Inflammation and ectopic lymphoid structures in rheumatoid arthritis synovial tissues dissected by genomics technology: identification of the interleukin-7 signaling pathway in tissues with lymphoid neogenesis

B cells in the pathogenesis and treatment of rheumatoid arthritis

PURPOSE OF REVIEW

Our understanding of the multiple physiological and pathogenic functions of B cells in rheumatoid arthritis (RA) continues to expand. In turn, the availability of effective agents targeting the B cell compartment increases. In this review, we discuss novel insights into the roles of B cells in RA and recent evidence regarding the efficacy of B cell depletion and biomarkers of treatment response.

RECENT FINDINGS

Recent data have further elucidated the requirements for the generation of ectopic lymphoid structures in the rheumatoid synovium, their frequency, and role in pathogenesis. Additional studies have described the phenotype of infiltrating B cells in the synovium and the unexpected role for B cells in bone homeostasis. In addition to pathogenic roles for B cells, there is also mounting evidence for regulatory B cell subsets that may play a protective role. New data on radiographic progression, efficacy in early disease, the role of retreatment, and biomarkers of treatment response continue to refine the role of B cell depletion in the treatment armamentarium.

SUMMARY

The past few years have seen new advances in immunology applied to the study of RA with surprising observations and interesting new insights into cause and pathogenesis.

Immunohistology of ectopic secondary lymph follicles in subcutaneous nodules from patients with hyperreactive onchocerciasis (sowda)

Ectopic secondary lymph follicles emerge in patients with autoimmune or infectious diseases, e.g. in the synovium in rheumatoid arthritis or the skin in Borrelia burgdorferi infection, but ectopic localisations in the skin are rarely described for helminth infections. We investigated the cellular composition of secondary lymph follicles in subcutaneous nodules from eight patients with hyperreactive onchocerciasis (synonymous “localised” form or sowda) using immunohistology. CD3- and CD45RO-positive T cells and CD20-positive B cells were present in the mantle zone. The germinal centre was characterised by many B cells and CD35-positive follicular dendritic cells, which formed a network of attached IgE- and CD23-positive cells with the low-affinity IgE (epsilon) receptor. Few of the B cells were labelled for IgG1, IgG2 and IgG4, whereas in other zones of the nodule IgG1 was expressed by plasma cells and IgG1-coated dead microfilariae. B cells and few macrophages expressed the MHC class II molecule HLA-DR. Mature CD68-positive tingible body macrophages with phagocytosed leukocytes and CD57-positive lymphocytes occurred in the germinal centre. Macrophages in the germinal centre only weakly expressed alpha1-antichymotrypsin in contrast to macrophages in other zones of the onchocercoma. Furthermore, the multifunctional cytokine TGF-beta was only weakly expressed by macrophages and lymphocytes in the secondary follicles. Only few tryptase-positive mast cells, calprotectin-positive young macrophages, eosinophils and neutrophils occurred in the secondary follicles, although these cells were abundant in the onchocercomas. In conclusion, the ectopic secondary lymph follicles in onchocercomas and lymph nodes from hyperreactive onchocerciasis patients are equally composed.

Interleukin-17 and its target genes: mechanisms of interleukin-17 function in disease

Interleukin-17 (IL-17) has emerged as a central player in the mammalian immune system. Although this cytokine exerts a host-defensive role in many infectious diseases, it promotes inflammatory pathology in autoimmunity and other settings. A myriad of studies have focused on how IL-17-producing cells are generated. However, the means by which IL-17 achieves its effects, either for the benefit or the detriment of the host, are due in large part to the induction of new gene expression. Whereas many IL-17 target genes are common to different disease states, in some cases the effects of IL-17 differ depending on the target cell, infectious site or pathogen. Gene products induced by IL-17 include cytokines (IL-6, granulocyte-colony-stimulating factor, tumour necrosis factor-alpha), chemokines (CXCL1, CXCL2, CCL20, among many others), inflammatory effectors (acute-phase protesins, complement) and antimicrobial proteins (defensins, mucins). Different cell types appear to respond differently to IL-17 in terms of target gene expression, with notable differences seen in mesenchymal and epithelial cells compared with cells of haematopoietic origin. Here, we summarize the major IL-17 target genes that mediate this cytokine's activities in both autoimmune and chronic diseases as well as during various types of infections.

