IDENTIFICATION OF ANGIOTENSINOGEN AND COMPLEMENT C3DG AS NOVEL PROTEINS BINDING THE PROFORM OF EOSINOPHIL MAJOR BASIC-PROTEIN IN HUMAN-PREGNANCY SERUM AND PLASMA

In sera from pregnant women, pregnancy-associated plasma protein-A (PA PP-A) circulates as a disulfide-bound complex (approximately 474 kDa) with the proform of eosinophil major basic protein (proMBP) (Oxvig, C. , Sand, O., Kristensen, T., Gleich, G. J., and Sottrup-Jensen, L. (199 3) J. Biol. Chem. 268, 12243-12246). We have produced monoclonal antib odies (mAbs) against the PAPP-A proMBP complex and established a radio immunoassay utilizing a mAb recognizing the PAPP-A subunit. Surprising ly, serum levels of proMBP exceed those of PAPP-A four to 10-fold on a molar basis throughout pregnancy. This result prompted an investigati on of the status of proMBP in pregnancy. Using a proMBP-specific mAb t wo novel proMBP complexes have been isolated by chromatographic techni ques. Based on sequence analysis, sodium dodecyl sulfate-polyacrylamid e gel electro phoresis, and reaction with specific antibodies, one is shown to be a 2:2 disulfide-bound complex (approximately 200 kDa) betw een proMBP and angiotensinogen. The other is a 2:2:2 complex (approxim ately 300 kDa) between proMBP, angiotensinogen, and complement C3dg. C irculating proMBP in pregnancy is thus present in three types of compl exes. These results suggest that specific interactions between the com plexed proteins occur in pregnancy, and the possibility is raised that their interactions are important in the pathophysiology of pregnancie s associated with hypertension.