Dynamics of T Lymphocyte between the Periphery and the Brain from the Acute to the Chronic Phase Following Ischemic Stroke in Mice

Systemic immune-inflammation index is associated with cardiac complications following acute ischemic stroke: A retrospective single-center study

BACKGROUND

Stroke-induced heart syndrome is a feared complication of ischemic stroke, that is commonly encountered and has a strong association with unfavorable prognosis. More research is needed to explore underlying mechanisms and inform clinical decision making. This study aims to explore the relationship between the early systemic immune-inflammation (SII) index and the cardiac complications after acute ischemic stroke.

METHODS

Consecutive patients with acute ischemic stroke were prospectively collected from January 2020 to August 2022 and retrospectively analyzed. We included subjects who presented within 24 hours after symptom onset and were free of detectable infections or cancer on admission. SII index [(neutrophils × platelets/ lymphocytes)/1000] was calculated from laboratory data at admission.

RESULTS

A total of 121 patients were included in our study, of which 24 (19.8 %) developed cardiac complications within 14 days following acute ischemic stroke. The SII level was found higher in patients with stroke-heart syndrome (p<.001), which was an independent predictor of stroke-heart syndrome (adjusted odds ratio 5.089, p=.002).

CONCLUSION

New-onset cardiovascular complications diagnosed following a stroke are very common and are associated with early SII index.

Drivers of Chronic Pathology Following Ischemic Stroke: A Descriptive Review

Stroke is the third leading cause of death and long-term disability in the world. Considered largely a disease of aging, its global economic and healthcare burden is expected to rise as more people survive into advanced age. With recent advances in acute stroke management, including the expansion of time windows for treatment with intravenous thrombolysis and mechanical thrombectomy, we are likely to see an increase in survival rates. It is therefore critically important to understand the complete pathophysiology of ischemic stroke, both in the acute and subacute stages and during the chronic phase in the months and years following an ischemic event. One of the most clinically relevant aspects of the chronic sequelae of stroke is its extended negative effect on cognition. Cognitive impairment may be related to the deterioration and dysfunctional reorganization of white matter seen at later timepoints after stroke, as well as ongoing progressive neurodegeneration. The vasculature of the brain also undergoes significant insult and remodeling following stroke, undergoing changes which may further contribute to chronic stroke pathology. While inflammation and the immune response are well established drivers of acute stroke pathology, the chronicity and functional role of innate and adaptive immune responses in the post-ischemic brain and in the peripheral environment remain largely uncharacterized. In this review, we summarize the current literature on post-stroke injury progression, its chronic pathological features, and the putative secondary injury mechanisms underlying the development of cognitive impairment and dementia. We present findings from clinical and experimental studies and discuss the long-term effects of ischemic stroke on both brain anatomy and functional outcome. Identifying mechanisms that occur months to years after injury could lead to treatment strategies in the chronic phase of stroke to help mitigate stroke-associated cognitive decline in patients.

Post-stroke immunosuppression: Exploring potential implications beyond infections

Stroke is a leading cause of mortality and disability. It occurs when cerebral blood flow is disrupted via vascular occlusion or rupture, causing tissue damage. Research has extensively examined the role of the immune response in stroke pathophysiology, focusing on infiltrated immune cells and inflammatory molecules. However, the stroke's impact on immune physiology remains underexplored. While initially stroke triggers the activation of peripheral inflammation, a subsequent profound immunosuppression occurs in a matter of hours/days. This response, potentially shielding the brain from excessive inflammation, significantly affects stroke patients. Beyond rendering patients more susceptible to infections, immunosuppression generates diverse consequences by disrupting immune system functions that are crucial for organ homeostasis. This review explores the effects of immunosuppression on stroke patients, shedding light on potential issues in immune organs such as the spleen and bone marrow, as well as non-immune organs like the small intestine, liver and heart. By synthesizing existing literature and offering additional insights, this manuscript highlights the multifaceted impact of post-stroke immunosuppression.

