Figure 1. Bird's-eye view of IgG hexamers. The complement component 1 q subcomponent (C1q) complex has six antibody-binding headpieces (blue circles) and activates the complement system.

Antigen-bound antibodies recruit and activate C1q, but individual IgG antibody molecules bind the complex with weak affinity.

As reported by Diebolder et al., monoclonal IgGs can be engineered with point mutations that enhance their ability to assemble into hexamers after binding to a target antigen on the cell surface.

This IgG hexamer structure is better able to recruit and activate the C1q complex, leading to increased complement activation and more potent complement-dependent cytotoxicity against the target cell compared with individual IgG molecules.