BACKGROUND: Adult hippocampal neurogenesis is altered after cerebral ischemia. Although stroke increases newborn neuron production, many cells display aberrant morphological and positional features that may impair functional integration and contribute to long-term cognitive deficits. Given the clinical heterogeneity of ischemic stroke and limited translational success of preclinical studies relying on single models, it remains unclear whether poststroke neurogenic alterations are conserved across experimental paradigms. This study aimed to identify common and model-specific features of hippocampal neurogenesis across focal ischemia models. METHODS: We conducted a multicenter, multimodel analysis within the Leducq-funded Stroke-Impact Transatlantic Network of Excellence using permanent and transient middle cerebral artery occlusion paradigms, including distal middle cerebral artery occlusion under normoxic or hypoxic conditions (distal middle cerebral artery occlusion+hypoxia), and filament-based transient middle cerebral artery occlusion, across 6 sites. Adult C57BL/6J mice were analyzed at 3 days, 7 days, and 2 months after ischemia, sham, or naïve conditions. Hippocampal proliferation (Ki67) and neuroblasts (DCX [doublecortin]) were quantified; morphological maturation of newborn neurons was assessed through high-resolution analyses of dendritic architecture and somatodendritic polarity. RESULTS: Across all stroke models, ischemia induced a robust bilateral increase in hippocampal proliferation, most pronounced at 3 days and still elevated at 7 days, returning to baseline by 2 months. Neuroblast density was similarly increased at 7 days, particularly in the ipsilateral hippocampus, but normalized over time. Despite recovery in cell number, long-term analyses revealed a consistent reduction in apical dendrite length and increased proportion of neurons with aberrant features, including ectopic positioning, polarity defects, and abnormal lateral growth, across models and centers. CONCLUSIONS: Aberrant hippocampal neurogenesis represents a robust hallmark of poststroke pathology in mice, independent of ischemia type or surgical approach, despite known differences in the spatial distribution of primary injury across models. Our findings underscore the importance of considering structural quality, and not only quantity, of newborn neurons when evaluating poststroke plasticity and developing therapeutic strategies.

Ischemic stroke induces prolonged T cell accumulation within injured brain tissue, yet it remains unclear whether these cells reflect nonspecific inflammatory persistence or organized adaptive immune responses. To define the clonal architecture of post-stroke T cells, we performed genomic DNA-based bulk T cell receptor (TCR) immunosequencing of CDR3α and CDR3β repertoires from infarcted brain and spleen during the chronic phase of experimental stroke across age and sex. TCRβ repertoires were further examined across three ischemic stroke models reproduced independently at sites in the United States and Europe. Chronic infarct tissue consistently exhibited oligoclonal T cell expansion across age, sex, stroke models, and laboratories; spleen and blood remained broadly polyclonal. Dominant clonotypes occupied a substantial fraction of the infarct repertoire, revealing a structured clonal architecture within the injured brain. Computational annotation identified recurrent sequence similarities to self-associated TCRs, including receptors linked to myelin, nuclear, and insulin-related antigens, although many expanded clonotypes lacked database matches. These annotations are presented as hypothesis-generating rather than evidence of antigen specificity. Together, these findings demonstrate that chronic ischemic brain injury is associated with a reproducible, infarct-associated clonal T cell signature whose conserved architecture is consistent with antigen-driven selection, although stochastic or cytokine-driven expansion cannot be excluded. The accompanying publicly available TCR repertoire dataset provides a clonotype-resolved reference resource for future investigations of antigen specificity and adaptive immune dynamics in chronic post-stroke neuroinflammation.

