Increased HLA-G Expression in Tissue-Infiltrating Cells in Inflammatory Bowel Diseases

Since HLA-G is an immune checkpoint molecule and since Crohn's disease (CD) and ulcerative colitis (UC) exhibit deregulated immune-mediated mechanisms, we aimed to evaluate intestinal HLA-G expression and soluble HLA-G (sHLA-G) levels in CD/UC patients stratified according to the CD phenotype/localization and UC extension.

HLA-G tissue expression was assessed by immunohistochemistry in biopsies collected from 151 patients (90 CD, 61 UC) and in surgical resection specimens (28 CD, 12 UC). Surgical material from 24 healthy controls was also assessed. Plasma sHLA-G levels (97 CD, 81 UC, and 120 controls) were evaluated using ELISA.

HLA-G expression was similarly observed in the intestinal epithelial cells of control and CD/UC specimens. However, in biopsies, the plasma cells/lymphocytes infiltrating the lamina propria in CD/UC presented (1) increased HLA-G expression compared to controls (P < 0.0001), (2) greater cell staining in UC cells than in CD cells irrespective of disease extent (P = 0.0011), and (3) an increased number of infiltrating cells in the inflammatory CD phenotype compared to that in the stenosing and fistulizing phenotypes (P = 0.0407). In surgical specimens, CD/UC patients exhibited higher infiltrating cell HLA-G expression in lesion areas than in margins. sHLA-G levels were higher in UC/CD patients (P < 0.0001) than in controls, but no difference was observed between diseases.

Increased infiltrating cell HLA-G expression associated with increased sHLA-G levels in CD/UC patients may reflect ongoing host strategies to suppress chronic inflammation.