MHC antigen expression in colorectal tumours.

This article reviews abnormalities in the expression of major histocompatibility antigens in colorectal neoplasia. These include the loss of HLA-A, B, C antigens and the loss of HLA-D antigen inducibility. Since these abnormalities are not seen in normal colorectal epithelium they are probably selected for during tumour progression. The crucial role of HLA-A, B, C and HLA-D molecules in the presentation of foreign antigens to the immune system suggests that their loss could directly confer a selective growth advantage to tumour cells expressing tumour specific antigens, through resistance to anti-tumour lymphocyte attack. The possible relationships between abnormalities in tumour HLA antigen expression and the presence of tumour specific antigens are discussed.