BAFF, a member of the TNF family of ligands, is expressed in T cells, macrophages, monocytes and dendritic cells. BAFF is involved in stimulation of B and T cell function, and is an important survival and maturation factor for peripheral B cells. BAFF signals through three different TNF receptors, TACI, BCMA and BAFFR. The human BAFF gene codes for a 285 amino acid type II transmembrane protein containing a 46 amino acid cytoplasmic domain, a 21 amino acid transmembrane domain, and a 218 amino acid extracellular domain. Recombinant human soluble BAFF is a 152 amino acid polypeptide (17kD), which contains the TNF-like portion of the extracellular domain of BAFF.