Figure 2.
Activation of complement by viral vector particles. AAV capsids bind to the C3 complement proteins C3, C3b, iC3b and complement regulatory factor H, hence increasing the uptake of virus into macrophages and enhancing their activation. C3-AAV capsid interactions are direct and can therefore occur independently of antibodies against capsid. However, the classical, antibody-dependent pathway also occurs. Similar interactions between Ad vector particles and complement have also been identified.