Increased expression of interleukin-7 in labial salivary glands of patients with primary Sjögren's syndrome correlates with increased inflammation

OBJECTIVE

To study the expression levels and immunostimulatory capacities of interleukin-7 (IL-7) in primary Sjögren's syndrome.

METHODS

Labial salivary gland (LSG) IL-7 expression was determined by immunohistochemistry, using a quantitative scoring system, in 30 patients with sicca syndrome: 15 patients with primary Sjögren's syndrome (SS) and 15 patients with non-SS sicca syndrome. The correlation of IL-7 expression in LSGs with parameters of local and peripheral disease was studied, and serum and salivary IL-7 levels were determined. Additionally, the effects of IL-7 on cytokine production by peripheral blood mononuclear cells (PBMCs) from patients with primary SS were determined in vitro by Luminex multicytokine assay and compared with the effects in control subjects.

RESULTS

The expression of IL-7 in LSGs was higher in patients with primary SS compared with that in patients with non-SS sicca syndrome. IL-7 was observed primarily in the vicinity of lymphocytic infiltrates. Salivary IL-7 levels in patients with primary SS were higher than those in control subjects. In all 30 patients with sicca syndrome, IL-7 expression in LSGs correlated with parameters of both local and peripheral disease. Furthermore, IL-7 stimulated T cell-attracting and T cell-differentiating cytokines (monokine induced by interferon-gamma [IFNgamma], IFNgamma-inducible 10-kd protein, IL-12, and IL-15), as well as Th1 (IFNgamma), Th2 (IL-4), Th17 (IL-17A), proinflammatory (tumor necrosis factor alpha and IL-1alpha), and regulatory (IL-10 and IL-13) cytokine production by PBMCs. All of these cytokines were previously shown to be associated with primary SS. The IL-7-induced increase in IL-10 production in patients with primary SS was reduced compared with that in control subjects.

CONCLUSION

The correlation between LSG IL-7 expression and (local) disease parameters in primary SS as well as the IL-7-mediated induction of inflammatory cytokines indicate that IL-7 might contribute to the immunopathology of primary SS.

A comprehensive molecular interaction map for rheumatoid arthritis

Background

Computational biology contributes to a variety of areas related to life sciences and, due to the growing impact of translational medicine - the scientific approach to medicine in tight relation with basic science -, it is becoming an important player in clinical-related areas. In this study, we use computation methods in order to improve our understanding of the complex interactions that occur between molecules related to Rheumatoid Arthritis (RA).

Methodology

Due to the complexity of the disease and the numerous molecular players involved, we devised a method to construct a systemic network of interactions of the processes ongoing in patients affected by RA. The network is based on high-throughput data, refined semi-automatically with carefully curated literature-based information. This global network has then been topologically analysed, as a whole and tissue-specifically, in order to translate the experimental molecular connections into topological motifs meaningful in the identification of tissue-specific markers and targets in the diagnosis, and possibly in the therapy, of RA.

Significance

We find that some nodes in the network that prove to be topologically important, in particular AKT2, IL6, MAPK1 and TP53, are also known to be associated with drugs used for the treatment of RA. Importantly, based on topological consideration, we are also able to suggest CRKL as a novel potentially relevant molecule for the diagnosis or treatment of RA. This type of finding proves the potential of in silico analyses able to produce highly refined hypotheses, based on vast experimental data, to be tested further and more efficiently. As research on RA is ongoing, the present map is in fieri, despite being -at the moment- a reflection of the state of the art. For this reason we make the network freely available in the standardised and easily exportable .xml CellDesigner format at ‘www.picb.ac.cn/ClinicalGenomicNTW/temp.html’ and ‘www.celldesigner.org’.

Inhibition of lymphangiogenesis and lymphatic drainage via vascular endothelial growth factor receptor 3 blockade increases the severity of inflammation in a mouse model of chronic inflammatory arthritis

OBJECTIVE

This study was undertaken to investigate the effect of lymphatic inhibition on joint and draining lymph node (LN) pathology during the course of arthritis progression in mice.

