Functional innervation of hepatic iNKT cells is immunosuppressive following stroke

Blocking Sympathetic Nervous System Reverses Partially Stroke-Induced Immunosuppression but does not Aggravate Functional Outcome After Experimental Stroke in Rats

Stoke results in activation of the sympathetic nervous system (SNS), inducing systemic immunosuppression. However, the potential mechanisms underlying stroke-induced immunosuppression remain unclear. Here, we determined the SNS effects on functional outcome and explored the interactions among SNS, β-arrestin2 and nuclear factor-κB (NF-κB) after experimental stroke in rats. In the current study, stroke was induced by a transient middle cerebral artery occlusion (MCAO) in rats, and SNS activity was inhibited by intraperitoneal injection of 6-hydroxydopamine HBr (6-OHDA). 7.0 T Micro-MRI and Longa score were employed to assess the functional outcome after stroke. Flow cytometry and ELISA assay were used to measure the expression of MHC class II, tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). Western blot was conducted to analyze β-arrestin2 and NF-κB protein expression levels after experimental stroke. We found significantly increased infarct volumes and functional impairment after MCAO at different post-surgery time points, which were not aggravated by 6-OHDA treatment. SNS blockade partially reversed the expression of MHC class II after stroke over time, as well as TNF-α and IFN-γ levels in lipopolysaccharide-stimulated macrophages in vitro. Treatment of MCAO rats with SNS-inhibitor significantly diminished NF-κB activation and enhanced β-arrestin2 expression after stroke. This study suggests that pharmacological SNS inhibition dose not aggravate functional outcome after stroke. Stroke-induced immunosuppression may be involved in the SNS-β-arrestin2-NF-κB pathway.

Exosomes in stroke pathogenesis and therapy

Stroke is one of the leading causes of death and disability worldwide. Stroke recovery is orchestrated by a set of highly interactive processes that involve the neurovascular unit and neural stem cells. Emerging data suggest that exosomes play an important role in intercellular communication by transferring exosomal protein and RNA cargo between source and target cells in the brain. Here, we review these advances and their impact on promoting coupled brain remodeling processes after stroke. The use of exosomes for therapeutic applications in stroke is also highlighted.

Atypical sensors for direct and rapid neuronal detection of bacterial pathogens

Bacterial infection can threaten the normal biological functions of a host, often leading to a disease. Hosts have developed complex immune systems to cope with the danger. Preceding the elimination of pathogens, selective recognition of the non-self invaders is necessary. At the forefront of the body’s defenses are the innate immune cells, which are equipped with particular sensor molecules that can detect common exterior patterns of invading pathogens and their secreting toxins as well as with phagocytic machinery. Inflammatory mediators and cytokines released from these innate immune cells and infected tissues can boost the inflammatory cascade and further recruit adaptive immune cells to maximize the elimination and resolution. The nervous system also seems to interact with this process, mostly known to be affected by the inflammatory mediators through the binding of neuronal receptors, consequently activating neural circuits that tune the local and systemic inflammatory states. Recent research has suggested new contact points: direct interactions of sensory neurons with pathogens. Latest findings demonstrated that the sensory neurons not only share pattern recognition mechanisms with innate immune cells, but also utilize endogenous and exogenous electrogenic components for bacterial pathogen detection, by which the electrical firing prompts faster information flow than what could be achieved when the immune system is solely involved. As a result, rapid pain generation and active accommodation of the immune status occur. Here we introduced the sensory neuron-specific detector molecules for directly responding to bacterial pathogens and their signaling mechanisms. We also discussed extended issues that need to be explored in the future.

First translational 'Think Tank' on cerebrovascular disease, cognitive impairment and dementia

As the human population continues to age, an increasing number of people will exhibit significant deficits in cognitive function and dementia. It is now recognized that cerebrovascular, metabolic and neurodegenerative diseases all play major roles in the evolution of cognitive impairment and dementia. Thus with our more recent recognition of these relationships and our need to understand and more positively impact on this world health problem, "The Leo and Anne Albert Charitable Trust" (Gene Pranzo, Trustee with significant support from Susan Brogan, Meeting Planner) provided generous support for this inaugural international workshop that was held from April 13-16, 2015 at the beautiful Ritz Carlton Golf Resort in North Naples, Florida. Researchers from SUNY Downstate Medical Center, Brooklyn, NY organized the event by selecting the present group of translationally inclined preclinical, clinical and population scientists focused on cerebrovascular disease (CVD) risk and its progression to vascular cognitive impairment (VCI) and dementia. Participants at the workshop addressed important issues related to aging, cognition and dementia by: (1) sharing new data, information and perspectives that intersect vascular, metabolic and neurodegenerative diseases, (2) discussing gaps in translating population risk, clinical and preclinical information to the progression of cognitive loss, and (3) debating new approaches and methods to fill these gaps that can translate into future therapeutic interventions. Participants agreed on topics for group discussion prior to the meeting and focused on specific translational goals that included promoting better understanding of dementia mechanisms, the identification of potential therapeutic targets for intervention, and discussed/debated the potential utility of diagnostic/prognostic markers. Below summarizes the new data-presentations, concepts, novel directions and specific discussion topics addressed by this international translational team at our "First Leo and Anne Albert Charitable Trust 'Think Tank' VCI workshop".

