Plasma cells Dynamics in the Bone Marrow Niche

Abstract Plasma cells (PCs) can become long-lived with age to maintain prophylactic antibody titer for decades in the bone marrow (BM) microenvironment that are enriched in supporting chemokines and pro-survival cytokines. It has been that PCs are sessile in the BM to receive various pro-survival signals, but how they access these signals in the dynamic BM microenvironment remains unknown. Here by establishing long-term intravital imaging of the mouse tibial BM, we show that PCs are overall motile within the BM parenchyma with unique intermittent and heterogenous motility over time. Their motility is reduced when they are in clusters or as they enter a cluster. PC cluster formation and motility requires the pro-survival cytokine APRIL. PCs motility also requires the chemokine receptor CXCR4 and its ligand CXCL12 that are known important for PC homing to BM. CXCR4/CXCL12 signaling-triggered integrin VLA-4 activation negatively regulates PC motility in the BM. Notably, not only do PCs migrate within the BM parenchyma, but they can also egress and recirculate under steady state condition or CXCR4 and VLA4 inhibition. PC motility, clustering, and recirculation are all increased with mouse age. Thus, PC motility and cluster formation underlie a dynamic BM survival niche, contributing to PC longevity and function.