High resolution MIC genotyping: Design and application to the investigation of inflammatory bowel disease susceptibility

Abstract:The highly polymorphic nonclassical MHC class I chain‐related (MIC) genesMICAandMICBencode stress inducible glycoproteins expressed on a variety of epithelial cells including intestinal cells. Interaction with the receptor NKG2D is likely to provide an important costimulatory signal for activation and proliferation of NK cells, activated macrophages and CD8 αβ and γδ T cells. Fifty‐fourMICAand 17MICBalleles have been described to date. Although the functional significance of this polymorphism is not known, the high degree of nonconservative substitution, concentration to the putative ligand‐binding site and recent observation that differentMICAalleles bind to NKG2D with varying affinity has generated much interest. TheMICgenes are attractive functional and positional candidate genes for inflammatory bowel disease susceptibility as a consequence of their position in the HLA region and expression on the gastrointestinal epithelium. We developed a robust, high‐resolution PCR‐SSP genotyping method that can be incorporated into the standard ‘Phototyping’ system and which effectively identifies 46 of 54MICAalleles, and all 17MICBalleles. We applied this system in combination with microsatellite genotyping of the exon 5 variable number of tandem repeats (VNTR) to the investigation of genetic susceptibility to the inflammatory bowel diseases, ulcerative colitis and Crohn's disease. We studied 248 patients with Crohn's disease, 329 with ulcerative colitis and 354 ethnically matched controls. Linkage disequilibrium patterns between HLA‐B,MICAandMICBare presented. Analysis by individual allele or by multilocus haplotype failed to identify any significant disease associations.