HLA-DR antigen expression in macroscopically uninvolved areas of intestinal epithelia in Crohn's disease

HLA-DR antigens in small and large intestinal epithelia were examined in Crohn's disease (CD). Seventy-two biopsy specimens (10 from the duodenum, 18 from the terminal ileum, and 44 from various sites of the large intestine) were obtained from 5 patients with CD chronologically; before treatment, during elemental diet (ED) treatment, and during home elemental enteral hyperalimentation (HEEH). HLA-DR antigens on the intestinal epithelia were identified by the indirect immunoperoxidase staining method using two mouse anti-HLA-DR monoclonal antibodies. In the small intestine, HLA-DR antigens were expressed differently from normal controls in macroscopically or microscopically pathological areas, but not in macro- or microscopically normal areas. In the large intestine, when the disease was in full vigor before treatment, HLA-DR antigens were always aberrantly expressed even in the macroscopically uninvolved areas, as well as in macroscopically involved areas. However, when the disease was suppressed after ED followed by HEEH treatment, the antigens were not always expressed in the macroscopically uninvolved areas, or in the macroscopically involved areas. These findings suggest that HLA-DR antigens are not merely expressed as a non-specific response to inflammation, but may be expressed as a primary change which results in macroscopic lesions. The possible role of HLA-DR antigens in the immunological mechanism in CD is proposed.