CD138 mediates selection of mature plasma cells by regulating their survival.

Antibody secreting cells (ASCs) are critical effector cells and long-lived sentinels for immune memory. ASCs are highly dependent on exogenous soluble factors such as interleukin-6 (IL-6) and APRIL, to prevent their cell death. We have found that the canonical surface marker of ASCs, CD138 (syndecan-1), which is upregulated during ASC maturation, is required in a cell-intrinsic manner to mount an effective long-term humoral immune response following immunization. Surface expression of CD138 increased heparan sulfate levels on ASCs, which are known to bind pro-survival cytokines, leading to increased survival in a cell-intrinsic manner in vivo. In IL-6 and APRIL-deficient hosts, ASCs underwent extensive apoptosis independently of CD138 expression. We propose a model in which CD138 expression on fully mature ASCs provides a selective survival advantage over less mature, newly minted ASCs, by enhancing pro-survival cytokine signaling.