Increased systemic levels of BAFF in serum and other body fluids like bronchoalveolar lavage, synovial fluid and gut lavage have been associated with disease activity of many autoimmune (e.g. systemic lupus erythematosus, rheumatoid arthritis, Sjögren’s syndrom, psoriatic arthritis [1], systemic sclerosis, myasthenia gravis, celiac disease, autoimmune hepatitis, primary biliary cirrhosis, bullous pemphigoid), allergic diseases (asthma, allergic rhinitis), and malignant diseases like B-CLL and multiple myeloma (reviewed in [2]). This evidence concerns the gene TNFSF13B and systemic lupus erythematosus.