Mechanism of C3dg-CR3–mediated erythrophagocytosis. The erythrocytes of patients with PNH and treated with eculizumab are opsonized by C3dg. C3dg serves as a ligand of CR3, facilitating the erythrophagocytosis by activated monocytes and potentially by macrophages. The cell shapes in the figure are taken from Servier Medical Art database (http://www.servier.fr/smart/banque-dimages-powerpoint). The atomic coordinates of the integrin I domain of the CR3-C3d complex (Protein Data Bank ID code 4M76) and the C3d domain taken out of it are used for the representation.