METHODS

Tumor necrosis factor (TNF)-transgenic mice were used as a model of chronic inflammatory arthritis. Mice were subjected to contrast-enhanced magnetic resonance imaging to obtain ankle and knee joint synovial volumes and draining popliteal LN volumes before and after 8 weeks of treatment with vascular endothelial growth factor receptor 3 (VEGFR-3) neutralizing antibody, VEGFR-2 neutralizing antibody, or isotype IgG. Animals were subjected to near-infrared lymphatic imaging to determine the effect of VEGFR-3 neutralization on lymph transport from paws to draining popliteal LNs. Histologic, immunohistochemical, and reverse transcriptase-polymerase chain reaction analyses were used to examine lymphatic vessel formation and the morphology of joints and popliteal LNs.

RESULTS

Compared with IgG treatment, VEGFR-3 neutralizing antibody treatment significantly decreased the size of popliteal LNs, the number of lymphatic vessels in joints and popliteal LNs, lymphatic drainage from paws to popliteal LNs, and the number of VEGF-C-expressing CD11b+ myeloid cells in popliteal LNs. However, it increased the synovial volume and area of inflammation in ankle and knee joints. VEGFR-2 neutralizing antibody, in contrast, inhibited both lymphangiogenesis and joint inflammation.

CONCLUSION

These findings indicate that lymphangiogenesis and lymphatic drainage are reciprocally related to the severity of joint lesions during the development of chronic arthritis. Lymphatic drainage plays a beneficial role in controlling the progression of chronic inflammation.

Increased expression of activation-induced cytidine deaminase is associated with anti-CCP and rheumatoid factor in rheumatoid arthritis

Rheumatoid arthritis (RA) is associated with higher levels of autoantibodies and IL-17. Here, we investigated if ectopic lymphoid follicles and peripheral blood mononuclear cells (PBMCs) from RA patients exhibit increased activation-induced cytidine deaminase (AID), and if increased AID is correlated with serum levels of autoantibodies and IL-17. The results of immunohistochemical staining showed that organized AID(+) germinal centres were observed in six of the 12 RA synovial samples, and AID(+) cells were found almost exclusively in the B-cell areas of these follicles. Aggregated but not organized lymphoid follicles were found in only one OA synovial sample without AID(+) cells. Significantly higher levels of AID mRNA (Aicda) detected by RT-PCR were found in the PBMCs from RA patients than PBMCs from normal controls (P < 0.01). In the PBMCs from RA patients, AID was expressed predominately by the CD10(+)IgM(+)CD20(+) B-cell population and the percentage of these cells that expressed AID was significantly higher than in normal controls (P < 0.01). AID expression in the PBMCs correlated significantly and positively with the serum levels of rheumatoid factor (RF) (P </= 0.0001) and anti-cyclic citrullinated peptide (CCP) (P = 0.0005). Serum levels of IFN-gamma (P = 0.0005) and IL-17 (P = 0.007), but not IL-4, also exhibited positive correlation with the expression of AID. These results suggest that the higher levels of AID expression in B cells of RA patients correlate with, and may be associated with the higher levels of T helper cell cytokines IFN-gamma and IL-17, leading to the development of anti-CCP and RF.

Alterations in peripheral blood memory B cells in patients with active rheumatoid arthritis are dependent on the action of tumour necrosis factor

INTRODUCTION

Disturbances in peripheral blood memory B cell subpopulations have been observed in various autoimmune diseases, but have not been fully delineated in rheumatoid arthritis (RA). Additionally, the possible role of tumour necrosis factor (TNF) in regulating changes in specific peripheral blood memory B cell subsets in RA is still unclear.

METHODS

The frequency and distribution of B cell subsets in the peripheral blood and synovial membrane of active RA patients with long-standing disease have been analysed. Additionally, the possible role of TNF in causing disturbances in memory B cell subsets in RA patients was assessed in a clinical trial with the specific TNF-neutralising antibody, infliximab.

RESULTS

RA patients, independent of disease duration, have a significantly lower frequency of peripheral blood pre-switch IgD+CD27+ memory B cells than healthy individuals, whereas post-switch IgD-CD27+ accumulate with increased disease duration. Notably, both pre-switch IgD+CD27+ and post-switch IgD-CD27+ memory B cells accumulate in the synovial membrane of RA patients. Finally, anti-TNF therapy increased the frequency of pre-switch IgD+CD27 memory B cells in the peripheral blood.

