T Cells and Cerebral Ischemic Stroke

The Involvement of Immune Cells Between Ischemic Stroke and Gut Microbiota

Ischemic stroke, a disease with high mortality and disability rate worldwide, currently has no effective treatment. The systemic inflammation response to the ischemic stroke, followed by immunosuppression in focal neurologic deficits and other inflammatory damage, reduces the circulating immune cell counts and multiorgan infectious complications such as intestinal and gut dysfunction dysbiosis. Evidence showed that microbiota dysbiosis plays a role in neuroinflammation and peripheral immune response after stroke, changing the lymphocyte populations. Multiple immune cells, including lymphocytes, engage in complex and dynamic immune responses in all stages of stroke and may be a pivotal moderator in the bidirectional immunomodulation between ischemic stroke and gut microbiota. This review discusses the role of lymphocytes and other immune cells, the immunological processes in the bidirectional immunomodulation between gut microbiota and ischemic stroke, and its potential as a therapeutic strategy for ischemic stroke.

Mechanisms of immune response and cell death in ischemic stroke and their regulation by natural compounds

Ischemic stroke (IS), which is the third foremost cause of disability and death worldwide, has inflammation and cell death as its main pathological features. IS can lead to neuronal cell death and release factors such as damage-related molecular patterns, stimulating the immune system to release inflammatory mediators, thereby resulting in inflammation and exacerbating brain damage. Currently, there are a limited number of treatment methods for IS, which is a fact necessitating the discovery of new treatment targets. For this review, current research on inflammation and cell death in ischemic stroke was summarized. The complex roles and pathways of the principal immune cells (microglia, astrocyte, neutrophils, T lymphocytes, and monocytes/macrophage) in the immune system after IS in inflammation are discussed. The mechanisms of immune cell interactions and the cytokines involved in these interactions are summarized. Moreover, the cell death mechanisms (pyroptosis, apoptosis, necroptosis, PANoptosis, and ferroptosis) and pathways after IS are explored. Finally, a summary is provided of the mechanism of action of natural pharmacological active ingredients in the treatment of IS. Despite significant recent progress in research on IS, there remain many challenges that need to be overcome.

Neuroinflammation and anti-inflammatory therapy for ischemic stroke

Stroke remains one of the most devastating and challenging neurological diseases worldwide. Inflammation, as well as oxidative stress is one of the main contributors to post-stroke injuries, and oxidative stress can further induce inflammation. Moreover, the inflammatory response is closely related to immune modulation in ischemic stroke progression. Hence, major ischemic stroke treatment strategies include targeting inflammatory responses, immune modulation (especially immune cells), and inflammatory response to suppress stroke progression. To date, several drugs have demonstrated clinical efficacy, such as Etanercept and Fingolimod. However, only edaravone dexborneol has successfully passed the phase III clinical trial and been approved by the National Medical Products Administration (NMPA) to treat ischemic stroke in China, which can restore redox balance and regulate inflammatory immune responses, thus providing neuroprotection in ischemic stroke. In this review, we will comprehensively summarize the current advances in the application of inflammatory biomarkers, neuroinflammation and neuro-immunotherapeutic scenarios for ischemic stroke, thus aiming to provide a theoretical basis and new prospects and frontiers for clinical applications.

NLRP3 inflammasome deficiency attenuates cerebral ischemia-reperfusion injury by inhibiting ferroptosis

BACKGROUND

The role of ferroptosis in ischemic stroke has been hotly debated recently, but the mechanism is not clearly clarified. It has been reported that the NLRP3 inflammasome is essential for the progression of ischemic stroke. Whether the ferroptosis after ischemic stroke mediated by the activation of NLRP3 inflammasome is still not reported. In this study, we investigated the effect of NLRP3 deficiency on ferroptosis following cerebral ischemia-reperfusion injury (CIRI) in vivo and in vitro.

MATERIALS

In vivo, we used C57BL/6J mice and NLRP3^-/- mice to establish a model of middle cerebral artery occlusion (MCAO). After 3 days of reperfusion, we assessed neurological function and then performed TTC staining to measure the infarct volume. Besides, we measured the expression of NLRP3 inflammasome-related proteins and the ferroptosis-inhibiting protein glutathione peroxidase 4 (GPX4) by western blotting (WB) and immunofluorescence (IF). Moreover, we evaluated the levels of ferroptosis-related factors (Fe²⁺, MDA and GSH) in the infarct area by using appropriate kits. Furthermore, we used WB to measure the expression of Kelch-like epichlorohydrin-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2), which participate in the progression of ischemic stroke. In vitro, we knocked down NLRP3 with small interfering RNAs (siRNAs) and established an oxygen glucose deprivation/Reperfusion (OGD/R) model in BV2 cells to simulate ischemic conditions. Next, we assessed the viability of BV2 cells by the Cell Counting Kit (CCK)-8 cytotoxicity assay. Moreover, we used WB to measure the expression of NLRP3, IL-1β, GPX4, Keap1 and Nrf2 proteins which are involved in CIRI.

RESULTS

Three days after MCAO, the NLRP3^-/- mice exhibited smaller cerebral infarct volumes and lower neurological deficit scores. The expression of NLRP3 inflammasome-associated proteins (IL-18 and IL-1β) and Keap1/Nrf2 signaling pathway moleculars (Keap1 and Nrf2) in mice brain tissue and BV2 cells were inhibited by NLRP3 knockout/knockdown, while the expression of GPX4, one of the ferroptosis-related factors was increased. Furthermore, the contents of Fe²⁺ and MDA in the brain tissues of NLRP3^-/- mice were decreased, while the content of GSH were increased significantly.

