Different Pairs of Monoclonal Antibodies Detect Variable Amounts of Soluble Endoglin in Human Blood Plasma

Soluble endoglin is produced as a result of extracellular domain cleavage of full-length membrane molecules. Numerous studies of recent years have shown that its excessive production is associated with vascular pathology, tumor growth and preeclampsia development. In this study we developed and explored ten sandwich-ELISA systems, based on monoclonal antibodies (MAbs) produced in our laboratory, to detect soluble endoglin in blood plasma. Here we demonstrated that values of endoglin concentration determined in the same samples varied greatly depending on pairs of MAbs used. Some measurements were up to two orders of magnitude higher compared with widely used commercial kit. Western blot analysis revealed four fractions of the antigen precipitated from plasma. Our data suggest that this molecular heterogeneity of soluble endoglin may lead to the pronounced differences in estimates of its concentration made using different sandwich-ELISA systems. Nevertheless, all studied systems revealed increment of endoglin content in plasma of pregnant women compared with healthy donors as well as its substantial production in preeclampsia patients.