Characterization of OM‐B Monoclonal Antibody‐defined Antigen Associated with Mucinous Type Human Ovarian Tumor

Partial characterization of the OM‐B antigen associated with mucinous‐type ovarian tumors was conducted. This antigen was defined by OM‐B monoclonal antibody, which was raised against a mucinous‐type ovarian tumor, and was present in all the mucinous‐type tumors tested, but only a fraction of serous‐type tumors. The OM‐B crude antigen preparation fractionated from cystic fluids had a density of 1.40–1.43 g/ml, with a high neutral sugar content. Molecular mass (Mr) estimated by gel filtration was more than 2,000,000. Trypsinization of the antigen preparation under appropriate conditions resulted in two major bands and one minor band with molecular sizes of less than Mr 250,000, as detected by immunoblotting. Immunoaffinity chromatography was then conducted and the amino acid composition of the purified product was determined; the high contents of serine, threonine and proline are characteristic of a mucin. Binding inhibition enzyme‐linked immunosorbent assay was developed to measure OM‐B antigen activity in cystic fluids and sera from patients with mucinous‐type tumors. The antigen was easily detected in most cystic fluids, but not in sera, suggesting that improvement in the sensitivity of this assay is necessary before its utilization for serum diagnosis will be feasible.