Ischemic stroke drives prolonged accumulation of lymphocytes within the injured brain, and we recently showed that the T-cell compartment of the chronic infarct is not a random infiltrate but a reproducibly organized oligoclonal repertoire. Whether this organization is a broader property of the post-stroke adaptive immune response, extending to B cells and coordinated across lymphocyte lineages, has remained unknown. Here we performed immunoglobulin heavy-chain (IGH) repertoire sequencing of chronic infarct tissue across different cohorts spanning age, sex, experimental stroke models, and independent study centers, and integrated these data with T-cell receptor β (TRB) repertoires from the same lesions. Chronic infarcts exhibited increased B-cell receptor clonality relative to matched splenic repertoires, a pattern reproducible across age, sex, models, and centers, yet heterogeneous among individual lesions owing to variable expansion of dominant clonotypes. Dominant B-cell clonotypes showed recurrent V(D)J gene usage across animals, and a subset of recurrent receptor frameworks contained public CDR3 amino-acid sequences despite substantial overall sequence diversity. Integrated analysis revealed that B- and T-cell repertoire concentration was positively associated within individual infarcts while remaining heterogeneous in its relative organization across lesions, and complementary immunoglobulin light-chain analyses supported the overall pattern of localized B-cell remodeling. Together, these findings show that persistent adaptive immunity after stroke is organized across multiple hierarchical levels, from clonal concentration to recurrent receptor architecture and paired B- and T-cell repertoire organization, yet remains biologically heterogeneous across individuals. This organizational framework, together with the publicly deposited repertoire dataset, provides a foundation for future studies of the antigenic drivers and functional consequences of chronic post-stroke adaptive immunity.

Cognitive decline is a significant long-term consequence of stroke and has no available treatments. To aid in therapy development, we sought to achieve robust detection of cognitive performance after stroke in a multi-site design. Ischemic stroke was induced in adult and middle-aged male C57BL/6J mice utilizing three well-established models: distal middle cerebral artery occlusion (dMCAO), dMCAO with hypoxia and transient MCAO. Cognitive outcomes were assessed via Novel Object Recognition (NOR) and Barnes Maze (BM) tests prior to surgery, and during sub-acute (1-2 weeks) and chronic (8 weeks) phases post-stroke. Histology and immunostaining were used to assess infarct size, tissue damage and neuronal loss, and plasma neurofilament light was quantified. We did not detect a reliable cognitive deficit after stroke using NOR but saw a promising signal from BM (single site tested only). Overall, our study highlights the often-encountered challenges in detecting post-stroke cognitive impairment within the pre-clinical stroke community, as well as a number of complexities in the design and execution of pre-clinical stroke cognition studies, particularly as applied to a multi-site structure. We provide recommendations and suggest important aspects of stroke cognition studies to consider in the future, whether operating as an individual lab or a multi-site group.

Stroke remains one of the main causes of mortality and morbidity worldwide. Immediately after stroke, a neuroinflammatory process starts in the brain, triggering a systemic immunodepression mainly through excessive activation of the autonomous nervous system. Manifestations of immunodepression include lymphopenia but also dysfunctional innate and adaptive immune cells. The resulting impaired antibacterial defenses render patients with stroke susceptible to infections. In addition, other risk factors like stroke severity, dysphagia, impaired consciousness, mechanical ventilation, catheterization, and older age predispose stroke patients for infections. Most common infections are pneumonia and urinary tract infection, both occur in ≈10% of the patients. Especially pneumonia increases unfavorable outcome and mortality in patients with stroke; systemic effects like hypotension, fever, delay in rehabilitation are thought to play a crucial role. Experimental and clinical data suggest that systemic infections enhance autoreactive immune responses against brain antigens and thus negatively affect outcome but convincing evidence is lacking. Prevention of poststroke infections by preventive antibiotic therapy did not improve functional outcome after stroke. Immunomodulatory approaches counteracting immunodepression to prevent stroke-associated pneumonia need to account for neuroinflammation in the ischemic brain and avoid further tissue damage. Experimental studies discovered interesting targets, but these have not yet been investigated in patients with stroke. A better understanding of the pathobiology may help to develop optimized approaches of preventive antibiotic therapy or immunomodulation to effectively prevent stroke-associated pneumonia while improving long-term outcome after stroke. In this review, we aim to characterize epidemiology, risk factors, cause, diagnosis, clinical presentation, and potential treatment of poststroke immunosuppression and associated infections.

