PD-L1 enhances CNS inflammation and infarct volume following experimental stroke in mice in opposition to PD-1

Plasma Inflammation Markers Linked to Complications and Outcomes after Spontaneous Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) could trigger inflammatory responses. However, the specific role of inflammatory proteins in the pathological mechanism, complications, and prognosis of ICH remains unclear. In this study, we investigated the expression of 92 plasma inflammation-related proteins in patients with ICH (n = 55) and healthy controls (n = 20) using an Olink inflammation panel and discussed the relation to the severity of stroke, clinical complications, 30-day mortality, and 90-day outcomes. Our result showed that six proteins were upregulated in ICH patients compared with healthy controls, while seventy-four proteins were downregulated. In patients with ICH, seven proteins were increased in the severe stroke group compared with the moderate stroke group. In terms of complications, two proteins were downregulated in patients with pneumonia, while nine proteins were upregulated in patients with sepsis. Compared with the survival group, three proteins were upregulated, and one protein was downregulated in the death group. Compared with the good outcome group, eight proteins were upregulated, and four proteins were downregulated in the poor outcome group. In summary, an in-depth exploration of the differential inflammatory factors in the early stages of ICH could deepen our understanding of the pathogenesis of ICH, predict patient prognosis, and explore new treatment strategies.

Nanomaterial-Based Strategies for Attenuating T-Cell-Mediated Immunodepression in Stroke Patients: Advancing Research Perspectives

This review article discusses the potential of nanomaterials in targeted therapy and immunomodulation for stroke-induced immunosuppression. Although nanomaterials have been extensively studied in various biomedical applications, their specific use in studying and addressing immunosuppression after stroke remains limited. Stroke-induced neuroinflammation is characterized by T-cell-mediated immunodepression, which leads to increased morbidity and mortality. Key observations related to immunodepression after stroke, including lymphopenia, T-cell dysfunction, regulatory T-cell imbalance, and cytokine dysregulation, are discussed. Nanomaterials, such as liposomes, micelles, polymeric nanoparticles, and dendrimers, offer advantages in the precise delivery of drugs to T cells, enabling enhanced targeting and controlled release of immunomodulatory agents. These nanomaterials have the potential to modulate T-cell function, promote neuroregeneration, and restore immune responses, providing new avenues for stroke treatment. However, challenges related to biocompatibility, stability, scalability, and clinical translation need to be addressed. Future research efforts should focus on comprehensive studies to validate the efficacy and safety of nanomaterial-based interventions targeting T cells in stroke-induced immunosuppression. Collaborative interdisciplinary approaches are necessary to advance the field and translate these innovative strategies into clinical practice, ultimately improving stroke outcomes and patient care.

Causal effects of immune cell surface antigens and functional outcome after ischemic stroke: a Mendelian randomization study

Objective

While observational studies link immune cells with post-stroke functional outcome, the underlying immune mechanisms are not well understood. Immune cell surface antigens are actively involved in the biological behavior of immune cells, investigating immune cell surface antigens could deepen our comprehension of their role and biological processes in stroke recovery. Therefore, we aimed to investigate the immunological basis of stroke outcome by exploring the causal relationship between immune cell surface antigens and functional outcome after ischemic stroke in a Mendelian randomization study.

Methods

Genetic variants related to immune cell surface antigens and post-stroke functional outcome were selected for two-sample Mendelian randomization (MR) analysis. 389 fluorescence intensities (MFIs) with surface antigens were included. Inverse variance weighted (IVW) modeling was used as the primary MR method to estimate the causal effect of exposure on the outcome, followed by several alternative methods and sensitivity analyses. Additional analysis of the association between immune cell surface antigens and risk of ischemic stroke for assessment of collider bias.

Results

We found that suggestive associations between CD20 on switched memory B cell (OR = 1.16, 95% CI: 1.01-1.34, p = 0.036) and PDL-1 on monocyte (OR = 1.32, 95% CI: 1.04-1.66, p = 0.022) and poor post-stroke functional outcome, whereas CD25 on CD39+ resting Treg (OR = 0.77, 95% CI: 0.62-0.96, p = 0.017) was suggestively associated with good post-stroke functional outcome.

Conclusion

The elevated CD20 on switched memory B cell, PDL-1 on monocyte, and CD25 on CD39+ resting Treg may be novel biomarkers and potential causal factors influencing post-stroke functional outcome.