CONCLUSION

Inhibition of the NLRP3 inflammasome alleviates CIRI by inhibiting ferroptosis and inflammation, possibly through a mechanism of the Keap1-Nrf2 pathway.

Monocyte-to-lymphocyte ratio affects prognosis in LAA-type stroke patients

Nowadays, the prognostic prediction of acute ischemic stroke (AIS) patients is still challenging because of the limited predictive properties of existing models. Blood-based biomarkers may provide additional information to the established prognostic factors. Markers of atherosclerosis have been identified as one of the most promising biomarkers for predicting prognosis, and inflammation, in turn, affects atherosclerosis. According to previous studies, the ratio of monocytes to lymphocytes (MLR) has been reported as a novel indicator of inflammation. Thus, our study was the first to conduct more in-depth research on the relationship between MLR and the prognosis of large artery atherosclerosis (LAA)-type AIS patients. A total of 296 patients with LAA-type stroke were recruited. Of these, 202 patients were assigned to the development cohort, and 94 patients were assigned to the validation cohort. In the development cohort, 202 patients were divided into groups A, B, C, and D according to the quartile method of MLR levels. The one-year prognosis of patients was tracked, and the modified Rankin scale (MRS, with a score ranging from 0 to 6) was mainly selected as the measurement result of the function. The relationship between MLR and prognosis was analyzed by building logistics regression models. The models showed that MLR made significant predictions in poor outcomes of LAA-type stroke patients (odds ratio: 4.037; p = 0.048). At the same time, receiver operating characteristics (ROC) curves were used to compare the predictive values between MLR and clinical prediction score (Barthel Index). This study demonstrated that patients with LAA-type stroke and high MLR had a poor prognosis. MLR might be a reliable, inexpensive, and novel predictor of LAA-type stroke prognosis.

Th1/Th2 polarization of peripheral immune response in atherothrombotic and cardioembolic stroke: a prospective study

Compelling evidence suggest a key role of immune system in the development and progression of ischemic stroke. Although the balance between proinflammatory CD4 + T helper (Th)-1 lymphocytes, expressing T-bet transcription factor, and anti-inflammatory Th2 cells expressing GATA3 seems to influence the outcome in experimental stroke, the role of peripheral immune response in acute stroke patients is poorly understood. We aimed to evaluate the peripheral Th1/Th2 balance in acute atherothrombotic (ATHS) and cardioembolic stroke (CES) patients and in age- and sex-matched healthy subjects. Using flow cytometry, we analyzed the percentage of CD4 + T-bet + T cells and CD4 + GATA3 + T cells from peripheral blood of ATHS and CES patients (2,4 and 7 days after stroke onset). Patients and controls were screened for infectious conditions, autoimmune, inflammatory, or cancerous diseases. On day 2 circulating CD4 + T-bet + T cells were significantly higher in stroke patients compared to controls, and in ATHS compared to CES and controls. On day 7, we observed a significant increase of CD4 + T-bet + T cells in both ATHS and CES patients compared to baseline. No difference was observed in circulating CD4 + GATA3 + T cells among ATHS, CES patients, and controls. These data suggest that circulating CD4 + T-bet + T cells could be useful marker indicating atherothrombotic genesis of stroke and provide new insight into the peripheral adaptive immune response in acute stroke.

Systemic immune responses after ischemic stroke: From the center to the periphery

Ischemic stroke is a leading cause of disability and death. It imposes a heavy economic burden on individuals, families and society. The mortality rate of ischemic stroke has decreased with the help of thrombolytic drug therapy and intravascular intervention. However, the nerve damage caused by ischemia-reperfusion is long-lasting and followed by multiple organ dysfunction. In this process, the immune responses manifested by systemic inflammatory responses play an important role. It begins with neuroinflammation following ischemic stroke. The large number of inflammatory cells released after activation of immune cells in the lesion area, along with the deactivated neuroendocrine and autonomic nervous systems, link the center with the periphery. With the activation of systemic immunity and the emergence of immunosuppression, peripheral organs become the second “battlefield” of the immune response after ischemic stroke and gradually become dysfunctional and lead to an adverse prognosis. The purpose of this review was to describe the systemic immune responses after ischemic stroke. We hope to provide new ideas for future research and clinical treatments to improve patient outcomes and quality of life.

Stroke-derived neutrophils demonstrate higher formation potential and impaired resolution of CD66b + driven neutrophil extracellular traps

Background

Recent evidence suggests a merging role of immunothrombosis in the formation of arterial thrombosis. Our study aims to investigate its relevance in stroke patients.

Methods

We compared the peripheral immunological profile of stroke patients vs. healthy controls. Serum samples were functionally analyzed for their formation and clearance of Neutrophil-Extracellular-Traps. The composition of retrieved thrombi has been immunologically analyzed.

Results

Peripheral blood of stroke patients showed significantly elevated levels of DNAse-I (p < 0.001), LDG (p = 0.003), CD4 (p = 0.005) as well as the pro-inflammatory cytokines IL-17 (p < 0.001), INF-γ (p < 0.001) and IL-22 (p < 0.001) compared to controls, reflecting a T_H1/T_H17 response. Increased counts of DNAse-I in sera (p = 0.045) and Neutrophil-Extracellular-Traps in thrombi (p = 0.032) have been observed in patients with onset time of symptoms longer than 4,5 h. Lower values of CD66b in thrombi were independently associated with greater improvement of NIHSS after mechanical thrombectomy (p = 0.045). Stroke-derived neutrophils show higher potential for Neutrophil-Extracellular-Traps formation after stimulation and worse resolution under DNAse-I treatment compared to neutrophils derived from healthy individuals.