Myeloid cells are suggested as an important player in Alzheimer´s disease (AD). However, its continuum of phenotypic and functional changes across different body compartments and their use as a biomarker in AD remains elusive. Here, we perform multiple state-of-the-art analyses to phenotypically and metabolically characterize immune cells between peripheral blood (n = 117), cerebrospinal fluid (CSF, n = 117), choroid plexus (CP, n = 13) and brain parenchyma (n = 13). We find that CSF cells increase expression of markers involved in inflammation, phagocytosis, and metabolism. Changes in phenotype of myeloid cells from AD patients are more pronounced in CP and brain parenchyma and upon in vitro stimulation, suggesting that AD-myeloid cells are more vulnerable to environmental changes. Our findings underscore the importance of myeloid cells in AD and the detailed characterization across body compartments may serve as a resource for future studies focusing on the assessment of these cells as biomarkers in AD.

Inflammation and immune mechanisms are crucially involved in the pathophysiology of the development, acute damage cascades, and chronic course after ischemic stroke. Atherosclerosis is an inflammatory disease, and, in addition to classical risk factors, maladaptive immune mechanisms lead to an increased risk of stroke. Accordingly, individuals with signs of inflammation or corresponding biomarkers have an increased risk of stroke. Anti-inflammatory drugs, such as IL (interleukin)-1β blockers, methotrexate, or colchicine, represent attractive treatment strategies to prevent vascular events and stroke. Lately, the COVID-19 pandemic shows a clear association between SARS-CoV2 infections and increased risk of cerebrovascular events. Furthermore, mechanisms of both innate and adaptive immune systems influence cerebral damage cascades after ischemic stroke. Neutrophils, monocytes, and microglia, as well as T and B lymphocytes each play complex interdependent roles that synergize to remove dead tissue but also can cause bystander injury to intact brain cells and generate maladaptive chronic inflammation. Chronic systemic inflammation and comorbid infections may unfavorably influence both outcome after stroke and recurrence risk for further stroke. In addition, stroke triggers specific immune depression, which in turn can promote infections. Recent research is now increasingly addressing the question of the extent to which immune mechanisms may influence long-term outcome after stroke and, in particular, cause specific complications such as poststroke dementia or even poststroke depression.

Stroke-induced immunosuppression contributes to the development of stroke-associated pneumonia (SAP). Experiments in mice demonstrated that apoptosis of IFN-γ producing cells and reduced IFN-γ secretion resulted in impaired immune responses and the development of pneumonia after middle cerebral artery occlusion (MCAo). In the present study, we investigated the efficacy of intratracheal IFN-γ treatment to prevent SAP and demonstrated that modest benefits on pulmonary cytokine response in IFN-γ treated stroke mice did not prevent spontaneously developing infections and even slightly reduced bacterial clearance of aspirated pneumococci. Our results suggest that pulmonary IFN-γ treatment is not an effective preventive measure for SAP.

CD4+ T lymphocytes are key mediators of tissue damage after ischemic stroke. However, their infiltration kinetics and interactions with other immune cells in the delayed phase of ischemia remain elusive. We hypothesized that CD4+ T cells facilitate delayed autoreactive B cell responses in the brain, which have been previously linked to post-stroke cognitive impairment (PSCI). Therefore, we treated myelin oligodendrocyte glycoprotein T cell receptor transgenic 2D2 mice of both sexes with anti-CD4 antibody following 60-minute middle cerebral artery occlusion and assessed lymphocyte infiltration for up to 72 days. Anti-CD4-treatment eliminated CD4+ T cells from the circulation and ischemic brain for 28 days and inhibited B cell infiltration into the brain, particularly in animals with large infarcts. Absence of CD4+ T cells did not influence infarct maturation or survival. Once the CD4+ population recovered in the periphery, both CD4+ T and B lymphocytes entered the infarct site forming follicle-like structures. Additionally, we provide further evidence for PSCI that could be attenuated by CD4 depletion. Our findings demonstrate that CD4+ T cells are essential in delayed B cell infiltration into the ischemic brain after stroke. Importantly, lymphocyte infiltration after stroke is a long-lasting process. As CD4 depletion improved cognitive functions in an experimental set-up, these findings set the stage to elaborate more specific immune modulating therapies in treating PSCI.

