Expression of CA19-9, DU-PAN-2, and SPan-1 antigens on two types of normal salivary mucins.

Mucins are important in cancer diagnosis and therapy. A better understanding of the characteristics of mucins in normal and malignant tissues could make them more effective clinical targets. Levels of the sialylated carbohydrate mucin antigens CA19-9, DU-PAN-2, SPan-1, and TAG-72 are elevated in sera from patients with pancreatic cancer. In this study we examined normal saliva for the presence of these antigens. TAG-72 reactivity was not detected in the samples examined. SPan-1 expression correlated with the expression of CA19-9 except in Le(a)- individuals. In these individuals CA19-9 was absent; SPan-1 was expressed to varying degrees. Little, if any, reactivity was detected with four monoclonal antibodies directed against the MUC1 mucin peptide. A high-buoyant-density-fraction (1.35 to 1.55 g/mL) of normal saliva, containing most of the sialic acids and O-linked oligosaccharides, was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Western blots showed that CA19-9, DU-PAN-2, and SPan-1 antigens were found on two forms of mucins. DU-PAN-2 reactivity was detected only in the absence of the sulfhydryl reducing agent beta-mercaptoethanol. The two main forms of antigens differed in molecular size (150 kDa and greater than 400 kDa) and buoyant density (1.38 and 1.49 g/mL) and have been reported to differ in amino-acid composition. In colon or pancreas, the CA19-9, DU-PAN-2, and SPan-1 carbohydrate structures have been reported to be present on the MUC1 mucin peptide. Our present results suggest that in saliva, these carbohydrate antigens may be found on mucin peptides other than MUC1.