Cutting edge: The dependence of plasma cells and independence of memory B cells on BAFF and APRIL

Memory B (B-MEM) cells and long-lived bone marrow plasma cells (BM-PO)persist within local environmental survival niches that afford cellular longevity. However, the factors supporting B-MEM cell survival within the secondary lymphoid organs and allowing BM-PC persistence in the bone marrow remain poorly characterized. We report herein that long-lived B-MEM cell survival and func- tion are completely independent of BAFF (B cell-activating-factor of the TNF family) or APRIL (a proliferation-inducing ligand). Thus, B-MEM cells represent the only mature B2 lineage subset whose survival is independent of these ligands. We have previously shown that the TNFR family member receptor BCAM (B cell maturation Ag) is a critical survival receptor for BM-PC survival in vivo. We identify in this study the ligands critical for BM-PC survival and show that either BAFF or APRIL supports the survival of BM-PCs in vivo. These data define the BAFF/APRIL-dependent and -independent components of long-lived humoral immunity.