Members in the TNF superfamily regulate immune responses and induce apoptosis. A novel member in the TNF family was recently identified by several groups and designated APRIL (for a proliferation-inducing ligand), TALL-2 (for TNF- and ApoL-related Leukocyte-expressed Ligand 2), and TRDL-1α (for TNF related death ligand 1α) in human and mouse. Two receptors for APRIL were recently identified and designated TACI and BCMA. APRIL stimulates B and T cell proliferation, triggers humoral immune responses, activates NF-κB, and induces cell death. APRIL and its close relative of BlyS and their receptors BCMA and TACI are involved in diseases of autoimmunity and cancer.