Abstract Background γδ T cells boost inflammatory responses and exacerbate tissue damage after ischemic stroke. However, the origin, dynamics, and tissue adaptation of γδ T cells in the ischemic brain and its border regions remain poorly understood. A systematic integration of large-scale datasets is urgently needed. Here, we investigated the impact of ischemic stroke on the state of meningeal and brain-infiltrating γδ T cells and explored their potential contributions to post-stroke inflammation. Methods We conducted an integrated analysis of publicly available single-cell RNA sequencing (scRNA-seq) datasets, which included meningeal and brain-infiltrating Ptprc + (CD45+) immune cells following experimental stroke. γδ T cells were identified and subsequently classified into distinct subtypes through data integration and reference mapping. Subtype-specific functions, tissue residency signatures, migratory programs, and the cellular interactions between γδ T cells and endothelial cells or fibroblasts in the dura and brain were investigated, respectively. Key findings were validated by flow cytometry and immunofluorescence assays in vivo. Results On day 2 post-experimental stroke, the number of parenchymal γδ T cells significantly increased while dural γδ T cells decreased. The majority of γδ T cells residing in the meninges and infiltrating the brain, both under homeostatic conditions and following stroke, were Rorc⁺ and belonged to the Vγ6⁺ γδ17 cell subset. Compared to dural γδ T cells, brain-infiltrating γδ T cells showed reduced tissue residency capacities, higher migratory pathway activation, and lower Ki‑67 positivity, indicating acute recruitment. In contrast, dural γδ T cells exhibited greater IL‑17-producing capacities on day 3. Redistributions of dural γδ T cells were analyzed, and immunofluorescence revealed a close spatial association between dural γδ T cells and CD31+ cells. Cell–cell communication analysis predicted increased interactions between γδ T cells and CD45− cells in both the dura and the brain. Conclusion Our data indicate that most meningeal and brain-infiltrating γδ T cells after stroke share an activated γδ17 phenotype but display compartmentalized dynamics in activation, proliferation, and migration. These results establish a foundation for further studies on the spatially distinct roles of γδ T cells in post-stroke immunity.

OBJECTIVE:Cerebral ischemia remains a major cause of disability, and the contribution of the hyperacute immune response is increasingly recognized. The aim of this study was to investigate the local inflammatory response in the affected brain of stroke patients with large vessel occlusion during the hyperacute phase of stroke. METHODS:To decipher the role of myeloid immune cells in stroke-induced inflammation, we performed an unsupervised multiomics analysis of innate immune pathways in ischemic blood obtained directly from the occluded middle cerebral artery in 54 patients undergoing mechanical recanalization. Paired nonischemic arterial blood served as an internal control. RESULTS:Stroke triggered a local hyperacute activation of classical monocytes and neutrophils in the ischemic cerebral vasculature, with interleukin (IL)-1β emerging as a key mediator of inflammation. Elevated plasma adenosine triphosphate levels and inflammasome priming in intravascular monocytes were associated with IL-1β production within the occluded middle cerebral artery within 4.5 hours of stroke onset. IL-1β release coincided with increased neutrophil-attracting chemokines (C-X-C motif chemokine ligand 1 [CXCL1], IL-8). Locally activated neutrophils formed neutrophil extracellular traps (NETs) within the ischemic vasculature, a hallmark of thromboinflammation. Postmortem analyses revealed NET deposition within ischemic brain parenchyma. INTERPRETATION:These findings indicate increased IL-1β expression and enhanced NET formation within the cerebral circulation in stroke caused by large vessel occlusion, suggesting that these mechanisms might contribute to early stroke pathophysiology and represent potential targets for immunomodulatory strategies. ANN NEUROL 2026.

The activation of the immune system is crucial for the fate of the ischemic brain tissue and neurological outcome in experimental stroke. Rapidly after stroke γδ (γδ17), T cells release IL-17A in the ischemic brain and thereby amplify the early detrimental immune response. Notably, IL-17A levels in γδ17 T cells are modulated by the intestinal microbiota which is, in turn, shaped by the diet. Importantly, besides their proinflammatory effects, meningeal γδ17 T cells have been recently implicated in regulating neuronal signaling, behavior, and cognition under homeostatic and pathological conditions at the brain-meningeal interface. Against this background, we propose that a dietary intervention represents a promising treatment option to improve poststroke outcomes by the modulation of the microbiota composition and IL-17A levels in γδ T cells.

This cohort study examines clinical judgment of large vessel occlusions compared with triage scales in a sample of patients admitted to the emergency department with suspicion of acute stroke.

