A high-affinity monoclonal antibody (M27), raised against the human thrombin–antithrombin complex, has been identifiedand characterized. The epitope recognizedbyM27 was located to the linear sequence FIREVP (residues 411– 416), located in the C-terminal cleavage peptide of regionoverlaps, by two residues, theputative binding site of antithrombin for the serpin–enzyme complex receptor. Studies in rats and with HepG2 cells in culture indicated that the Fab fragment of M27 does not block binding anduptake of the thrombin–antithrombin complex, suggesting that this region does not play a major role in the recognition and clearance of the thrombin–antithrombin complex