Ischemia, Immunosuppression and Infection--Tackling the Predicaments of Post-Stroke Complications

The incidence of stroke has risen over the past decade and will continue to be one of the leading causes of death and disability worldwide. While a large portion of immediate death following stroke is due to cerebral infarction and neurological complications, the most common medical complication in stroke patients is infection. In fact, infections, such as pneumonia and urinary tract infections, greatly worsen the clinical outcome of stroke patients. Recent evidence suggests that the disrupted interplay between the central nervous system and immune system contributes to the development of infection after stroke. The suppression of systemic immunity by the nervous system is thought to protect the brain from further inflammatory insult, yet this comes at the cost of increased susceptibility to infection after stroke. To improve patient outcome, there have been attempts to lessen the stroke-associated bacterial burden through the prophylactic use of broad-spectrum antibiotics. However, preventative antibiotic treatments have been unsuccessful, and therefore have been discouraged. Additionally, with the ever-rising obstacle of antibiotic-resistance, future therapeutic options to reverse immune impairment after stroke by augmentation of host immunity may be a viable alternative option. However, cautionary steps are required to ensure that collateral ischemic damage caused by cerebral inflammation remains minimal.

Traumatic Brain Injury and Peripheral Immune Suppression: Primer and Prospectus

Nosocomial infections are a common occurrence in patients following traumatic brain injury (TBI) and are associated with an increased risk of mortality, longer length of hospital stay, and poor neurological outcome. Systemic immune suppression arising as a direct result of injury to the central nervous system (CNS) is considered to be primarily responsible for this increased incidence of infection, a view strengthened by recent studies that have reported novel changes in the composition and function of the innate and adaptive arms of the immune system post-TBI. However, our knowledge of the mechanisms that underlie TBI-induced immune suppression is equivocal at best. Here, after summarizing our current understanding of the impact of TBI on peripheral immunity and discussing CNS-mediated regulation of immune function, we propose roles for a series of novel mechanisms in driving the immune suppression that is observed post-TBI. These mechanisms, which have never been considered before in the context of TBI-induced immune paresis, include the CNS-driven emergence into the circulation of myeloid-derived suppressor cells and suppressive neutrophil subsets, and the release from injured tissue of nuclear and mitochondria-derived damage associated molecular patterns. Moreover, in an effort to further our understanding of the mechanisms that underlie TBI-induced changes in immunity, we pose throughout the review a series of questions, which if answered would address a number of key issues, such as establishing whether manipulating peripheral immune function has potential as a future therapeutic strategy by which to treat and/or prevent infections in the hospitalized TBI patient.

Role of IL-12 in overcoming the low responsiveness of NK cells to missing self after traumatic brain injury

Blood samples from 32 patients with severe Traumatic brain injury (TBI) were studied and compared with 11 cardiac surgery patients, and 29 healthy controls. A dramatic decreased expression of HLA class I molecules on monocytes was associated with increased KIR+ NK cell frequency in TBI patients. Overall, the phenotype of TBI NK cells marked by KIR and CD57 expression and lower level of NKp46 and DNAM-1 reflected a differentiated state. The NK-cell response to missing self was marked by lower degranulation and lower IFN-γ production after stimulation with HLA class I deficient cell line. In contrast, the NK-cell ADCC was not altered. IL-12 was able to restore both IFN-γ production and the cytotoxicity capacities of NK cells. This study provides the first extensive description of the phenotype and functions of NK cells in TBI patients. Further evaluation of IL-12 treatment to overcome immunosuppression-induced nosocomial infections is warranted.

Remote Ischemic Preconditioning-Mediated Neuroprotection against Stroke is Associated with Significant Alterations in Peripheral Immune Responses

AIMS

Remote ischemic preconditioning (RIPC) of a limb is a clinically feasible strategy to protect against ischemia-reperfusion injury after stroke. However, the mechanism underlying RIPC remains elusive.

METHODS

We generated a rat model of noninvasive RIPC by four repeated cycles of brief blood flow constriction (5 min) in the hindlimbs using a tourniquet. Blood was collected 1 h after preconditioning and 3 days after brain reperfusion. The impact of RIPC on immune cell and cytokine profiles prior to and after transient middle cerebral artery occlusion (MCAO) was assessed.

RESULTS

Remote ischemic preconditioning protects against focal ischemia and preserves neurological functions 3 days after stroke. Flow cytometry analysis demonstrated that RIPC ameliorates the post-MCAO reduction of CD3(+)CD8(+) T cells and abolishes the reduction of CD3(+)/CD161a(+) NKT cells in the blood. In addition, RIPC robustly elevates the percentage of B cells in peripheral blood, thereby reversing the reduction in the B-cell population after stroke. RIPC also markedly elevates the percentage of CD43(+)/CD172a(+) noninflammatory resident monocytes, without any impact on the percentage of CD43(-)/CD172a(+) inflammatory monocytes. Finally, RIPC induces IL-6 expression and enhances the elevation of TNF-α after stroke.

CONCLUSION

Our results reveal dramatic immune changes during RIPC-afforded neuroprotection against cerebral ischemia.

Understanding liver immunology using intravital microscopy

The liver has come a long way since it was considered only a metabolic organ attached to the gastrointestinal tract. The simultaneous ascension of immunology and intravital microscopy evidenced the liver as a central axis in the immune system, controlling immune responses to local and systemic agents as well as disease tolerance. The multiple hepatic cell populations are organized in a vascular environment that promotes intimate cellular interactions, including initiation of innate and adaptive immune responses, rapid leukocyte recruitment, pathogen clearance and production of a variety of immune mediators. In this review, we focus on the advances in liver immunology supported by intravital microscopy in diseases such as isquemia/reperfusion, acute liver injury and infections.