Conclusions

Our data provide new insight in the role of activated neutrophils and Neutrophil-Extracellular-Traps in ischemic stroke. Future larger studies are warranted to further investigate the role of immunothrombosis in the cascades of stroke.

Trial registration

DRKS, DRKS00013278, Registered 15 November 2017, https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00013278

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02707-0.

Immunocytes Rapid Responses Post-ischemic Stroke in Peripheral Blood in Patients With Different Ages

Objectives

To explore the alterations in immune cell composition in peripheral blood in patients with acute ischemic stroke (AIS) based on their age group.

Methods

Patients with imaging confirmed AIS were enrolled from April 2019 to January 2020 and were divided into three groups according to their ages: <55 years (group-A), 55–65 years (group-B), and >65 years (group-C). Blood samples were collected immediately when the patients were admitted to our ward prior to any intervention. Flow cytometry was used to analyze immune cell composition in peripheral blood.

Results

A total of 41 eligible patients were included for final analysis. Among the three groups, the proportions of CD56⁺ CD16dim NK cells were least to greatest in group-B, group-A, then group-C, respectively. With increasing age, there was a decrease in the proportion of CD3⁺ T-cells (group-A vs. group-C, P = 0.016) and CD3+CD4+ T-cells (group-C vs. group-A, P = 0.008; group-C vs. group-B P = 0.026). Meanwhile, no significant differences in proportions of monocytes and B cells were observed.

Conclusions

The compositions of immune cells in peripheral blood of AIS patients were distinct when divided by age groups. Differences in immune cell ratios may affect clinical outcomes and foreshadows possible need for customized treatment of AIS in different age groups.

γδ T Cell in Cerebral Ischemic Stroke: Characteristic, Immunity-Inflammatory Role, and Therapy

Gamma-delta (γδ) T cells are a small subset of T cells that are reported to have a proinflammatory role in the pathophysiology of cerebral ischemia stroke (CIS). Upon activation by interleukin-1 beta (IL-1β), IL-23 and IL-18, γδ T cells are stimulated to secrete various cytokines, such as IL-17a, IL-21, IL-22, and interferon-gamma (IFN-γ). In addition, they all play a pivotal role in the inflammatory and immune responses in ischemia. Nevertheless, the exact mechanisms responsible for γδ T cell proinflammatory functions remain poorly understood, and more effective therapies targeting at γδ T cells and cytokines they release remain to be explored, particularly in the context of CIS. CIS is the second most common cause of death and the major cause of permanent disability in adults worldwide. In this review, we focus on the neuroinflammatory and immune functions of γδ T cells and related cytokines, intending to understand their roles in CIS, which may be crucial for the development of novel effective clinical applications.

Lymphocyte-Related Immunomodulatory Therapy with Siponimod (BAF-312) Improves Outcomes in Mice with Acute Intracerebral Hemorrhage

Modulators of the sphingosine-1-phosphate receptor (S1PR) have been proposed as a promising strategy for treating stroke. However, the detailed mechanisms and the potential translational value of S1PR modulators for intracerebral hemorrhage (ICH) therapy warrant exploration. Using collagenase VII-S-induced ICH in the left striatum of mice, we investigated the effects of siponimod on cellular and molecular immunoinflammatory responses in the hemorrhagic brain in the presence or absence of anti-CD3 monoclonal antibodies (Abs). We also assessed the severity of short- and long-term brain injury and evaluated the efficacy of siponimod in long-term neurologic function. Siponimod treatment significantly decreased brain lesion volume and brain water content on day 3 and the volume of the residual lesion and brain atrophy on day 28. It also inhibited neuronal degeneration on day 3 and improved long-term neurologic function. These protective effects may be associated with a reduction in the expression of lymphotactin (XCL1) and T-helper 1 (Th1)-type cytokines (interleukin 1β and interferon-γ). It may also be associated with inhibition of neutrophil and lymphocyte infiltration and alleviation of T lymphocyte activation in perihematomal tissues on day 3. However, siponimod did not affect the infiltration of natural killer cells (NK) or the activation of CD3-negative immunocytes in perihematomal tissues. Furthermore, it did not influence the activation or proliferation of microglia or astrocytes around the hematoma on day 3. Siponimod appears to have a profound impact on infiltration and activation of T lymphocytes after ICH. The effects of neutralized anti-CD3 Abs-induced T-lymphocyte tolerance on siponimod immunomodulation further confirmed that siponimod alleviated the cellular and molecular Th1 response in the hemorrhagic brain. This study provides preclinical evidence that encourages future investigation of immunomodulators, including siponimod, which target the lymphocyte-related immunoinflammatory reaction in ICH therapy.

Role of cellular prion protein in splenic CD4+ T cell differentiation in cerebral ischaemic/reperfusion

Objective

Cellular prion protein (PrP^C), the primary form of prion diseases pathogen, has received increasing attention for its protective effect against ischaemic stroke. Little is known about its role in peripheral immune responses after cerebral ischaemia/reperfusion (I/R) injury. This study is to detect the variation of splenic CD4⁺ T lymphocytes differentiation and the concentration of inflammatory cytokines after murine cerebral I/R injury in the context of PRNP expression as well as its influence on the ischaemic neuronal apoptosis.

Methods

We established the cerebral ischaemic murine model of different PRNP genotypes. We detected the percentage of splenic CD4⁺PrP^C+ T cells of PRNP wild‐type mice and the ratio of splenic Th1/2/17 lymphocytes of mice of different PRNP expression. The relevant inflammatory cytokines were then measured. Oxygen glucose deprivation/reperfusion (OGD/R) HT22 mouse hippocampal neurons were co‐cultured with the T‐cell‐conditioned medium harvested from the spleen of modelled mice and then the neuronal apoptosis was detected.