CONCLUSIONS

The data suggest that decreases in peripheral blood IgD+CD27+ pre-switch memory B cells in RA reflect their accumulation in the synovial tissue. Moreover, the significant increase in the peripheral blood pre-switch memory B cells in patients who underwent specific TNF-blockade with infliximab indicates that trafficking of memory B cells into inflamed tissue in RA patients is regulated by TNF and can be corrected by neutralising TNF.

Involvement of breast cancer resistance protein expression on rheumatoid arthritis synovial tissue macrophages in resistance to methotrexate and leflunomide

OBJECTIVE

To determine whether multidrug-resistance efflux transporters are expressed on immune effector cells in synovial tissue from patients with rheumatoid arthritis (RA) and compromise the efficacy of methotrexate (MTX) and leflunomide (LEF).

METHODS

Synovial tissue biopsy samples obtained from RA patients before treatment and 4 months after starting treatment with MTX (n = 17) or LEF (n = 13) were examined by immunohistochemical staining and digital image analysis for the expression of the drug efflux transporters P-glycoprotein, multidrug resistance-associated protein 1 (MRP-1) through MRP-5, MRP-8, MRP-9, and breast cancer resistance protein (BCRP), and the relationship to clinical efficacy of MTX and LEF was assessed.

RESULTS

BCRP expression was observed in all RA synovial biopsy samples, both pretreatment and posttreatment, but not in control noninflammatory synovial tissue samples from orthopedic patients. BCRP expression was found both in the intimal lining layer and on macrophages and endothelial cells in the synovial sublining. Total numbers of macrophages in RA patients decreased upon treatment; in biopsy samples with persistently high macrophage counts, 2-fold higher BCRP expression was observed. Furthermore, median BCRP expression was significantly increased (3-fold) in nonresponders to disease-modifying antirheumatic drugs (DMARDs) compared with responders to DMARDs (P = 0.048). Low expression of MRP-1 was found on synovial macrophages, along with moderate expression in T cell areas of synovial biopsy specimens from one-third of the RA patients.

CONCLUSION

These findings show that the drug resistance-related proteins BCRP and MRP-1 are expressed on inflammatory cells in RA synovial tissue. Since MTX is a substrate for both BCRP and MRP-1, and LEF is a high-affinity substrate for BCRP, these transporters may contribute to reduced therapeutic efficacy of these DMARDs.

Ectopic lymphoid structures support ongoing production of class-switched autoantibodies in rheumatoid synovium

BACKGROUND

Follicular structures resembling germinal centres (GCs) that are characterized by follicular dendritic cell (FDC) networks have long been recognized in chronically inflamed tissues in autoimmune diseases, including the synovium of rheumatoid arthritis (RA). However, it is debated whether these ectopic structures promote autoimmunity and chronic inflammation driving the production of pathogenic autoantibodies. Anti-citrullinated protein/peptide antibodies (ACPA) are highly specific markers of RA, predict a poor prognosis, and have been suggested to be pathogenic. Therefore, the main study objectives were to determine whether ectopic lymphoid structures in RA synovium: (i) express activation-induced cytidine deaminase (AID), the enzyme required for somatic hypermutation and class-switch recombination (CSR) of Ig genes; (ii) support ongoing CSR and ACPA production; and (iii) remain functional in a RA/severe combined immunodeficiency (SCID) chimera model devoid of new immune cell influx into the synovium.

METHODS AND FINDINGS

Using immunohistochemistry (IHC) and quantitative Taqman real-time PCR (QT-PCR) in synovial tissue from 55 patients with RA, we demonstrated that FDC+ structures invariably expressed AID with a distribution resembling secondary lymphoid organs. Further, AID+/CD21+ follicular structures were surrounded by ACPA+/CD138+ plasma cells, as demonstrated by immune reactivity to citrullinated fibrinogen. Moreover, we identified a novel subset of synovial AID+/CD20+ B cells outside GCs resembling interfollicular large B cells. In order to gain direct functional evidence that AID+ structures support CSR and in situ manufacturing of class-switched ACPA, 34 SCID mice were transplanted with RA synovium and humanely killed at 4 wk for harvesting of transplants and sera. Persistent expression of AID and Igamma-Cmu circular transcripts (identifying ongoing IgM-IgG class-switching) was observed in synovial grafts expressing FDCs/CD21L. Furthermore, synovial mRNA levels of AID were closely associated with circulating human IgG ACPA in mouse sera. Finally, the survival and proliferation of functional B cell niches was associated with persistent overexpression of genes regulating ectopic lymphoneogenesis.

