Determining ADAMTS13 Conformation for the Diagnosis of Immune Thrombotic Thrombocytopenic Purpura and Prediction of Relapse.

In healthy individuals, ADAMTS13 exists in a closed conformation, characterized by interactions between the spacer and CUB domains. The shift from the closed to the open conformation of ADAMTS13 involves the disruption of the spacer-CUB interaction and occurs upon binding to von Willebrand factor (VWF) or murine anti-ADAMTS13 monoclonal antibodies. This conformational transition exposes the cryptic epitope recognized by the murine anti-spacer monoclonal antibody 1C4, making 1C4 a highly selective tool for capturing open ADAMTS13 while leaving closed ADAMTS13 unaffected. In the context of immune-mediated thrombotic thrombocytopenic purpura (iTTP), both acute and subclinical forms, patient-derived anti-ADAMTS13 antibodies have been shown to induce this conformational shift, emphasizing open ADAMTS13 as a biomarker for diagnosing iTTP and predicting relapse risk. This chapter elaborates on the methodology employed to detect open ADAMTS13 in plasma samples, using the monoclonal antibody 1C4 in the 1C4 Open/Closed enzyme-linked immunosorbent assay (ELISA).