Soluble PD-L1 reprograms blood monocytes to prevent cerebral edema and facilitate recovery after ischemic stroke

Acute cerebral ischemia triggers a profound inflammatory response. While macrophages polarized to an M2-like phenotype clear debris and facilitate tissue repair, aberrant or prolonged macrophage activation is counterproductive to recovery. The inhibitory immune checkpoint Programmed Cell Death Protein 1 (PD-1) is upregulated on macrophage precursors (monocytes) in the blood after acute cerebrovascular injury. To investigate the therapeutic potential of PD-1 activation, we immunophenotyped circulating monocytes from patients and found that PD-1 expression was upregulated in the acute period after stroke. Murine studies using a temporary middle cerebral artery (MCA) occlusion (MCAO) model showed that intraperitoneal administration of soluble Programmed Death Ligand-1 (sPD-L1) significantly decreased brain edema and improved overall survival. Mice receiving sPD-L1 also had higher performance scores short-term, and more closely resembled sham animals on assessments of long-term functional recovery. These clinical and radiographic benefits were abrogated in global and myeloid-specific PD-1 knockout animals, confirming PD-1+ monocytes as the therapeutic target of sPD-L1. Single-cell RNA sequencing revealed that treatment skewed monocyte maturation to a non-classical Ly6Clo, CD43hi, PD-L1+ phenotype. These data support peripheral activation of PD-1 on inflammatory monocytes as a therapeutic strategy to treat neuroinflammation after acute ischemic stroke.

A study of programmed death-1/programmed death ligand and iodine-induced autoimmune thyroiditis in NOD.H-2h4 mice

Excess iodine will trigger the occurrence of autoimmune thyroiditis (AIT), and programmed death-1 (PD-1)/programmed death ligand (PD-L) will also contribute to the development of AIT. The purpose of this study was to explore the role that negative regulatory signals mediated by PD-1/PD-L play in the development of spontaneous autoimmune thyroiditis (SAT) in NOD.H-2h4 mice when they are exposed to iodine. Programmed death ligand 1 (PD-L1) antibody was administered intraperitoneally to NOD.H-2h4 mice. The relevant indicators were determined by flow cytometry, real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, immunohistochemistry, pathological hematoxylin and eosin staining, and arsenic-cerium catalytic spectrophotometry. Results showed that the level of urinary iodine, the level of thyroid lymphocyte infiltration, the level of thyroglobulin antibodies (TgAb) and interferon (IFN-γ)/tumor necrosis factor (TNF-α)/interleukin (IL-2)/IL-17, and the relative expression of PD-1/PD-L1/programmed death-2 (PD-L2) increased with the intervention of excess iodine. After the intervention of the PD-L1 antibody, the expression of PD-1/PD-L1/PD-L2 in different degrees was inhibited, but the level of thyroid lymphocyte infiltration and serum TgAb/IFN-γ/TNF-α/ IL-2/IL-17 did not decrease. Collectively, although PD-1/PD-L participates in the occurrence of SAT and induces inflammation, administration of the PD-L1 antibody does not effectively improve the pathological process of SAT. More research is needed to determine whether PD-1/PD-L intervention can treat autoimmune thyroid disease.

Inhibiting leukocyte-endothelial cell interactions by Chinese medicine Tongxinluo capsule alleviates no-reflow after arterial recanalization in ischemic stroke

AIMS

Despite successful vascular recanalization in stroke, one-fourth of patients have an unfavorable outcome due to no-reflow. The pathogenesis of no-reflow is fully unclear, and therapeutic strategies are lacking. Upon traditional Chinese medicine, Tongxinluo capsule (TXL) is a potential therapeutic agent for no-reflow. Thus, this study is aimed to investigate the pathogenesis of no-reflow in stroke, and whether TXL could alleviate no-reflow as well as its potential mechanisms of action.

METHODS

Mice were orally administered with TXL (3.0 g/kg/d) after transient middle cerebral artery occlusion. We examined the following parameters: neurological function, no-reflow, leukocyte-endothelial cell interactions, HE staining, leukocyte subtypes, adhesion molecules, and chemokines.

RESULTS

Our results showed stroke caused neurological deficits, neuron death, and no-reflow. Adherent and aggregated leukocytes obstructed microvessels as well as leukocyte infiltration in ischemic brain. Leukocyte subtypes changed after stroke mainly including neutrophils, lymphocytes, regulatory T cells, suppressor T cells, helper T type 1 (Th1) cells, Th2 cells, B cells, macrophages, natural killer cells, and dendritic cells. Stroke resulted in upregulated expression of adhesion molecules (P-selectin, E-selectin, and ICAM-1) and chemokines (CC-chemokine ligand (CCL)-2, CCL-3, CCL-4, CCL-5, and chemokine C-X-C ligand 1 (CXCL-1)). Notably, TXL improved neurological deficits, protected neurons, alleviated no-reflow and leukocyte-endothelial cell interactions, regulated multiple leukocyte subtypes, and inhibited the expression of various inflammatory mediators.

