Normal salivary mucin contains the gastrointestinal cancer-associated antigen detected by monoclonal antibody 19-9 in the serum mucin of patients.

Monoclonal antibody 19-9 produced by a hybridoma prepared from spleen cells of a mouse immunized with a human colon carcinoma cell line, detects an antigen in sera from many patients with gastrointestinal and pancreatic cancer. This antibody is directed against a carbohydrate with the sugar sequence (Formula: see text) In many gastrointestinal and pancreatic cancers this sequence occurs in a monosialoganglioside containing a sialylated Lea-active pentasaccharide (sialylated lacto-N-fucopentaose II, IV3-alpha-NeuNAc-III4-alpha-Fuc-LcOse4). In the sera of cancer patients the antigen occurs as a mucin. The antigen is also found in salivary mucin from many normal individuals belonging to the Le(a+b-) or Le(a-b+) blood group but not in salivary mucin from normal individuals belonging to the Le(a-b-) blood group. There is more antigen in mucin from individuals belonging to the Le(a+b-) blood group than in mucin from individuals belonging to the Le(a-b+) blood group.