Spondyloarthritis: update on pathogenesis and management

A review of pediatric uveitis: part II. Autoimmune diseases and treatment modalities

Uveitis is a manifestation of complex processes that can represent an infectious process or a dysfunction of the immune system that may have grave effects on the eye. Although infectious causes, once properly identified, may be successfully treated by addressing the inciting organism with recognized interventions, the immune-modulated chronic forms of uveitis often provide more complex challenges in management. Recent strides in understanding the inflammatory pathway and better bioengineering capabilities have resulted in some new modalities of treatment.

[Synovitis score: value of histopathological diagnostics in unclear arthritis. Case reports from rheumatological pathological practice]

Histopathological assessment of synovial biopsies has an established value. The value for inflammatory joint diseases without standardized rating mechanisms was, however, unknown until recently. The exemplary use of the synovitis score in four cases all including recurrent bruises of the knee joint portrays its value for diagnosis and therapy. Usage of the score includes assessing the enlargement of the lining layer, cellular density of synovial stroma and leucocyte infiltration by giving each a score of 0-3 points and adding them. Presence of high-grade synovitis (>or=4 points) in all cases displayed the reason for the joint bruises within a primarily inflammatory, rheumatoid circle. In this report we show the broad variety of uses for the synovitis score dealing with cases of Lyme arthritis, rheumatoid arthritis, seronegative monarthritis and HLA-B27-positive peripheral arthritis.

Internet-based randomised controlled trials for the evaluation of complementary and alternative medicines: probiotics in spondyloarthropathy

Background

The clinical effectiveness of complementary and alternative medicines (CAMs) is widely debated because of a lack of clinical trials. The internet may provide an effective and economical approach for undertaking randomised controlled trials (RCTs) of low-risk interventions. We investigated whether the internet could be used to perform an internet-based RCT of a CAM fulfilling the revised CONSORT (Consolidated Standards of Reporting Trials) statement quality checklist for reporting of RCTs. A secondary aim was to examine the effect of probiotics compared to placebo in terms of well-being over 12 weeks.

Methods

People aged ≥18 years with confirmed spondyloarthropathy living in the United Kingdom with internet access were invited to participate in an internet-based RCT of probiotic compared to placebo for improving well-being and bowel symptoms. The intervention was a probiotic containing 4 strains of live bacteria or identical placebo taken by mouth daily for 3 months. The primary outcome measure was the performance of the trial according to the revised CONSORT statement.

Results

147 people were randomised into the trial. The internet-based trial of the CAM fulfilled the revised CONSORT statement such as efficient blinding, allocation concealment, intention to treat analysis and flow of participants through the trial. Recruitment of the required number of participants was completed in 19 months. Sixty-five percent (96/147) completed the entire 3 months of the trial. The trial was low cost and demonstrated that in an intention to treat analysis, probiotics did not improve well-being or bowel symptoms.

Conclusion

The internet-based RCT proved to be a successful and economical method for examining this CAM intervention. Recruitment, adherence and completion rate were all similar to those reported with conventional RCTs but at a fraction of the cost. Internet-based RCTs can fulfil all the criteria of the revised CONSORT statement and are an appropriate method for studying low-risk interventions.

Trial registration

ISRCTN36133252

The expression of IL-20 and IL-24 and their shared receptors are increased in rheumatoid arthritis and spondyloarthropathy

The purpose of this study was to analyze the expression of the two proinflammatory cytokines IL-20 and IL-24 and their shared receptors in rheumatoid arthritis and spondyloarthropathy. IL-20 was increased in plasma of rheumatoid arthritis patients compared with osteoarthritis patients and IL-24 was increased in synovial fluid and plasma of rheumatoid arthritis and spondyloarthropathy patients compared with osteoarthritis patients. IL-20 and IL-24 mRNA was only present at low levels in the synovium. In the synovial membrane, IL-20 protein was present in mononuclear cells and neutrophil granulocytes whereas IL-24 protein was observed in endothelial cells and mononuclear cells. IL-20 receptor type 1 and IL-22 receptor were expressed by granulocytes in the synovial fluid. In synovial fluid mononuclear cell cultures, stimulation with recombinant human IL-20 or recombinant human IL-24 induced monocyte chemoattractant protein 1 (CCL2/MCP-1) secretion, but not tumour necrosis factor alpha mRNA synthesis or IL-6 secretion. Both IL-20 and IL-24 showed correlations to CCL2/MCP-1 in plasma from rheumatoid arthritis and spondyloarthropathy patients. This study associates IL-20 and IL-24 to the synovium of rheumatoid arthritis and spondyloarthropathy and results indicate that the two cytokines contribute to disease pathogenesis through recruitment of neutrophil granulocytes and induction of CCL2/MCP-1.