CONCLUSIONS

Our demonstration that FDC+ follicular units invariably express AID and are surrounded by ACPA-producing plasma cells provides strong evidence that ectopic lymphoid structures in the RA synovium are functional and support autoantibody production. This concept is further confirmed by evidence of sustained AID expression, B cell proliferation, ongoing CSR, and production of human IgG ACPA from GC+ synovial tissue transplanted into SCID mice, independently of new B cell influx from the systemic circulation. These data identify AID as a potential therapeutic target in RA and suggest that survival of functional synovial B cell niches may profoundly influence chronic inflammation, autoimmunity, and response to B cell-depleting therapies.

Reduced thymic Aire expression and abnormal NF-kappa B2 signaling in a model of systemic autoimmunity

The thymic stromal niche normally directs the production and export of a self-tolerant T cell repertoire. Many models of spontaneous autoimmunity, however, develop thymic architectural abnormalities before disease onset. Although this is suspected to affect central tolerance induction, creating an autoimmune predisposition, in-depth analysis of the microenvironment within these thymi is lacking, such that the mechanisms and likely direct effects on the T cell repertoire are unknown or speculative. Here we show that NZB mice, the first described model for systemic autoimmunity, demonstrate a complex thymic phenotype, including a lack of the autoimmune regulator (Aire), early defects in thymic epithelial cell (TEC) expansion, and evidence for altered NF-kappaB2 signaling. Analysis of medullary TEC revealed a numerical loss of the Aire-expressing MHC class II(high) (mTEC-high) subset as well reduced Aire protein and mRNA per cell. RelB expression was also reduced, while chemokines CCL19 and CCL21 were increased. Unexpectedly, the proportion of cortex and medulla in the NZB mice was normal from 36 wk, despite worsening architectural abnormalities. These data show that the NZB defect is more complex than previously appreciated, segregating into early numerical TEC deficiencies that correct with age, late degeneration of the niche architecture that does not affect TEC number, and a persistent reduction in Aire and RelB expression per cell acquired upon mTEC-high differentiation.

B-cell-directed therapy for inflammatory skin diseases

The basic understanding of inflammatory dermatoses and autoimmune-mediated skin disorders has greatly advanced and broadened our understanding of underlying immune mechanisms that shape the complex network of chronic inflammation and autoimmunity. The new treatment options for psoriasis exemplify how new insights into (auto)immune responses, especially the role and function of various immune cells and proinflammatory cytokines, may lead to new therapeutic strategies. The concept of targeting B cells in autoimmune-mediated disorders is closely related to the discovery of autoantibodies and their cellular origin. However, the appreciation of B cells in autoimmunity has significantly changed and is not limited to their role as progenitors of autoantibody secreting plasma cells. Recent investigations of various inflammatory skin diseases, that is, autoimmune blistering disorders, collagen vascular diseases, and atopic dermatitis, actually support the concept that B cells might be as important as T cells in the etiopathogenesis of these disorders. The striking clinical improvement seen in patients with rheumatoid arthritis following B-cell depletion with the anti-CD20 mAb rituximab has tremendously catalyzed the interest in B-cell-targeted therapies in different autoimmune diseases. Future translational and clinical investigations are mandatory to precisely define the role and the contribution of impaired B-cell function in (auto)immune-mediated skin diseases.

Transcription profiling of rheumatic diseases

Rheumatic diseases are a diverse group of disorders. Most of these diseases are heterogeneous in nature and show varying responsiveness to treatment. Because our understanding of the molecular complexity of rheumatic diseases is incomplete and criteria for categorization are limited, we mainly refer to them in terms of group averages. The advent of DNA microarray technology has provided a powerful tool to gain insight into the molecular complexity of these diseases; this technology facilitates open-ended survey to identify comprehensively the genes and biological pathways that are associated with clinically defined conditions. During the past decade, encouraging results have been generated in the molecular description of complex rheumatic diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome and systemic sclerosis. Here, we describe developments in genomics research during the past decade that have contributed to our knowledge of pathogenesis, and to the identification of biomarkers for diagnosis, patient stratification and prognostication.