CONCLUSION

Leukocyte-endothelial cell interactions mediated by multiple inflammatory factors are an important cause of no-reflow in stroke. Accordingly, TXL could alleviate no-reflow via suppressing the interactions through modulating various leukocyte subtypes and inhibiting the expression of multiple inflammatory mediators.

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.

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.

Emerging Targets for Modulation of Immune Response and Inflammation in Stroke

The inflammatory and immunological responses play a significant role after stroke. The innate immune activation stimulated by microglia during stroke results in the migration of macrophages and lymphocytes into the brain and are responsible for tissue damage. The immune response and inflammation following stroke have no defined targets, and the intricacies of the immunological and inflammatory processes are only partially understood. Innate immune cells enter the brain and meninges during the acute phase, which can cause ischemia damage. Activation of systemic immunity is caused by danger signals sent into the bloodstream by injured brain cells, which is followed by a significant immunodepression that encourages life-threatening infections. Neuropsychiatric sequelae, a major source of post-stroke morbidity, may be induced by an adaptive immune response that is initiated by antigen presentation during the chronic period and is directed against the brain. Thus, the current review discusses the role of immune response and inflammation in stroke pathogenesis, their role in the progression of injury during the stroke, and the emerging targets for the modulation of the mechanism of immune response and inflammation that may have possible therapeutic benefits against stroke.

Divergent roles of PD-L1 in immune regulation during ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury is a type of pathological injury that commonly arises in various diseases. Various forms of immune response are involved in the process of I/R injury. As a member of the B7 costimulatory molecule family, programmed death 1-ligand 1 (PD-L1) is an important target for immune regulation. Therefore, PD-L1 may be implicated in the regulation of I/R injury. This review briefly describes the immune response during I/R injury and how PD-L1 is involved in its regulation by focusing on findings from various I/R models. Despite the limited number of studies in this field of research, PD-L1 has shown sufficient potential as a clinical therapeutic target.

Role of the PD-1/PD-L1 Pathway in Experimental Trypanosoma cruzi Infection and Potential Therapeutic Options

Chagas disease (CD) is a neglected chronic infection caused by the protozoan parasite Trypanosoma cruzi (T. cruzi). A significant portion of infected people develops cardiac or digestive alterations over a lifetime. Since several chronic infections associated with antigen persistence and inflammation have been shown to lead to T cell exhaustion, new therapies targeting co-inhibitory receptors to regain T cell activity are under consideration. This study explored immune therapeutic approaches targeting the inhibitory PD-1/PD-L pathway in an experimental model for CD. Infected PD-L1 knockout mice (PD-L1 KO) showed increased systemic parasitemia in blood although no significant differences in parasite load were observed in different organs. Furthermore, we found no significant differences in the frequency of activated T cells or proinflammatory cytokine production when compared to WT counterparts. PD-L1 deficiency led to the production of IL-10 by CD8+ T cells and an upregulation of Tim-3 and CD244 (2B4). Unexpectedly, the lack of PD-L1 did not contribute to a significantly improved T cell response to infection. Single blockade and combined blockade of PD-1 and Tim-3 using monoclonal antibodies confirmed the results observed in infected. PD-L1 KO mice. Our results describe for the first time that the interruption of the PD-1/PD-L1 axis during acute T. cruzi infection does not necessarily enhance the immune response against this parasite. Its interruption favors increased levels of parasitemia and sustained upregulation of other co-inhibitory receptors as well as the production of regulatory cytokines. These results suggest that the clinical application of immune therapeutic approaches targeting the PD-1/PD-L1 axis in CD might be risky and associated with adverse events. It highlights that more research is urgently needed to better understand the immune regulation of T cells in CD before designing immune therapeutic approaches for a clinical context.

PD-L1 Regulates Platelet Activation and Thrombosis via Caspase-3/GSDME Pathway

Platelets play a central role in hemostasis and thrombosis, regulating the occurrence and development of thrombotic diseases, including ischemic stroke. Programmed death ligand 1 (PD-L1) has recently been detected in platelet, while the function of PD-L1 in platelets remain elusive. Our data reveal a novel mechanism for the role of PD-L1 on platelet activation and arterial thrombosis. PD-L1 knockout does not affect platelet morphology, count, and mean volume under homeostasis and without risk of bleeding, which inhibits platelet activation by suppressing outside-in-activation of integrin by downregulating the Caspase-3/GSDME pathway. Platelet adoptive transfer experiments demonstrate that PD-L1 knockout inhibits thrombosis. And the absence of PD-L1 improves ischemic stroke severity and increases mice survival. Immunohistochemical staining of the internal structure of the thrombus proves that PD-L1 enhances the seriousness of the thrombus by inhibiting platelet activation. This work reveals a regulatory role of PD-L1 on platelet activation and thrombosis while providing novel platelet intervention strategies to prevent thrombosis.