Usefulness of human leucocyte antigen-B27 subtypes in predicting ankylosing spondylitis: Taiwan experience

BACKGROUND

Genetic factors are clearly attributed to the susceptibility of ankylosing spondylitis (AS). The human leucocyte antigen (HLA)-B27 proved to be the very useful marker for diagnosing AS. The aim of this study was to determine the prevalence of HLA-B27 subtypes in Taiwan and to investigate whether these subtypes may be of help in predicting the diagnosis of AS.

METHODS

A total of 314 patients with AS and a control group of 71 subjects positive for HLA-B27 detected by flow cytometry analysis were recruited for the study. HLA-B27 subtypes were confirmed by the polymerase chain reaction-sequence-specific primers and sequence-specific oligonucleotide probing.

RESULTS

Four B27 alleles were identified: B*2704, B*2705, B*2706 and B*2707. HLA-B*2704 was the predominant allele. There were significant differences in the distribution of HLA-B27 subtypes between patients with AS and controls. Five of them who were homozygous for the B*2704 allele were solely found in AS group but not in controls. Statistical analysis showed that B*2704 was positively associated with AS, which suggested an increased possibility of having AS. Other HLA-B27 subtypes showed no strong correlation with AS.

CONCLUSION

In the Taiwanese population, susceptibility to AS was determined by the presence of HLA-B*2704. Although B*2706 was reported to have a negative association with AS in Taiwanese, Thai and Chinese Singaporean populations, we report, in our study, two AS patients with B*2706 (0.6%). Disease heterogeneity suggests that other than genetic background, many pathogenic factors could be associated with AS. This may need to be investigated with a larger group of patients with AS and controls.

Ankylosing spondylitis, HLA-B27 positivity and the need for biologic therapies

OBJECTIVES

HLA-B27 positivity strongly influences Ankylosing spondylitis (AS) disease susceptibility and phenotype. The aim of this study was to analyse an AS cohort with respect to quality of life (ASQoL), extra-articular disease, markers of disease activity (BASDAI), functional capacity (BASFI), biologic requirement, and the influence of HLA-B27 on these parameters.

METHODS

Data recorded in 82 patients included demographics (age, sex), extra-articular disease (GI, ocular, dermatological, GU), cardiac and pulmonary diagnoses. BASDAI, BASFI, ASQoL, joint counts, disease duration and past/present treatment (NSAID, DMARD, steroid and biologic use) were also recorded.

RESULTS

90.2% of the cohort was B27 positive with significantly longer disease duration (17.6 v 6.9 years, p<0.05). BASFI (42.2 v 5.9), BASDAI (3.22 v 1.3), ASQoL (10 v 4), physician assessment of biologic need (24 v 5), steroid (15.7% v 12.5%) and NSAID use (98.6% v 75%) were higher in the B27 positive group, as were ocular (38.9% v 12.5%), pulmonary (4.2% v 0%) and cardiac (4.3% v 0%) features. Negative patients displayed more GI (37.5% v 19.4%), dermatological (25% v 19.7%) and GU (25% v 4.2%) features. Patients satisfying ASAS (AS assessment study group) criteria and receiving biologic therapy were 18.9% (B27 positive group) and 0% (B27 negative group).

CONCLUSIONS

AS patients have significantly longer disease duration if B27 positive, higher markers of disease activity, poorer functional status, poorer quality of life, and more extra-articular manifestations. These findings were reflected in the percentage of patients needing biologic therapies.

Ankylosing Spondylitis: A Contemporary Perspective on Diagnosis and Treatment

OBJECTIVES

In recent years, great progress has been made in the development of diagnostic tools, therapeutic approaches, and validated outcome measures in the understanding of the pathogenesis of ankylosing spondylitis (AS). The purpose of this review was to summarize these developments.

