Our recent research revealed that adoptively transferred regulatory T cells (Tregs) reduced acute ischemic brain injury by inhibiting neutrophil-derived matrix metalloproteinase-9 (MMP-9) and protecting against blood-brain barrier damage. The mechanisms underlying Treg interactions with neutrophils remain elusive. This study evaluates the contribution of program death 1-ligand 1 (PD-L1) to Treg-mediated neutrophil inhibition and neuroprotection after cerebral ischemia.