A proliferation-inducing ligand (APRIL), also known as TNFSF13, is a member of the tumor necrosis factor (TNF) ligand superfamily. Nineteen cytokine ligands have been identified as part of the TNF family on the basis of sequence, functional, and structural similarities. Family members include TNF beta (TNFSF1), TNF alpha (TNFSF2), Lymphotoxin beta (TNFSF3), OX40 Ligand (TNFSF4), CD40 Ligand (TNFSF5), Fas Ligand (TNFSF6), CD27 Ligand (TNFSF7), CD30 Ligand (TNFSF8), 4-1BB Ligand (TNFSF9), TRAIL (TNFSF10), TRANCE/RANKL (TNFSF11), TWEAK (TNFSF12), APRIL(TNFSF13), BAFF (TNFSF13B), LIGHT (TNFSF14), TL1A/VEGI (TNFSF15), and GITR Ligand (TNFSF18).
The TNFSF13 ligand (APRIL) is expressed by macrophages and dendritic cells. APRIL/TNFSF13 has been shown to play a role in protecting cells from undergoing apoptosis and promoting B cell development.