Expression of MHC class II products on human colorectal cancer. An immunohistological and flow cytometric study.

The MHC status of epithelial cells from 32 primary colorectal neoplasms, villous adenomata (VA; 2) and inflammatory bowel disease (IBD; 3) were evaluated using a panel of monoclonal antibodies (mAbs). Class I antigens and beta 2 microglobulin (beta 2m) were expressed on all normal, benign, inflammatory and malignant epithelia with the exception of two carcinomas. A more complex pattern of reactivity was encountered with anti-class II mAbs. Some expression was detected on normal glandular and luminal epithelium, particularly adjacent to the tumour. Inflammatory tissues, VA and 23/32 carcinomas were also antigen-positive, the proportion of stained epithelial cells ranging from 5% to 90%. Expression was usually non-coordinate, DR being the predominant specificity followed by DP and DQ, which is suggestive of independent D region gene regulation. The hypothesis that class II expression is induced in vivo by locally generated IFN gamma was not confirmed by in vitro treatment with this agent of epithelial colorectal carcinoma-derived cell lines. These provisional data suggest that although IFN gamma may be a necessary stimulus for class II expression it is insufficient and that other factors also influence the responsiveness of tumour cells in this respect.