Differential expression of HLA‐D gene products in the normal and coeliac small bowel

Monoclonal antibodies to monomorphic determinants of the MHC class II region products, HLA‐DR, DP and DQ were used to investigate their expression on cells of the normal and coeliac (both treated and untreated) small bowel. HLA‐DR antigens showed a characteristic distribution in the normal small bowel: epithelial cells in the apical portions of the villi stained heavily, and this staining decreased in intensity towards the villous base. The crypt epithelial cells were clearly unstained. Stellate cells within the lamina propria were also HLA‐DR positive. HLA‐DP antigens showed a similar distribution, although the intensity of staining was less than that seen with HLA‐DR. HLA‐DQ antigens were absent from epithelial cells and were confined solely to cells within the lamina propria. In untreated coeliac disease, the intensities of both HLA‐DR and HLA‐DP were increased, and in addition a more extensive distribution of these antigens was observed. In addition to occurring on the surface epithelial cells, DR and DP antigens were now present on crypt epithelial cells. Despite this change in expression of DR and DP antigens, the distribution of HLA‐DQ was essentially unaltered from that of the normal small bowel. The findings in treated coeliac disease were intermediate between those in the normal and untreated coeliac small bowel. The differential expression of class II antigens by normal and diseased small bowel epithelium which has been demonstrated may have implications for interactions of these cells with cells of the immune system.