Stroke is the second leading cause of death and disability worldwide. Current treatments, such as pharmacological thrombolysis or mechanical thrombectomy, reopen occluded arteries but do not protect against ischemia-induced damage that occurs before reperfusion or neuronal damage induced by ischemia/reperfusion. It has been shown that disrupting the conversion of glyoxal to glycolic acid (GA) results in a decreased tolerance to anhydrobiosis in Caenorhabditis elegans dauer larva and that GA itself can rescue this phenotype. During the process of desiccation/rehydration, a metabolic stop/start similar to the one observed during ischemia/reperfusion occurs. In this study, the protective effect of GA is tested in different ischemia models, i.e., in commonly used stroke models in mice and swine. The results show that GA, given during reperfusion, strongly protects against ischemic damage and improves functional outcome. Evidence that GA exerts its effect by counteracting the glutamate-dependent increase in intracellular calcium during excitotoxicity is provided. These results suggest that GA treatment has the potential to reduce mortality and disability in stroke patients.

BACKGROUND:There is emerging evidence of a network of natural autoantibodies against GPCR which is dysregulated in various diseases. β2 adrenergic and M3 and M4 cholinergic receptor (β2 AdR and M3/4 mAChR) antibodies were found to be elevated in a subset of ME/CFS patients.METHODS:We comparatively analyzed the effects of polyclonal IgG on β2 AdR signaling and immune cell function in vitro. 16 IgG fractions were isolated from serum of 5 ME/CFS patients with elevated (CFS AABhigh) and 5 with normal levels (CFS AABnorm) of β2 AdR autoantibodies, and from 6 healthy controls (HC). The effect of each IgG on β-arrestin recruitment and cAMP production in β2 AdR and M3/4R reporter cell lines was studied. Further effect of each IgG on human monocyte cytokine production and on T cell proliferation in vitro was analyzed. In addition, studies on cytokine production in β2 AdR wild type and knockout mice splenocytes incubated with IgG fractions were performed.RESULTS:We found that IgGs from HC could stimulate β-arrestin recruitment and cAMP production in β2 AdR reporter cell lines whereas IgGs from CFS AABhigh had no effect. The IgG-mediated activation of β2 AdR was confirmed in β2 AdR wt and ko mice. In accordance with previous studies IgG fractions from HC inhibited LPS-induced TNFα and stimulated LPS-induced IL-10 production of monocytes. Further IgG fractions from HC enhanced proliferation of T-cells stimulated with anti-CD3/CD28. IgG fractions from CFS AABhigh patients had no significant effect on both cytokine production and T cell proliferation, while IgGs from CFS AABnorm had an intermediate effect. We could also observe that IgG can modulate the signaling of β2 AdR ligands isoprenline and propranolol.CONCLUSIONS:We provide evidence that IgG can activate β2 AdR. The β2 AdR activation by IgG is attenuated in ME/CFS patients. A dysregulation of β2 AdR function could explain many symptoms of ME/CFS.