Immune interventions in stroke

Approaches for the effective management of acute stroke are sparse, and many measures for brain protection fail. However, our ability to modulate the immune system and modify the progression of multiple sclerosis is increasing. As a result, immune interventions are currently being explored as therapeutic interventions in acute stroke. In this Review, we compare the immunological features of acute stroke with those of multiple sclerosis, identify unique immunological features of stroke, and consider the evidence for immune interventions. In patients with acute stroke, microglial activation and cell death products trigger an inflammatory cascade that damages vessels and the parenchyma within minutes to hours of the ischaemia or haemorrhage. Immune interventions that restrict brain inflammation, vascular permeability and tissue oedema must be administered rapidly to reduce acute immune-mediated destruction and to avoid subsequent immunosuppression. Preliminary results suggest that the use of drugs that modify disease in multiple sclerosis might accomplish these goals in ischaemic and haemorrhagic stroke. Further elucidation of the immune mechanisms involved in stroke is likely to lead to successful immune interventions.

Blocking stroke-induced immunodeficiency increases CNS antigen-specific autoreactivity but does not worsen functional outcome after experimental stroke

Stroke-induced immunodepression (SIDS) is an essential cause of poststroke infections. Pharmacological inhibition of SIDS appears promising in preventing life-threatening infections in stroke patients. However, SIDS might represent an adaptive mechanism preventing autoreactive immune responses after stroke. To address this, we used myelin oligodendrocyte glycoprotein (MOG) T-cell receptor transgenic (2D2) mice where >80% of peripheral CD4(+) T cells express a functional receptor for MOG. We investigated in a murine model of middle cerebral artery occlusion the effect of blocking SIDS by inhibiting body's main stress axes, the sympathetic nervous system (SNS) with propranolol and the hypothalamic-pituitary-adrenal axis (HPA) with mifepristone. Blockade of both stress axes robustly reduced infarct volumes, decreased infection rate, and increased long-term survival of 2D2 and C57BL/6J wild-type mice. Despite these protective effects, blockade of SIDS increased CNS antigen-specific Type1 T helper cell (Th1) responses in the brains of 2D2 mice 14 d after middle cerebral artery occlusion. One month after experimental stroke, 2D2 mice developed signs of polyradiculitis, which were diminished by SIDS blockade. Adoptive transfer of CD4(+) T cells, isolated from 2D2 mice, into lymphocyte-deficient Rag-1KO mice did not reveal differences between SIDS blockade and vehicle treatment in functional long-term outcome after stroke. In conclusion, inhibiting SIDS by pharmacological blockade of body's stress axes increases autoreactive CNS antigen-specific T-cell responses in the brain but does not worsen functional long-term outcome after experimental stroke, even in a mouse model where CNS antigen-specific autoreactive T-cell responses are boosted.

Control of intestinal homeostasis through crosstalk between natural killer T cells and the intestinal microbiota

The human host and the intestinal microbiota co-exist in a mutually beneficial relationship, which contributes to host and microbial metabolism as well as maturation of the host's immune system, among many other pathways (Tremaroli and Backhed, 2012; Hooper et al., 2012). At mucosal surfaces, and particularly in the intestine, the commensal microbiota provides 'colonization resistance' to invading pathogens and maintains homeostasis through microbial regulation of mucosal innate and adaptive immunity (Renz et al., 2012). Recent evidence suggests that natural killer T cells (NKT cells), a subgroup of lipid-reactive T cells, play central roles in bidirectional interactions between the host and the commensal microbiota, which govern intestinal homeostasis and prevent inflammation. Here, we provide a brief overview of recently identified pathways of commensal microbial regulation of NKT cells, discuss feedback mechanisms of NKT cell-dependent control of microbial colonization and composition, and highlight the critical role of host-microbial cross-talk for prevention of NKT cell-dependent mucosal inflammation.

T Cells and Cerebral Ischemic Stroke

Stroke results in cerebral inflammation that causes brain injury and triggers immunodepression, resulting in an increased incidence of morbidity and mortality secondary to remote infection. It is well known that T cells modulate brain inflammation after ischemic stroke, and targeting T cells may be an innovative therapeutic strategy for stroke treatment. T cell deficiency is neuro-protective, but the observed protective effects differ between ischemic models. Recent studies suggest different T cell subsets may have distinct effects on the injured brain. In addition to their role in cerebral inflammation, T cells also play a role in stroke-induced immunodepression. Therefore, T cell-targeted therapies designed to provide protection against brain inflammation might paradoxically contribute to remote organ infection and mortality. Further investigations are required to determine the role of specific T cell subsets in cerebral inflammation and stroke-induced immunodepression, the optimal therapeutic window for treatment, and the appropriate dose of anti-T cell therapy.

Spatiotemporal dynamics of effector CD8+ T cell responses within the liver

CD8(+) T cells play a critical role in controlling hepatotropic viral infections, such as those caused by hepatitis B and hepatitis C viruses. The capacity of these cells to protect against such pathogens is mediated by antigen-experienced effector cells and relies on their ability to home to the liver, recognize pathogen-derived antigens, and deploy effector functions. Here, we review how dynamic imaging of hepatic effector CD8(+) T cell migration and function in mouse models of hepatitis B virus pathogenesis has recently revealed a unique and novel mode of adaptive immune surveillance. Circulating effector CD8(+) T cells initially arrest within liver sinusoids by docking onto adherent platelets and then actively crawl along the liver vasculature, probing hepatocytes for the presence of antigens by extending protrusions through the fenestrated sinusoidal endothelial cells. Hepatocellular antigen recognition and effector functions occur while CD8(+) T cells are still confined to the intravascular space and are inhibited by the pathologic processes that characterize liver fibrosis. A detailed understanding of the spatiotemporal dynamics of effector CD8(+) T cells within the liver is important for the rational design of targeted immunotherapeutic approaches for chronic liver infections.

