Quantification and Characterization of Pregnancy-associated Complexes of Angiotensinogen and the Proform of Eosinophil Major Basic Protein in Serum and Amniotic Fluid

Abstract

Background: The proform of eosinophil major basic protein (ProMBP) exists in serum from pregnant women complexed with a variable fraction of angiotensinogen (Ang). A subfraction further binds complement C3dg in a 2:2:2 complex. The function, physiology, and clinical importance of ProMBP complexes are unknown, and the specific quantification of these complexes has not been possible. Methods: We developed an ELISA for the ProMBP/Ang complexes, using a monoclonal antibody against ProMBP for capture and a chicken anti-human Ang antiserum for detection. Calibrators were standardized with WHO IRP 78/610 for pregnancy 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 interval of 985-3655 mIU/L. In pregnancy, mean serum concentrations were increased from week 7, and the concentrations reached term concentrations in week 18. ProMBP/Ang complexes eluted in gel filtration as a broad peak with a molecular mass of ∼230 kDa. The concentration of ProMBP/Ang/C3dg increased during blood coagulation, suggesting that the ProMBP/Ang/C3dg complex may be a marker of complement activation. Conclusions: ProMBP/Ang complexes are present in serum from nonpregnant persons as well as pregnant women, and the direct assays described here will make it possible to study the biochemistry and the clinical significance of different ProMBP complexes in pathological conditions and pregnancy.

Pregnancy‐associated plasma protein‐A proteolytic activity in rat vertebral cell cultures: Stimulation by dexamethasone–a potential mechanism for glucocorticoid regulation of osteoprogenitor proliferation and differentiation

“…More likely is the involvement of other factors that modulate PAPP‐A activity by forming binding complex with PAPP‐A. Among the known modulators are the proform of eosinophil major basic protein (proMBP) (Overgaard et al, 2000), cell surface heparan sulfate proteoglycan (Laursen et al, 2002), angiotensinogen and complement C3dg (Oxvig et al, 1995; Christiansen et al, 2000). GC regulation of some of these molecules, direct or indirect, has been reported.…”

Biology of pregnancy‐associated plasma protein‐A in relation to prenatal diagnostics: an overview

“…Model studies with recombinant proteins have shown that PAPP‐A bound to the cell surface readily forms a complex with proMBP, and that this complex is unable to bind to the cell surface and therefore enters the circulation (23,24). Throughout pregnancy there is a molar excess of proMBP in the circulation, a portion of which has been demonstrated to form a covalent 2:2 complex with angiotensinogen (25,26).…”

Pregnancy‐associated plasma protein A in a large cohort of Type 1 diabetic patients with and without diabetic nephropathy—a prospective follow‐up study

“…Levels of eosinophil major basic protein (proMBP), the endogenous inhibitor of PAPP-A, were determined by means of an immunoassay developed at Statens Serum Institute, Copenhagen. Within the calibrator range used, the intra-assay variation was < 5% [16].…”