Characterisation of cell-surface procoagulant activities using a microcarrier model.

A novel model is described for characterisation of cell-surface procoagulant activities and their inhibitors. Microcarrier beads were used to present living cells to recalcified blood plasma in the stirred measuring wells of an electromagnetic coagulometer. By this means the procoagulant activity on the surface of the cells could be automatically determined as clotting time. Procoagulant activity was investigated on normal and transformed cells, and representing hemopoietic, endothelial, muscle and connective tissue phenotypes. The procoagulant activity on each cell type was characterised by the use of specifically immunodepleted plasmas and specific inhibitors, including monoclonal antibodies. The predominant cell surface trigger of coagulation found in this series was tissue factor, and only blood monocytes provided some evidence for direct activation of factor X independent of FVII. Human ECV304 transformed endothelial cells were more closely studied as representative of a cell type constitutively expressing procoagulant. Coagulation mediated by ECV304 cells was found to be strictly dependent on tissue factor, as shown by an inhibitory monoclonal antibody, and on coagulation factors V, VII and X. ECV304 procoagulant activity was strongly inhibited by active-site-inactivated FVIIa, a synthetic peptide inhibitor of FXa (Tenstop) and the thrombin inhibitor, hirudin. While not appropriate for routine clinical assessment of coagulation factor function, we have found this model to be valuable in characterising the procoagulant activity on different cell types and particularly useful as a drug discovery tool in the search for new anticoagulants.