Interactions between IL17A, IL23R, and STAT4 polymorphisms confer susceptibility to intestinal Behcet's disease in Korean population

Abstract

Aims

Although polymorphisms in IL23R have recently been proposed to predispose to Behcet's disease (BD), associations between IL23R polymorphisms and intestinal BD have yet to be elucidated. We therefore performed a study to evaluate whether IL17A, IL23R, and STAT4 polymorphisms are associated with susceptibility to intestinal BD in the Korean population.

Main methods

Single nucleotide polymorphisms (SNP) in the IL17A, IL23R, and STAT4 genes were analyzed using DNA sequencing, denaturing high performance liquid chromatography, and TaqMan genotyping assays.

Key findings

Individual polymorphism analysis revealed that the TT genotype of IL17A rs8193036 (odds ratio (OR) 2.10, 95% confidence interval (CI) (1.12–3.92), p = 0.021), and GG + GT genotype of IL23R rs1884444 (OR 1.92, 95% CI (1.03–3.57), p = 0.034) was associated with the development of intestinal BD. When these two genotypes were combined, the risk of BD increased compared to that of patients with no-risk or one-risk genotype (OR 2.21, 95% CI (1.13–4.34), p = 0.021). Furthermore, statistically significant gene–gene interactions were observed between G149R in IL23R vs. rs11685878 in STAT4, rs2275913 in IL17A vs. rs7574865 in STAT4, and rs11889341 in STAT4 vs. rs2275913 in IL17A. The haplotypes of IL17A had a positive association with intestinal BD risks, whereas those of IL23R were protective for disease development.

Significance

Our results indicate that the interaction of specific IL17A, IL23R, and STAT4 SNPs modulate susceptibility to intestinal BD in the Korean population, suggesting that the IL-17/23 axis plays a significant role in disease pathogenesis.

Introduction

Behcet's disease (BD) is a multi-systemic, chronic relapsing inflammatory disorder characterized by recurrent ulcerations of the oral cavity and genitalia as well as ocular inflammation. Other organ involvement such as the skin, joints, blood vessels, gastrointestinal tract, and central nervous system may occur concurrently. This disease is predominantly found in East Asia and in the Mediterranean countries and is relatively uncommon in the United States and Northern Europe (Dilsen, 1996, James, 1979). Although epidemiologic studies have shown that the development of the disease might be attributable to both genetic and environmental factors, the exact etiology has yet to be fully identified (Sakane et al., 1999). The disease can be classified as “intestinal BD” when patients with BD present with gastrointestinal symptoms and show typical intestinal ulcerations (Baba et al., 1976, Kasahara et al., 1981). While the prevalence of intestinal BD varies from 3 to 16% of all patients with BD by area, it appears to be more prevalent in East Asian countries (Kobayashi et al., 2007). The most frequent clinical symptom of intestinal BD is abdominal pain, followed by bleeding and diarrhea (Cheon et al., 2009). The most common site of involvement in the gastrointestinal tract is the ileocecal area, and lesions typically appear as ovoid-shaped deep ulcers with discrete borders (Lee et al., 2001, Sakane et al., 1999). Because of its scarcity and the lack of clinical evidence, it has been a great challenge for clinicians to make an accurate diagnosis of intestinal BD. Given the chronologic delay in systemic manifestations of BD, we have argued that the patients who do not fully satisfy the diagnostic criteria of systemic BD should be included in the category of intestinal BD patients when typical intestinal lesions are identified, and we have reported previously regarding this issue (Cheon et al., 2009, Shin et al., 2010).

The cytokines IL-23 and IL-17 are essential inflammatory mediators of various autoimmune pathologies such as multiple sclerosis, rheumatoid arthritis (RA), psoriasis, and Crohn's disease (CD). IL-23 is produced mainly by antigen-presenting dendritic cells and macrophages. IL-23 drives and promotes the development of a unique T-helper cell population (Th17 cells) that produces IL-17. These IL-23-driven Th17 cells are highly pathogenic and elicit IL-17-dependent inflammation in autoimmune diseases (Langrish et al., 2005). This effect of IL-23 is mediated through the IL-23 receptor (IL-23R), which is a heterodimer of the IL-12RB1 subunit. IL-17 is a pleiotropic inflammatory cytokine that plays a pivotal role in a variety of pathologic conditions by inducing numerous inflammatory molecules and the recruitment of neutrophils (Kolls and Linden, 2004). IL-17 expression is increased in patients with CD, ulcerative colitis (UC), RA, asthma, and BD compared to healthy individuals (Chabaud et al., 1999, Fujino et al., 2003, Hamzaoui et al., 2002, Linden, 2001, Lubberts et al., 2001, Zhang et al., 2006). In addition, serum IL-17A levels increase in active BD patients, suggesting that Th17 and IL-17 pathway has an important role in acute attacks of the disease (Ekinci et al., 2010). The signal transducer and activator of transcription 4 (STAT4) protein regulates the immune response by transmitting signals activated in response to several cytokines such as IFN, IL-12, and IL-23 (Watford et al., 2004). Furthermore, STAT4 is essential for the expansion of Th17 cells activated by IL-23, which perpetuates chronic inflammation in adaptive and innate immune responses and contributes to the development of many autoimmune diseases (Mathur et al., 2007). Taken together, it can be postulated that interactions among IL17, IL23R, and STAT4 variants may be involved in the pathogenesis of autoimmune diseases such as BD.

Recently, genome-wide association (GWA) studies have revealed that variants in IL10 and IL23R-IL12RB2 are associated with BD (Mizuki et al., 2010, Remmers et al., 2010). Other studies have also identified a strong relationship between polymorphisms of IL23R and IL17 and BD (Jang et al., 2008, Jiang et al., 2010). However, to the best of our knowledge, no studies on genetic variants in intestinal BD have been conducted to date. Therefore, our aim in this study was to evaluate the association between polymorphisms of IL17A, IL23R, and STAT4 genes and susceptibility to intestinal BD in the Korean population. Furthermore, we assessed the relationships between these genetic variants and disease phenotypes.