeting.

Rituximab abrogates joint destruction in rheumatoid arthritis by inhibiting osteoclastogenesis

Objectives To examine how rituximab may result in the inhibition of joint destruction in rheumatoid arthritis (RA) patients. Methods Twenty-eight patients with active RA were treated with rituximab. Radiographs of hands and feet before and 1 year after therapy were assessed using the Sharp–van der Heijde score (SHS). Expression of bone destruction markers was evaluated by immunohistochemistry and immunofluorescence of synovial biopsies obtained before and 16 weeks after the initiation of treatment. Serum levels of osteoprotegerin, receptor activator of nuclear factor κB ligand (RANKL), osteocalcin and cross-linked N-telopeptides of type I collagen (NTx) were measured by ELISA before and 16 weeks post-treatment. Results After 1 year, the mean (SD) change in total SHS was 1.4 (10.0). Sixteen weeks after treatment there was a decrease of 99% in receptor activator of nuclear factor κB-positive osteoclast precursors (p=0.02) and a decrease of 37% (p=0.016) in RANKL expression in the synovium and a trend towards reduced synovial osteoprotegerin expression (25%, p=0.07). In serum, both osteoprotegerin (20%, p=0.001) and RANKL (40%, p<0.0001) levels were significantly reduced 16 weeks after treatment, but the osteoprotegerin/RANKL ratio increased (157%, p=0.006). A trend was found towards an increase of osteocalcin levels (p=0.053), while NTx concentrations did not change. Conclusions Rituximab treatment is associated with a decrease in synovial osteoclast precursors and RANKL expression and an increase in the osteoprotegerin/RANKL ratio in serum. These observations may partly explain the protective effect of rituximab on the progression of joint destruction in RA.

Expression of FcRL4 defines a pro-inflammatory, RANKL-producing B cell subset in rheumatoid arthritis

Objectives The success of B cell targeting therapies has highlighted the importance of B cells in rheumatoid arthritis pathogenesis. We have previously shown that B cells in the RA synovium are capable of producing pro-inflammatory and bone-destructive cytokines including RANKL. Here we sought to characterise the nature and functional relevance of the RANKL-producing B cell subset in the RA synovium. Methods Synovial fluid and peripheral blood B cells from patients with RA were analysed by flow cytometry for markers of B cell differentiation and activation and for chemokine receptors. FcRL4+ and FcRL4− B cells sorted from synovial fluid were analysed for cytokine expression using Taqman low-density arrays. Synovial tissue biopsies obtained from patients with RA were analysed by immunofluorescence for CD20, RANKL and FcRL4. FCRL4 mRNA expression was determined in synovial tissue of RA patients and non-inflammatory control subjects by real-time PCR. Results RANKL-producing B cells in RA synovial tissue and fluid were identified as belonging to a distinct subset of B cells defined by expression of the transmembrane protein FcRL4. FcRL4+ B cells express a distinct combination of cytokines and surface proteins indicating a function distinct from that of FcRL4− B cells. Notably, FcRL4+ B cells expressed high levels of TNF-α and RANKL mRNA. Conclusions We have identified a novel pro-inflammatory B cell population in the RA synovium which is defined by expression of FcRL4 and responsible for RANKL production. This B cell population expresses high levels of CD20, and its removal by rituximab may contribute to the anti-inflammatory effect of this drug.

Expression of chemokines CXCL4 and CXCL7 by synovial macrophages defines an early stage of rheumatoid arthritis

Background and objectives For our understanding of the pathogenesis of rheumatoid arthritis (RA), it is important to elucidate the mechanisms underlying early stages of synovitis. Here, synovial cytokine production was investigated in patients with very early arthritis. Methods Synovial biopsies were obtained from patients with at least one clinically swollen joint within 12 weeks of symptom onset. At an 18-month follow-up visit, patients who went on to develop RA, or whose arthritis spontaneously resolved, were identified. Biopsies were also obtained from patients with RA with longer symptom duration (>12 weeks) and individuals with no clinically apparent inflammation. Synovial mRNA expression of 117 cytokines was quantified using PCR techniques and analysed using standard and novel methods of data analysis. Synovial tissue sections were stained for CXCL4, CXCL7, CD41, CD68 and von Willebrand factor. Results A machine learning approach identified expression of mRNA for CXCL4 and CXCL7 as potentially important in the classification of early RA versus resolving arthritis. mRNA levels for these chemokines were significantly elevated in patients with early RA compared with uninflamed controls. Significantly increased CXCL4 and CXCL7 protein expression was observed in patients with early RA compared with those with resolving arthritis or longer established disease. CXCL4 and CXCL7 co-localised with blood vessels, platelets and CD68+ macrophages. Extravascular CXCL7 expression was significantly higher in patients with very early RA compared with longer duration RA or resolving arthritis Conclusions Taken together, these observations suggest a transient increase in synovial CXCL4 and CXCL7 levels in early RA.

