Monoclonal antibodies in analysis of oncoplacental protein SP1 in vivo and in vitro.

Three monoclonal antibodies were developed to the placenta-specific glycoprotein SP1. The antibodies were used in the characterization of SP1 in placental tissue, pregnancy serum and urine, cancer serum, and cell culture. The three antibodies reacted similarly with purified SP1 of placental origin in radio- and enzyme immunoassay, and all three decorated the syncytiotrophoblast layer of placental villi in immunoperoxidase staining applied to fixed placental tissue. However, the three antibodies were found to have different and unique specificities and affinities. One antibody of relatively low affinity was used to isolate SP1 from placenta and fibroblast culture medium. The other two antibodies were used to develop a new and simple immunoassay for SP1. A panel of samples including cancer sera, pregnancy sera and urine, as well as cell culture fluids gave similar results in the monoclonal assay as in a conventional radioimmunoassay. Our work with monoclonal antibodies to SP1 provides further evidence for the production of authentic SP1 by fibroblastic cells in vitro and offers improved reagents for the isolation, characterization, and quantitation of an important marker of cancer and fetal development.