METHODS

We performed a PubMed search for the period 1978 to 2005, using the keyword, "ankylosing spondylitis," resulting in a total of 4878 publications, including 778 reviews. Articles were then selected based on their discussion of recent diagnostic tools and new treatment approaches in the pathogenesis of AS, leading to a final total of 104 articles.

RESULTS

In recent years, there have been 2 major developments in the management of AS that make earlier diagnosis possible and offer the hope of alleviating pain and preventing structural changes that result in loss of function. These developments include the use of magnetic resonance imaging to visualize the inflammatory changes in the sacroiliac joint and the axial spine, and the demonstration that tumor necrosis factor blocking agents are highly efficacious in reducing spinal inflammation and possibly in slowing radiographic progression.

CONCLUSIONS

There have been major advances in both the diagnostic tools and the therapeutic regimens available for patients with AS.

Ankylosing spondylitis presenting with macrophage activation syndrome

Macrophage activation syndrome (MAS), which can also be considered as reactive hemophagocytic syndrome (HPS), is a rare and potentially fatal complication of rheumatic diseases. We describe a 42-year-old woman in whom MAS developed as a complication of ankylosing spondylitis (AS). She suffered from fever and low back pain before admission. Laboratory findings were pancytopenia, abnormal liver enzymes, increased ferritin levels, and positive for B27. Hyperplasia of hemophagocytic macrophages was confirmed in her bone marrow. High-dose steroids therapy resulted in clinical and laboratory improvements. In this patient, there was no possible causative factor of HPS (such as viral infection, lymphoma, and systemic lupus erythematosus) except the presence of AS. There have been no previously reported cases describing the relationship between AS and HPS. This case indicates that attention should be given to the possibility that certain patients with AS-associated cytopenia may display accompanying intramedullary hemophagocytic phenomena.

Pulmonary involvement in ankylosing spondylitis

PURPOSE OF REVIEW

Anti-tumor necrosis factor-alpha agents have recently been approved and recommended as effective and relatively safe drug therapy for ankylosing spondylitis. In light of this major advance in the management of these patients, recent observations on the pulmonary manifestations of ankylosing spondylitis are reviewed.

RECENT FINDINGS

High-resolution computed tomography abnormalities were found to be prevalent (range 50-85%) in ankylosing spondylitis even in patients with early disease, and in those with normal chest radiographs and without respiratory symptoms. The high-resolution computed tomography changes included apical fibrosis, interstitial lung disease, emphysema, bronchietasis and pleural thickening. In general, the high-resolution computed tomography changes were of mild degree, and no correlation was observed between high-resolution computed tomography abnormalities, pulmonary function test variables and indices of ankylosing spondylitis symptoms and disease structural severity. Spontaneous pneumothorax was reported to be a rare complication, but tended to occur in those patients with fibrobullous disease.

SUMMARY

The clinical significance of the high-resolution computed tomography abnormalities remains to be determined. Most of the published studies are cross-sectional, and are limited by lack of control subjects matched for age, gender and tobacco use. Studies to correlate high-resolution computed tomography changes with bronchoalveolar lavage and lung biopsies as well as prospective studies on long-term evolution of these findings including those patients receiving anti-tumor necrosis factor-alpha agents are needed.

Reactive arthritis

Reactive arthritis (ReA) has been recognized as a clinical disease entity for nearly 100 years. The prevalence is estimated to be 30-40/100,000 adults. The HLA-B27-associated form is part of the spondyloarthritis concept. According to the current hypothesis the arthritis follows a primary extra-articular infection and is characterized by the presence of bacterial antigen and/or of viable but non-culturable bacteria persisting within the joint. Pathogenesis involves the modification of host cells by pathogen-associated molecular patterns (PAMPs, e.g. lipopolysaccharide), bacterial effector proteins, the adaptive immune system, and the genetic background. Up to 30% of patients develop chronic symptoms, and therapeutic options for these patients are still limited. Data for recommendations to apply conventional disease-modifying anti-rheumatic drugs (DMARDs) are rare; however, sulfasalazine seems to be effective, and first reports on agents that block tumour necrosis factor (TNF) are promising. Combination therapy of several antibiotics might open the window to curing the disease; however, controlled clinical studies are needed.

