Immunological Profile of Vasospasm after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) carries high mortality and disability rates, which are substantially driven by complications. Early brain injury and vasospasm can happen after SAH and are crucial events to prevent and treat to improve prognosis. In recent decades, immunological mechanisms have been implicated in SAH complications, with both innate and adaptive immunity involved in mechanisms of damage after SAH. The purpose of this review is to summarize the immunological profile of vasospasm, highlighting the potential implementation of biomarkers for its prediction and management. Overall, the kinetics of central nervous system (CNS) immune invasion and soluble factors' production critically differs between patients developing vasospasm compared to those not experiencing this complication. In particular, in people developing vasospasm, a neutrophil increase develops in the first minutes to days and pairs with a mild depletion of CD45+ lymphocytes. Cytokine production is boosted early on after SAH, and a steep increase in interleukin-6, metalloproteinase-9 and vascular endothelial growth factor (VEGF) anticipates the development of vasospasm after SAH. We also highlight the role of microglia and the potential influence of genetic polymorphism in the development of vasospasm and SAH-related complications.