Simplified scheme of the complement cascade. In blue: proteins of the classical and lectins pathways; green: convertases of the classical and lectins pathways; orange: proteins of the alternative pathway; purple: convertases of the alternative pathway; red: proteins common to all the pathways; gray: soluble regulators. Complement cell receptors are depicted at the surface of the host cell. Red symbols: points of therapeutic interventions in rare diseases. Abbreviations: C1INH-C1 inhibitor, C4BP-C4b binding protein, CR-complement receptor, DAF-decay accelerating factor, FB-factor B, FD-factor D, FH-factor H, FI-factor I, MAC-membrane attack complex, MBL-mannose binding lectin, MCP-membrane cofactor protein. *ALN-CC5 inhibits C5 expression.