Cellular Immune Signal Exchange From Ischemic Stroke to Intestinal Lesions Through Brain-Gut Axis

As a vital pivot for the human circulatory system, the brain-gut axis is now being considered as an important channel for many of the small immune molecules’ transductions, including interleukins, interferons, neurotransmitters, peptides, and the chemokines penetrating the mesentery and blood brain barrier (BBB) during the development of an ischemic stroke (IS). Hypoxia-ischemia contributes to pituitary and neurofunctional disorders by interfering with the molecular signal release and communication then providing feedback to the gut. Suffering from such a disease on a long-term basis may cause the peripheral system’s homeostasis to become imbalanced, and it can also lead to multiple intestinal complications such as gut microbiota dysbiosis (GMD), inflammatory bowel disease (IBD), necrotizing enterocolitis (NEC), and even the tumorigenesis of colorectal carcinoma (CRC). Correspondingly, these complications will deteriorate the cerebral infarctions and, in patients suffering with IS, it can even ruin the brain’s immune system. This review summarized recent studies on abnormal immunological signal exchange mediated polarization subtype changes, in both macrophages and microglial cells as well as T-lymphocytes. How gut complications modulate the immune signal transduction from the brain are also elucidated and analyzed. The conclusions drawn in this review could provide guidance and novel strategies to benefit remedies for both IS and relative gut lesions from immune-prophylaxis and immunotherapy aspects.

Programmed Death-1 Deficiency Aggravates Motor Dysfunction in MPTP Model of Parkinson's Disease by Inducing Microglial Activation and Neuroinflammation in Mice

Abundant reactive gliosis and neuroinflammation are typical pathogenetic hallmarks of brains in Parkinson's disease (PD) patients, but regulation mechanisms are poorly understood. We are interested in role of programmed death-1 (PD-1) in glial reaction, neuroinflammation and neuronal injury in PD pathogenesis. Using PD mouse model and PD-1 knockout (KO) mice, we designed wild-type-control (WT-CON), WT-1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (WT-MPTP), PD-1-KO-control (KO-CON) and PD-1-KO-MPTP (KO-MPTP), and observed motor dysfunction of animal, morphological distribution of PD-1-positive cells, dopaminergic neuronal injury, glial activation and generation of inflammatory cytokines in midbrains by motor behavior detection, immunohistochemistry and western blot. WT-MPTP mouse model exhibited decrease of PD-1/Iba1-positive microglial cells in the substantia nigra compared with WT-CON mice. By comparison of four groups, PD-1 deficiency showed exacerbation in motor dysfunction of animals, decreased expression of TH protein and TH-positive neuronal protrusions. PD-1 deficiency enhanced microglial activation, production of proinflammatory cytokines like inducible nitric oxide synthase, tumor necrosis factor-α, interleukin-1β and interleukin-6, and expression and phosphorylation of AKT and ERK1/2 in the substantia nigra of MPTP model. We concluded that PD-1 deficiency could aggravate motor dysfunction of MPTP mouse model by inducing microglial activation and neuroinflammation in midbrains, suggesting that PD-1 signaling abnormality might be possibly involved in PD pathogenesis.

Regulatory T cells in ischemic stroke

Recent evidence shows that when ischemic stroke (IS) occurs, the BBB would be destructed, thereby promoting the immune cells to migrate into the brain, suggesting that the immune responses can play a vital role in the pathology of IS. As an essential subpopulation of immunosuppressive T cells, regulatory T (Treg) cells are involved in maintaining immune homeostasis and suppressing immune responses in the pathophysiological conditions of IS. During the past decades, the regulatory role of Treg cells has attracted the interest of numerous researchers. However, whether they are beneficial or detrimental to the outcomes of IS remains controversial. Moreover, Treg cells exert distinctive effects in the different stages of IS. Therefore, it is urgent to elucidate how Treg cells modulate the immune responses induced by IS. In this review, we describe how Treg cells fluctuate and play a role in the regulation of immune responses after IS in both experimental animals and humans, and summarize their biological functions and mechanisms in both CNS and periphery. We also discuss how Treg cells participate in poststroke inflammation and immunodepression and the potential of Treg cells as a novel therapeutic approach.

