Technozym^® ADAMTS-13 ANTIGEN ELISA - A New Assay for Specific Quantification of the vWF Cleaving Protease ADAMTS-13.

Defects in activity and/or antigen levels of ADAMTS-13, the von Willebrand Factor (vWF) cleaving protease, are viewed as the main cause inducing the microvascular thrombotic disorder TTP (thrombotic thrombocytopenic purpura) that is in more than 90% of cases fatal if not treated early and appropriately. Malfunction of ADAMTS-13 with respect to cleave multimeric vWF can be caused by auto-antibodies directed against ADAMTS-13, by decreased presence of ADAMTS-13 in the circulation or by defective activity of ADAMTS-13. Therefore rapid and reliable diagnosis of ADAMTS-13 parameters is a clinical need. We present here an assay for quantification of ADAMTS-13 antigen levels. The assay is a regular double sandwich ELISA employing a monoclonal antibody for capturing ADAMTS-13 from the sample by binding to the CUB domains. The bound ADAMTS-13 is detected by a polyclonal antibody conjugate. The sensitivity of the assay is below 10% of the normal antigen level. In normal samples a wide range (50% to 200%) of the mean level was observed. In idiopathic TTP plasmas also a wide range of antigen levels was observed but with a slighltly lower mean value than in normal samples. Samples from hereditary TTP mostly showed lower antigen levels than normal samples. Thus we could show that this assay provides a useful tool for measuring ADAMTS-13 antigen levels. In combination with our activity assay, which is being developed in parallel, it will be possible to establish ratios of activity and antigen which could provide more insight into the mechanisms of ADAMTS-13 deficiencies than the individual values for antigen and activity.