Pregnancy-Specific β-1-Glycoprotein (SP1) in Culture Amniotic Fluid Cells*

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Abstract
The synthesis of pregnancy-specific β-1-glycoprotein (SP1) was studied in amniotic fluid cell cultures using RIA, immunoperoxidase, and immunofluorescence techniques. SP1 was found by RIA in all 11 sonicates and in 21 of 26 culture media. The SP1-immunoreactive material was immunologically similar to maternal serum SP1. Immunoperoxidase and indirect immunofluorescence staining were positive in large cells identified as epithelial amniotic cells by labeling with antikeratin antibodies. Fibroblast-like cells were occasionally found in cultures, but they did not contain demonstrable amounts of SP1. The physiological significance of the findings presented remains unclear.