Results

CD4⁺ PrP^C+ T lymphocytes in wild‐type mice elevated after MCAO/R. PRNP expression deficiency led to an elevation of Th1/17 phenotypes and the promotion of pro‐inflammatory cytokines, while PRNP overexpression led to the elevation of Th2 phenotype and upregulation of anti‐inflammatory cytokines. In addition, PrP^C‐overexpressed CD4⁺T cells weakened the apoptosis of OGD/R HT‐22 murine hippocampal neurons caused by MCAO/R CD4⁺ T‐cell‐conditioned medium, while PrP^C deficiency enhanced apoptosis.

Interpretation

PrP^C works as a neuron protector in the CNS when I/R injury occurs and affects the peripheral immune responses and defends against stroke‐induced neuronal apoptosis.

Necrotizing enterocolitis induces T lymphocyte-mediated injury in the developing mammalian brain

Necrotizing enterocolitis (NEC) causes acute intestinal necrosis in premature infants and is associated with severe neurological impairment. In NEC, Toll-like receptor 4 is activated in the intestinal epithelium, and NEC-associated brain injury is characterized by microglial activation and white matter loss through mechanisms that remain unclear. We now show that the brains of mice and humans with NEC contained CD4⁺ T lymphocytes that were required for the development of brain injury. Inhibition of T lymphocyte influx into the brains of neonatal mice with NEC reduced inflammation and prevented myelin loss. Adoptive intracerebroventricular delivery of gut T lymphocytes from mice with NEC into Rag1 ^-/- recipient mice lacking CD4⁺ T cells resulted in brain injury. Brain organoids derived from mice with or without NEC and from human neuronal progenitor cells revealed that IFN-γ release by CD4⁺ T lymphocytes induced microglial activation and myelin loss in the organoids. IFN-γ knockdown in CD4⁺ T cells derived from mice with NEC abrogated the induction of NEC-associated brain injury after adoptive transfer to naïve Rag1 ^-/- recipient mice. T cell receptor sequencing revealed that NEC mouse brain-derived T lymphocytes shared homology with gut T lymphocytes from NEC mice. Intraperitoneal injection of NEC gut-derived CD4⁺ T lymphocytes into naïve Rag1 ^-/- recipient mice induced brain injury, suggesting that gut-derived T lymphocytes could mediate neuroinflammation in NEC. These findings indicate that NEC-associated brain injury may be induced by gut-derived IFN-γ-releasing CD4⁺ T cells, suggesting that early management of intestinal inflammation in children with NEC could improve neurological outcomes.

Evaluation of monocyte-to-high-density lipoprotein cholesterol ratio and monocyte-to-lymphocyte ratio in ischemic stroke

Objectives

We aimed to evaluate the diagnostic value of the combination of the monocyte-to-high-density lipoprotein cholesterol ratio (MHR) with the monocyte-to-lymphocyte ratio (MLR) in ischemic stroke patients.

Methods

There were 253 patients who were diagnosed with ischemic stroke and 211 healthy subjects enrolled into this retrospective study.

Result

MHR and MLR were significantly higher in ischemic stroke patients compared with controls. MHR and MLR remained as independent variables for the presence of ischemic stroke. In receiver operating characteristic analyses, the optimal cut-off values for MHR and MLR were 0.28 and 0.19, respectively. The area under the curve for MHR was 0.777 (sensitivity, 66.01%; specificity, 77.25%), and that for MLR was 0.742 (sensitivity, 70.36%; specificity, 67.77%) in ischemic stroke patients. Moreover, the combination MHR and MLR increased the sensitivity compared with MHR or MLR alone.

Conclusion

The present study shows that a high MHR and MLR are each predictive for the risk of ischemic stroke, and together, they exhibit a better diagnostic value compared with each ratio alone.

Mucosal-Associated Invariant T Cells Are Involved in Acute Ischemic Stroke by Regulating Neuroinflammation

Background Mucosal-associated invariant T (MAIT) cells have been associated with inflammation in several autoimmune diseases. However, their relation to ischemic stroke remains unclear. This study attempted to elucidate the role of MAIT cells in acute ischemic stroke in mice. Methods and Results We used MR1 knockout C57BL/6 (MR1-/-) mice and wild-type littermates (MR1+/+). After performing a transient middle cerebral artery occlusion (tMCAO), we evaluated the association with inflammation and prognosis in the acute cerebral ischemia. Furthermore, we analyzed the tMCAO C57BL/6 mice administered with the suppressive MR1 ligand and the vehicle control. We also evaluated the infiltration of MAIT cells into the ischemic brain by flow cytometry. Results showed a reduction of infarct volume and an improvement of neurological impairment in MR1-/- mice (n=8). There was a reduction in the number of infiltrating microglia/macrophages (n=3-5) and in their activation (n=5) in the peri-infarct area of MR1-/- mice. The cytokine levels of interleukin-6 and interleukin-17 at 24 hours after tMCAO (n=3-5), and for interleukin-17 at 72 hours after tMCAO (n=5), were lower in the MR1-/- mice. The administration of the suppressive MR1 ligand reduced the infarct volume and improved functional impairment (n=5). Flow cytometric analysis demonstrated there was a reduction of MAIT cells infiltrating into the ischemic brain at 24 hours after tMCAO (n=17). Conclusions Our results showed that MAIT cells play an important role in neuroinflammation after focal cerebral ischemia and the use of MAIT cell regulation has a potential role as a novel neuroprotectant for the treatment of acute ischemic stroke.