Ectopic lymphoid structures support ongoing production of class-switched autoantibodies in rheumatoid synovium

BACKGROUND

Follicular structures resembling germinal centres (GCs) that are characterized by follicular dendritic cell (FDC) networks have long been recognized in chronically inflamed tissues in autoimmune diseases, including the synovium of rheumatoid arthritis (RA). However, it is debated whether these ectopic structures promote autoimmunity and chronic inflammation driving the production of pathogenic autoantibodies. Anti-citrullinated protein/peptide antibodies (ACPA) are highly specific markers of RA, predict a poor prognosis, and have been suggested to be pathogenic. Therefore, the main study objectives were to determine whether ectopic lymphoid structures in RA synovium: (i) express activation-induced cytidine deaminase (AID), the enzyme required for somatic hypermutation and class-switch recombination (CSR) of Ig genes; (ii) support ongoing CSR and ACPA production; and (iii) remain functional in a RA/severe combined immunodeficiency (SCID) chimera model devoid of new immune cell influx into the synovium.

METHODS AND FINDINGS

Using immunohistochemistry (IHC) and quantitative Taqman real-time PCR (QT-PCR) in synovial tissue from 55 patients with RA, we demonstrated that FDC+ structures invariably expressed AID with a distribution resembling secondary lymphoid organs. Further, AID+/CD21+ follicular structures were surrounded by ACPA+/CD138+ plasma cells, as demonstrated by immune reactivity to citrullinated fibrinogen. Moreover, we identified a novel subset of synovial AID+/CD20+ B cells outside GCs resembling interfollicular large B cells. In order to gain direct functional evidence that AID+ structures support CSR and in situ manufacturing of class-switched ACPA, 34 SCID mice were transplanted with RA synovium and humanely killed at 4 wk for harvesting of transplants and sera. Persistent expression of AID and Igamma-Cmu circular transcripts (identifying ongoing IgM-IgG class-switching) was observed in synovial grafts expressing FDCs/CD21L. Furthermore, synovial mRNA levels of AID were closely associated with circulating human IgG ACPA in mouse sera. Finally, the survival and proliferation of functional B cell niches was associated with persistent overexpression of genes regulating ectopic lymphoneogenesis.

CONCLUSIONS

Our demonstration that FDC+ follicular units invariably express AID and are surrounded by ACPA-producing plasma cells provides strong evidence that ectopic lymphoid structures in the RA synovium are functional and support autoantibody production. This concept is further confirmed by evidence of sustained AID expression, B cell proliferation, ongoing CSR, and production of human IgG ACPA from GC+ synovial tissue transplanted into SCID mice, independently of new B cell influx from the systemic circulation. These data identify AID as a potential therapeutic target in RA and suggest that survival of functional synovial B cell niches may profoundly influence chronic inflammation, autoimmunity, and response to B cell-depleting therapies.

Evidence that cytokines play a role in rheumatoid arthritis

A large number of cytokines are active in the joints of patients with rheumatoid arthritis (RA). It is now clear that these cytokines play a fundamental role in the processes that cause inflammation, articular destruction, and the comorbidities associated with RA. Following the success of TNF-alpha blockade as a treatment for RA, other cytokines now offer alternative targets for therapeutic intervention or might be useful as predictive biomarkers of disease. In this Review, we discuss the biologic contribution and therapeutic potential of the major cytokine families to RA pathology, focusing on molecules contained within the TNF-alpha, IL-1, IL-6, IL-23, and IL-2 families.

