B-cell Activating Factor (BAFF)

B-cell activating factor (BAFF, also BLyS, TNFSF13B, CD257) is a TNF family cytokine essential for B-cell survival and maturation, produced by monocytes, macrophages, dendritic cells, neutrophils and stromal cells. BAFF exists as a membrane-bound type II transmembrane protein that is cleaved by furin into a soluble trimer, and can assemble into 60-mer viral-like clusters that greatly enhance its potency. It binds three receptors: BAFF-R (specific to mature B cells), TACI and BCMA; signaling through BAFF-R activates the non-canonical NF-κB pathway, delivering tonic survival signals and supporting the transitional B-cell checkpoint, germinal center maintenance and plasma-cell longevity. BAFF overexpression drives lupus-like autoimmunity, Sjögren's syndrome and rheumatoid arthritis, whereas excessive BAFF blockade reduces immunoglobulin levels. Belimumab, an anti-BAFF antibody, is approved for systemic lupus erythematosus; atacicept, which neutralizes BAFF and APRIL together, is in late development.