Association between KIR-HLA combination and ulcerative colitis and Crohn's disease in a Japanese population

Inflammatory bowel disease (IBD) consists of ulcerative colitis (UC) and Crohn's disease (CD). Natural killer cell responses play a crucial role in autoimmune disease through innate immunity, in which killer cell immunoglobulin-like receptors (KIRs) are closely involved. Although the genetic combination of KIRs with their specific HLA class I ligands has been associated with IBD in Caucasians, such KIR-HLA receptor-ligand combinations are not fully understood in the Japanese. We investigated 14 KIR genes along with HLA-Bw and -C ligands in 90 patients with UC and 50 patients with CD and compared them with the characteristics of 325 healthy control subjects. The frequency of HLA-Bw4 was significantly increased in patients with UC (P = 1.3 × 10-6; odds ratio [OR] = 3.39) and CD (P = 0.0065; OR = 2.32) versus controls. The UC group had a significantly higher frequency of KIR2DS3 (P = 0.024; OR = 1.94) and lower frequency of KIR2DS4 (P = 0.019; OR = 0.40) and KIR2DL1-HLA-C2 (P = 0.035; OR = 0.47). The Tel-A/B haplotype was significantly decreased in UC patients (P = 0.0056; OR = 0.49). The frequency of KIR3DL1-HLA-Bw4 was significantly higher in patients with UC (P = 4.3 × 10-6; OR = 3.12) and CD (P = 0.0067; OR = 2.30). In conclusion, HLA-Bw4 and KIR-HLA pairs may play an important role in the genetic susceptibility to IBD in the Japanese.