The immune response of T cells and therapeutic targets related to regulating the levels of T helper cells after ischaemic stroke

Through considerable effort in research and clinical studies, the immune system has been identified as a participant in the onset and progression of brain injury after ischaemic stroke. Due to the involvement of all types of immune cells, the roles of the immune system in stroke pathology and associated effects are complicated. Past research concentrated on the functions of monocytes and neutrophils in the pathogenesis of ischaemic stroke and tried to demonstrate the mechanisms of tissue injury and protection involving these immune cells. Within the past several years, an increasing number of studies have elucidated the vital functions of T cells in the innate and adaptive immune responses in both the acute and chronic phases of ischaemic stroke. Recently, the phenotypes of T cells with proinflammatory or anti-inflammatory function have been demonstrated in detail. T cells with distinctive phenotypes can also influence cerebral inflammation through various pathways, such as regulating the immune response, interacting with brain-resident immune cells and modulating neurogenesis and angiogenesis during different phases following stroke. In view of the limited treatment options available following stroke other than tissue plasminogen activator therapy, understanding the function of immune responses, especially T cell responses, in the post-stroke recovery period can provide a new therapeutic direction. Here, we discuss the different functions and temporal evolution of T cells with different phenotypes during the acute and chronic phases of ischaemic stroke. We suggest that modulating the balance between the proinflammatory and anti-inflammatory functions of T cells with distinct phenotypes may become a potential therapeutic approach that reduces the mortality and improves the functional outcomes and prognosis of patients suffering from ischaemic stroke.

Mechanism underlying treatment of ischemic stroke using acupuncture: transmission and regulation

The inflammatory response after cerebral ischemia/reperfusion is an important cause of neurological damage and repair. After cerebral ischemia/reperfusion, microglia are activated, and a large number of circulating inflammatory cells infiltrate the affected area. This leads to the secretion of inflammatory mediators and an inflammatory cascade that eventually causes secondary brain damage, including neuron necrosis, blood-brain barrier destruction, cerebral edema, and an oxidative stress response. Activation of inflammatory signaling pathways plays a key role in the pathological process of ischemic stroke. Increasing evidence suggests that acupuncture can reduce the inflammatory response after cerebral ischemia/reperfusion and promote repair of the injured nervous system. Acupuncture can not only inhibit the activation and infiltration of inflammatory cells, but can also regulate the expression of inflammation-related cytokines, balance the effects of pro-inflammatory and anti-inflammatory factors, and interfere with inflammatory signaling pathways. Therefore, it is important to study the transmission and regulatory mechanism of inflammatory signaling pathways after acupuncture treatment for cerebral ischemia/reperfusion injury to provide a theoretical basis for clinical treatment of this type of injury using acupuncture. Our review summarizes the overall conditions of inflammatory cells, mediators, and pathways after cerebral ischemia/reperfusion, and discusses the possible synergistic intervention of acupuncture in the inflammatory signaling pathway network to provide a foundation to explore the multiple molecular mechanisms by which acupuncture promotes nerve function restoration.

Interleukin-17 and ischaemic stroke

Interleukin-17 (IL-17) is a cytokine family that includes 6 members, IL-17A through IL-17F, most of them are reported to have pro-inflammatory role. Through binding to their receptors (IL-17Rs), IL-17 activates the intracellular signalling pathways to play an important role in autoimmune diseases, including rheumatoid arthritis (RA) and multiple sclerosis (MS). Ischaemic stroke is a complex pathophysiological process mainly caused by regional cerebral ischaemia. Inflammatory factors contribute to the physiological process of stroke that leads to poor prognosis. IL-17 plays a crucial role in promoting inflammatory response and inducing secondary injury in post-stroke. Though immune cells and inflammatory factors have been reported to be involved in the damage of stroke, the functions of IL-17 in this process need to be elucidated. This review focuses on the pathological modulation and the mechanism of IL-17 family in ischaemic stroke and seeking to provide new insights for future therapies.

Role of B cells and the aging brain in stroke recovery and treatment

As mitigation of brain aging continues to be a key public health priority, a wholistic and comprehensive consideration of the aging body has identified immunosenescence as a potential contributor to age-related brain injury and disease. Importantly, the nervous and immune systems engage in bidirectional communication and can exert profound influence on each other. Emerging evidence supports numerous impacts of innate, inflammatory immune responses and adaptive T cell-mediated immunity in neurological function and diseased or injured brain states, such as stroke. Indeed, a growing body of evidence supports key impacts of brain-resident immune cell activation and peripheral immune infiltration in both the post-stroke acute injury phase and the long-term recovery period. As such, modulation of the immune system is an attractive strategy for novel therapeutic interventions for a devastating age-related brain injury for which there are few readily available neuroprotective treatments or neurorestorative approaches. However, the role of B cells in the context of brain function, and specifically in response to stroke, has not been thoroughly elucidated and remains controversial, leaving our understanding of neuroimmune interactions incomplete. Importantly, emerging evidence suggests that B cells are not pathogenic contributors to stroke injury, and in fact may facilitate functional recovery, supporting their potential value as novel therapeutic targets. By summarizing the current knowledge of the role of B cells in stroke pathology and recovery and interpreting their role in the context of their interactions with other immune cells as well as the immunosenescence cascades that alter their function in aged populations, this review supports an increased understanding of the complex interplay between the nervous and immune systems in the context of brain aging, injury, and disease.

