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Physicochemical purification and immunological characteristics of ductal carcinoma antigen

Ductal carcinoma antigen (DCA), as recognized by monoclonal antibody (MAb) F36/22, was purified in high yield and to homogeneity from malignant effusions by means of physicochemical techniques. Fractionation procedures were monitored by immunoenzymometric assays. Preparations purified over 2,000‐fold were obtained through acid‐extraction, lectin‐chromatographies and gel filtration steps. Purified antigen demonstrated a single component upon electrophoretic examination. This material had a high molecular weight and high immunoreactivity. Neuaminidase treatments failed to perturb the antigenicity of the component, indicating an absence of sialic acid residues at the antibody‐combining site. Further, extensive proteolytic digestion effected the release of heterogeneous glycopeptides which retained immunologic activity, suggesting the presence of carbohydrate at the active site. Immunologically, DCA was compared with other tumor‐associated mucin‐like gly‐coproteins which have been detected in the circulation of patients. Results indicated no cross‐reactivity between DCA and other mucins, including CA 19–9 and CA‐125. Further, no antigenic relationship was noted for purified carcinoembryonic antigen (CEA), also a heavily‐glycosylated structure. These data thus suggest that immunological monitoring of disease may be approached using a selected panel of antigenically distinct reagents.