A sensitive immunochemical assay for measuring the concentration of the activated protein C-protein C inhibitor complex in plasma: Use of a catcher antibody specific for the complexed/cleaved form of the inhibitor
K. Strandberg et al., A sensitive immunochemical assay for measuring the concentration of the activated protein C-protein C inhibitor complex in plasma: Use of a catcher antibody specific for the complexed/cleaved form of the inhibitor, THROMB HAEM, 86(2), 2001, pp. 604-610
Activated protein C (APC) is a serine proteinase that regulates blood coagu
lation. In plasma it is inhibited mainly by the protein C inhibitor (PCI).
The plasma concentrations of APC-PCI complex is increased in hypercoagulati
ve states such as deep venous thrombosis. Formation of the APC-PCI complex
induces a drastic conformational change in PCI that exposes new epitopes (n
eoepitopes) on the molecule. We have devised a simple immunofluorometric sa
ndwich assay for measurements of the concentrations of APC-PCI complex, emp
loying as the catcher, a monoclonal antibody that has a high affinity (K-D
approximate to 4 X 10(-11) M) for a complexation-specific neoepitope that i
s expressed on PCI. A monoclonal antibody against protein C is employed as
the tracer. The method gives a linear dose-response curve (0.06-50 mug/l),
has a low detection limit (0.06 mug/l) and no crossreactivity with native P
CI at physiologic plasma concentrations. We have now determined the concent
ration of the APC-PCl complex in healthy individuals.