HLA-B27-associated acute anterior uveitis in the University Referral Centre in North Thailand: clinical presentation and visual prognosis

BACKGROUND

Acute anterior uveitis (AAU) is the most frequent type of uveitis encountered in the west. Although human leucocyte antigen (HLA)-B27-associated ankylosing spondylitis was reported in South East Asia, it is not known whether HLA-B27-associated ocular disease is prevalent in Thailand.

METHODS

A prospective study of 100 unrelated blood donors and 121 consecutive patients with AAU was carried out. All people underwent HLA-B27 typing and full ocular examination. Radiological examination of the sacroiliac joints was conducted in patients with low back pain or arthralgias.

RESULTS

The prevalence of HLA-B27 was 10% among the blood donors in contrast with 44% in the AAU group (p<0.001). The clinical characteristics of HLA-B27-associated AAU were similar to those published throughout the world (unilaterality in 74%, hypopyon in 31%, recurrent AAU in 64%). However, the increased intraocular pressure (IOP) was more common in the HLA-B-27-negative group (p = 0.03) than in their HLA-B27-positive counterparts. At least 15% of the HLA B27-positive group had radiological signs of ankylosing spondylitis.

CONCLUSION

The prevalence of HLA-B27 in the population without uveitis in Thailand is about 10% and clinical characteristics of HLA-B27-positive AAU are similar to those reported in the west. In contrast with earlier reports, HLA-B27-negative AAU in Thailand was associated with increased IOP and should be further studied.

[Inflammatory spine disease as a cause of back pain]

PURPOSE

The aim of this review is to evaluate the role of inflammatory spine disease in patients with chronic back pain. The contribution of imaging modalities for the diagnostic evaluation of back pain is discussed.

MATERIAL AND METHODS

A systematic literature search based on the classification of seronegative spondyloarthropathies and rheumatoid arthritis was performed. The results of this search and the experiences in a large collective of rheumatological patients are analyzed.

RESULTS

The prevalence of rheumatoid arthritis (1-2%) is comparable to that of spondyloarthropathies (1.9%). The etiology of these entities is not fully elucidated. Magnetic resonance imaging is increasingly used for early detection and surveillance of therapy with TNF-alpha antagonists.

DISCUSSION

Bone marrow edema, which is only detectable with MRI, represents an early sign of inflammation. Therapy with TNF-alpha antagonists is based on clinical and laboratory criteria, and signs of inflammation in MRI. MRI is useful for assessment of the effectiveness of anti-inflammatory therapy.

Immunogénétique de la spondylarthrite ankylosante

BACKGROUND

Ankylosing spondylitis (AS) is an inflammatory rheumatic disease with axial involvement but its physiopathology remains unexplained. This latter combines genetic and environmental factors as well as an abnormal immune response.

CURRENT TOPICS AND IMPORTANT RESULT

This review addresses the different aspects of AS immunogenetic. A genetic background in AS is suggested by familial cases, concordance rate in twins and transmission of the disease in siblings. Ankylosing spondylitis is strongly associated with the expression of the HLA Class I antigen, B27, but also with other genes not yet identified since currently, only chromosomic area have been linked to AS. Studies of candidate genes or genome screening allow to determine these chromosomic regions. HLA-B27 is directly associated with the disease physiopathology as suggested by animal models of rats transgenic for human HLA-B27 and beta2 microglobulin. This HLA molecule have original biological properties, in particular a slow heavy chain folding and the formation of heavy chain homodimers without light chain. However, HLA B27 is a functional molecule and assumes its property of presenting peptide of 9 amino acids to CD8+ T cells. Interaction modelling studies between HLA B27 and peptides have identified peptide and peptide groove amino acid sequences, with the identification of critical positions on the HLA B27 molecule for the peptide interaction. Original biochemical properties of HLA-B27 include diminished bacterial antigen response and CD4+ T lymphocyte stimulation. Innate immunity is also of interest in AS, as suggested by the presence of macrophage and polymorphonuclear neutrophils in AS synovitis, as well as the contribution of Toll-like receptors.

FUTURE PROSPECTS AND PROJECTS

Thus in AS, the inflammatory process and then the clinical consequences may be explained by the involvement of HLA-B27, a bacterial antigen presentation, an abnormal immune response and the contribution of innate immunity, T CD4+ but also T CD8+ cells. The original molecular structures of HLA-B27 are certainly involved in this complex physiopathology, but their direct influence on the disease remains to be precised.