Regulatory T cells: A suppressor arm in post-stroke immune homeostasis

The activation of the immune system and the onset of pro- and anti-inflammatory responses play crucial roles in the pathophysiological processes of ischaemic stroke (IS). CD4+ regulatory T (Treg) cells is the main immunosuppressive cell population that is studied in the context of peripheral tolerance, autoimmunity, and the development of chronic inflammatory diseases. In recent years, more studies have focused on immune modulation after IS, and Treg cells have been demonstrated to be essential in the remission of inflammation, nerve regeneration, and behavioural recovery. However, the exact effects of Treg cells in the context of IS remain controversial, with some studies suggesting a negative correlation with stroke outcomes. In this review, we aim to provide a comprehensive overview of the current understanding of Treg cell involvement in post-stroke homeostasis. We summarized the literature focusing on the temporal changes in Treg cell populations after IS, the mechanisms of Treg cell-mediated immunomodulation in the brain, and the potential of Treg cell-based therapies for treatment. The purposes of the current article are to address the importance of Treg cells and inspire more studies to help physicians, as well as scientists, understand the whole map of immune responses during IS.

Imaging increased metabolism in the spinal cord in mice after middle cerebral artery occlusion

Emerging evidence indicates crosstalk between the brain and hematopoietic system following cerebral ischemia. Here, we investigated metabolism and oxygenation in the spleen and spinal cord in a transient middle cerebral artery occlusion (tMCAO) model. Sham-operated and tMCAO mice underwent [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) to assess glucose metabolism. Naïve, sham-operated and tMCAO mice underwent multispectral optoacoustic tomography (MSOT) assisted by quantitative model-based reconstruction and unmixing algorithms for accurate mapping of oxygenation patterns in peripheral tissues at 24 h after reperfusion. We found increased [18F]FDG uptake and reduced MSOT oxygen saturation, indicating hypoxia in the thoracic spinal cord of tMCAO mice compared with sham-operated mice but not in the spleen. Reduced spleen size was observed in tMCAO mice compared with sham-operated mice ex vivo. tMCAO led to an increase in the numbers of mature T cells in femoral bone marrow tissues, concomitant with a stark reduction in these cell subsets in the spleen and peripheral blood. The combination of quantitative PET and MSOT thus enabled observation of hypoxia and increased metabolic activity in the spinal cord of tMCAO mice at 24 h after occlusion compared to sham-operated mice.

T-cell receptor signaling modulated by the co-receptors: Potential targets for stroke treatment

Stroke is a severe and life-threatening disease, necessitating more research on new treatment strategies. Infiltrated T lymphocytes, an essential adaptive immune cell with extensive effector function, are crucially involved in post-stroke inflammation. Immediately after the initiation of the innate immune response triggered by microglia/macrophages, the adaptive immune response associated with T lymphocytes also participates in the complex pathophysiology of stroke and partially informs the outcome of stroke. Preclinical and clinical studies have revealed the conflicting roles of T cells in post-stroke inflammation and as potential therapeutic targets. Therefore, exploring the mechanisms that underlie the adaptive immune response associated with T lymphocytes in stroke is essential. The T-cell receptor (TCR) and its downstream signaling regulate T lymphocyte differentiation and activation. This review comprehensively summarizes the various molecules that regulate TCR signaling and the T-cell response. It covers both the co-stimulatory and co-inhibitory molecules and their roles in stroke. Because immunoregulatory therapies targeting TCR and its mediators have achieved great success in some proliferative diseases, this article also summarizes the advances in therapeutic strategies related to TCR signaling in lymphocytes after stroke, which can facilitate translation. DATA AVAILABILITY: No data was used for the research described in the article.

Targeting p53 for neuroinflammation: New therapeutic strategies in ischemic stroke

Ischemic stroke (IS) is characterized by high incidence, high recurrence, and high mortality and places a heavy burden on society and families. The pathological mechanisms of IS are complex, among which secondary neurological impairment mediated by neuroinflammation is considered to be the main factor in cerebral ischemic injury. At present, there is still a lack of specific therapies to treat neuroinflammation. The tumor suppressor protein p53 has long been regarded as a key substance in the regulation of the cell cycle and apoptosis in the past. Recently, studies have found that p53 also plays an important role in neuroinflammatory diseases, such as IS. Therefore, p53 may be a crucial target for the regulation of the neuroinflammatory response. Here, we provide a comprehensive review of the potential of targeting p53 in the treatment of neuroinflammation after IS. We describe the function of p53, the major immune cells involved in neuroinflammation, and the role of p53 in inflammatory responses mediated by these cells. Finally, we summarize the therapeutic strategies of targeting p53 in regulating the neuroinflammatory response after IS to provide new directions and ideas for the treatment of ischemic brain injury.