Association of Tim-4 expression in monocyte subtypes with clinical course and prognosis in acute ischemic stroke patients

Background: It has been proven that T cell immunoglobin and mucin domain (Tim)-4 and monocytes (Mo) are involved in regulation of immunity, which is important for the recovery of acute ischemic stroke (AIS).Methods: In this study, the expression of Tim-4 in both circulating Mo subtypes and plasma in 32 consecutive AIS patients and 32 control patients was assessed to determine their correlation with the clinical course and prognosis of AIS.Results: It was found that, compared to the control patients, the percentage of Tim-4 expression in overall Mo, classical Mo and non-classical Mo was significantly elevated after 2 and 5 days of stroke (p < 0.05), while it was promoted from 0 to 10 days of stoke in intermediate Mo (p < 0.05). Furthermore, Tim-4 expressions in non-classical Mo and intermediate Mo were obviously correlated with National Institutes of Health Stroke Scale (NIHSS) scores at 2 days of stroke (r = 0.351, p = 0.048; r = 0.358, p = 0.044, respectively). In poor outcome (PO) patients, the expression of Tim-4 in non-classical Mo was remarkably promoted at 2 days of stroke in comparison with non-PO patients (p < 0.05). More importantly, our results revealed a positive correlation between Tim-4 expression in non-classical Mo and interleukin (IL)-6 plasma levels in AIS patients without infection.Conclusion: In summary, our findings proved that Tim-4 expression in non-classical Mo could be an appropriate target for the prediction of the clinical course and prognosis in AIS patients.

Inflammatory Responses Induced by the Rupture of Intracranial Aneurysms Are Modulated by miRNAs

Influence of an intracranial aneurysm (IA) rupture on the expression of miRNAs and the potential significance of the resulting changes remains poorly understood. We aimed to characterize the response to the IA rupture through the analysis of miRNAs in peripheral blood cells. Expression of small RNAs was investigated using deep transcriptome sequencing in patients in the acute phase of an IA rupture (first 72 h), in the chronic phase (3–15 months), and controls. A functional analysis and the potential interactions between miRNAs and target genes were investigated. We also measured the levels of proteins that were influenced by regulated miRNAs. We found that 106 mature miRNAs and 90 miRNA precursors were differentially expressed among the groups. The regulated miRNAs were involved in a variety of pathways, and the top pathway involved cytokine-cytokine receptor interactions. The identified miRNAs targeted the inflammatory factors HMGB1 and FASLG. Changes in their expression were detected at the mRNA and protein levels. IA rupture strongly influences the transcription profiles in peripheral blood cells. The regulated miRNAs were involved in the control of immune cell homeostasis. In summary, these results may aid in the elucidation of the molecular mechanisms that orchestrate the inflammatory response to IA rupture.

The Hedgehog Signaling Pathway in Ischemic Tissues

Hedgehog (Hh) proteins are prototypical morphogens known to regulate epithelial/mesenchymal interactions during embryonic development. In addition to its pivotal role in embryogenesis, the Hh signaling pathway may be recapitulated in post-natal life in a number of physiological and pathological conditions, including ischemia. This review highlights the involvement of Hh signaling in ischemic tissue regeneration and angiogenesis, with particular attention to the heart, the brain, and the skeletal muscle. Updated information on the potential role of the Hh pathway as a therapeutic target in the ischemic condition is also presented.

The intracerebral hemorrhage blood transcriptome in humans differs from the ischemic stroke and vascular risk factor control blood transcriptomes

Understanding how the blood transcriptome of human intracerebral hemorrhage (ICH) differs from ischemic stroke (IS) and matched controls (CTRL) will improve understanding of immune and coagulation pathways in both disorders. This study examined RNA from 99 human whole-blood samples using GeneChip® HTA 2.0 arrays to assess differentially expressed transcripts of alternatively spliced genes between ICH, IS and CTRL. We used a mixed regression model with FDR-corrected p(Dx) < 0.2 and p < 0.005 and |FC| > 1.2 for individual comparisons. For time-dependent analyses, subjects were divided into four time-points: 0(CTRL), <24 h, 24-48 h, >48 h; 489 transcripts were differentially expressed between ICH and CTRL, and 63 between IS and CTRL. ICH had differentially expressed T-cell receptor and CD36 genes, and iNOS, TLR, macrophage, and T-helper pathways. IS had more non-coding RNA. ICH and IS both had angiogenesis, CTLA4 in T lymphocytes, CD28 in T helper cells, NFAT regulation of immune response, and glucocorticoid receptor signaling pathways. Self-organizing maps revealed 4357 transcripts changing expression over time in ICH, and 1136 in IS. Understanding ICH and IS transcriptomes will be useful for biomarker development, treatment and prevention strategies, and for evaluating how well animal models recapitulate human ICH and IS.

The Role of High Mobility Group Box 1 in Ischemic Stroke

High-mobility group box 1 protein (HMGB1) is a novel, cytokine-like, and ubiquitous, highly conserved, nuclear protein that can be actively secreted by microglia or passively released by necrotic neurons. Ischemic stroke is a leading cause of death and disability worldwide, and the outcome is dependent on the amount of hypoxia-related neuronal death in the cerebral ischemic region. Acting as an endogenous danger-associated molecular pattern (DAMP) protein, HMGB1 mediates cerebral inflammation and brain injury and participates in the pathogenesis of ischemic stroke. It is thought that HMGB1 signals via its presumed receptors, such as toll-like receptors (TLRs), matrix metalloproteinase (MMP) enzymes, and receptor for advanced glycation end products (RAGEs) during ischemic stroke. In addition, the release of HMGB1 from the brain into the bloodstream influences peripheral immune cells. However, the role of HMGB1 in ischemic stroke may be more complex than this and has not yet been clarified. Here, we summarize and review the research into HMGB1 in ischemic stroke.