Elevated Plasma Soluble PD-L1 Levels in Out-of-Hospital Cardiac Arrest Patients

Background: A deregulated immune system has been implicated in the pathogenesis of post-cardiac arrest syndrome (PCAS). A soluble form of programmed cell death-1 (PD-1) ligand (sPD-L1) has been found at increased levels in cancer and sustained inflammation, thereby deregulating immune functions. Here, we aim to study the possible involvement of sPD-L1 in PCAS. Methods: Thirty out-of-hospital cardiac arrest (OHCA) patients consecutively admitted to the ER of Mie University Hospital were prospectively enrolled. Plasma concentrations of sPD-L1 were measured by an enzyme-linked immunosorbent assay in blood samples of all 30 OHCA patients obtained during cardiopulmonary resuscitation (CPR). In 13 patients who achieved return-of-spontaneous-circulation (ROSC), sPD-L1 levels were also measured daily in the ICU. Results: The plasma concentrations of sPD-L1 in OHCA were significantly increased; in fact, to levels as high as those observed in sepsis. sPD-L1 levels during CPR correlated with reduced peripheral lymphocyte counts and increased C-reactive protein levels. Of 13 ROSC patients, 7 cases survived in the ICU for more than 4 days. A longitudinal analysis of sPD-L1 levels in the 7 ROSC cases revealed that sPD-L1 levels occurred in parallel with organ failure. Conclusions: This study suggests that ischemia- reperfusion during CPR may aberrantly activate immune and endothelial cells to release sPD-L1 into circulation, which may play a role in the pathogenesis of immune exhaustion and organ failures associated with PCAS.

Emerging Role of PD-1 in the Central Nervous System and Brain Diseases

Programmed cell death protein 1 (PD-1) is an immune checkpoint modulator and a major target of immunotherapy as anti-PD-1 monoclonal antibodies have demonstrated remarkable efficacy in cancer treatment. Accumulating evidence suggests an important role of PD-1 in the central nervous system (CNS). PD-1 has been implicated in CNS disorders such as brain tumors, Alzheimer's disease, ischemic stroke, spinal cord injury, multiple sclerosis, cognitive function, and pain. PD-1 signaling suppresses the CNS immune response via resident microglia and infiltrating peripheral immune cells. Notably, PD-1 is also widely expressed in neurons and suppresses neuronal activity via downstream Src homology 2 domain-containing protein tyrosine phosphatase 1 and modulation of ion channel function. An improved understanding of PD-1 signaling in the cross-talk between glial cells, neurons, and peripheral immune cells in the CNS will shed light on immunomodulation, neuromodulation, and novel strategies for treating brain diseases.

The role of PD-L1 in the immune dysfunction that mediates hypoxia-induced multiple organ injury

Hypoxia is a pathological condition common to many diseases, although multiple organ injuries induced by hypoxia are often overlooked. There is increasing evidence to suggest that the hypoxic environment may activate innate immune cells and suppress adaptive immunity, further stimulating inflammation and inhibiting immunosurveillance. We found that dysfunctional immune regulation may aggravate hypoxia-induced tissue damage and contribute to secondary injury. Among the diverse mechanisms of hypoxia-induced immune dysfunction identified to date, the role of programmed death-ligand 1 (PD-L1) has recently attracted much attention. Besides leading to tumour immune evasion, PD-L1 has also been found to participate in the progression of the immune dysfunction which mediates hypoxia-induced multiple organ injury. In this review, we aimed to summarise the role of immune dysfunction in hypoxia-induced multiple organ injury, the effects of hypoxia on the cellular expression of PD-L1, and the effects of upregulated PD-L1 expression on immune regulation. Furthermore, we summarise the latest information pertaining to the involvement, diagnostic value, and therapeutic potential of immunosuppression induced by PD-L1 in various types of hypoxia-related diseases, including cancers, ischemic stroke, acute kidney injury, and obstructive sleep apnoea. Video Abstract.

Exploring the VISTA of microglia: immune checkpoints in CNS inflammation

Negative checkpoint regulators (NCR) are intensely pursued as targets to modulate the immune response in cancer and autoimmunity. A large variety of NCR is expressed by central nervous system (CNS)-resident cell types and is associated with CNS homeostasis, interactions with peripheral immunity and CNS inflammation and disease. Immunotherapy blocking NCR affects the CNS as patients can develop neurological issues including encephalitis and multiple sclerosis (MS). How these treatments affect the CNS is incompletely understood, since expression and function of NCR in the CNS are only beginning to be unravelled. V-type immunoglobulin-like suppressor of T cell activation (VISTA) is an NCR that is expressed primarily in the haematopoietic system by myeloid and T cells. VISTA regulates T cell quiescence and activation and has a variety of functions in myeloid cells including efferocytosis, cytokine response and chemotaxis. In the CNS, VISTA is predominantly expressed by microglia and macrophages of the CNS. In this review, we summarize the role of NCR in the CNS during health and disease. We highlight expression of VISTA across cell types and CNS diseases and discuss the function of VISTA in microglia and during CNS ageing, inflammation and neurodegeneration. Understanding the role of VISTA and other NCR in the CNS is important considering the adverse effects of immunotherapy on the CNS, and in view of their therapeutic potential in CNS disease.

