Serum from healthy carriers of complement gene mutations induces C3 and C5b-9 deposition on ADP-activated microvascular endothelial cells (HMEC-1). (A-B) Endothelial surface area covered by C3 (A) or C5b-9 (B) staining after incubation of ADP-activated HMEC-1 for 4 hr with serum (diluted 1:2 in test medium) from aHUS patients (C3 deposits: n = 6, 4 with CFH mutations, 1 with C3 mutation, and 1 with CFI mutation; C5b-9 deposits: n = 7, 4 with CFH mutations, 1 with C3 mutation, 1 with CFI mutation, and 1 with CFHR1/CFH hybrid gene) or from their healthy relatives carrying the same mutations (C3 deposits: n = 5, 3 with CFH mutation, 1 with C3 mutation, and 1 with CFI mutation; C5b-9 deposits: n = 6, 3 with CFH mutation, 1 with C3 mutation, 1 with CFI mutation, and 1 with CFHR1/CFH hybrid gene) in the presence or not of the complement inhibitor sCR1 (150 μg/mL) or from 7 healthy relatives without mutations (C5b-9 deposits). Control serum range: dotted horizontal areas. Data are mean ± SE. °P < .001, °°P < .01, vs control serum; *P < .001, **P < .01 vs aHUS patients without sCR1; §P < .001 vs mutation carriers without sCR1; #P < .01 vs carrier; &P < .001, &&P < .01 vs no carrier. (C) Data of plasma SC5b-9 levels and serum-induced C3 and C5b-9 deposition on ADP-activated HMEC-1 in unaffected relatives carrying complement gene mutations (healthy mutation carrier, n = 7) and unaffected relatives without mutations (only C5b-9, healthy no carrier, n = 7). °Limits of normal ranges (as defined in supplemental “Methods”). *P < .05 vs control serum (statistical comparisons were made for each relative by comparing deposits in pixel² recorded in 15 fields analyzed for the relative and for the corresponding control run in parallel, as detailed in supplemental “Methods”). £: Serum-induced C3 or C5b-9 deposits on ADP-activated HMEC-1. mut, mutation; n.a., not available; n.d., not done.