TUMOR-ASSOCIATED SIALYLATED ANTIGENS ARE CONSTITUTIVELY EXPRESSED IN NORMAL HUMAN COLONIC MUCOSA

Immunohistochemical studies have indicated that sialylated carbohydrat e antigens such as sialyl-Tn, sialyl-le(a), and sialyl-Le(x) are expre ssed in a tumor-associated fashion in human colon, Since sialic acid r esidues are O-acetylated more extensively in normal colonic epithelium than in colon cancer cells, we examined whether deacetylation of colo nic tissues might enable monoclonal antibodies to recognize these tumo r-associated sialylated antigens, In normal colon, deacetylation turne d most cases (82%) positive with anti-sialyl-Tn mAb TKH2; and in colon cancers, it increased the number of TKH2-positive cells, Sialyl-Le(a) and sialyl-Le(X) detection was also increased after deacetylation of normal and malignant colonic tissues so that the frequency of positive cases in normal tissues was similar to that in the cancers, However, in the stomach and pancreas, the same treatment rarely increased the d etection of the sialylated epitopes in normal or cancerous tissues, Th us, the same sialylated epitopes can be expressed in a tumor-associate d fashion by different mechanisms in different gastrointestinal organs ; in the colon, these antigens are constitutively expressed and O-acet ylated, whereas in the upper gastrointestinal tract, they are rarely O -acetylated, suggesting that other mechanisms such as differences in g lycosylation account for the cancer-associated expression.