CD256 (APRIL, TNFSF13, TALL2, TRDL1) a transmembranal protein of 26 kD, forms a homotrimeric molecule that is cleaved from the cell surface resulting in the soluble form of APRIL; it also forms heterotrimers with BLyS. Its receptor are TNFRSF13b/TACI and TNFRSF17/BCMA. Expressed by T cells, B cells, dendritic cells, monocytes, and macrophages, APRIL induces proliferation of T and B cells, promotes IgA class switching, downregulates T-cell dependent antibody responses, and regulates the growth of a variety of tumor cells.