This review synthesizes evidence linking BAFF system overexpression to multiple autoimmune diseases, including systemic lupus erythematosus (SLE), Sjögren’s syndrome (SS), bullous pemphigoid (BP), pemphigus vulgaris (PV), and alopecia areata (AA), where elevated BAFF system molecule levels correlate with autoantibody titers, disease activity, and post-B cell depletion relapse. The gene discussed is TNFSF13B; the disease is autoimmune disease.