The invention features compositions and methods of using a dimeric inhibitor, e.g., A1-A1, to selectively target β2GPI in β2GPI/antibody complexes. The compositions can be administered to subjects (e.g., a mammal, such as a human) having or likely to develop APS, or one or more symptoms of APS, in order to treat or inhibit the disease or treat or reduce its symptoms. The inhibitors of the invention include two ligand-binding A1 modules, e.g., from ApoER2, connected by a flexible linker.
