Interleukin-21 Polymorphism Affects Gene Expression and is Associated with Risk of Ischemic Stroke

There has been more and more evidence to confirm the essential role of inflammatory processes in the development of ischemic stroke. Interleukin-21 (IL-21), the most recently discovered CD132-dependent cytokine, plays a key role in regulating inflammation. The aim of the study was to understand the association between IL-21 polymorphisms and ischemic stroke, and the effects of these polymorphisms on gene expression. Two polymorphisms in IL-21, rs907715G/A and rs4833837A/G, were identified in 278 ischemic stroke patients and 282 healthy controls. Results showed that frequencies of rs907715GA and AA genotypes were significantly increased in cases than in controls (odd ratio (OR) = 1.49, 95 % confidence interval (CI): 1.01–2.14, P = 0.042; OR = 2.21, 95 % CI: 1.38–3.53, P = 0.001). Similarly, rs907715A allele revealed a positive association with the disease (OR = 1.52, P = 0.001). The rs4833837A/G polymorphism did not show any correlation with ischemic stroke. We further evaluated IL-21 messenger RNA (mRNA) and protein levels in peripheral blood mononuclear cells (PBMCs) from subjects carrying different polymorphism genotypes. Results revealed that subjects carrying polymorphic rs907715GA and AA genotypes had significantly higher IL-21 mRNA levels, whereas protein level was increased only in subjects with rs907715AA genotype. Serum level of IL-21 was also significantly elevated in subjects with rs907715AA genotype. These data suggest that IL-21 polymorphism is associated with increased susceptibility to ischemic stroke possibly by upregulating gene expression.