OBJECTIVES Recent evidence suggests that functional deficiency in regulatory T cells (Tregs), an innate immuno-modulator, exacerbates brain damage after cerebral ischemia. We therefore evaluated the effect of Treg transfer in rodent models of ischemic stroke and further investigated the mechanism underlying Treg-afforded neuroprotection. METHODS We examined the therapeutic potential of Tregs and the mechanisms of neuroprotection in vivo in 2 rodent models of ischemic stroke and in vitro in Treg-neutrophil co-cultures using a combined approaches including cell-specific depletion, gene knockout mice, and bone marrow chimeras. RESULTS Systemic administration of purified Tregs at 2, 6 or even 24 hours after MCAO resulted in a marked reduction of brain infarct and prolonged improvement of neurological functions lasting out to 4 weeks. Treg-afforded neuroprotection was accompanied by attenuated blood-brain barrier (BBB) disruption during early stages of ischemia, decreased cerebral inflammation and reduced infiltration of peripheral inflammatory cells into the lesioned brain. Surprisingly, Tregs exerted early neuroprotection without penetrating into the brain parenchyma or inhibiting the activation of residential microglia. Rather, both in vivo and in vitro studies demonstrated that Tregs suppressed peripheral neutrophil-derived matrix metallopeptidase-9 production, thus preventing proteolytic damage of the BBB. In additions to its potent central neuroprotection, Treg treatment was shown to ameliorate post-stroke lymphopenia, suggesting a beneficial effect on immune status. INTERPREATION Our study suggests that Treg adoptive therapy is a novel and potent cell-based therapy targeting post-stroke inflammatory dysregulation and neurovascular disruption.

To kill invading bacteria, neutrophils must interpret spatial cues, migrate, and reach target sites. Although initiation of chemotactic migration has been extensively studied, little is known about its termination. Here we report that two mitogen-activated protein kinases played opposing roles in neutrophil trafficking. The extracellular signal-regulated kinase (Erk) potentiated G protein-coupled receptor kinase GRK2 activity and inhibited neutrophil migration, whereas p38 MAPK acted as a non-canonical GRK that phosphorylated the formyl peptide receptor FPR1 and facilitated neutrophil migration by blocking GRK2 function. Therefore, the dynamic balance between Erk and p38 MAPK controls neutrophil “stop” and “go” behaviors, ensuring neutrophils precisely reach their final destination as the first line of host-defense.