Mucociliary clearance, the continuous removal of mucus-trapped particles by cilia-driven directed transport of the airway lining fluid, is the primary innate defense mechanism of the airways. It is potently activated by acetylcholine (ACh) addressing muscarinic receptors with a currently less defined role of nicotinic ACh receptors (nAChR). We here set out to determine their contribution in driving ciliary activity in an explanted mouse trachea preparation utilizing selected agonists and antagonists and nAChR-subunit deficient mice. Nicotine (100 mu M) induced an increase in ciliary beat frequency, accompanied by a sharp, but not long lasting increase in particle transport speed (PTS) on the mucosal surface showing marked desensitization within the next 30 min. Nicotine-induced PTS acceleration was sensitive to the general nAChR inhibitors mecamylamine and d-tubocurarine as well as to the alpha 3 beta 4-nAChR antagonist alpha-conotoxin AulB, but not to other antagonists primarily addressing alpha 3 beta 2-nAChR or alpha 4-, alpha 7- and alpha 9-containing nAChR. Agonists at alpha 3 beta*-nAChR (epibatidine, cytisine), but not cotinine mimicked the effect. Tracheas from mice with genetic deletion of nAChR subunits alpha 5, alpha 7, alpha 9, alpha 10, alpha 9/10, and beta 2 retained full PTS response to nicotine, whereas this was entirely lost in tracheas from mice lacking the beta 4-subunit Collectively, our data show that nicotinic stimulation of alpha 3 beta 4-nAChR acutely increases PTS to the same extent as the established strong activator ATP. In view of the marked desensitization observed in the present setting, the physiological relevance of these receptors in adapting mucociliary clearance to rapidly changing endogenous or environmental stimuli remains open.

Mucociliary clearance, the continuous removal of mucus-trapped particles by cilia-driven directed transport of the airway lining fluid, is the primary innate defense mechanism of the airways. It is potently activated by acetylcholine (ACh) addressing muscarinic receptors with a currently less defined role of nicotinic ACh receptors (nAChR). We here set out to determine their contribution in driving ciliary activity in an explanted mouse trachea preparation utilizing selected agonists and antagonists and nAChR-subunit deficient mice. Nicotine (100 µM) induced an increase in ciliary beat frequency, accompanied by a sharp, but not long lasting increase in particle transport speed (PTS) on the mucosal surface showing marked desensitization within the next 30 min. Nicotine-induced PTS acceleration was sensitive to the general nAChR inhibitors mecamylamine and d-tubocurarine as well as to the α3β4-nAChR antagonist α-conotoxin AulB, but not to other antagonists primarily addressing α3β2-nAChR or α4-, α7- and α9-containing nAChR. Agonists at α3β*-nAChR (epibatidine, cytisine), but not cotinine mimicked the effect. Tracheas from mice with genetic deletion of nAChR subunits α5, α7, α9, α10, α9/10, and β2 retained full PTS response to nicotine, whereas this was entirely lost in tracheas from mice lacking the β4-subunit. Collectively, our data show that nicotinic stimulation of α3β4-nAChR acutely increases PTS to the same extent as the established strong activator ATP. In view of the marked desensitization observed in the present setting, the physiological relevance of these receptors in adapting mucociliary clearance to rapidly changing endogenous or environmental stimuli remains open.

Significance Ischemic stroke triggers peripheral immunosuppression, increasing the susceptibility to poststroke pneumonia that is linked with poor survival. The poststroke brain initiates intensive communication with the immune system, and acetylcholine contributes to these messages; but the responsible molecules are yet unknown. We discovered a “changing of the guards,” where microRNA levels decreased but small transfer RNA fragments increased in poststroke blood. This molecular switch may rebalance acetylcholine signaling in CD14 + monocytes by regulating their gene expression and modulating poststroke immunity. Our observations point to transfer RNA fragments as molecular regulators of poststroke immune responses that may be potential therapeutic targets.

Pneumonia is the most frequent severe medical complication after stroke. An overactivation of the cholinergic signaling after stroke contributes to immunosuppression and the development of spontaneous pneumonia caused by Gram-negative pathogens. The α7 nicotinic acetylcholine receptor (α7nAChR) has already been identified as an important mediator of the anti-inflammatory pathway after stroke. However, whether the α2, α5 and α9/10 nAChR expressed in the lung also play a role in suppression of pulmonary innate immunity after stroke is unknown. In the present study, we investigate the impact of various nAChRs on aspiration-induced pneumonia after stroke. Therefore, α2, α5, α7 and α9/10 nAChR knockout (KO) mice and wild type (WT) littermates were infected with Streptococcus pneumoniae (S. pneumoniae) three days after middle cerebral artery occlusion (MCAo). One day after infection pathogen clearance, cellularity in lung and spleen, cytokine secretion in bronchoalveolar lavage (BAL) and alveolar-capillary barrier were investigated. Here, we found that deficiency of various nAChRs does not contribute to an enhanced clearance of a Gram-positive pathogen causing post-stroke pneumonia in mice. In conclusion, these findings suggest that a single nAChR is not sufficient to mediate the impaired pulmonary defense against S. pneumoniae after experimental stroke.

