Neutrophil extracellular traps, released from neutrophil, promote microglia inflammation and contribute to poor outcome in subarachnoid hemorrhage.

Evidence indicates that neutrophil has promoted inflammation in several central nervous system diseases. However, whether the peripheral blood levels of neutrophils are associated with the functional outcome after subarachnoid hemorrhage and its potential mechanism remain unclear. In this study, we showed that neutrophil levels in peripheral blood were higher in patients with subarachnoid hemorrhage (P < 0.001) than in healthy subjects. Neutrophil levels were positively associated with Hunt and Hess grade (P < 0.001) and modified Rankin Scale scores at 3 months after SAH (P = 0.008). In terms of the mechanism, neutrophil extracellular traps markedly increased the proinflammatory subtype transition of microglia. After treatment with DNAse I, the proinflammatory subtype transition of microglia involving CD16 positive and IL-1β positive microglia was limited (P < 0.05). This mechanism was also verified in vitro. These results indicate that the existence of neutrophil extracellular traps, released from neutrophils after subarachnoid hemorrhage, can shift microglia toward a more proinflammatory phenotype and contribute to neuroinflammation and poor outcome in subarachnoid hemorrhage.