Brain endothelial CXCL12 attracts protective Natural Killer cells during ischemic stroke
Innate lymphoid cells (ILCs) have a function in homeostasis and immune responses, but their role in ischemic brain insult is unknown. Here, we report that ILCs are not resident within the mouse brain parenchyma during steady-state conditions, but are attracted after ischemic stroke. Specifically, we identified NK cells, ILC1s, ILC2s and ILC3s within the lesion, the highest influx being observed for NK cells and ILC1s. We further show that Cxcl12 expressed at the blood-brain barrier is essential for NK cells and NKp46+ ILC3s to migrate toward the lesion. Complementary, Cxcr4-deficiency in NK cells prevented NK cells from entering the infarct area. The lack of NK cell migration resulted in a higher neurological deficit in the beam-walk sensorimotor test. Our data show a new role for blood-brain barrier-derived Cxcl12 in attracting protective NK cells to ischemic brain lesions and identifies a new Cxcl12/ Cxcr4-mediated component of the innate immune response to stroke.