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Figure 1. Schematic representation of complement activation by anionic lipid-mPEG conjugates. In A, antibodies bind to both phospholipid head-groups in bilayer as well as to the phosphate oxygen moiety of the lipid-mPEG conjugates. All 3 modules of C1q may subsequently interact with antibody (Ab)-coated liposomes leading to activation of the classical pathway of the complement. In addition, C1q (through its basic head) may electrostatically interact with the anionic charge localized on phosphate oxygen of lipid-mPEG conjugate (B). Ether oxygen groups of the mobile mPEG may also accommodate C1q via hydrogen bonding (B). Methylation of phosphate oxygen could sterically interfere with Ab and C1q binding (C).