Regulatory T lymphocytes as a therapy for ischemic stroke

Unrestrained excessive inflammatory responses exacerbate ischemic brain injury and impede post-stroke brain recovery. CD4+CD25+Foxp3+ regulatory T (Treg) cells play important immunosuppressive roles to curtail inflammatory responses and regain immune homeostasis after stroke. Accumulating evidence confirms that Treg cells are neuroprotective at the acute stage after stroke and promote brain repair at the chronic phases. The beneficial effects of Treg cells are mediated by diverse mechanisms involving cell-cell interactions and soluble factor release. Multiple types of cells, including both immune cells and non-immune CNS cells, have been identified to be cellular targets of Treg cells. In this review, we summarize recent findings regarding the function of Treg cells in ischemic stroke and the underlying cellular and molecular mechanisms. The protective and reparative properties of Treg cells endorse them as good candidates for immune therapy. Strategies that boost the numbers and functions of Treg cells have been actively developing in the fields of transplantation and autoimmune diseases. We discuss the approaches for Treg cell expansion that have been tested in stroke models. The application of these approaches to stroke patients may bring new hope for stroke treatments.

Glial roles in sterile inflammation after ischemic stroke

Stroke is a leading cause of death and disability worldwide, but there are a limited number of therapies that improve patients' functional recovery. The complicated mechanisms of post-stroke neuroinflammation, which is responsible for secondary ischemic neuronal damage, have been clarified by extensive research. Activation of microglia and astrocytes due to ischemic insults is implicated in the production of pro-inflammatory factors, formation of the glial scar, and breakdown of the blood-brain barrier. This leads to the infiltration of leukocytes, which are activated by damage-associated molecular patterns (DAMPs) to produce pro-inflammatory factors and induce additional neuronal damage. In this review, we focus on the glial mechanisms underlying sterile post-ischemic inflammation after stroke.

T-cell infiltration in the central nervous system and their association with brain calcification in Slc20a2-deficient mice

Primary familial brain calcification (PFBC) is a rare neurodegenerative and neuropsychiatric disorder characterized by bilateral symmetric intracranial calcification along the microvessels or inside neuronal cells in the basal ganglia, thalamus, and cerebellum. Slc20a2 homozygous (HO) knockout mice are the most commonly used model to simulate the brain calcification phenotype observed in human patients. However, the cellular and molecular mechanisms related to brain calcification, particularly at the early stage much prior to the emergence of brain calcification, remain largely unknown. In this study, we quantified the central nervous system (CNS)-infiltrating T-cells of different age groups of Slc20a2-HO and matched wild type mice and found CD45⁺CD3⁺ T-cells to be significantly increased in the brain parenchyma, even in the pre-calcification stage of 1-month-old -HO mice. The accumulation of the CD3⁺ T-cells appeared to be associated with the severity of brain calcification. Further immunophenotyping revealed that the two main subtypes that had increased in the brain were CD3⁺ CD4^- CD8^- and CD3⁺ CD4⁺ T-cells. The expression of endothelial cell (EC) adhesion molecules increased, while that of tight and adherents junction proteins decreased, providing the molecular precondition for T-cell recruitment to ECs and paracellular migration into the brain. The fusion of lymphocytes and EC membranes and transcellular migration of CD3-related gold particles were captured, suggesting enhancement of transcytosis in the brain ECs. Exogenous fluorescent tracers and endogenous IgG and albumin leakage also revealed an impairment of transcellular pathway in the ECs. FTY720 significantly alleviated brain calcification, probably by reducing T-cell infiltration, modulating neuroinflammation and ossification process, and enhancing the autophagy and phagocytosis of CNS-resident immune cells. This study clearly demonstrated CNS-infiltrating T-cells to be associated with the progression of brain calcification. Impairment of blood-brain barrier (BBB) permeability, which was closely related to T-cell invasion into the CNS, could be explained by the BBB alterations of an increase in the paracellular and transcellular pathways of brain ECs. FTY720 was found to be a potential drug to protect patients from PFBC-related lesions in the future.

