THE DIRECT BINDING OF HUMAN FACTOR-VII IN PLASMA TO RECOMBINANT HUMANTISSUE FACTOR

The extrinsic pathway of coagulation is initiated when zymogen factor VII binds to its cell surface receptor tissue tactor. Recently recombi nant human tissue factor has become available and therefore in this st udy the direct binding of human factor VII in plasma to recombinant ti ssue factor was explored. Factor VII binding was quantitated by a stan dard ELISA protocol using monospecific polyclonal rabbit anti-human fa ctor VII as the primary antibody and goat anti-rabbit IgG conjugated t o alkaline phosphatase as the second antibody. Both the oxidation stat e of the recombinant tissue factor and calcium ion concentration were found to be critical for the efficient binding of factor VII. A linear relationship was observed between absorbance and factor VII concentra tion when normal pooled human plasma was diluted in the range 1:25 to 1:1000 (factor VII concentration 0.5-20 ng/ml). Evidence is provided t o show that binding is both specific for human coagulation factor VII and can be utilized to detect factor VII molecular variants with impai red tissue factor binding.