HLA-DR ANTIGEN EXPRESSION IN COLONIC ADENOMAS AND ADENOCARCINOMAS

Previous studies have shown that malignant transformation is sometimes associated with the aberrant expression of HLA class II antigens. The functional significance of such aberrant expression is not known. Sin ce HLA-DR antigen is expressed in normal colonic mucosa, it would be i nteresting to see if malignant transformation could result in the aber rant suppression of this antigen. Sixteen colonic adenocarcinomas, 29 colonic adenomatous polyps and 23 samples of normal colonic mucosa, in cluding 9 cases of colonic mucosa adjacent to carcinoma, were stained immunohistochemically for HLA-DR antigen. The intensity and distributi on of the antigen staining in the cytoplasm and luminal surface of the epithelial elements were analysed semiquantitatively. The lymphoplasm acytic infiltrate in the lamina propria was also evaluated. Cytoplasmi c HLA-DR antigen expresion was found to be significantly diminished in moderately and poorly differentiated adenocarcinomas but not in adeno mas or well-differentiated adenocarcinomas, This suggests that the cha nge in HLA-DR expression is not intrinsic to the neoplastic process bu t may merely be due to the fact that malignant cells, as they become l ess differentiated, tend to show alterations in their antigenic phenot ype.