Multiple consensus statements have called for preclinical randomized controlled trials to improve translation in stroke research. We investigated the efficacy of an interleukin-17A neutralizing antibody in a multi-centre preclinical randomized controlled trial using a murine ischaemia reperfusion stroke model. Twelve-week-old male C57BL/6 mice were subjected to 45 min of transient middle cerebral artery occlusion in four centres. Mice were randomly assigned (1:1) to receive either an anti-interleukin-17A (500 mu g) or isotype antibody (500 mu g) intravenously 1 h after reperfusion. The primary endpoint was infarct volume measured by magnetic resonance imaging three days after transient middle cerebral artery occlusion. Secondary analysis included mortality, neurological score, neutrophil infiltration and the impact of the gut microbiome on treatment effects. Out of 136 mice, 109 mice were included in the analysis of the primary endpoint. Mixed model analysis revealed that interleukin-17A neutralization significantly reduced infarct sizes (antiinterleukin-17A: 61.77 +/- 31.04 mm(3); IgG control: 75.66 +/- 34.79 mm(3); P = 0.01). Secondary outcome measures showed a decrease in mortality (hazard ratio = 3.43, 95% confidence interval = 1.157-10.18; P = 0.04) and neutrophil invasion into ischaemic cortices (anti-interleukin-17A: 7222 +/- 6108 cells; IgG control: 28 153 +/- 23 206 cells; P < 0.01). There was no difference in Bederson score. The analysis of the gut microbiome showed significant heterogeneity between centres (R = 0.78, P < 0.001, n = 40). Taken together, neutralization of interleukin-17A in a therapeutic time window resulted in a significant reduction of infarct sizes and mortality compared with isotype control. It suggests interleukin-17A neutralization as a potential therapeutic target in stroke.

As a prototypical proinflammatory cytokine, interleukin-1 (IL-1) exacerbates the early post-stroke inflammation, whereas its neutralization is protective. To further investigate the underlying cell-type-specific IL-1 effects, we subjected IL-1 (α/β) knockout (Il1−/−) and wildtype (WT) littermate mice to permanent middle cerebral artery occlusion (pMCAO) and assessed immune cell infiltration and cytokine production in the ischemic hemisphere by flow cytometry 24 h and 72 h after stroke. Il1−/− mice showed smaller infarcts and reduced neutrophil infiltration into the ischemic brain. We identified γδ T cells and astrocytes as target cells of IL-1 signaling-mediated neutrophil recruitment. First, IL-1-induced IL-17A production in γδ T cells in vivo, and IL-17A enhanced the expression of the main neutrophil attracting chemokine CXCL1 by astrocytes in the presence of tumor necrosis factor (TNF) in vitro. Second, IL-1 itself was a potent activator of astrocytic CXCL1 production in vitro. By employing a novel FACS sorting strategy for the acute isolation of astrocytes from ischemic brains, we confirmed that IL-1 is pivotal for Cxcl1 upregulation in astrocytes in vivo. Our results underscore the pleiotropic effects of IL-1 on immune and non-immune cells within the CNS to mount and amplify the post-stroke inflammatory response.

Abstract Background Lymphocytes have dichotomous functions in ischemic stroke. Regulatory T cells are protective, while IL-17A from innate lymphocytes promotes the infarct growth. With recent advances of T cell-subtype specific transgenic mouse models it now has become possible to study the complex interplay of T cell subpopulations in ischemic stroke. Methods In a murine model of experimental stroke we analyzed the effects of IL-10 on the functional outcome for up to 14 days post-ischemia and defined the source of IL-10 in ischemic brains based on immunohistochemistry, flow cytometry, and bone-marrow chimeric mice. We used neutralizing IL-17A antibodies, intrathecal IL-10 injections, and transgenic mouse models which harbor a deletion of the IL-10R on distinct T cell subpopulations to further explore the interplay between IL-10 and IL-17A pathways in the ischemic brain. Results We demonstrate that IL-10 deficient mice exhibit significantly increased infarct sizes on days 3 and 7 and enlarged brain atrophy and impaired neurological outcome on day 14 following tMCAO. In ischemic brains IL-10 producing immune cells included regulatory T cells, macrophages, and microglia. Neutralization of IL-17A following stroke reversed the worse outcome in IL-10 deficient mice and intracerebral treatment with recombinant IL-10 revealed that IL-10 controlled IL-17A positive lymphocytes in ischemic brains. Importantly, IL-10 acted differentially on αβ and γδ T cells. IL-17A producing CD4+ αβ T cells were directly controlled via their IL-10-receptor (IL-10R), whereas IL-10 by itself had no direct effect on the IL-17A production in γδ T cells. The control of the IL-17A production in γδ T cells depended on an intact IL10R signaling in regulatory T cells (Tregs). Conclusions Taken together, our data indicate a key function of IL-10 in restricting the detrimental IL-17A-signaling in stroke and further supports that IL-17A is a therapeutic opportunity for stroke treatment.

Stroke triggers a complex inflammatory process in which the balance between pro- and antiinflammatory mediators is critical for the development of the brain infarct. However, systemic changes may also occur in parallel with brain inflammation. Here we demonstrate that administration of recombinant IL-33, a recently described member of the IL-1 superfamily of cytokines, promotes Th2-type effects following focal ischemic stroke, resulting in increased plasma levels of Th2-type cytokines and fewer proinflammatory (3-nitrotyrosine+F4/80+) microglia/macrophages in the brain. These effects of IL-33 were associated with reduced infarct size, fewer activated microglia and infiltrating cytotoxic (natural killer-like) T cells, and more IL-10-expressing regulatory T cells. Despite these neuroprotective effects, mice treated with IL-33 displayed exacerbated post-stroke lung bacterial infection in association with greater functional deficits and mortality at 24 hours. Supplementary antibiotics (gentamicin and ampicillin) mitigated these systemic effects of IL-33 after stroke. Our findings highlight the complex nature of the inflammatory mechanisms differentially activated in the brain and periphery during the acute phase after ischemic stroke. The data indicate that a Th2-promoting agent can provide neuroprotection without adverse systemic effects when given in combination with antibiotics.