Effect of β-Adrenergic Antagonists on In-Hospital Mortality after Ischemic Stroke

BACKGROUND

Ischemic stroke accounts for 85%-90% of all strokes and currently has very limited therapeutic options. Recent studies of β-adrenergic antagonists suggest they may have neuroprotective effects that lead to improved functional outcomes in rodent models of ischemic stroke; however, there are limited data in patients. We aimed to determine whether there was an improvement in mortality rates among patients who were taking β-blockers during the acute phase of their ischemic stroke.

METHODS

A retrospective analysis of a prospectively collected database of ischemic stroke patients was performed. Patients who were on β-adrenergic antagonists both at home and during the first 3 days of hospitalization were compared with patients who were not on β-adrenergic antagonists to determine the association with patient mortality rates.

RESULTS

The study included a patient population of 2804 patients. In univariate analysis, use of β-adrenergic antagonists was associated with older age, atrial fibrillation, hypertension, and more-severe initial stroke presentation. Despite this, multivariable analysis revealed a reduction in in-hospital mortality among patients who were treated with β-adrenergic antagonists (odds ratio, .657; 95% confidence interval, .655-.658).

CONCLUSIONS

The continuation of home β-adrenergic antagonist medication during the first 3 days of hospitalization after an ischemic stroke is associated with a decrease in patient mortality. This supports the work done in rodent models suggesting neuroprotective effects of β-blockers after ischemic stroke.

Role of Innate T Cells in Anti-Bacterial Immunity

Innate T cells are a heterogeneous group of αβ and γδ T cells that respond rapidly (<2 h) upon activation. These innate T cells also share a non MHC class I or II restriction requirement for antigen recognition. Three major populations within the innate T cell group are recognized, namely, invariant NKT cells, mucosal associated invariant T cells, and gamma delta T cells. These cells recognize foreign/self-lipid presented by non-classical MHC molecules, such as CD1d, MR1, and CD1a. They are activated during the early stages of bacterial infection and act as a bridge between the innate and adaptive immune systems. In this review, we focus on the functional properties of these three innate T cell populations and how they are purposed for antimicrobial defense. Furthermore, we address the mechanisms through which their effector functions are targeted for bacterial control and compare this in human and murine systems. Lastly, we speculate on future roles of these cell types in therapeutic settings such as vaccination.

Catecholamines and acetylcholine are key regulators of the interaction between microbes and the immune system

Recent studies suggest that catecholamines (CAs) and acetylcholine (ACh) play essential roles in the crosstalk between microbes and the immune system. Host cholinergic afferent fibers sense pathogen-associated molecular patterns and trigger efferent cholinergic and catecholaminergic pathways that alter immune cell proliferation, differentiation, and cytokine production. On the other hand, microbes have the ability to produce and degrade ACh and also regulate autogenous functions in response to CAs. Understanding the role played by these neurotransmitters in host-microbe interactions may provide valuable information for the development of novel therapies.

Regulation of NKT Cell Localization in Homeostasis and Infection

Natural killer T (NKT) cells are a specialized subset of T lymphocytes that regulate immune responses in the context of autoimmunity, cancer, and microbial infection. Lipid antigens derived from bacteria, parasites, and fungi can be presented by CD1d molecules and recognized by the canonical T cell receptors on NKT cells. Alternatively, NKT cells can be activated through recognition of self-lipids and/or pro-inflammatory cytokines generated during infection. Unlike conventional T cells, only a small subset of NKT cells traffic through the lymph nodes under homeostatic conditions, with the largest NKT cell populations localizing to the liver, lungs, spleen, and bone marrow. This is thought to be mediated by differences in chemokine receptor expression profiles. However, the impact of infection on the tissue localization and function of NKT remains largely unstudied. This review focuses on the mechanisms mediating the establishment of peripheral NKT cell populations during homeostasis and how tissue localization of NKT cells is affected during infection.

Intravital imaging - dynamic insights into natural killer T cell biology

Natural killer T (NKT) cells were first recognized more than two decades ago as a separate and distinct lymphocyte lineage that modulates an expansive range of immune responses. As innate immune cells, NKT cells are activated early during inflammation and infection, and can subsequently stimulate or suppress the ensuing immune response. As a result, researchers hope to harness the immunomodulatory properties of NKT cells to treat a variety of diseases. However, many questions still remain unanswered regarding the biology of NKT cells, including how these cells traffic from the thymus to peripheral organs and how they play such contrasting roles in different immune responses and diseases. In this new era of intravital fluorescence microscopy, we are now able to employ this powerful tool to provide quantitative and dynamic insights into NKT cell biology including cellular dynamics, patrolling, and immunoregulatory functions with exquisite resolution. This review will highlight and discuss recent studies that use intravital imaging to understand the spectrum of NKT cell behavior in a variety of animal models.

Higher vagal activity as related to survival in patients with advanced breast cancer: an analysis of autonomic dysregulation

OBJECTIVE

High levels of high-frequency heart rate variability (HF-HRV), related to parasympathetic-nervous-system functioning, have been associated with longer survival in patients with myocardial infarction and acute trauma and in patients undergoing palliative care. From animal studies linking higher vagal activity with better immune system functioning and reduced metastases, we hypothesized that higher HF-HRV would predict longer survival in patients with metastatic or recurrent breast cancer (MRBC).

METHODS

Eighty-seven patients with MRBC participated in a laboratory task including a 5-minute resting baseline electrocardiogram. HF-HRV was computed as the natural logarithm of the summed power spectral density of R-R intervals (0.15-0.50 Hz). In this secondary analysis of a study testing whether diurnal cortisol slope predicted survival, we tested the association between resting baseline HF-HRV on survival using Cox proportional hazards models.

