Functional evaluation of the C3 mutations: complement activation on endothelial cells. (A) Resting or (B) cytokine-activated HUVECs were incubated with different sera, and the C3 deposition was evaluated by flow cytometery. Sera from healthy donors are represented in gray (filled area under 3 different histograms, corresponding to 3 different donors); sera from aHUS patients with C3 mutations: R139W, violet; A1072D, red; or FH depleted serum as a positive control shown in blue. The black line represents a no serum control. (C) The capacity of purified FH to control the enhanced C3 deposition from FH depleted serum or patients sera on cytokines activated HUVECs was measured by flow cytometry. The percent decrease in the C3 deposition in the presence of FH compared with the serum alone is plotted vs the FH concentration used.