Immune Cells Invade the Collateral Circulation during Human Stroke: Prospective Replication and Extension

Abstract

It remains unclear if principal components of the local cerebral stroke immune response can be reliably and reproducibly observed in patients with acute large-vessel-occlusion (LVO) stroke. We prospectively studied a large independent cohort of n = 318 consecutive LVO stroke patients undergoing mechanical thrombectomy during which cerebral blood samples from within the occluded anterior circulation and systemic control samples from the ipsilateral cervical internal carotid artery were obtained. An extensive protocol was applied to homogenize the patient cohort and to standardize the procedural steps of endovascular sample collection, sample processing, and laboratory analyses. N = 58 patients met all inclusion criteria. (1) Mean total leukocyte counts were significantly higher within the occluded ischemic cerebral vasculature (I) vs. intraindividual systemic controls (S): +9.6%, I: 8114/µL ± 529 vs. S: 7406/µL ± 468, p = 0.0125. (2) This increase was driven by neutrophils: +12.1%, I: 7197/µL ± 510 vs. S: 6420/µL ± 438, p = 0.0022. Leukocyte influx was associated with (3) reduced retrograde collateral flow (R2 = 0.09696, p = 0.0373) and (4) greater infarct extent (R2 = 0.08382, p = 0.032). Despite LVO, leukocytes invade the occluded territory via retrograde collateral pathways early during ischemia, likely compromising cerebral hemodynamics and tissue integrity. This inflammatory response can be reliably observed in human stroke by harvesting immune cells from the occluded cerebral vascular compartment.

Defining cerebral leukocyte populations in local ischemic blood samples from patients with hyperacute stroke

“… 5 While leukocyte isolation and cryopreservation led to a significant cellular loss within the granulocyte population in the study by Shaw et al., we could show by automatic cell counting that the absolute numbers of granulocytes increased within the secluded ischemic vasculature and made up the predominant leukocyte population, confirming our previous results from two independent prospective cohorts, which were based on manual cell counting. 2 , 4 In line with the data of Shaw and colleagues, we detected a shift within the lymphocyte population towards higher percentages of T cells in the ischemic compartment compared to systemic blood samples. This was due to a decrease in the number of B and NK cells, but an increase of CD4 + helper/inducer T cells at the cost of decreasing cytotoxic/suppressor CD8 + T cells.…”

“…Local microcatheter aspiration within the cerebral ischemic arterial compartment and the cervical internal carotid artery (systemic control) was performed as previously described. 2 , 4 A cohort of patients meeting all a priori defined inclusion criteria comprised 43 patients. 2 Due to the time-critical flow-cytometry work-up, only 36 patients admitted during regular working hours could be analyzed.…”

“…2,3 Thereby, we observed a robust local infiltration of granulocytes during hyperacute human stroke. 2,4 In parallel, the Blood and Clot Thrombectomy Registry and Collaboration (BACTRAC) collected the clot and arterial blood during standard of care thrombectomy for laboratory analysis in which leukocytes are isolated and then cryopreserved. 3,5 Recently, Shaw et al reported on flow-cytometry analysis of 16 stroke patients from this biobank.…”

An intravascular perspective on hyper-acute neutrophil, T-cell and platelet responses: Similarities between human and experimental stroke

“… 12 This observation could be prospectively replicated in a large independent cohort using the exact same sampling protocol. 12 , 20 Flow cytometric automated detection and counting of leukocyte (sub-)populations again corroborated a strong predominance of neutrophils, and, in addition, disclosed a local shift in the relative distribution of lymphocytes towards CD4+ T-cells. 21 , 22 However, absolute lymphocyte numbers did not differ between local ischemic target and systemic control samples.…”

Leptomeningeal anastomoses: Mechanisms of pial collateral remodeling in ischemic stroke

“…Importantly, collateral circulation may play a key role in the broad immunological response to stroke. In stroke patients, it was found that even though the extent of collateral circulation did not impact the concentration of leukocytes circulating in the blood after LVO (Tarkanyi et al, 2020), the extent of collateral circulation was an indicator of how well immune cells were able to infiltrate into the ischemic tissue of the brain (Strinitz et al, 2021). The extent of LMAs coincident with immune status, also predicts hemorrhagic complications, with patients admitted with leukopenia showing poor collateral status coupled are more at risk for intracerebral hemorrhage (Semerano et al, 2019).…”