The response of T cells to interleukin-6 is differentially regulated by the microenvironment of the rheumatoid synovial fluid and tissue

OBJECTIVE Interleukin-6 (IL-6) is a proinflammatory cytokine with regulatory effects on the survival and differentiation of T cells. It exerts its biologic function in 2 ways: by directly binding to the IL-6 receptor (IL-6R; CD126) or via trans-signaling, in which soluble IL-6R/IL-6 complexes bind to the signaling component CD130. This study was undertaken to assess the expression and regulation of CD126 and CD130 and determine how these affect the response of CD4+ T cells to IL-6 in the joints of patients with rheumatoid arthritis (RA). METHODS Flow cytometry and immunofluorescence microscopy were used to determine the expression, function, and regulation of CD126 and CD130 in CD4+ T cells from the peripheral blood (PB), synovial fluid (SF), and synovial tissue of RA patients. RESULTS Compared to the findings in RA PB, CD4+ T cells in the SF and synovial tissue expressed low levels of CD126. In contrast, whereas CD4+ T cell expression of CD130 was minimal in the SF, its level in the synovial tissue was high. Consistent with this phenotype, synovial tissue T cells responded to trans-signaling by soluble IL-6R/IL-6 complexes, whereas no response was evident in CD4+ T cells from the SF. Down-regulation of both receptor components in SF T cells could be explained by exposure to high levels of IL-6. Increased levels of CD130 messenger RNA and protein in synovial tissue CD4+ T cells suggested that CD130 is up-regulated locally. Among a range of cytokines tested, only IL-10 induced CD130 expression in T cells. CONCLUSION The inflamed microenvironment in the synovial tissue maintains responsiveness to IL-6 trans-signaling through the up-regulation of CD130 expression in CD4+ T cells, and this process may be driven by IL-10.

B cells expressing the IgA receptor FcRL4 participate in the autoimmune response in patients with rheumatoid arthritis

The clinical efficacy of B cell targeting therapies highlights the pathogenic potential of B cells in inflammatory diseases. Expression of Fc Receptor like 4 (FcRL4) identifies a memory B cell subset, which is enriched in the joints of patients with rheumatoid arthritis (RA) and in mucosa-associated lymphoid tissue. The high level of RANKL production by this B cell subset indicates a unique pathogenic role. In addition, recent work has identified a role for FcRL4 as an IgA receptor, suggesting a potential function in mucosal immunity. Here, the contribution of FcRL4+ B cells to the specific autoimmune response in the joints of patients with RA was investigated. Single FcRL4+ and FcRL4- B cells were sorted from synovial fluid and tissue from RA patients and their immunoglobulin genes characterized. Levels of hypermutation in the variable regions in both populations were largely consistent with memory B cells selected by an antigen- and T cell-dependent process. Recombinant antibodies were generated based on the IgH and IgL variable region sequences and investigated for antigen specificity. A significantly larger proportion of the recombinant antibodies generated from individual synovial FcRL4+ B cells showed reactivity towards citrullinated autoantigens. Furthermore, both in analyses based on heavy chain sequences and flow cytometric detection, FcRL4+ B cells have significantly increased usage of the IgA isotype. Their low level of expression of immunoglobulin and plasma cell differentiation genes does not suggest current antibody secretion. We conclude that these activated B cells are a component of the local autoimmune response, and through their RANKL expression, can contribute to joint destruction. Furthermore, their expression of FcRL4 and their enrichment in the IgA isotype points towards a potential role for these cells in the link between mucosal and joint inflammation.

DKK1 expression by synovial fibroblasts in very early rheumatoid arthritis associates with lymphocyte adhesion in an in vitro flow co-culture system.

BackgroundSynovial fibroblasts play a key role in joint destruction and regulation of the inflammatory infiltrate in established rheumatoid arthritis (RA). The mechanisms by which this occurs in the earliest stages of RA are largely unknown. We investigated the role of Dickkopf-related protein 1 (DKK1) produced by synovial fibroblasts of patients with very early rheumatoid arthritis (VeRA).MethodsFibroblasts were isolated from the disease-modifying anti-rheumatic drug–naive Birmingham early arthritis cohort of patients with new onset of clinically apparent arthritis and inflammatory symptoms of ≤12 weeks’ duration, who at follow-up had either resolving arthritis or RA. Endothelial fibroblast co-cultures were formed using porous filters, and lymphocyte adhesion to co-cultures was assessed using phase-contrast microscopy. DKK1 gene expression and secretion were quantified by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively.ResultsSynovial fibroblasts from patients with VeRA expressed significantly higher levels of DKK1 messenger RNA than those from patients with resolving arthritis. A similar trend was observed for DKK1 protein secretion. In co-culture constructs, more DKK1 tended to be secreted in co-cultures incorporating fibroblasts from VeRA than in co-cultures from non-inflamed joints and resolving arthritis. DKK1 secretion during co-culture positively correlated with lymphocyte adhesion.ConclusionsAlterations in DKK1 could be involved in the pathogenesis and perpetuation of the inflammatory response in the earliest clinically apparent stages of RA.

1.66 CXCL4 and CXCL7 expression on macrophages: a potential predictor of disease outcome in patients presenting with early synovitis?

