TNFSF13B encodes BAFF (B-cell activating factor), a critical cytokine belonging to the TNF superfamily that serves as a fundamental survival factor for transitional and mature B cells 1. BAFF functions primarily by binding to its receptors (BAFFR, TACI, BCMA) on B cells, promoting their survival, proliferation, and homeostasis 2. The importance of this pathway is demonstrated by BAFFR deficiency in humans, which causes severe B-lymphopenia and agammaglobulinemia 2. BAFF is produced by various immune cells, particularly neutrophils and myeloid cells, in response to inflammatory stimuli 34. Dysregulation of BAFF signaling has significant disease relevance: overexpression leads to B cell expansion and autoimmunity in mice, while elevated serum BAFF levels are found in autoimmune patients 1. A rare TNFSF13B variant (BAFF-var) is associated with increased susceptibility to rheumatoid arthritis and systemic lupus erythematosus 5. In cancer contexts, neutrophil-derived BAFF creates tumor-supportive microenvironments, as observed in multiple myeloma and hidradenitis suppurativa 63. Clinically, the BAFF system represents an important therapeutic target for modulating B cell responses in autoimmune diseases and cancer immunotherapy.