Two pregnancy-associated serum proteins with pregnancy-specific beta1-glycoprotein determinants

A protein showing strong antigenic cross-reactivity with the "pregnancy-specific" beta1-glycoprotein (PSbetaG) was demonstrated in serum of pregnant women during the second and third trimesters, but not in sera from normal men and nonpregnant women. The described protein had alpha2-electrophoretic mobility and its molecular weight was estimated to be around 200,000 as compared to 80,000 for PSbetaG. Crossed immunoelectrophoretic analysis, using antiserum to PSbetaG, indicated the presence of additional antigenic determinants in PSbetaG not demonstrable in the cross-reacting alpha2-protein. The PSbetaG/alpha2-protein ratio was rather constant in consecutive serum samples from one woman during pregnancy, but showed a marked variation when sera from different women were compared. Results of rocket immunoelectrophoresis gave a rough estimate of the ratio between these two proteins in a sample of pregnancy serum. The reported findings point to the need for development of specific methods for quantitation of the two proteins and the necessity to re-evaluate earlier quantitative PSbetaG data.