TNFα antagonist therapy in ankylosing spondylitis and psoriatic arthritis: recommendations of the French Society for Rheumatology

OBJECTIVES

To develop recommendations for TNFalpha antagonist therapy in patients with spondyloarthropathies.

METHODS

The Delphi consensus procedure was used to select questions, to which evidence-based answers were sought in the literature. Expert opinion was used when needed to estimate the risks and benefits of TNFalpha antagonists. TNFalpha antagonists exert potent antiinflammatory effects but fail to provide a definitive cure.

RESULTS

Recommendations were developed for patients with ankylosing spondylitis (AS) or psoriatic arthritis (PsA). The following criteria for TNFalpha antagonist therapy were selected: definitive diagnosis of AS or PsA, active disease for at least 4 consecutive weeks documented during two physician visits, overall physician's assessment of disease activity>/=4/10 and BASDAI>/=4/10 in axial disease or at least three tender and swollen joints in peripheral disease, failure to respond adequately to at least three nonsteroidal antiinflammatory drugs given in optimal dosages for at least 3 months in axial disease or at least one disease-modifying antirheumatic drug (methotrexate, leflunomide, sulfasalazine) for at least 4 months, with local glucocorticoid injections if appropriate, in peripheral disease. Effectiveness and safety should be evaluated by a rheumatologist. The frequency of monitoring depends on the drug. Lack of effectiveness should be defined as inadequate improvement after 6-12 weeks, with a less than two-point decrease in the BASDAI in axial disease or a less than 30% decrease in the tender and swollen joint counts in peripheral disease.

CONCLUSION

These clinical practice recommendations should help rheumatologists in their everyday decisions regarding the use of TNFalpha antagonist therapy in patients with AS or PsA.

A Mariner with Crippling Arthritis and Bleeding Eyes

A 41-year-old mariner developed acute arthritis affecting his legs more than his arms or hands during a violent storm on his return from the first of four voyages of discovery. He experienced repeated attacks of the arthritis over the ensuing 14 years, which on at least two occasions were accompanied by painful eyes "much affected with bleeding." He died shortly before his 55 birthday "quite paralyzed and bedridden." Who was he, and what was the likely etiology of his disorder?

A possible link between Crohn's disease and ankylosing spondylitis via Klebsiella infections

Crohn's disease (CD) is an immune-mediated gastrointestinal inflammatory disease, which could arise from an interplay between genetic and environmental factors. Klebsiella microbes were suggested to have a vital role in the initiation and perpetuation of the disease through the mechanism of molecular mimicry. This proposition is based on the results of various studies where significantly elevated levels of antibodies against the whole bacteria or preparations from Klebsiella microbes and antibodies to collagen types I, III, IV, and V were detected in patients with CD and patients with ankylosing spondylitis (AS). Molecular similarities were found between Klebsiella nitrogenase and HLA-B27 genetic markers and between Klebsiella pullulanase and collagen fibers types I, III, and IV. Furthermore, significantly positive correlations and cross-reactivity binding activities were observed between anti-Klebsiella and anticollagen antibodies among patients with CD and AS. Early treatment of CD patients with anti-Klebsiella measures is proposed, which may involve the use of antibiotics and low starch diet together with other traditionally used immunomodulatory, immunosuppressive, or biologic agents.

Spondyloarthropathy-Associated Aortitis and Massive Thickening of the Aortic-Mitral Curtain: Diagnosis by Echocardiography

Cardiac involvement in reactive arthritis is well-recognized, and usually results in aortic regurgitation, proximal aortitis, and conduction system abnormalities. Aortitis is usually recognized in conjunction with aortic regurgitation, but can be diagnosed in isolation as aortic root thickening and subaortic fibrous ridging. We report a case of spondyloarthropathy-associated aortitis diagnosed by transesophageal echocardiography. The case illustrates the aortic root pathology and highlights the unique morphologic echocardiographic feature of this condition, prominent thickening of the aortic-mitral curtain.

PSORS1: linking genetics and immunology

Previous studies have localized the psoriasis susceptibility 1 (PSORS1) locus to the proximal major histocompatibility complex class I region, but approximately a dozen genes in the candidate region have thus far been genetically inseparable. According to a team of researchers in the United States and Germany, the primary genetic association has now been worked out, implicating HLA-Cw6 "after all." The results integrate genetics and immunology, further reinforcing our emerging understanding of psoriasis.

