Group 2 innate lymphoid cells suppress neuroinflammation and brain injury following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) mobilizes circulating leukocytes that contribute to neuroinflammation and neural injury. However, little is known about the endogenous regulatory immune mechanisms to restrict neuroinflammation following ICH. We examined the role of group 2 innate lymphoid cells (ILC2) that are a specialized subset of innate immune modulators in a mouse model of ICH. We found accumulation of ILC2 in the brain following acute ICH and a concomitant increase of ILC2 within the peripheral lymph nodes. Depletion of ILC2 exacerbated neurodeficits and brain edema after ICH in male and female mice. This aggravated ICH injury was accompanied by augmented microglia activity and leukocyte infiltration. In contrast, expansion of ILC2 using IL-33 led to reduced ICH injury, microglia activity and leukocyte infiltration. Notably, elimination of microglia using a colony stimulating factor 1 receptor inhibitor diminished the exacerbation of ICH injury induced by depletion of ILC2. Brain-infiltrating ILC2 had upregulation of IL-13 after ICH. Results from in vitro assays revealed that ILC2 suppressed thrombin-induced inflammatory activity in microglia-like BV2 cells. Thus, our findings demonstrate that ILC2 suppress neuroinflammation and acute ICH injury.