A Proliferation-inducing Ligand (April)) also known as TNSF13A, Tall-2, and TRDL-1, is a member of the TNF ligand (TNFL) superfamily. April is most similar to B-cell activation factor (BAFF) with which it shares 30% sequence identity, compete for two receptors, TACI and BCMA. APRIL is expressed at low levels in lymphoid tissue and is over-expressed by a number of tumors. April has a proliferative effect on both normal and tumor cell lines in vitro and in vivo. APRIL seems to be involved in the regulation of death and proliferation of tumor cells, but there are still contradictory findings regarding its overall biological effects.

> 95% as determined by SDS-PAGE; > 95% as determined by HPLC