Thanks for the complement (inhibitor)‏ by Charles Parker Blood Volume 118(17):4503-4504 October 27, 2011 ©2011 by American Society of Hematology

Illustration of covalent binding of activated C3 (C3b) to glycophorin A (GPA) on the erythrocyte membrane surface. Illustration of covalent binding of activated C3 (C3b) to glycophorin A (GPA) on the erythrocyte membrane surface. The bound C3b serves as the nidus for formation of the APC C3 convertase (C3b, activated factor B [Bb], and factor P) that enzymatically activates many molecules of C3 to C3b that then bind covalently via an exposed thioester bond to carbohydrate residues on GPA. Supported by interaction with sialic acid residues on GPA, the plasma protein, factor H, binds to C3b and serves as a cofactor for degradation of C3b to iC3b by the plasma protein factor I. Complement receptor I (CR1) also binds to C3b and to iC3b and serves as a cofactor for degradation of C3b to iC3b and then C3dg by factor I. TT30 binds to both iC3b and C3dg through its CR2 domain (red circles). This binding positions the factor H–derived inhibitory component of TT30 (blue circles) to interact with nascent C3b molecules generated by an active C3 convertase. Charles Parker Blood 2011;118:4503-4504 ©2011 by American Society of Hematology