Interrelationship between ADAMTS13 Activity, von Willebrand Factor, and Complement Activation in Remission from Immune-Mediated Thrombotic Thrombocytopenic Purpura.

Severely deficient ADAMTS13 activity (<10%) is an important risk factor to predict relapse in immune-mediated thrombotic thrombocytopenic purpura (iTTP) (Ferrari  et al. ,  2007 ; Jin  et al. ,  2008 ; Peyvandi  et al. ,  2008 ). It is also presumed that the  in vitro  ADAMTS13 activity correlates with  in vivo  function as defined by von Willebrand factor (VWF) multimers. Activation of complement plays a role in the pathophysiology of iTTP (Reti  et al. ,  2012 ; Wu  et al. ,  2013 ; Feng  et al. ,  2015 ; Turner  et al. ,  2015 ). Published data suggest that the ULVWF multimers serve as a scaffold for the activation of the alternative complement pathway, and less efficiently inhibit complement activation compared to physiologic sized VWF multimers (Feng  et al. ,  2015 ; Turner  et al. ,  2015 ). Complement activation has been demonstrated to be increased in acute iTTP episodes (Reti  et al. ,  2012 ) and be associated with an increased mortality rate (Wu  et al. ,  2013 ). We analyzed the ADAMTS13 biomarker data, VWF multimer status, and complement activation biomarker data in banked samples obtained during clinical remission in patients with a diagnosis of iTTP.