Alcohol induces programmed death receptor-1 and programmed death-ligand-1 differentially in neuroimmune cells

Engagement of programmed death-1 (PD-1) receptor by its ligands (PD-L1/PD-L2) in activated immune cells is known to be involved in inflammatory neurological disease via a co-inhibitory signal pathway. Interaction of PD-1/PD-L1 is believed to occur only in activated neuroimmune cells because there are undetectable levels of PD-1/PD-L1 in normal physiological conditions. Here, we evaluated whether activation of neuroimmune cells such as human macrophage, brain endothelial cells (hBECs), astrocytes, microglia, and neurons by non-toxic concentrations of ethanol (EtOH) exposure can alter PD-1/PD-L1 expression. Thus, the present study is limited to the screening of PD-1/PD-L1 alterations in neuroimmune cells following ethanol exposure. We found that exposure of human macrophage or microglia to EtOH in primary culture immediately increased the levels of PD-L1 and gradually up-regulated PD-1 levels (beginning at 1-2 h). Similarly, ethanol exposure was able to induce PD-1/PD-L1 levels in hBECs and neuronal culture in a delayed process (occurring at 24 h). Astrocyte culture was the only cell type that showed endogenous levels of PD-1/PD-L1 that was decreased by EtOH exposure time-dependently. We concluded that ethanol (alcohol) mediated the induction of PD-1/PD-L1 differentially in neuroimmune cells. Taken together, our findings suggest that up-regulation of PD-1/PD-L1 by chronic alcohol use may dampen the innate immune response of neuroimmune cells, thereby contributing to neuroinflammation and neurodegeneration.

Neuroinflammation after Intracerebral Hemorrhage and Potential Therapeutic Targets

Spontaneous intracerebral hemorrhage (ICH) is a catastrophic illness causing significant morbidity and mortality. Despite advances in surgical technique addressing primary brain injury caused by ICH, little progress has been made treating the subsequent inflammatory cascade. Pre-clinical studies have made advancements identifying components of neuroinflammation, including microglia, astrocytes, and T lymphocytes. After cerebral insult, inflammation is initially driven by the M1 microglia, secreting cytokines (e.g., interleukin-1β [IL-1β] and tumor necrosis factor-α) that are involved in the breakdown of the extracellular matrix, cellular integrity, and the blood brain barrier. Additionally, inflammatory factors recruit and induce differentiation of A1 reactive astrocytes and T helper 1 (Th1) cells, which contribute to the secretion of inflammatory cytokines, augmenting M1 polarization and potentiating inflammation. Within 7 days of ICH ictus, the M1 phenotype coverts to a M2 phenotype, key for hematoma removal, tissue healing, and overall resolution of inflammation. The secretion of anti-inflammatory cytokines (e.g., IL-4, IL-10) can drive Th2 cell differentiation. M2 polarization is maintained by the secretion of additional anti-inflammatory cytokines by the Th2 cells, suppressing M1 and Th1 phenotypes. Elucidating the timing and trigger of the anti-inflammatory phenotype may be integral in improving clinical outcomes. A challenge in current translational research is the absence of an equivalent disease animal model mirroring the patient population and comorbid pathophysiologic state. We review existing data and describe potential therapeutic targets around which we are creating a bench to bedside translational research model that better reflects the pathophysiology of ICH patients.

LRP-1 functionalized polymersomes enhance the efficacy of carnosine in experimental stroke

Stroke is one of the commonest causes of death with limited treatment options. L-Carnosine has shown great promise as a neuroprotective agent in experimental stroke, but translation to the clinic is impeded by the large doses needed. We developed and evaluated the therapeutic potential of a novel delivery vehicle which encapsulated carnosine in lipoprotein receptor related protein-1 (LRP-1)-targeted functionalized polymersomes in experimental ischemic stroke. We found that following ischemic stroke, polymersomes encapsulating carnosine exhibited remarkable neuroprotective effects with a dose of carnosine 3 orders of magnitude lower than free carnosine. The LRP-1-targeted functionalization was essential for delivery of carnosine to the brain, as non-targeted carnosine polymersomes did not exhibit neuroprotection. Using Cy3 fluorescence in vivo imaging, we showed that unlike non-targeted carnosine polymersomes, LRP-1-targeted carriers accumulated in brain in a time dependent manner. Our findings suggest that these novel carriers have the ability to deliver neuroprotective cargo effectively to the brain.