Background and Objectives Within the context of a comprehensive study of the pathology of the early stages of rheumatoid arthritis (RA) we compared cytokine mRNA expression in the synovium of patients with early inflammatory arthritis who later progressed to rheumatoid arthritis with that of patients with a resolving disease course. Interestingly, we found a trend towards higher expression of platelet related chemokines CXCL4 and CXCL7 mRNA in early RA synovium. We therefore investigated CXCL4 and CXCL7 expression at the protein level and its co-localisation with platelets, macrophages and blood vessels. Methods Synovial tissue biopsies were obtained from treatment naïve patients presenting with at least one clinically swollen joint within the first 12 weeks of symptom onset. Patients who went on to develop RA (according to the 1987 ACR criteria) at an 18 month follow-up (n = 8), as well as patients whose arthritis spontaneously resolved (n = 9) were included. In addition, biopsies collected from longer duration (> 12 weeks) treatment naïve RA patients (n = 10) and patients with mechanical symptoms undergoing knee arthroscopy without obvious signs of inflammation were included as controls (n = 7). Synovial tissue sections were stained with antibodies specific to CXCL4 or CXCL7, CD41, CD68 and vWF using immunofluorescence and staining was quantified using Zeiss imaging software. Specificity of CXCL7 staining was confirmed by blocking with recombinant cytokine. Results We observed a statistically significant increase of CXCL4 and CXCL7 protein expression in patients with early RA when compared to early resolvers (CXCL4 p = 0.036, CXCL7 p = 0.011). This increase reflected a transient stage of early disease, as in treatment-naïve patients with more than 12 weeks disease duration the expression level of these chemokines was found at levels comparable to non-inflamed synovium. Both CXCL4 and CXCL7 co-localised with blood vessels, platelets and CD68+ macrophages within the synovial tissue. However, only staining found outside blood vessels, which co-localised largely with CD68 as a marker for macrophages, differed between synovium from patients with resolving, early and established arthritis (CXCL4 p = 0.063, CXCL7 p = 0.028). Conclusions We have identified two chemokines, CXCL4 and CXCL7, that are expressed at higher levels on macrophages during a transient phase in early RA. Future work will investigate whether these chemokines play a role in disease progression and/or may be used as biomarkers for prediction of disease outcome.

Immunoglobulin characteristics and RNAseq data of FcRL4+ B cells sorted from synovial fluid and tissue of patients with rheumatoid arthritis

This manuscript is a companion paper to Amara et al. [1]. Data shown here include detailed clinical characteristics from anonymized patients, the Ig subclass data generated from B cells sorted from four individual patients, tables detailing variable gene region sequences from sorted cells linked to the patient information and the sequence yields from individual patients. Furthermore a URL link to the RNAseq datasets submitted to GEO is included.

A2.20 Synovial FCRl4+ B cells are enriched in citrulline reactivity without displaying signs of differentiation to a plasma cell phenotype

Background and objectives Expression of Fc Receptor like 4 (FcRL4) identifies a memory B cell subset, which is enriched in the joints of patients with rheumatoid arthritis (RA) and in mucosa associated lymphoid tissue. Their high level of RANKL production indicates a unique pathogenic role. Here, B cell receptor characteristics, antigen specificity and transcriptomic profile of FcRL4+ B cells sorted from the joints of RA patients were investigated. Materials and methods FcRL4+ and FcRL4- B cells were sorted from synovial fluid (SF) and tissue of patients with active RA. Their immunoglobulin variable region (IgVH) genes were sequenced and expressed to generate recombinant monoclonal antibodies (mAbs). Reactivity of 63 mAbs towards native and citrullinated peptides derived from α-enolase, fibrinogen, vimentin, histones 3 and 4 was determined by ELISA and Phadia’s ImmunoCAP ISAC microarray system. RNA sequencing was carried out on sorted SF FcRL4+ and FcRL4- B cells. After preamplification using the SMARTer amplification kit, library preparation was carried out using Illumina’s TruSeq Stranded prep and sequenced on the Illumina platform. Data analysis was carried out using the programs rna-star, DESeq2 and ToppGene. Results Analysis of IgVH genes usage in FcRL4+ and FcRL4- B cells indicated that the Ig repertoire was highly diverse in both B cell subsets, however VH1–69 gene segment was significantly over-represented in the FcRL4+ B cell population (P = 0.013). Out of the 63 mAbs tested, eight antibodies displayed high level of binding to citrullinated peptides. These were exclusively derived from the FcRL4+ subset (p = 0.018). Another eleven antibodies showed low levels of binding to citrullinated peptides. These were derived from both FcRL4+ and FcRL4- B cells. Global transcriptome analysis showed clear differences between the two B cell subsets, including 64 genes which were significantly over or under-expressed in FcRL4+ B cells. Among the genes underexpressed in FcRL4+ B cells, the majority were associated with antibody production and plasma cell differentiation. Conclusions Reactivity of FcRL4+ B cells towards citrullinated autoantigens suggests that they are a component of the citrulline-specific autoimmune response, however, their low level of expression of immunoglobulin and plasma cell differentiation genes suggests functions alternative to antibody production.