BAFF, also known as B cell activating factor, tumor necrosis factor ligand superfamily 13B, B lymphocyte stimulator (BLYS), TNF and APOL-related leukocyte expressed ligand 1 (TALL1), and TNF homolog, activates apoptosis, NF-κ B, and JNK (THANK). BAFF is a type II transmembrane protein and is a member of the tumor necrosis factor ligand superfamily. BAFF can be proteolytically cleaved to form a soluble protein. BAFF, like other TNF ligand family members, forms homotrimers. The predicted molecular weight of a BAFF monomer is approximately 31 kD. BAFF is expressed on peripheral blood B and T lymphocytes, monocytes, macrophages, and dendritic cells. It is upregulated by IFN-γ and downregulated by PMA/ionomycin treatment.