Preliminary results in the analysis of the immune response after aneurysmal subarachnoid hemorrhage

Abstract

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.

Non-invasive Assessment of Neurovascular Coupling After Aneurysmal Subarachnoid Hemorrhage: A Prospective Observational Trial Using Retinal Vessel Analysis

“…Given that complications like DCI and DCI-related infarctions, which have been proposed to be the result of microvascular dysfunction in the brain, are typically restricted to the first two or at most 3 weeks after the ictus as well, these findings support the assumption that retinal vessels could serve as a surrogate marker for changes in cerebral small vessels after aSAH. The observed time-course also matches the pathophysiological cascades traditionally thought to be responsible for vascular dysfunction after aSAH, namely hemolysis of subarachnoid blood and intrathecal immune activation during the early phase, secondary immune infiltration and formation of various vasoactive hemoglobin metabolites during the critical phase and their gradual clearance during the late phase ( 42 – 44 ). Further support for the idea comes from recent discovery of cerebral and retinal glymphatic systems ( 22 ), which could provide a perivascular pathway through which vasoactive agents formed during the critical phase reach the retinal microvasculature.…”

The Role of the Blood Neutrophil-to-Lymphocyte Ratio in Aneurysmal Subarachnoid Hemorrhage

“…The potent homeostatic function of Tregs in the peripheral immune system involves the inhibition of early immune overactivation that may result in an exhausted immune phenotype ( 62 ). In contrast, Th17 cells promote the inflammatory response ( 63 ) and are an important source of pro-inflammatory cytokines to aggravate brain injury ( 64 ).…”

The blood–brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

“…In the delayed phase (10 days after SAH), M1 microglia are converted to M2 phenotype characterized by scavenging debris, expression of anti-inflammatory molecules, and promoting angiogenesis. Despite the finding that BBB is altered after SAH, the majority of Iba1-positive cells 5 days following SAH are Ccr2 − /Cx3cr1 + cells, suggesting that resident microglia rather than peripheral immune cells are the cellular mediators of inflammation in the CNS after SAH [ 312 , 355 , 356 ]. Similar results were published by Xu et al, who found that CCR2 macrophages do not enter until at least 48 h following induction of SAH [ 357 ].…”