Decreased expression of protectin (CD59) in gut epithelium in ulcerative colitis and Crohn's disease.

Without adequate protection, the cells of the human body would be susceptible to destruction by the complement system. The main defense against complement lysis is a molecule called protectin (CD59) that is widely distributed in human tissues. Because the complement system has been suggested to be involved in the pathogenesis of inflammatory bowel diseases, we examined the expression of protectin in the colonic epithelium of patients with ulcerative colitis or Crohn's disease and controls. Colorectal specimens from 6 patients with ulcerative colitis, 8 patients with Crohn's disease, and 4 controls were obtained from surgical resections. Frozen sections of the specimens were immunostained for protectin using the Bric 229 monoclonal antibody. The expression of protectin was found to be decreased in the epithelium of patients with ulcerative colitis. In patients with Crohn's disease, the epithelial expression of protectin was decreased in diseased areas of gut while the expression did not significantly differ from that in controls in macroscopically normal areas. There was no difference in the expression of protectin on vascular endothelium, mononuclear cells, or smooth muscle. The reduction in epithelial expression of protectin in patients with ulcerative colitis or Crohn's disease may render epithelial cells vulnerable to complement lysis and lead to the destruction of gut epithelium as seen typically in these diseases.