Sex differences in the therapeutic effects of anti-PDL2 neutralizing antibody on stroke

Inflammation involving migration of immune cells across the damaged blood-brain barrier (BBB), activation of resident innate microglia and production of inflammatory humoral mediators such as cytokines and chemokines play a critical role in the pathogenesis of ischemic stroke. Cell-cell signaling involved in the process also includes checkpoint interaction between programmed death receptor (PD1) and programmed death ligands, PDL1 and PDL2. Based on our previous studies showing reduced MCAO infarct volumes in PDL2 deficient mice, we evaluated the ability of anti-PDL2 mAb to treat MCAO in male and female C57BL/6 mice. We found that anti-PDL2 neutralizing antibody treatment of MCAO significantly reduced infarct volumes in male mice but had no protective effects in female mice even at a 5-fold increased dose of anti-PDL2 mAb. The protection in male mice was likely mediated by reduced percentages in the spleen of PDL2⁺CD19⁺ B cells, PDL1⁺CD4⁺ T cells and CD86⁺CD11b⁺ macrophages in concert with reduced expression of PDL1 and TNFα and continued expression of CD206, in the injured ipsilateral brain hemisphere. The lack of a therapeutic benefit of anti-PDL2 on stroke-induced infarct volumes in female mice was reflected by no detectable reduction in expressed PDL2 or PDL1 and an increased frequency of Th₁ and Th₁₇ pro-inflammatory T cell subsets in the spleen, an effect not seen in PDL2 mAb treated males. This result potentially limits the utility of anti-PDL2 mAb therapy in stroke to males but underscores the importance of meeting the STAIR requirements for development of new stroke therapies for both sexes.

Does the Apparent Diffusion Coefficient Value Predict Permanent Cerebral Ischemia/Reperfusion Injury in Rats?

RATIONALE AND OBJECTIVES

Variation in tissue damage after cerebral ischemia/reperfusion (I/R) can cause uncertainty in stroke-related studies, which can be reduced if the damage can be predicted early after ischemia by measuring the apparent diffusion coefficient (ADC). We investigated whether ADC measurement in the acute phase can predict permanent cerebral I/R injury.

MATERIALS AND METHODS

The middle cerebral artery occlusion model was established using the intraluminal suture method to induce 60 minutes of ischemia followed by reperfusion in rats. T2-weighted images and diffusion-weighted images were obtained at 30 minutes and 24 hours after ischemia. Neuronal cell survival was assessed by neuronal nuclei (NeuN) immunofluorescence staining. The correlation between relative ADC (rADC) values at 30 minutes and I/R injury at 24 hours after ischemia was analyzed. Magnetic resonance imaging results were confirmed by histologic analysis.

RESULTS

The correlation between rADC values at 30 minutes and 24 hours was strong in the ischemic core and peri-infarct region but moderate in the anterior choroidal and hypothalamic region. Histologic analysis revealed that the correlation between rADC values at 30 minutes and the number of NeuN-positive cells at 24 hours was strong in the ischemic core and peri-infarct region but moderate in the anterior choroidal and hypothalamic region. Furthermore, there was a strong positive correlation between the sum of rADC values of three regions at 30 minutes and the infarct volume at 24 hours.

CONCLUSION

ADC measurement in the acute phase can predict permanent cerebral I/R injury and provide important information for the evaluation of ischemic stroke.

The Diverse Function of PD-1/PD-L Pathway Beyond Cancer

The recent success of PD-1 and PD-L1 blockade in cancer therapy illustrates the important role of the PD-1/PD-L1 pathway in the regulation of antitumor immune responses. However, signaling regulated by the PD-1/PD-L pathway is also associated with substantial inflammatory effects that can resemble those in autoimmune responses, chronic infection, and sepsis, consistent with the role of this pathway in balancing protective immunity and immunopathology, as well as in homeostasis and tolerance. Targeting PD-1/PD-L1 to treat cancer has shown benefits in many patients, suggesting a promising opportunity to target this pathway in autoimmune and inflammatory disorders. Here, we systematically evaluate the diverse biological functions of the PD-1/PD-L pathway in immune-mediated diseases and the relevant mechanisms that control these immune reactions.

Association Between Programed Cell Death-1 and CD4+ T Cell Alterations in Different Phases of Ischemic Stroke Patients

Objective: We aimed to analyze alterations in T cell subgroups during different post-ischemic stroke (IS) phases to explore the possible mechanisms underlying stroke-induced immune depression (SIID).

