Quantification and characterization of pregnancy-associated complexes of angiotensinogen and the proform of eosinophil major basic protein in serum and amniotic fluid

Background: The preform of eosinophil major basic protein (ProMBP) exists i n serum from pregnant women complexed with a variable fraction of angiotens inogen (Ang). A subfraction further binds complement C3dg in a 2:2:2 comple x. The function, physiology, and clinical importance of ProMBP complexes ar e unknown, and the specific quantification of these complexes has not been possible. Methods: We developed an ELISA for the ProMBP/Ang complexes, using a monocl onal antibody against ProMBP for capture and a chicken anti-human Ang antis erum for detection. Calibrators were standardized with WHO IRP 78/610 for p regnancy proteins in the assay range 0.95-15.6 mIU/L. Results: The concentrations of ProMBP/Ang complexes in serum of nonpregnant blood donors (n = 79) were log-normally distributed with a central 95th in terval of 985-3655 mIU/L. In pregnancy, mean serum concentrations were incr eased from week 7, and the concentrations reached term concentrations in we ek 18. ProMBP/ Ang complexes eluted in gel filtration as a broad peak with a molecular mass of similar to 230 kDa. The concentration of ProMBP/Ang/C3d g increased during blood coagulation, suggesting that the ProMBP/Ang/C3dg c omplex may be a marker of complement activation. Conclusions: ProMBP/Ang complexes are present in serum from nonpregnant per sons as well as pregnant women, and the direct assays described here will m ake it possible to study the biochemistry and the clinical significance of different ProMBP complexes in pathological conditions and pregnancy. (C) 20 00 American Association for Clinical Chemistry.