B cell activating factor (BAFF) is part of the tumor necrosis factor (TNF) superfamily and is expressed by monocytes, macrophages, dendritic cells, and neutrophils (Mackay & Browning; Scapini et al.). It binds to 3 receptors: BAFF-R, TACI, and BCMA, all of which are expressed by B cells at various times in their development (Liu & Davidson). BAFF-R signaling activates the NF-kB signaling pathway, and promotes B cell survival, Ig class switching, and antigen presentation (Bossen & Schneider; Liu & Davidson; Naradikian et al.). BAFF also has functions in other cell types: it promotes monocyte survival and activation, proinflammatory cytokine secretion, and differentiation into macrophages (Chang et al.), and co-stimulates anti-CD3-mediated activation of human T cells (Huard et al.; Mackay & Leung).