Stuart I. Davidson

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.

Association of ERAP1, but not IL23R, with ankylosing spondylitis in a Han Chinese population

OBJECTIVE The results of a recent genome-wide association study have shown that ERAP1 and IL23R are associated with ankylosing spondylitis (AS) in Caucasian populations from North America and the UK. Based on these findings, we undertook the current study to investigate whether single-nucleotide polymorphisms (SNPs) covering the genes ERAP1 and IL23R are associated with AS in a Han Chinese population. METHODS A case-control study was performed in Han Chinese patients with AS (n = 527) and controls (n = 945) from Shanghai and Nanjing. All patients met the modified New York criteria for AS. The Sequenom iPlex platform was used to genotype cases and controls for 21 tag SNPs covering IL23R and 38 tag SNPs covering ERAP1. Statistical analysis was performed using the Cochran-Armitage test for trend. RESULTS Multiple SNPs in ERAP1 were significantly associated with AS (for rs27980, P = 0.0048; for rs7711564, P = 0.0081). However, no association was observed between IL23R and AS (for all SNPs, P > 0.1). The nonsynonymous SNP in IL23R, rs11209026, widely thought to be the primary AS-associated SNP in IL23R in Europeans, was found not to be polymorphic in Chinese. CONCLUSION Our results demonstrate that genetic polymorphisms in ERAP1 are associated with AS in Han Chinese, suggesting a common pathogenic mechanism for the disease in Chinese and Caucasian populations, and that IL23R is not associated with AS in Chinese, indicating a difference in the mechanism of disease pathogenesis between Chinese and Caucasian populations. This may result from the fact that rs11209026, the nonsynonymous SNP in IL23R, is not polymorphic in Chinese patients, providing further evidence that rs11209026 is the key polymorphism associated with AS (and likely inflammatory bowel disease and psoriasis) in this gene.

Association of STAT3 and TNFRSF1A with ankylosing spondylitis in Han Chinese

Objectives Recent association studies by the Australo-Anglo-American Spondyloarthritis Consortium (TASC) in Caucasian European populations from Australia, North America and the UK have identified a number of genes as being associated with ankylosing spondylitis (AS). A candidate gene study in a Han Chinese population was performed based on these findings to identify associated genes in this population. Methods A case-control study was performed in a Han Chinese population of patients with AS (n=775) and controls (n=1587) from Shanghai and Nanjing. All patients met the modified New York criteria for AS. The cases and controls were genotyped for 115 single nucleotide polymorphisms (SNPs) tagging IL23R, ERAP1, STAT3, JAK2, TNFRSF1A and TRADD, as well as other confirmation SNPs from the TASC study, using the Sequenom iPlex and the ABI OpenArray platforms. Statistical analysis of genotyped SNPs was performed using the Cochran–Armitage test for trend and meta-analysis was performed using METAL. SNPs in AS-associated genes in this study were then imputed using MaCH, and association with AS tested by logistic regression. Results SNPs in TNFRSF1A (rs4149577, p=8.2×10−4), STAT3 (rs2293152, p=0.0015; rs1053005, p=0.017) and ERAP1 (rs27038, p=0.0091; rs27037, p=0.0092) were significantly associated with AS in Han Chinese. Association was also observed between AS and the intergenic region 2p15 (rs10865331, p=0.023). The lack of association between AS and IL23R in Han Chinese was confirmed (all SNPs p>0.1). Conclusions The study results demonstrate for the first time that genetic polymorphisms in STAT3, TNFRSF1A and 2p15 are associated with AS in Han Chinese, suggesting common pathogenic mechanisms for the disease in Chinese and Caucasian European populations. Furthermore, previous findings demonstrating that ERAP1, but not IL23R, is associated with AS in Chinese patients were confirmed.

The genomics and genetics of ankylosing spondylitis

The spondyloarthropathies are a group of arthritides which specifically target the spine and pelvis with ankylosing spondylitis (AS) being the most prevalent and debilitating of these conditions. Unique to AS is the progression to excessive uncontrolled bone formation following an initial inflammatory phase that can result in joint fusion and significant disability. Spondyloarthritis is estimated to affect 1%–2% of the population, twice as many as rheumatoid arthritis and thus constitutes a significant health problem. Currently AS pathogenesis is very poorly understood but recent large-scale genetics and gene expression profiling studies have identified some of the underlying mechanisms and pathways contributing to the disease. Genome-wide association studies have identified a number of candidate genes associated with AS sharing the same pathways which are now being targeted for therapeutic intervention. However, although such approaches can identify genes contributing to the disease process and are very informative as to disease aetiopathogenesis, they cannot profile the actual changes in gene/cell activity at any point in the disease process or possibly more importantly at specific sites. Such information is generated using expression profiling. A number of expression profiling studies have been undertaken in AS, looking at both circulating cells and tissues from affected joints. Although some common genes/pathways have been identified, overall the results to date have been somewhat disappointing due to differences in experimental design and tissue source as well as the low power of the studies. More recent better powered studies have shown some potential in developing gene expression profiling as a diagnostic tool in AS. True future success will rely on larger genetic and genomic studies and the combination of these datasets in eQTL studies requiring significant collaborative efforts. Such larger-scale approaches will also generate sufficient power to target specific disease stages and sites.