Drug Insight: anti-tumor-necrosis-factor therapy for ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disorder of the spine and peripheral joints that can lead to significant disability if left untreated. Conventional treatments can be successful in alleviating symptoms; however, this approach has not been shown to halt the progression of disease. The proinflammatory cytokine tumor necrosis factor (TNF) is central to the pathogenesis of AS. Several anti-TNF drugs have been developed and have been shown to control symptoms effectively, and possibly to prevent both clinical and radiographic progression of disease, in patients with AS. This review discusses the data from clinical trials that have assessed the use of TNF inhibitors in patients with AS, and briefly outlines other biologic therapies that have been studied.

Newer Therapeutic Approaches: Spondyloarthritis and Uveitis

Over the last 5 years considerable progress has taken place in the therapeutic approach to spondyloarthritis (SpA). This progress is due in large part to the development of effective biologic therapies and to improved clinical trial design and implementation. This article summarizes treatment advances in SpA with emphasis on the efficacy and safety of biologic agents in the treatment of psoriatic arthritis, ankylosing spondylitis, undifferentiated spondyloarthropathy, and uveitis.

Peptic ulcer disease in a patient with ankylosing spondylitis receiving a conventional nonsteroidal anti-inflammatory drug

BACKGROUND

A 42-year-old man with a 10-year history of HLA-B27-positive ankylosing spondylitis presented with upper abdominal pain and nausea after receiving oral ketoprofen 200 mg/day. His gastrointestinal symptoms did not improve with the addition of ranitidine 150 mg twice daily. He had previously responded well to conventional nonsteroidal anti-inflammatory drugs.

INVESTIGATIONS

Physical examination, Bath Ankylosing Spondylitis Disease Activity Index, Bath Ankylosing Spondylitis Functional Index, radiography, laboratory tests, upper gastrointestinal endoscopy, histopathologic examination and culture of biopsy specimens.

DIAGNOSIS

Helicobacter pylori-positive duodenal ulcer.

TREATMENT

For eradication of H. pylori: omeprazole 20 mg twice daily, clarithromycin 500 mg twice daily and amoxicillin 1 g twice daily for 1 week. For ankylosing spondylitis: diclofenac 150 mg/day in combination with omeprazole 20 mg/day for 2 months.

Additional human β2-microglobulin curbs HLA–B27 misfolding and promotes arthritis and spondylitis without colitis in male HLA–B27–transgenic rats

OBJECTIVE

Ankylosing spondylitis and related spondylarthritides are associated with HLA-B27, and also with intestinal inflammation, by unknown mechanisms. The folded HLA-B27 molecule is a trimer of heavy chain, beta2-microglobulin (beta2m), and short peptide. However, B27 heavy chain has an unusual propensity to misfold and trigger the unfolded protein response (UPR). This study was initiated to test the hypothesis that B27 misfolding plays a role in the pathogenesis of spondylarthritis.

METHODS

Rats with high transgene copy numbers of HLA-B27 heavy chain together with human beta2m (Hubeta2m) spontaneously develop colitis, peripheral arthritis, and occasional spondylitis, and those with lower transgene copy numbers remain healthy. We crossed disease-prone and healthy HLA-B27/Hubeta2m-transgenic rat lines with a healthy line, 283-2, carrying only the Hubeta2m transgene. HLA-B27 assembly was assessed by pulse-chase analysis of B27 molecules, and UPR triggering was assessed by measuring BiP/Grp78 messenger RNA (mRNA) in splenic concanavalin A blasts. Surface expression of B27 and Hubeta2m was determined by flow cytometry. Disease manifestations were identified by clinical observation, histology, and measurement of cytokine mRNA.

RESULTS

The extra Hubeta2m from the 283-2 line significantly reduced B27 misfolding and UPR triggering. Unexpectedly, however, F1 male offspring of the healthy 21-3 line crossed with the 283-2 line showed a high prevalence, severity, and duration of arthritis and spondylitis, in the absence of colitis. The arthropathy showed many features characteristic of human spondylarthritis.

CONCLUSION

These results suggest that B27 misfolding is associated with intestinal inflammation, but that neither B27 misfolding nor intestinal inflammation is critical to the development of B27-associated arthropathy.