Neutrophil granulocytes in cerebral ischemia - Evolution from killers to key players.

Neutrophil granulocytes (or polymorphonuclear cells, PMNs) have long been considered as crude killing machines, particularly trained to attack bacterial or fungal pathogens in wounds or infected tissues. That perspective has fundamentally changed over the last decades, as PMNs have been shown to exert a livery exchange between other cells of the innate and adaptive immune system. PMNs do provide major immunomodulatory contribution during acute inflammation and subsequent clearance. Following sterile inflammation like cerebral ischemia, PMNs are among the first hematogenous cells attracted to the ischemic tissue. As inflammation is a crucial component within stroke pathophysiology, several studies regarding the role of PMNs following cerebral ischemia have been carried out. And indeed, recent research suggests a direct connection between PMNs' influx and brain damage severity. This review highlights the latest research regarding the close interconnection between PMNs and co-working cells following cerebral ischemia. We describe how PMNs are attracted to the site of injury and their tasks within the inflamed brain tissue and the periphery. We further report of new findings regarding the interaction of PMNs with resident microglia, immigrating macrophages and T cells after stroke. Finally, we discuss recent research results from experimental studies in the context with current clinical trials and point out potential new therapeutic applications that could emerge from this new knowledge on the action and interaction of PMNs following cerebral ischemia.