Microglia-mediated BAFF-BAFFR ligation promotes neuronal survival in brain ischemia injury

The innate immune responses of brain to vascular occlusion are primarily orchestrated by activated microglia. However, the roles of microglia in inflammatory responses to brain ischemic injuries are controversial. Here, we report a new mechanism by which microglia confer protective effects on ischemic neuronal cells. We found that under ischemic condition, the B-cell-activating factor (BAFF) was vastly upregulated in microglia and this upregulation could at least be attributed to JAK-STAT signaling pathway activated by IFN-γ and IL-10, which were spatio-temporally enriched in I/R-injured brain as well. Meanwhile, the expression of BAFFR, one member of BAFF receptors, was also upregulated on neurons after I/R injury. More importantly, recombinant BAFF treatment not only promoted neuronal survival under ischemic stresses in vitro but also attenuated infarct volume and neural deficit caused by middle cerebral artery occlusion (MCAO) in vivo. Furthermore, blocking BAFF-BAFFR ligation with TACI-Ig abrogated these therapeutic benefits. Taken together, these results indicate that the BAFF-BAFFR ligation bridged between microglia and neurons could play a critical neuroprotective role in I/R injury. Thus, augmenting BAFF-BAFFR signaling might represent a potential target for clinical stroke therapy.