Figure 6.

Structural features of eculizumab. Adapted from Rother et.al.¹⁵ Constant regions CH2 and CH3 from IgG4 are fused to the IgG2 hinge region and CH1 domain and then paired with a κ light chain. The variable regions of the light and heavy chains are composed of the murine-derived sequences that have high affinity for C5, admixed with human germline framework regions. The result is a hybrid Ig with high affinity for C5 but without the ability to activate complement or bind Fc receptors. Post-treatment biopsies show evidence of eculizumab binding to glomeruli, TBMs, and vessel walls in the form of immunofluorescence staining for IgG2, IgG4, and κ light chain, with negative staining for IgG1, IgG3, and λ light chain.