Evidence for the presence of oncoplacental SP1-like protein in normal nonpregnant serum.

To seek the pregnancy-specific beta 1-glycoprotein (SP1) in nonpregnant serum, normal human serum was applied to immunoadsorbent containing monoclonal anti-SP1 antibodies. SP1 eluted with 8 M urea was further analyzed by sodium dodecyl sulfate-gel electrophoresis and immunoblotting. A SP1-positive band with the same electrophoretic mobility as purified placental SP1 was found. The results suggest that serum from normal nonpregnant subjects contains material closely related to the placental protein SP1. The mean serum concentrations of SP1 were similar in men and women, ranging from 1.1-3.4 ng/ml.