RESULTS

A total of 50 patients died during a median follow-up of 7.99 years. Higher baseline HF-HRV predicted significantly longer survival, with a hazard ratio of 0.75 (95% confidence interval = 0.60-0.92, p = .006). Visceral metastasis status and baseline heart rate were related to both HF-HRV and survival. However, a combination of HF-HRV and heart rate further improved survival prediction, with a hazard ratio of 0.64 (95% confidence interval = 0.48-0.85, p = .002).

CONCLUSIONS

Vagal activity of patients with MRBC strongly predicted their survival, extending the known predictive window of HF-HRV in cancer beyond palliative care. Vagal activity can be altered by behavioral, pharmacological, and surgical interventions and may be a promising target for extending life expectancy in patients with metastasizing cancer.

Immunosurveillance of the liver by intravascular effector CD8(+) T cells

Effector CD8(+) T cells (CD8 TE) play a key role during hepatotropic viral infections. Here, we used advanced imaging in mouse models of hepatitis B virus (HBV) pathogenesis to understand the mechanisms whereby these cells home to the liver, recognize antigens, and deploy effector functions. We show that circulating CD8 TE arrest within liver sinusoids by docking onto platelets previously adhered to sinusoidal hyaluronan via CD44. After the initial arrest, CD8 TE actively crawl along liver sinusoids and probe sub-sinusoidal hepatocytes for the presence of antigens by extending cytoplasmic protrusions through endothelial fenestrae. Hepatocellular antigen recognition triggers effector functions in a diapedesis-independent manner and is inhibited by the processes of sinusoidal defenestration and capillarization that characterize liver fibrosis. These findings reveal the dynamic behavior whereby CD8 TE control hepatotropic pathogens and suggest how liver fibrosis might reduce CD8 TE immune surveillance toward infected or transformed hepatocytes.

DAMP signaling is a key pathway inducing immune modulation after brain injury

Acute brain lesions induce profound alterations of the peripheral immune response comprising the opposing phenomena of early immune activation and subsequent immunosuppression. The mechanisms underlying this brain-immune signaling are largely unknown. We used animal models for experimental brain ischemia as a paradigm of acute brain lesions and additionally investigated a large cohort of stroke patients. We analyzed release of HMGB1 isoforms by mass spectrometry and investigated its inflammatory potency and signaling pathways by immunological in vivo and in vitro techniques. Features of the complex behavioral sickness behavior syndrome were characterized by homecage behavior analysis. HMGB1 downstream signaling, particularly with RAGE, was studied in various transgenic animal models and by pharmacological blockade. Our results indicate that the cytokine-inducing, fully reduced isoform of HMGB1 was released from the ischemic brain in the hyperacute phase of stroke in mice and patients. Cytokines secreted in the periphery in response to brain injury induced sickness behavior, which could be abrogated by inhibition of the HMGB1-RAGE pathway or direct cytokine neutralization. Subsequently, HMGB1-release induced bone marrow egress and splenic proliferation of bone marrow-derived suppressor cells, inhibiting the adaptive immune responses in vivo and vitro. Furthermore, HMGB1-RAGE signaling resulted in functional exhaustion of mature monocytes and lymphopenia, the hallmarks of immune suppression after extensive ischemia. This study introduces the HMGB1-RAGE-mediated pathway as a key mechanism explaining the complex postischemic brain-immune interactions.

Recent and near-future advances in nucleic acid-based diagnosis of stroke

Stroke is a leading cause of death and disability in adults, but at present, treatment for ischemic stroke reaches only a small percentage of patients. This is because of the very short time window for treatment and the time-consuming evaluation involved. Intense efforts are underway to find novel approaches to expedite stroke diagnosis and treatment. In this review, we provide the rationale for the use of blood-based nucleic acid biomarkers to advance stroke diagnosis. We describe mRNA markers identified in genomic profiling of circulating leukocytes and then outline technological issues involved in the application of these results. We then describe the novel point-of-care technology that is in development for the rapid detection of multiple mRNA molecules in circulating leukocytes.

Causes of death among persons who survive an acute ischemic stroke

Stroke and especially its complications are a leading cause of death. Despite reduced morbidity in some developed countries, mortality in stroke patients is still high worldwide. In the past decades, treatment of acute stroke has focused on early intervention, such as revascularization and cerebral edema prevention. However, long-term clinical observations indicate that poststroke pneumonia, cardiovascular complications, and vascular embolism are the major reasons for the increased death rate after stroke. Few evidence-based data are available currently to guide the management of these complications. Thus, systematic studies of these adverse events are essential and urgent to improve survival after stroke.

Effect of beta-blocker therapy on the risk of infections and death after acute stroke--a historical cohort study

Background

Infections are a frequent cause for prolonged hospitalization and increased mortality after stroke. Recent studies revealed a stroke-induced depression of the peripheral immune system associated with an increased susceptibility for infections. In a mice model for stroke, this immunosuppressive effect was reversible after beta-blocker administration. The aim of our study was to investigate the effect of beta-blocker therapy on the risk of infections and death after stroke in humans.

Methods

625 consecutive patients with ischemic or hemorrhagic stroke, admitted to a university hospital stroke unit, were included in this historical cohort study. The effect of beta-blocker therapy on post-stroke pneumonia, urinary tract infections and death was investigated using multivariable Poisson and Cox regression models.

