Primary and memory B cells occupy independent homeostatic niches (B20)

Abstract The cytokines BLyS (B lymphocyte stimulator) and APRIL (a proliferation-inducing ligand) interact with three receptors – BR3, TACI, and BCMA – to regulate peripheral B cell homeostasis. Experimental evidence indicates that the BLyS-BR3 interaction governs the size and composition of primary B cell subsets by controlling the proportion of transitional (TR) cells that complete differentiation and determining the lifespan of follicular (FO) and marginal zone (MZ) B cells. The role of the BLyS family in the regulation and maintenance of memory B cell subsets remains less understood. Accordingly, we have directly tested the role of BLyS in the maintenance of memory B cells in vivo using a neutralizing anti-BLyS antibody. Mice injected with anti-BLyS show profoundly reduced numbers of TR, FO, and MZ B cells within two weeks following treatment, as well as significantly reduced serum BLyS levels. However, for mice previously immunized with NP-CGG and injected with anti-BLyS, this treatment, while similarly reducing primary B cell pools, has no effect on NP-specific memory B cell numbers. Further, upon rechallenge, the expansion of NP specific memory B cells and serum anti-NP antibody levels are similar to controls that did not receive anti-BLyS. Together, these findings indicate that memory B cells are largely independent of BLyS availability, and therefore occupy a separate homeostatic niche from primary B cells. Supported by USPHS AI054488 to MPC and T32-AI-055428 to JEC