Increased Peripheral CD137 Expression in a Mouse Model of Permanent Focal Cerebral Ischemia

Various studies demonstrate that CD137 (TNFRSF9, 4-1BB) promotes atherosclerosis and vascular inflammation in experimental models via interactions with the CD137 ligand (CD137L). However, the exact role of CD137 in ischemic stroke remains unclear. In this study, we analyzed dynamic changes of peripheral CD137 expression on T cells in a mouse model of cerebral ischemia-middle cerebral artery occlusion (MCAO), as well as alternation of neurological function, infarct size and cerebral inflammatory status after inhibition of the CD137/CD137L pathway using an anti-CD137L monoclonal antibody. MCAO mice showed elevated surface expression of CD137 on T cells in both peripheral blood and lymphoid tissues during early cerebral ischemia. Remarkably, blockade of the CD137/CD137L pathway reduced the post-ischemic brain damage. Our findings indicate that enhanced CD137 costimulation occurs in early cerebral ischemia and promotes T cell activation, which in turn upregulates inflammatory immune response and possibly exerting deleterious effects on cerebral ischemia.

A review of the role of cav-1 in neuropathology and neural recovery after ischemic stroke

Ischemic stroke starts a series of pathophysiological processes that cause brain injury. Caveolin-1 (cav-1) is an integrated protein and locates at the caveolar membrane. It has been demonstrated that cav-1 can protect blood–brain barrier (BBB) integrity by inhibiting matrix metalloproteases (MMPs) which degrade tight junction proteins. This article reviews recent developments in understanding the mechanisms underlying BBB dysfunction, neuroinflammation, and oxidative stress after ischemic stroke, and focuses on how cav-1 modulates a series of activities after ischemic stroke. In general, cav-1 reduces BBB permeability mainly by downregulating MMP9, reduces neuroinflammation through influencing cytokines and inflammatory cells, promotes nerve regeneration and angiogenesis via cav-1/VEGF pathway, reduces apoptosis, and reduces the damage mediated by oxidative stress. In addition, we also summarize some experimental results that are contrary to the above and explore possible reasons for these differences.

Lymphocyte-to-Monocyte Ratio Is an Independent Predictor for Neurological Deterioration and 90-Day Mortality in Spontaneous Intracerebral Hemorrhage

BACKGROUND Lymphocyte-to-monocyte ratio (LMR) is an independent predictive factor of clinical outcome of acute ischemic stroke and cancer, but the predictive effect of LMR in spontaneous intracerebral hemorrhage (ICH) is unknown. Thus, the aim of this study was to explore the impact of peripheral LMR on the neurological deterioration (ND) during the initial week after spontaneous ICH onset, as well as 90-day mortality. MATERIAL AND METHODS The clinical data of 558 consecutive patients with ICH were retrospectively analyzed. LMR is calculated by absolute lymphocyte count divided by absolute monocyte count. RESULTS Of these patients, 166 patients experienced ND during the first week after admission and 72 patients died within 90 days. Multivariate analysis indicated that white blood cells (WBC), absolute neutrophil count (ANC), absolute lymphocyte count (ALC), neutrophil-to-lymphocyte ratio (NLR), LMR were significantly associated with ND during the initial week after ICH onset and also were associated with 90-day mortality. Moreover, NLR and LMR showed a higher predictive ability in ND during the initial week after ICH onset than 90-day mortality in receiver operating characteristic analysis. The best cut-off points of NLR and LMR in predicting ND and 90-day mortality were 10.24 and 2.21 and 16.81 and 2.19, respectively. CONCLUSIONS Our results suggest that LMR on admission is a predictive factor for ND during the initial week after ICH onset, as well as 90-day mortality.

FasL incapacitation alleviates CD4+ T cells-induced brain injury through remodeling of microglia polarization in mouse ischemic stroke

Inflammation responses involving the crosstalk between infiltrated T cells and microglia play crucial roles in ischemia stroke. Recent studies showed that Fas ligand (FasL) mutation could reduce post-stroke T cell invasion and microglia activation. In this study, we demonstrated that CD4⁺ T cells could induce M1 microglia polarization through NF-κB signaling pathway, whereas FasL mutant CD4⁺ T cells significantly reversed this effect. Besides, Th17/Treg cells balance was skewed into Treg cells after FasL mutation. In addition, conditioned medium from co-culture of FasL mutant CD4⁺ T cells and microglia could alleviate neuronal injury. Collectively, FasL incapacitation could alleviate CD4⁺ T cells-induced inflammation through remodeling microglia polarization, suggesting a therapeutic potential for control of inflammation responses after ischemic stroke.

Decreased Lymphocyte-to-Monocyte Ratio Predicts Poor Prognosis of Acute Ischemic Stroke Treated with Thrombolysis

Background

Our previous study found that lower lymphocyte-to-monocyte ratio (LMR) is an independent risk factor of clinical outcome of acute ischemic stroke (AIS). However, whether lower LMR is independently associated with adverse prognosis of AIS treated with thrombolysis has not been determined. In this study, we explored the relationship between LMR and prognosis of AIS treated with thrombolysis.

Material/Methods

We retrospectively enrolled 108 patients treated with thrombolysis. LMR was calculated according to lymphocyte count and monocyte count on admission. Patients were classified into 3 groups according to LMR values on admission (group 1 LMR >4.34, group 2 LMR 2.79 to 4.34, group 3 LMR <2.79). Neurologic impairment was estimated by use of the National Institute of Health Stroke Scale. Clinical prognosis at 3 months was assessed by modified Rankin Scale. The relationship between LMR and neurologic impairment was analyzed by Spearman rank correlation. Receiver operating characteristic curve (ROC) was used to evaluate the ability of LMR to predict outcome.

