Upregulated mRNA expression of major histocompatibility complex class I chain‐related gene A in colon and activated natural killer cells of Chinese patients with ulcerative colitis

OBJECTIVE:  To explore the expression of major histocompatibility complex class I chain-related gene A (MICA) and its ligand in colonic mucosa and the role of MICA-natural killer (NK) group 2D (NKG2D) interaction in activating NK cells in ulcerative colitis (UC) patients. METHODS:  Intestinal mucosal biopsies were obtained from patients with UC and the controls. The expression of major histocompatibility complex class I-related gene (MIC) genes was determined by a reverse transcription polymerase chain reaction (RT-PCR) and the imaging of MICA expressed on colonic mucosa was measured by confocal microscopy resonance scanning. NKG2D and intracellular interferon (IFN)-γ expressions on NK cells were assayed by flow cytometry. RESULTS:  The relative amount of MICA mRNA in the colonic mucosa of UC patients was significantly higher than in that of the controls (3.5408 ± 2.6658 vs 1.0477 ± 0.7201, P = 0.001), as were the major histocompatibility complex class I chain-related gene B (MICB) (8.9879 ± 3.2893 vs 4.6293 ± 1.2616, P < 0.001) and NKG2D mRNA expression (2.4395 ± 0.8147 vs 1.1624 ± 0.3954, P < 0.001). Confocal microscopy resonance scanning had shown that MICA was localized predominantly on the basolateral membranes of the epithelium. Further flow cytometry confirmed that the percentage of IFN-γ producer NK cells that expressed NKG2D in peripheral blood lymphocytes was higher in UC patients than in the healthy controls (45.36% ± 12.47% vs 27.45% ± 9.30%, P < 0.001). CONCLUSION:  MICA, MICB and NKG2D were upregulated in the colonic mucosa of UC and were associated with activating NK cells with promoted NKG2D and IFN-γ production.