Stroke is the second leading cause of death and disability worldwide. Current treatments, like pharmacological thrombolysis or mechanical thrombectomy, re-open occluded arteries but do not protect against ischemia-induced damage caused before reperfusion or ischemia/reperfusion- induced neuronal damage. It has been shown that knocking out djr-1.1 and djr-1.2 or glod-4 results in a decreased tolerance to anhydrobiosis in C elegans dauer larva and that Glycolic Acid (GA) can rescue this phenotype. During the process of desiccation/rehydration, a metabolic stop/start similar to the one observed during ischemia/reperfusion occurs. In this study we tested the protective effect of GA against ischemia in three different models (oxygen-glucose deprivation in vitro and global cerebral ischemia as well as Middle Cerebral Artery Occlusion in vivo). Our results show that GA, given during reperfusion, strongly protects against ischemia-induced neuronal death, reduces the mortality in mice with large infarcts, significantly reduces the ischemic area in the brain and improves the functional outcome. The effect of GA is stronger when the substance is applied near the damaged tissue (i.e. directly to the neurons in vitro or intra-arterially via the internal carotid artery in vivo). These results suggest that GA treatment has the potential to dramatically reduce the mortality and disability caused by stroke in patients.

Purpose. To compare the intraocular cytokine and chemokine profiles in patients with acute primary acquired ocular toxoplasmosis (pOT) or recurrent ocular toxoplasmosis (rOT) and to correlate them with their clinical characteristics.Methods. Aqueous humor samples were collected from 62 consecutive patients (21 pOT, 30 rOT, and 11 noninfected controls) and analyzed by multiplex assay. Correlations were assessed between cytokine/chemokine levels, type of inflammatory response (Th1, Th2, and Th17), and clinical characteristics. In all OT patients, the clinical diagnosis of either pOT or rOT was confirmed by positive intraocular Goldmann/Witmer-Desmonts coefficient. Correlations were assessed between a preselected panel of immune mediators and the clinical characteristics of OT.Results. In pOT patients, increased levels of IL-2, IFN-γ, TNF-α, IL-15, IL-4, IL-5, IL-9, IL-13, IL-17, IL-1Rα, IL-6, IL-1β, and chemokines MIP-1α, MIP-1β, IP-10, Eotaxin, IL-8, RANTES, PDGF-bb, GM-CSF, G-CSF, and MCP-1 were found in comparison to those in controls (p<0.05). Patients with rOT showed elevated levels of IL-2, IFN-γ, TNF-α, IL-15, IL-4, IL-5, IL-9, IL-17, IL-1Rα, IL-6, IL-1β, and chemokines MIP-1α, IP-10, Eotaxin, IL-8, RANTES, PDGF-bb, G-CSF, and MCP-1 compared to controls (p<0.05). In addition, IL-7 (p=0.028) differed between pOT and rOT; IL-9 (p=0.054) and IL-13 (p=0.051) showed a tendency of higher concentration in pOT than in rOT. A negative correlation was found between IL-7 (p=0.017) as well as IL-9 (p=0.008) and the number of recurrences. Cytokine ratios showed no difference between pOT and rOT, indicating a dominant Th1-type response in both infectious groups. Moreover, a positive correlation was detected between IL-7, VEGF, IL-13 and age at aqueous humor sampling (p<0.05).Conclusions. This study for the first time shows subtle differences between the intraocular cytokine profiles in patients with either acute pOT or rOT.