Results

553 (88.3%) patients were admitted with ischemic stroke, the remaining 72 (11.7%) had a hemorrhagic stroke. Median baseline NIHSS was 8 (IQR 5–16) points. 301 (48.2%) patients received beta-blocker therapy. There was no difference in the risk of post-stroke pneumonia between patients with and without beta-blocker therapy (Rate Ratio = 1.00, 95%CI 0.77–1.30, p = 0.995). Patients with beta-blocker therapy showed a decreased risk for urinary tract infections (RR = 0.65, 95%CI 0.43–0.98, p = 0.040). 7-days mortality did not differ between groups (Hazard Ratio = 1.36, 95%CI 0.65–2.77, p = 0.425), while patients with beta-blocker therapy showed a higher 30-days mortality (HR = 1.93, 95%CI 1.20–3.10, p = 0.006).

Conclusions

Beta-blocker therapy did not reduce the risk for post-stroke pneumonia, but significantly reduced the risk for urinary tract infections. Different immune mechanisms underlying both diseases might explain these findings that need to be confirmed in future studies.

Cross-talk between the inflammatory response, sympathetic activation and pulmonary infection in the ischemic stroke

The immune system response and inflammation play a key role in brain injury during and after a stroke. The acute immune response is responsible for secondary brain tissue damage immediately after the stroke, followed by immunosuppression due to sympathetic nervous system activation. The latter increases risk of infection complications, such as pneumonia. The pneumonia-related inflammatory state can release a bystander autoimmune response against central nervous system antigens, thereby initiating a vicious circle. The aim of this review is to summarize the relationship between ischemic stroke, sympathetic nervous system activation and pulmonary infection.

Alterations of natural killer cells in traumatic brain injury

To investigate the relationship between natural killer (NK) cells and traumatic brain injury (TBI), we tracked an established phenotype of circulating NK cells at several time points in patients with different grades of TBI. In serial peripheral blood samples, NK cells were prospectively measured by flow cytometry of CD3(-) CD56(+) lymphocytes. Compared to healthy controls, TBI patients had reductions in both the percentage and the absolute number of NK cells. Furthermore, the magnitude of NK cell reduction correlated with the degree of TBI severity at several time points. That is, NK cell population size was independently associated with lower Glasgow Coma Scale scores. In addition, at some time points, a positive correlation was found between the NK cell counts and Glasgow Outcome Scale scores. Our results indicate that TBI induces a reduction in the number of NK cells, and the magnitude of the reduction appears to parallel the severity of TBI.

Control of lymphocyte egress from lymph nodes through β2-adrenergic receptors

Using pharmacological activation and genetic ablation of β₂-adrenergic receptors (β₂ARs) in mice, Nakai et al. show that β₂ARs expressed on lymphocytes can regulate egress of these cells from lymph nodes, while altering the responsiveness of chemokine receptors CCR7 and CXCR4. They identify that β₂ARs can physically interact with these chemokine receptors. And, in mouse models of T cell–mediated inflammation, β₂AR-mediated signals are shown to inhibit trafficking of antigen-primed T cells, reducing their numbers in inflamed peripheral tissues.

Lymphocyte recirculation through secondary lymphoid organs is essential for immunosurveillance and lymphocyte effector functions. Here, we show that signals through β₂-adrenergic receptors (β₂ARs) expressed on lymphocytes are involved in the control of lymphocyte dynamics by altering the responsiveness of chemoattractant receptors. Agonist stimulation of lymphocyte β₂ARs inhibited egress of lymphocytes from lymph nodes (LNs) and rapidly produced lymphopenia in mice. Physiological inputs from adrenergic nerves contributed to retention of lymphocytes within LNs and homeostasis of their distribution among lymphoid tissues. β₂ARs physically interacted with CCR7 and CXCR4, chemokine receptors promoting lymphocyte retention in LNs. Activation of β₂ARs enhanced retention-promoting signals through CCR7 and CXCR4, and consequently inhibited lymphocyte egress from LNs. In models of T cell–mediated inflammatory diseases, β₂AR-mediated signals inhibited LN egress of antigen-primed T cells and reduced their recruitment into peripheral tissues. Thus, this study reveals a novel mechanism for controlling lymphocyte trafficking and provides additional insights into immune regulation by the nervous system.

Approaching the next revolution? Evolutionary integration of neural and immune pathogen sensing and response

Mammalian immunity evolved by the process of natural selection that produced differential survival and reproduction advantages through combinations of hereditary traits underlying the response to pathogens. Primitive animals sense the presence of microbial pathogens through recognition of pathogen-derived molecules in their rudimentary immune and nervous systems. No molecular biological mechanism assigns primacy of pathogen sensing mechanisms to immune cells over neurons. Rather, in animals as diverse as Caenorhabditis elegans to mammals, neural reflexes are activated by the presence of pathogens and transduce neural mechanisms that control the development of immunity. A coming revolution in immunological thinking will require immunologists to incorporate neural circuits into understanding pathogen signal transduction, and the molecular mechanisms of learning, that culminate in immunity.

