Our findings identify PTX3 as a unique FH ligand in that it can bind both of the two hot-spots of FH, namely SCR7 and SCR19-20 and indicate that PTX3 participates in the localization of functionally active FH. PTX3 binds FH without interfering with its complement inhibitory function. Therefore PTX3 may contribute to focusing FH regulatory action, prevent excessive complement activation, and thus exert an important function in the control of inflammation in response to tissue injury.