The cytokines BAFF (B-cell activating factor), sometimes referred to as B-lymphocyte stimulator (BLys or CD257), and its closely related homolog APRIL (a proliferation-inducing ligand), both members of the TNF superfamily, have received much attention in recent years centered around their crucial roles in the pathology of autoimmune diseases, such as lupus erythematosus and rheumatoid arthritis [108]. The gene discussed is TNFSF13B; the disease is lupus erythematosus.