Differential effects of sympathetic nervous system and hypothalamic-pituitary-adrenal axis on systemic immune cells after severe experimental stroke

Infectious complications are the leading cause of death in the post-acute phase of stroke. Post-stroke immunodeficiency is believed to result from neurohormonal dysregulation of the sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA) axis. However, the differential effects of these neuroendocrine systems on the peripheral immune cells are only partially understood. Here, we determined the impact of the hormones of the SNS and HPA on distinct immune cell populations and characterized their interactions after stroke. At various time points after cortical or extensive hemispheric cerebral ischemia, plasma cortisone, corticosterone, metanephrine and adrenocorticotropic hormone (ACTH) levels were measured in mice. Leukocyte subpopulations were flow cytometrically analyzed in spleen and blood. To investigate their differential sensitivity to stress hormones, splenocytes were incubated in vitro with prednisolone, epinephrine and their respective receptor blockers. Glucocorticoid receptor (GCR) and beta2-adrenergic receptor (β2-AR) on leukocyte subpopulations were quantified by flow cytometry. In vivo effects of GCR and selective β2-AR blockade, respectively, were defined on serum hormone concentrations, lymphopenia and interferon-γ production after severe ischemia. We found elevated cortisone, corticosterone and metanephrine levels and associated lymphocytopenia only after extensive brain infarction. Prednisolone resulted in a 5 times higher cell death rate of splenocytes than epinephrine in vitro. Prednisolone and epinephrine-induced leukocyte cell death was prevented by GCR and β2-AR blockade, respectively. In vivo, only GCR blockade prevented post ischemic lymphopenia whereas β2-AR preserved interferon-γ secretion by lymphocytes. GCR blockade increased metanephrine levels in vivo and prednisolone, in turn, decreased β2-AR expression on lymphocytes. In conclusion, mediators of the SNS and the HPA axis differentially affect the systemic immune system after stroke. Moreover, our findings suggest a negative-feedback of corticosteroids on the sympathetic axis which may control the post-stroke stress-reaction. This complex interplay between the HPA and the SNS after stroke has to be considered when targeting the neurohormonal systems in the post acute phase of severe stroke.

Neuroendocrine regulation of inflammation

The interaction between the sympathetic nervous system and the immune system has been documented over the last several decades. In this review, the neuroanatomical, cellular, and molecular evidence for neuroimmune regulation in the maintenance of immune homeostasis will be discussed, as well as the potential impact of neuroimmune dysregulation in health and disease.

The Immune Response to Acute Focal Cerebral Ischemia and Associated Post-stroke Immunodepression: A Focused Review

It is currently well established that the immune system is activated in response to transient or focal cerebral ischemia. This acute immune activation occurs in response to damage, and injury, to components of the neurovascular unit and is mediated by the innate and adaptive arms of the immune response. The initial immune activation is rapid, occurs via the innate immune response and leads to inflammation. The inflammatory mediators produced during the innate immune response in turn lead to recruitment of inflammatory cells and the production of more inflammatory mediators that result in activation of the adaptive immune response. Under ideal conditions, this inflammation gives way to tissue repair and attempts at regeneration. However, for reasons that are just being understood, immunosuppression occurs following acute stroke leading to post-stroke immunodepression. This review focuses on the current state of knowledge regarding innate and adaptive immune activation in response to focal cerebral ischemia as well as the immunodepression that can occur following stroke. A better understanding of the intricate and complex events that take place following immune response activation, to acute cerebral ischemia, is imperative for the development of effective novel immunomodulatory therapies for the treatment of acute stroke.

Catecholamines, steroids and immune alterations in ischemic stroke and other acute diseases

The outcome of stroke patients is not only determined by the extent and localization of the ischemic lesion, but also by stroke-associated infections. Stroke-induced immune alterations, which are related to stroke-associated infections, have been described over the last decade. Here we review the evidence that catecholamines and steroids induced by stroke result in stroke-induced immune alterations. In addition, we compare the immune alterations observed in other acute diseases such as myocardial infarction, brain trauma, and surgical trauma with the changes seen in stroke-induced immune alterations.

Different subsets of natural killer T cells may vary in their roles in health and disease

Natural killer T cells (NKT) can regulate innate and adaptive immune responses. Type I and type II NKT cell subsets recognize different lipid antigens presented by CD1d, an MHC class-I-like molecule. Most type I NKT cells express a semi-invariant T-cell receptor (TCR), but a major subset of type II NKT cells reactive to a self antigen sulphatide use an oligoclonal TCR. Whereas TCR-α dominates CD1d-lipid recognition by type I NKT cells, TCR-α and TCR-β contribute equally to CD1d-lipid recognition by type II NKT cells. These variable modes of NKT cell recognition of lipid-CD1d complexes activate a host of cytokine-dependent responses that can either exacerbate or protect from disease. Recent studies of chronic inflammatory and autoimmune diseases have led to a hypothesis that: (i) although type I NKT cells can promote pathogenic and regulatory responses, they are more frequently pathogenic, and (ii) type II NKT cells are predominantly inhibitory and protective from such responses and diseases. This review focuses on a further test of this hypothesis by the use of recently developed techniques, intravital imaging and mass cytometry, to analyse the molecular and cellular dynamics of type I and type II NKT cell antigen-presenting cell motility, interaction, activation and immunoregulation that promote immune responses leading to health versus disease outcomes.

A Genomic Profile of the Immune Response to Stroke With Implications for Stroke Recovery

Objectives:

The objectives of this study were to determine the change in gene expression between two time points following stroke and to identify biomarkers of stroke recovery through gene expression profiling and pathway analysis.

Methods:

Peripheral blood was collected from 34 ischemic stroke patients (confirmed by magnetic resonance imaging) ≥18 years of age, within 24 hr of symptom onset and 24–48 hr later, and from healthy controls. The Modified Rankin Scale (MRS) was used to determine 30-day recovery. Total RNA was extracted from whole blood in Paxgene RNA tubes, amplified, and hybridized to Illumina HumanRef-8v2 bead chips. Gene expression was compared in a univariate manner between stroke patients at both time points and good versus bad outcome using t-test in GeneSpring. Inflation of Type 1 error was corrected by false discovery rate (FDR), and Ingenuity Systems Pathway analysis (IPA) was performed. A secondary validation cohort was recruited from a local hospital.

