Monoclonal antibodies against bovine tissue factor, which block interaction with factor VII(a)

Two monoclonal antibodies that recognize bovine tissue factor (coagulation factor III) have been obtained following the fusion of hyperimmune mouse spleen cells with NS-1 plasmacytoma cells. Both antibodies, TF1-E2 and TF1-F7, have 1/4 heavy chains and λ light chains. TF1-E2 and TF1-F7 have each been used to purify bovine tissue factor from a crude detergent extract of bovine brain by immunoaffinity chromatography. Both antibodies inhibit tissue factor procoagulant activity and block the association of factor VII(a) with tissue factor. The association of TF1-F7 and tissue factor solubilized in Triton X-100 was measured under equilibrium conditions. The K(d) for this antibody-antigen interaction was 2.1 ± 0.2 nmol/L. TF1-E2 effectively competes with TF1-F7 for tissue factor binding, indicating that the monoclonal antibodies recognize over-lapping sites on the protein. These antibodies will be useful reagents for large-scale purification and for structure-function studies of bovine tissue factor. In particular, since they appear to bind to the same region of the tissue factor molecule as factor VII(a), they will be useful as specific probes for studying the kinetics of tissue factor-initiated coagulation and for immunocytochemical localization of tissue factor in bovine cells.