TNFSF13B and rheumatoid arthritis: Also, the inflamed RA synovium releases CXCL12 (SDF-1), interleukin-6, TNF, BAFF (B-cell activating factor of TNF family), and APRIL (a proliferation-inducing ligand), all known to promote the accumulation and survival of long-lived plasma cells, which are normally found mainly in bone marrow [25].