Cerebral vasospasm (VSP) is a common phenomenon after aneurysmal subarachnoid hemorrhage (aSAH) and contributes to neurocognitive decline. The natural history of the pro-inflammatory immune response after aSAH has not been prospectively studied in human cerebrospinal fluid (CSF). In this pilot study, we aimed to identify specific immune mediators of VSP after aSAH. Peripheral blood (PB) and CSF samples from patients with aSAH were prospectively collected at different time-points after hemorrhage: days 0–1 (acute); days 2–4 (pre-VSP); days 5–9 (VSP) and days 10 + (post-VSP peak). Presence and severity of VSP was assessed with computed tomography angiography/perfusion imaging and clinical examination. Cytokine and immune mediators’ levels were quantified using ELISA. Innate and adaptive immune cells were characterized by flow cytometry, and cell counts at different time-points were compared with ANOVA. Confocal immunostaining was used to determine the presence of specific immune cell populations detected in flow cytometry. Thirteen patients/aneurysms were included. Five (38.5%) patients developed VSP after a mean of 6.8 days from hemorrhage. Flow cytometry demonstrated decreased numbers of CD45+ cells during the acute phase in PB of aSAH patients compared with healthy controls. In CSF of VSP patients, NK cells (CD3-CD161 +) were increased during the acute phase and progressively declined, whereas CD8+CD161+ lymphocytes significantly increased at days 5–9. Microglia cells (CD45dimCD11b +) increased over time after SAH. This increase was particularly significant in patients with VSP. Levels of VEGF and MMP-9 were consistently higher in VSP patients, with the highest difference occurring at the acute phase. Confocal immunostaining demonstrated the presence of CD8+CD161+ lymphocytes in the arterial wall of two unruptured intracranial aneurysms. In this preliminary study, human CSF showed active presence of innate and adaptive immune cells after aSAH. CD8+CD161+ lymphocytes may have an important role in the inflammatory response after aneurysmal rupture and were identified in the aneurysmal wall of unruptured brain aneurysms. Microglia activation occurs 6 + days after aSAH.

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Introduction: Cerebral vasospasm (CVS) and delayed cerebral ischemia (DCI) are frequently observed after aneurysmal subarachnoid hemorrhage (aSAH) and contribute to neurocognitive decline and worse outcomes. We hypothesize that aSAH initiates a cascade of neuroinflammatory events which contributes to the development of DCI. Methods: Patients who presented with aSAH requiring external ventricular drainage (EVD) for concomitant hydrocephalus were prospectively enrolled. Cerebrospinal fluid (CSF) samples were collected at different time-points relative to index aSAH injury: acute (days 0-1); pre-vasospasm (days 2-5); vasospasm peak (days 6-9) and post-vasospasm (days 10+). Presence and severity of CVS were assessed using CTA/CTP scans and clinical exam. VEGF and MMP9 (immune affectors) protein levels in the CSF were quantified using ELISA. Mobilization of the immune system was characterized by quantification of innate and adaptive immune cells in the CSF using flow cytometry. Production of inflammatory effector proteins was evaluated using intracellular cytokine staining. Results: Of 13 patients analyzed, 6 (46.2%) experienced CVS. Levels of VEGF and MMP9 were consistently higher in aSAH patients who developed CVS, with the highest difference occurring at the acute phase. Similarly, cellularity analysis revealed elevated counts of monocytes (CD11b + ) in the CSF during the acute phase, with progressive decline at later phases. Microglia (CD45 dim CD11b + ) cells were found to be significantly increased at the post-vasospasm phase. A higher percentage of IFN-γ production cytotoxic T helper cells were found at the acute phase, while the later time points revealed an elevated leveled of CD45RA - CD27 + cytotoxic T cells. Conclusion: Our preliminary data shows an active production of proteins with known immunological functions, mobilization of innate cells, production of inflammatory mediators by adaptive immune cells and altered differentiation status. Our overall goal is to determine if there are potential targets of immunomodulatory therapies which can be used to prevent or treat vasospasms and its related deleterious outcomes.