The role of killer-cell immunoglobulin-like receptor (KIR) genes in susceptibility to inflammatory bowel disease: systematic review and meta-analysis

Background Inflammatory bowel disease (IBD) is a chronic inflammatory disease, which involves the gut and comprises of Crohn’s disease (CD) and ulcerative colitis (UC). Immune cells, including natural killer (NK) cells, play an important role in the pathogenesis of the disease. Killer immunoglobulin-like receptors (KIRs) are NK cell surface receptors, which ligate to the class I major histocompatibility complex (MHC) and have inhibitory or activating effects on the NK cells. The aim of this study was to perform a meta-analysis of the six studies evaluating the association in the polymorphisms of these KIR genes and the IBD risk (4 UC and 5 CD studies). Methods A systematic search was conducted in the electronic databases to find all the studies on the KIR gene polymorphism in IBD patients prior to December 2017. The odds ratio (OR) and 95% confidence interval (CI) were used to find any association between KIR gene polymorphisms and the IBD risk. Results Following extraction of the data from the studies, which were screened by inclusion and exclusion criteria, collectively 432 patients and 886 controls for UC and 1677 patients and 1308 controls for CD were included in the meta-analysis. The statistical evaluation demonstrated positive associations between 2DL5 (OR=1.31, 95% CI=1.01–1.69) and 2DS1 (OR=1.33, 95% CI=1.01–1.76) members of KIR genes and UC risk, as well a negative association between 2DS3 gene and CD risk was detected (OR=0.74, 95% CI=0.60–0.90). Conclusions There are positive associations between 2DL5 and 2DS1 members of KIR genes and UC risk and a negative association between 2DS3 and CD risk.