Fig. 3

Effect of complement activation by mild acidification on PNH red cells. a Kinetics of C3 binding on PNH red cells from a representative untreated PNH patient after complement activation in vitro by mild acidification in presence of eculizumab. Red cells from a patient not on eculizumab incubated with acidified ABO-compatible sera without eculizumab show almost complete lysis of PNH (CD59-negative) red cells by 2 h: compare the first panel (0 h: before any acidification) and the second panel (2 h, no ECU). C3 binding (C3+) on PNH (CD59-negative) red cells is shown before (time 0) and after 5 min, 2 h and 24 h from complement activation in ABO-compatible sera with eculizumab. b Kinetics of C3 binding on PNH red cells from a series of PNH patients not on eculizumab after complement activation in vitro by mild acidification in presence of eculizumab. The line diagram shows the average (+SD) proportion of PNH (CD59-negative) red cells bound with C3 in a series of untreated patients at different time points (from 5 min to 24 h) since complement activation in ABO-compatible sera with eculizumab (continuous line without MgCl₂; dotted line with 1.25 mM MgCl₂). n: number of different patients studied at the indicated time points. C3 binding on PNH red cells increased significantly along the time (Friedman rank sum test: P < 0.001 for both series with and without MgCl₂). At any time C3 binding of samples with MgCl₂ was significantly higher than that of the same samples without MgCl₂ (Wilcoxon signed paired test: P < 0.03 at 5 min and 1 h; P < 0.005 at 30 min and 2, 6, and 24 h)