Results:

Three genes were significantly downregulated over time ( LY96, IL8, and SDPR; FDR corrected p < .05). This finding was confirmed in a validation cohort of stroke patients ( n = 8). IPA revealed cytotoxic T-lymphocyte antigen 4 (CTLA4) signaling was the most significant pathway present in the peripheral whole blood of stroke patients 24–48 hr after onset. When controlling for age and National Institutes of Health Stroke Scale score, high baseline expression of TLR2 and TLR4 significantly predicted worse scores on the MRS.

Conclusion:

CTLA4 signaling is a novel pathway for the study of stroke-induced immune suppression. Markers of immune dysfunction early after stroke may prove useful for identifying patients with increased risk of poor recovery.

Understanding and preventing the development of post-stroke dementia

Post-stroke dementia (PSD) is a clinical entity but it now appears that most of PSD may be categorized as vascular dementia. The well-established relationship between vascular factors and dementia provides a rationale for the implementation of intervention and prevention efforts. Larger primary prevention trials related to lifestyle factors are warranted in association with dementia. Published clinical trials have not been promising and there is meager information on whether PSD can be prevented through the use of pharmacological agents. Control of vascular disease risk and prevention of recurrent strokes are obviously key to reducing the burden of cognitive decline and dementia after stroke. However, modern imaging and analysis techniques will help to elucidate the mechanism of PSD and establish better treatment.

Neural control of the immune system

Neural reflexes support homeostasis by modulating the function of organ systems. Recent advances in neuroscience and immunology have revealed that neural reflexes also regulate the immune system. Activation of the vagus nerve modulates leukocyte cytokine production and alleviates experimental shock and autoimmune disease, and recent data have suggested that vagus nerve stimulation can improve symptoms in human rheumatoid arthritis. These discoveries have generated an increased interest in bioelectronic medicine, i.e., therapeutic delivery of electrical impulses that activate nerves to regulate immune system function. Here, we discuss the physiology and potential therapeutic implications of neural immune control.

Radiopharmaceutical stem cell tracking for neurological diseases

Although neurological ailments continue to be some of the main causes of disease burden in the world, current therapies such as pharmacological agents have limited potential in the restoration of neural functions. Cell therapies, firstly applied to treat different hematological diseases, are now being investigated in preclinical and clinical studies for neurological illnesses. However, the potential applications and mechanisms for such treatments are still poorly comprehended and are the focus of permanent research. In this setting, noninvasive in vivo imaging allows better understanding of several aspects of stem cell therapies. Amongst the various methods available, radioisotope cell labeling has become one of the most promising since it permits tracking of cells after injection by different routes to investigate their biodistribution. A significant increase in the number of studies utilizing this method has occurred in the last years. Here, we review the different radiopharmaceuticals, imaging techniques, and findings of the preclinical and clinical reports published up to now. Moreover, we discuss the limitations and future applications of radioisotope cell labeling in the field of cell transplantation for neurological diseases.

Pre-existing hypertension dominates γδT cell reduction in human ischemic stroke

T lymphocytes may play an important role in the evolution of ischemic stroke. Depletion of γδT cells has been found to abrogate ischemia reperfusion injury in murine stroke. However, the role of γδT cells in human ischemic stroke is unknown. We aimed to determine γδT cell counts and γδT cell interleukin 17A (IL-17A) production in the clinical setting of ischemic stroke. We also aimed to determine the associations of γδT cell counts with ischemic lesion volume, measures of clinical severity and with major stroke risk factors. Peripheral blood samples from 43 acute ischemic stroke patients and 26 control subjects matched on race and gender were used for flow cytometry and complete blood count analyses. Subsequently, cytokine levels and gene expression were measured in γδT cells. The number of circulating γδT cells was decreased by almost 50% (p = 0.005) in the stroke patients. γδT cell counts did not correlate with lesion volume on magnetic resonance diffusion-weighted imaging or with clinical severity in the stroke patients, but γδT cells showed elevated levels of IL-17A (p = 0.048). Decreased γδT cell counts were also associated with older age (p = 0.004), pre-existing hypertension (p = 0.0005) and prevalent coronary artery disease (p = 0.03), with pre-existing hypertension being the most significant predictor of γδT cell counts in a multivariable analysis. γδT cells in human ischemic stroke are reduced in number and show elevated levels of IL-17A. A major reduction in γδT lymphocytes also occurs in hypertension and may contribute to the development of hypertension-mediated stroke and vascular disease.

Hypoxia Induces autophagic cell death through hypoxia-inducible factor 1α in microglia

As phagocytic cells of central nervous system, excessive activation or cell death of microglia is involved in a lot of nervous system injury and degenerative disease, such as stroke, epilepsy, Parkinson's disease, Alzheimer's disease. Accumulating evidence indicates that hypoxia upregulates HIF-1α expression leading to cell death of microglia. However, the exact mechanism of cell death induced by hypoxia in microglia is not clear. In the current study, we showed that hypoxia induced cell death and autophagy in microglia. The suppression of autophagy using either pharmacologic inhibitors (3-methyladenine, bafilomycin A1) or RNA interference in essential autophagy genes (BECN1 and ATG5) decreased the cell death induced by hypoxia in microglia cells. Moreover, the suppression of HIF-1α using either pharmacologic inhibitors (3-MA, Baf A1) or RNA interference decreased the microglia death and autophagy in vitro. Taken together, these data indicate that hypoxia contributes to autophagic cell death of microglia through HIF-1α, and provide novel therapeutic interventions for cerebral hypoxic diseases associated with microglia activation.