Results

Patients in group 3 had lower lymphocyte counts and LMR values and higher monocyte counts (P<0.001). LMR value was negatively correlated with the degree of neurologic impairment (r=−0.372, P<0.001). The ROC suggested a moderate sensitivity (71.6%) and specificity (80.5%) of LMR for predicting prognosis with an optimal cut-off point at 3.48. Higher LMR value was an independent protective factor against adverse prognosis (odds ratio 0.683, 95% confidence interval 0.490−0.952, P=0.024).

Conclusions

A lower LMR value is an independent predictor of poor prognosis of AIS treated with thrombolytic therapy.

Ischemic stroke damages the intestinal mucosa and induces alteration of the intestinal lymphocytes and CCL19 mRNA in rats

The immunoreaction has a pivotal effect on ischemic stroke. It has been demonstrated that intestinal lymphocytes infiltrate into the brain and aggravate tissue injury after stroke. However, less attention has been paid to the influence on the intestinal immunology as well as morphology. Here, we utilized a rat permanent middle cerebral artery occlusion (MCAO) model to investigate the influences on intestinal mucosa, lymphocytes of the gut-associated lymphoid tissue (GALT), and the intestinal expression of CCL25 mRNA and CCL19 mRNA of stroke. Rats were randomly divided into stroke, sham, and control groups. Stroke and sham groups were further divided into interval groups of 6h, 12h, and 24h after surgery. Intestinal pathophysiological changes were observed by hematoxylin-eosin (H&E) staining. The lymphocyte numbers were detected by flow cytometry. The expression of CCL25 mRNA and CCL19 mRNA was tested with the PCR technique. We found significant necrosis and shedding of the epithelium after stroke. Moreover, the lesion aggravated with time. In addition, there was a significant increase of T lymphocytes in Peyer's patches (PPs), especially at 12h and 24h after stroke, while no differences in the number of B lymphocytes and the intraepithelial lymphocytes (IELs) were found. The data displayed no alteration of CCL25 mRNA expression. In contrast, an upregulation of CCL19 mRNA expression was detected at 6h after stroke. This study showed that ischemic stroke significantly damaged the intestinal epithelium and activated intestinal immunity.

Regulatory T CD4 + CD25+ lymphocytes increase in symptomatic carotid artery stenosis

BACKGROUND

Atherosclerosis is a multifactorial disease characterized by an immune-inflammatory remodeling of the arterial wall. Treg and Th17 subpopulations are detectable inside atherosclerotic plaque; however, their behavior in symptomatic carotid artery stenosis (CAS) is not fully elucidated. The aim of this study was to evaluate Th17 and Treg subsets and their ratio in patients affected by symptomatic and asymptomatic CAS.

METHODS

14 patients with symptomatic CAS (CAS-S group), 41 patients with asymptomatic CAS (CAS-A group), 32 subjects with traditional cardiovascular risk factors (RF group), and 10 healthy subjects (HS group) were enrolled. Th17 and Treg frequency was determined by flow cytometry and by histology and immunohistochemistry. Interleukin (IL)-10, IL-17, and metalloproteinase (MMP)-12 levels were measured by ELISA.

RESULTS

Th17 were significantly increased in CAS-A versus RF and versus HS. Tregs were significantly increased in CAS-S versus CAS-A. Tregs/Th17 ratio was significantly reduced in CAS-A versus RF and versus HS, whereas it was significantly increased in CAS-S versus CAS-A.

CONCLUSIONS

The results of this study suggest that Th17 are related to the late stages of CAS but not to plaque instability. Moreover, Treg expansion seems to represent a specific cellular pattern displayed by patients with symptomatic CAS and associated with brain injury. KEY MESSAGES Tregs expansion seems to represent a specific cellular pattern displayed by patients with symptomatic CAS and associated with CD4+ effector depletion and brain ischemic injury. Th17 lymphocytes are related to the late stages of CAS but not to plaque instability.

Insulin-Like Growth Factor (IGF)-I Modulates Endothelial Blood-Brain Barrier Function in Ischemic Middle-Aged Female Rats

In comparison with young females, middle-aged female rats sustain greater cerebral infarction and worse functional recovery after stroke. These poorer stroke outcomes in middle-aged females are associated with an age-related reduction in IGF-I levels. Poststroke IGF-I treatment decreases infarct volume in older females and lowers the expression of cytokines in the ischemic hemisphere. IGF-I also reduces transfer of Evans blue dye to the brain, suggesting that this peptide may also promote blood-brain barrier function. To test the hypothesis that IGF-I may act at the blood-brain barrier in ischemic stroke, 2 approaches were used. In the first approach, middle-aged female rats were subjected to middle cerebral artery occlusion and treated with IGF-I after reperfusion. Mononuclear cells from the ischemic hemisphere were stained for CD4 or triple-labeled for CD4/CD25/FoxP3 and subjected to flow analyses. Both cohorts of cells were significantly reduced in IGF-I-treated animals compared with those in vehicle controls. Reduced trafficking of immune cells to the ischemic site suggests that blood-brain barrier integrity is better maintained in IGF-I-treated animals. The second approach directly tested the effect of IGF-I on barrier function of aging endothelial cells. Accordingly, brain microvascular endothelial cells from middle-aged female rats were cultured ex vivo and subjected to ischemic conditions (oxygen-glucose deprivation). IGF-I treatment significantly reduced the transfer of fluorescently labeled BSA across the endothelial monolayer as well as cellular internalization of fluorescein isothiocyanate-BSA compared with those in vehicle-treated cultures, Collectively, these data support the hypothesis that IGF-I improves blood-brain barrier function in middle-aged females.