TACI-Fc binds to syndecan-2. (A-B) To verify that syndecan-2 was the interacting protein from the 293T library, TAg Jurkat cells were transiently transfected with an expression plasmid containing the syndecan-2 cDNA. Cells were stained with TACI-Fc, 0-Fc, BCMA-Fc (A), or BAFF-R-Fc (B), as indicated, and analyzed by flow cytometry. Some transfected cells bound to TACI-Fc, as shown by the right-shifted peak. Transient transfection does not deliver DNA to all cells in the culture; thus, some of the curve overlaps that of mock-transfected cells. (C) TACI coprecipitates with FLAG-tagged syndecan-2. 293T cells were transiently transfected with plasmids expressing TACI and FLAG epitope-tagged syndecan-2 (top and bottom panels, lanes 1 and 2), or TACI and the parent plasmid pFLEX (top, lane 3), or control plasmid pBJ5 and FLAG-tagged syndecan-2 (bottom, lane 3). Immunoprecipitations were carried out with antibodies specific for the FLAG epitope on syndecan-2 or for TACI, or control antibodies as indicated. Coprecipitated proteins were detected by Western blotting with TACI (top panel) or FLAG (bottom panel) antibodies.