TACI （Transmembrane activator and CAML interactor） is a type III transmembrane protein and a member of the TNF receptor superfamily. It consists of an extracellular domain containing two cysteine-rich regions, a transmembrane domain, and an intracellular domain. TACI shares high homology with BCMA and binds to APRIL and BAFF, key ligands involved in immune regulation. Expressed on B cells and activated T cells, TACI plays a crucial role in B cell development and function. Its interactions with APRIL and BAFF suggest involvement in immune signaling pathways, making it a potential target for immunotherapy.