Further studies of HLA-DR antigens on colonic epithelium in ulcerative colitis.

The aim of this study was to determine whether HLA-DR antigens are expressed on colonic epithelium in macroscopically involved areas in all cases of ulcerative colitis and whether the expression precedes inflammation (colitis). Thirty-four cases of active ulcerative colitis were studied including two cases in which island-like lesions were observed proximally apart from the main lesion, and three cases in which distal colitis became entire colitis in 8 months or less. Detection of HLA-DR antigens on colonic epithelium was performed with the immunoperoxidase method using anti-HLA-DR monoclonal antibodies. HLA-DR antigens were expressed on colonic epithelium in macroscopically involved areas in all 34 cases. In the macroscopically normal areas, the antigens were modestly expressed in six of 16 specimens (cases) in the presence of microscopic inflammation. The antigens were expressed on colonic epithelium in island-like lesions, but not in the intervening mucosa between the proximal island-like lesions and the distal main lesion. HLA-DR antigens were not expressed on colonic epithelium in the proximal non-inflamed mucosa where colitis later developed. These results lead to the conclusion that HLA-DR antigen expression does not precede, but is associated with the inflammation.