Similar levels of complement activation in both patients with thrombotic thrombocytopenic purpura and atypical hemolytic uremic syndrome: The report from the Korean TTP registry

Background: Uncontrolled complement activation has a major role in the pathogenesis of atypical HUS (aHUS) and the restraint of this process by eculizumab is life saving. However, the evidence of complement dysregulation in the pathogenesis of Thrombotic Thrombocytopenic Purpura (TTP) is still unclear. In this study we examined the presence of complement activation biomarkers in patients with aHUS and TTP and the levels were compared to normal healthy controls . Patients and Methods: Patients with thrombotic microangiopathic thrombocytopenia diagnosed either as TTP with low ADAMTS13 activity less than 10% or aHUS with impaired renal function, Cr> 2mg/dL and normal ADAMTS13 activity were chosen from the Korean TTP registry from February 2012 to June 2014. Prospective plasma and serum samples prior to intervention were collected from newly diagnosed patients with TTP (n=20), aHUS (n=20), and 20 healthy controls and frozen at -700C. Complement activation products (C3a, Bb as alternative pathway; C4d as classic pathway; C5a, C5b-9; terminal pathway) were measured by ELISA. Results: Significantly increased levels of Bb and C5b-9 were observed in TTP (median [range], ng/mL; Bb, 1220 [540.0 – 16560], p=0.048; C5b - 9, 390.1 [238.5 - 938.7], p<0.0001) when compared with controls (Bb, 870.0 [630.0 - 2070]; C5b - 9, 190.8 [77.96 - 458.9]). Increased levels of C3a, C5a, C5b - 9, and Factor Bb were observed in HUS (C3a, 231.3 [80.70 - 791.8], p<0.0001; C5a, 21.38 [5.590 - 34.96], p= 0.006; C5b - 9, 0.49 [0.21 - 1.41], p