C3 and age-related macular degeneration: CCPs 1–4 of FH bind C3b (but not iC3b/C3d), are crucial for FI cofactor and C3bBb decay-accelerating activities (21), and harbor mutations or single nucleotide polymorphisms linked to age-related macular degeneration, aHUS, and C3 glomerulonephritis (22, 23).