Systemic immune derangements are shared across various CNS pathologies and reflect novel mechanisms of immune privilege

Background

The nervous and immune systems interact in a reciprocal manner, both under physiologic and pathologic conditions. Literature spanning various CNS pathologies including brain tumors, stroke, traumatic brain injury and de-myelinating diseases describes a number of associated systemic immunologic changes, particularly in the T-cell compartment. These immunologic changes include severe T-cell lymphopenia, lymphoid organ contraction, and T-cell sequestration within the bone marrow.

Methods

We performed an in-depth systematic review of the literature and discussed pathologies that involve brain insults and systemic immune derangements.

Conclusions

In this review, we propose that the same immunologic changes hereafter termed 'systemic immune derangements', are present across CNS pathologies and may represent a novel, systemic mechanism of immune privilege for the CNS. We further demonstrate that systemic immune derangements are transient when associated with isolated insults such as stroke and TBI but persist in the setting of chronic CNS insults such as brain tumors. Systemic immune derangements have vast implications for informed treatment modalities and outcomes of various neurologic pathologies.

Inflammatory Responses After Ischemic Stroke

Ischemic stroke generates an immune response that contributes to neuronal loss as well as tissue repair. This is a complex process involving a range of cell types and effector molecules and impacts tissues outside of the CNS. Recent reviews address specific aspects of this response, but several years have passed and important advances have been made since a high-level review has summarized the overall state of the field. The present review examines the initiation of the inflammatory response after ischemic stroke, the complex impacts of leukocytes on patient outcome, and the potential of basic science discoveries to impact the development of therapeutics. The information summarized here is derived from broad PubMed searches and aims to reflect recent research advances in an unbiased manner. We highlight valuable recent discoveries and identify gaps in knowledge that have the potential to advance our understanding of this disease and therapies to improve patient outcomes.

Interactions between the Autonomic Nervous System and the Immune System after Stroke

Acute stroke is one of the leading causes of morbidity and mortality worldwide. Stroke-induced immune-inflammatory response occurs in the perilesion areas and the periphery. Although stroke-induced immunosuppression may alleviate brain injury, it hinders brain repair as the immune-inflammatory response plays a bidirectional role after acute stroke. Furthermore, suppression of the systemic immune-inflammatory response increases the risk of life-threatening systemic bacterial infections after acute stroke. Therefore, it is essential to explore the mechanisms that underlie the stroke-induced immune-inflammatory response. Autonomic nervous system (ANS) activation is critical for regulating the local and systemic immune-inflammatory responses and may influence the prognosis of acute stroke. We review the changes in the sympathetic and parasympathetic nervous systems and their influence on the immune-inflammatory response after stroke. Importantly, this article summarizes the mechanisms on how ANS regulates the immune-inflammatory response through neurotransmitters and their receptors in immunocytes and immune organs after stroke. To facilitate translational research, we also discuss the promising therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response to promote neurologic recovery after stroke. © 2022 American Physiological Society. Compr Physiol 12:3665-3704, 2022.

Prunus cerasoides Extract and Its Component Compounds Upregulate Neuronal Neuroglobin Levels, Mediate Antioxidant Effects, and Ameliorate Functional Losses in the Mouse Model of Cerebral Ischemia

Prunus cerasoides (PC) has been reported to have antimicrobial and anti-inflammatory properties, but its potential as a neuroprotective agent in a mouse model of cerebral ischemia has not been explored. Considering neuroglobin (Ngb), an endogenous neuroprotective factor, as a novel approach to neuroprotection, in this study, Ngb promoter activity, Ngb expression changes, and antioxidant protection by PC extract (PCE) and PC component compounds (PCCs) were analyzed in oxygen-glucose deprivation (OGD)-treated neurons. In vivo analysis involved transient middle cerebral artery occlusion (tMCAO) in mice with pre- and post-treatment exposure to PCE. Following ischemic stroke induction, neurological behavior scores were obtained, and cellular function-related signals were evaluated in the ischemic infarct areas. In addition to PCE, certain component compounds from PCE also significantly increased Ngb levels and attenuated the intracellular ROS production and cytotoxicity seen with OGD in primary neurons. Administration of PCE reduced the infarct volume and improved neurological deficit scores in ischemic stroke mice compared with the vehicle treatment. Increased Ngb levels in infarct penumbra with PCE treatment were also accompanied by decreased markers of apoptosis (activated p38 and cleaved caspase-3). Our findings point to the benefits of Ngb-mediated neuroprotection via PCE and its antioxidant activity in an ischemic stroke model.