Tumor necrosis factor receptor superfamily member 13B, also known as TNFRSF13B or more commonly as TACI, is a transmembrane receptor protein found predominantly on the surface of B cells, which are an important part of the immune system.TACI is a lymphocyte-specific member of the tumor necrosis factor (TNF) receptor superfamily. It was orignially discovered because of its ability to interact with calcium-modulator and cyclophilin ligand (CAML). TACI was later found to play a crucial role in humoral immunity by interacting with two members of the TNF family: BAFF and APRIL. These proteins signal through TACI inducing activation of several transcription factors including NFAT, AP-1, and NF-kappa-B which then modulate cellular activities. Defects in the function of TACI can lead to immune system diseases.