Lymphotoxin beta receptor signaling promotes tertiary lymphoid organogenesis in the aorta adventitia of aged ApoE-/- mice

Atherosclerosis involves a macrophage-rich inflammation in the aortic intima. It is increasingly recognized that this intimal inflammation is paralleled over time by a distinct inflammatory reaction in adjacent adventitia. Though cross talk between the coordinated inflammatory foci in the intima and the adventitia seems implicit, the mechanism(s) underlying their communication is unclear. Here, using detailed imaging analysis, microarray analyses, laser-capture microdissection, adoptive lymphocyte transfers, and functional blocking studies, we undertook to identify this mechanism. We show that in aged apoE^−/− mice, medial smooth muscle cells (SMCs) beneath intimal plaques in abdominal aortae become activated through lymphotoxin β receptor (LTβR) to express the lymphorganogenic chemokines CXCL13 and CCL21. These signals in turn trigger the development of elaborate bona fide adventitial aortic tertiary lymphoid organs (ATLOs) containing functional conduit meshworks, germinal centers within B cell follicles, clusters of plasma cells, high endothelial venules (HEVs) in T cell areas, and a high proportion of T regulatory cells. Treatment of apoE^−/− mice with LTβR-Ig to interrupt LTβR signaling in SMCs strongly reduced HEV abundance, CXCL13, and CCL21 expression, and disrupted the structure and maintenance of ATLOs. Thus, the LTβR pathway has a major role in shaping the immunological characteristics and overall integrity of the arterial wall.

Identification of interleukin-7 as a candidate disease mediator in spondylarthritis

OBJECTIVE

Understanding of the molecular pathophysiology of spondylarthritis (SpA) remains largely elusive. This is related both to the complexity of the disease (axial versus peripheral disease, inflammation versus tissue remodeling) and to the difficulty in obtaining samples from primary disease sites. This study was undertaken to explore a gene expression approach for identifying novel candidate mediators of SpA.

METHODS

Sacroiliac joint fluid aspirates from 3 SpA patients with active sacroiliitis were studied by microarray analysis. The expression of selected candidate molecules in peripheral synovitis was confirmed by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

Microarray analysis identified 4 sacroiliitis gene clusters, containing a total of 47 messenger RNA (mRNA) transcripts. Two clusters contained genes expressed in all sacroiliitis samples, corresponding to both known and unsuspected candidate mediators of SpA pathology. These included proinflammatory molecules as well as molecules involved in tissue remodeling, such as transforming growth factor beta2. Of the novel candidate genes selected for confirmation, interleukin-7 (IL-7) mRNA expression was higher in SpA peripheral synovial fluid and synovial tissue samples than in osteoarthritis samples, and similar to expression in rheumatoid arthritis (RA) samples. At the protein level, synovial fluid IL-7 levels were even higher in SpA than in RA, despite lower levels of tumor necrosis factor alpha and IL-1beta.

CONCLUSION

In the present study, both known and unsuspected candidate mediators of SpA pathogenesis were identified, including IL-7. The specific overexpression of IL-7 at sites of peripheral synovitis in SpA suggests that further functional investigations of the role of this cytokine in SpA pathogenesis are warranted.

T cells in rheumatoid arthritis

Over the past decade and a half, advances in our understanding of the pathogenesis of immune-mediated diseases such as rheumatoid arthritis (RA) have translated directly into benefit for patients. Much of this benefit has arisen through the introduction of targeted biological therapies. At the same time, technological advances have made it possible to define, at the cellular and molecular levels, the key pathways that influence the initiation and persistence of chronic inflammatory autoimmune reactions. As our understanding grows, it is likely that this knowledge will be translated into a second generation of biological therapies that are tailor-made for the patient. This review summarizes current perspectives on RA disease pathogenesis, with particular emphasis on what RA T cells look like, what they are likely to see, and how they contribute to persistence of the chronic inflammatory response.

B lymphocyte autoimmunity in rheumatoid synovitis is independent of ectopic lymphoid neogenesis

B lymphocyte autoimmunity plays a crucial role in the pathogenesis of rheumatoid arthritis. The local production of autoantibodies and the presence of ectopic lymphoid neogenesis in the rheumatoid synovium suggest that these dedicated microenvironments resembling canonical lymphoid follicles may regulate the initiation and maturation of B cell autoimmunity. In this study, we assessed experimentally the relevance of ectopic lymphoid neogenesis for B cell autoimmunity by a detailed structural, molecular, and serological analysis of seropositive and seronegative human synovitis. We demonstrate that synovial lymphoid neogenesis is a reversible process associated with inflammation which is neither restricted to nor preferentially associated with autoantibody positive rheumatic conditions. Despite the abundant expression of key chemokines and cytokines required for full differentiation toward germinal center reactions, synovial lymphoid neogenesis in rheumatoid arthritis only occasionally progresses toward fully differentiated follicles. In agreement with that observation, we could not detect Ag-driven clonal expansion and affinity maturation of B lymphocytes. Furthermore, ectopic lymphoid neogenesis is not directly associated with local production of anti-citrullinated protein Abs and rheumatoid factor in the rheumatoid joint. Therefore, we conclude that synovial lymphoid neogenesis is not a major determinant of these rheumatoid arthritis-specific autoantibody responses.

