Immunological heterogeneity of pregnancy-associated plasma protein-A (PAPP-A). Effects on the radioimmunoassay of PAPP-A.

Pregnancy-associated plasma protein-A (PAPP-A) is a macromolecular glycoprotein produced by the trophoblast during pregnancy. Because the presence of PAPP-A in non-pregnant females is controversial, we re-evaluated our own radioimmunoassay technique for PAPP-A in the light of new observations about its immunological heterogeneity. Irrespective of the antibody (Geneva anti-PAPP-A or Dako anti-PAPP-A) the use of EDTA pregnancy plasma instead of pregnancy serum as a standard yielded different slopes of the standard curves and estimated significantly different amounts of PAPP-A in test samples. Moreover, highly purified tracers, isolated from maternal EDTA pregnancy plasma or pregnancy serum also produced significantly different results. So that the use of a tracer purified from EDTA plasma and EDTA pregnancy plasma as a standard will yield measurable levels of PAPP-A in non-pregnant female serum whereas the use of a tracer purified from maternal pregnancy serum and maternal pregnancy serum as a standard will not detect PAPP-A in the same samples. We conclude that, irrespective of the antiserum used, but depending on the biological origin of the tracer and the standard, different results will be obtained. PAPP-A is clearly immunologically heterogeneous, and the immunorecognition of PAPP-A will depend on whether or not blood coagulation has taken place.