PANCREATIC TUMOR-MARKER ANTI-MUCIN ANTIBODY CAM-17.1 REACTS WITH A SIALYL BLOOD-GROUP ANTIGEN, PROBABLY I, WHICH IS EXPRESSED THROUGHOUT THE HUMAN GASTROINTESTINAL-TRACT

CAM 17.1 is an antimucin monoclonal antibody which has recently been p roven valuable as a reagent for serological diagnosis of pancreatic ca ncer. A series of studies have been performed to characterise its epit ope. First it was screened immunohistochemically against a wide range of formalin-fixed normal and neoplastic human tissues and showed wides pread binding to mucin throughout the gastro-intestinal tract, in both normal and malignant tissues. In pancreas, strong intracellular stain ing of acinar and ductal cells was found in normal tissue and in carci noma cells in tumours. Normal stomach showed only weak staining (n = 6 ), but gastritis with metaplasia showed strong staining (n = 4). Stain ing of colonic mucosa from patients of known Lewis phenotype showed Le (a+b-) (7/8) and Le(a-b+) (4/6) samples to be positive, but not Le(a-b -) (0/3) samples. CAM 17.1 agglutinated all donor erythrocytes tested at 4 degrees C regardless of blood group, whereas cord blood red cells were not agglutinated. Since I antigen is the only antigen known to b e present on all adult red blood cells but absent from cord blood, thi s suggests probable involvement of this antigen in the binding site. T he agglutination was abolished by sialidase treatment of the red cells and immunoblotting with slot-blotted mucin showed that binding was bo th acid and sialidase sensitive indicating the involvement of sialic a cid in the binding site. These studies show that CAM 17.1 binds to a s ialic-acid-containing determinant of mucin, probably sialyl-I, which e pitope shows wide distribution throughout the gastro-intestinal tract.