Synovial lymphoid neogenesis does not define a specific clinical rheumatoid arthritis phenotype

OBJECTIVE

To investigate the relationship between lymphoid neogenesis in the synovium of patients with rheumatoid arthritis (RA) and characteristics of inflammation and disease severity.

METHODS

Arthroscopic synovial biopsy was performed in 103 patients with active RA (Disease Activity Score 28-joint assessment >or=3.2) who had not received treatment with biologic agents. Sections were stained and assessed by digital image analysis. Lymphocyte aggregates were counted and graded for size (1-3). Synovial lymphoid neogenesis was defined as the presence of grade 2 or 3 aggregates and subclassified based on the presence of follicular dendritic cells (FDCs).

RESULTS

Lymphoid neogenesis was present in 31% of the RA synovial tissues, whereas an additional 25% contained only grade 1 aggregates. FDCs were present in 28% of the samples with lymphoid neogenesis, corresponding to 8% of the total RA cohort. Histologically, synovia with lymphoid neogenesis showed increased infiltration by T and B lymphocytes, plasma cells, and macrophages, and increased expression of tumor necrosis factor alpha and lymphotoxin beta compared with samples without lymphoid neogenesis. Patients with lymphoid neogenesis also had higher C-reactive protein levels, erythrocyte sedimentation rates, and leukocyte and thrombocyte counts, but exhibited no increase in the severity of clinical signs and symptoms. Of importance, there was no relationship between the presence of lymphoid neogenesis and IgM rheumatoid factor or anti-citrullinated protein antibodies. The presence of lymphocyte aggregates with FDCs did not define a specific clinical phenotype compared with lymphocyte aggregates without FDCs.

CONCLUSION

These findings indicate that synovial lymphoid neogenesis is associated with more severe synovial and systemic inflammation, but this is not confined to a specific clinical subset of RA.

The influence of the NOD Nss1/Idd5 loci on sialadenitis and gene expression in salivary glands of congenic mice

The nonobese diabetic (NOD) Nss1 and Idd5 loci have been associated with sialadenitis development in mice. In this study the NOD Nss1 and Idd5 loci were backcrossed onto the healthy control strain B10.Q by using the speed congenic breeding strategy, resulting in three congenic strains: B10.Q.Nss1, B10.Q.Nss1/Idd5 heterozygous and B10.Q.Nss1/Idd5 homozygous. We investigated the effects of the Nss1 and Idd5 loci on sialadenitis and gene expression in NOD congenic mice. One submandibular salivary gland from each mouse was used for histological analysis of sialadenitis, whereas the contralateral salivary gland was used for gene expression profiling with the Applied Biosystems Mouse Genome Survey chip v.1.0. The results were validated using quantitative reverse transcriptase PCR. The NOD Nss1 and Idd5 loci had clear influence on the onset and progression of sialadenitis in congenic mice. Double congenic mice exhibited the most severe phenotype. We successfully identified several genes that are located in the NOD congenic regions to be differentially expressed between the congenic strains and the control strain. Several of these were found to be co-regulated, such as Stat1, complement component C1q genes and Tlr12. Also, a vast contingency of interferon-regulated genes (such as Ltb, Irf7 and Irf8) and cytokine and chemokine genes (such as Ccr7 and Ccl19) were differentially expressed between the congenic strains and the control strain. Over-representation of inflammatory signalling pathways was observed among the differentially expressed genes. We have found that the introgression of the NOD loci Nss1 and Idd5 on a healthy background caused sialadenitis in NOD congenic mouse strains, and we propose that genes within these loci are important factors in the pathogenesis. Furthermore, gene expression profiling has revealed several differentially expressed genes within and outside the NOD loci that are similar to genes found to be differentially expressed in patients with Sjögren's syndrome, and as such are interesting candidates for investigation to enhance our understanding of disease mechanisms and to develop future therapies.