A proliferation-inducing ligand (APRIL) and B-cell activating factor (BAFF) are two ligands of the tumor necrosis factor (TNF) superfamily with a crucial regulatory role in B-cell maturation and differentiation. APRIL and BAFF action occurs through binding to three TNF receptors: TACI (transmembrane activator and Ca2+ modulator interactor), B-cell maturation antigen (BCMA), and BAFF receptor (BAFF-R) with different affinities.