Ca 125 and Ca 19–9: two cancer‐associated sialylsaccharide antigens on a mucus glycoprotein from human milk

Abstract

The cancer‐associated antigens Ca 125 and Ca 19–9 were demonstrated by radioimmunoassay to form structural units of a mucus glycoprotein in human milk taken from healthy women four days after parturition. The glycoprotein precipitated with the casein fraction at pH 4.6 and was completely absent in the whey as judged from Ca 19–9 assay. It could be effectively enriched by phenol‐saline extraction from soluble milk proteins and further purified by gel filtration on Sephacryl S300 and Sephacryl S400. The active component with a bouyant density of 1.41 g/ml in isopycnic density gradient centrifugation (CsCl) shared common physico‐chemical and chemical characteristics of mucus glycoproteins. Carbohydrates representing about 68% by weight were conjugated to protein by alkali‐labile linkages, exclusively and were essentially free of d‐mannose. Activities of Ca 125 and Ca 19–9 were both destroyed by treatment with periodate, mild alkali or neuraminidase suggesting the antigens are sialylated saccharides bound to protein by alkali‐labile linkages. The fraction of monosialylated saccharide alditols isolated after reductive β‐elimination from the mucus glycoprotein was shown to inhibit monoclonal antibodies anti‐(Ca 125) and anti‐(Ca 19–9) in radioimmunoassay.