Methods: Sixty-four IS patients who met the entry criteria were divided into three groups: an acute phase group, a sub-acute phase group and a stable phase group. Fourteen healthy individuals were selected as normal controls. The phenotype distribution of T cells in patient peripheral blood was analyzed, and the immune checkpoint receptors programed cell death-1 (PD-1) and T cell immunoglobulin and mucin domain 3 (Tim-3) were detected in different T cell phenotypes.

Results: Compared with the control group, the absolute number of CD4⁺ T cells and CD4⁺ T central memory (TCM) cells was significantly increased in the acute phase group but decreased in the sub-acute phase and stable phase groups compared with that in the acute phase group. PD-1 expression in CD4⁺ T cells in the stable phase group showed a significant increase compared with that in the acute phase group. The expression of PD-1 on CD4⁺ TCM cells and CD4⁺ T effector memory (TEM) cells showed significant decreases in the acute phase compared with control cells; however, in the sub-acute phase and the stable phase, PD-1 expression was significantly increased compared with that in the acute phase.

Conclusions: T cell dysfunction, especially CD4⁺ T cell dysfunction, occurred during different IS phases. PD-1 was highly expressed in CD4⁺ T cells of different phenotypes after the acute phase and was associated with alterations in CD4⁺ T cells. Particularly, PD-1 was negatively correlated with the absolute number of TCM cells among different CD4⁺ T cell phenotypes, which may be one of the possible mechanisms of SIID.

The human blood DNA methylome identifies crucial role of β-catenin in the pathogenesis of Kawasaki disease

Kawasaki disease (KD) is a type of acute febrile vasculitis syndrome and is the most frequent cause of cardiac illness in children under the age of five years old. Although the etiology of KD remains largely unknown, some recent genome-wide studies have indicated that epigenetic factors may be important in its pathogenesis. We enrolled 24 KD patients and 24 non-KD controls in this study to access their DNA methylation status using HumanMethylation450 BeadChips. Another 34 KD patients and 62 control subjects were enrolled for expression validation. Of the 3193 CpG methylation regions with a methylation difference ≥ 20% between KD and controls, 3096 CpG loci revealed hypomehtylation, with only 3% being hypermethylated. Pathway buildup identified 11 networked genes among the hypermethylated regions, including four transcription factors: nuclear factor of activated T-cells 1, v-ets avian erythroblastosis virus E26 oncogene homolog 1, runt related transcription factor 3, and retinoic acid receptor gamma, as well as the activator β-catenin. Ten of these network-selected genes demonstrated a significant decrease in mRNA in KD patients, whereas only CTNNB1 significantly decreased in correlation with coronary artery lesions in KD patients. Furthermore, CTNNB1-silenced THP-1 monocytic cells drastically increased the expression of CD40 and significantly increased the expression of both CD40 and CD40L in cocultured human coronary artery endothelial cells. This study is the first to identify network-based susceptible genes of hypermethylated CpG loci, their expression levels, and the functional impact of β-catenin, which may be involved in both the cause and the development of KD.

Brain-immune interactions in perinatal hypoxic-ischemic brain injury

Perinatal hypoxia-ischemia remains the primary cause of acute neonatal brain injury, leading to a high mortality rate and long-term neurological deficits, such as behavioral, social, attentional, cognitive and functional motor deficits. An ever-increasing body of evidence shows that the immune response to acute cerebral hypoxia-ischemia is a major contributor to the pathophysiology of neonatal brain injury. Hypoxia-ischemia provokes an intravascular inflammatory cascade that is further augmented by the activation of resident immune cells and the cerebral infiltration of peripheral immune cells response to cellular damages in the brain parenchyma. This prolonged and/or inappropriate neuroinflammation leads to secondary brain tissue injury. Yet, the long-term effects of immune activation, especially the adaptive immune response, on the hypoxic-ischemic brain still remain unclear. The focus of this review is to summarize recent advances in the understanding of post-hypoxic-ischemic neuroinflammation triggered by the innate and adaptive immune responses and to discuss how these mechanisms modulate the brain vulnerability to injury. A greater understanding of the reciprocal interactions between the hypoxic-ischemic brain and the immune system will open new avenues for potential immunomodulatory therapy in the treatment of neonatal brain injury.

Sex differences in the immune response to experimental stroke: Implications for translational research

Ischemic stroke is a leading cause of death and disability in the United States. It is known that males and females respond differently to stroke. Depending on age, the incidence, prevalence, mortality rate, and disability outcome of stroke differ between the sexes. Females generally have strokes at older ages than males and, therefore, have a worse stroke outcome. There are also major differences in how the sexes respond to stroke at the cellular level. Immune response is a critical factor in determining the progress of neurodegeneration after stroke and is fundamentally different for males and females. Additionally, females respond to stroke therapies differently from males, yet they are often left out of the basic research that is focused on developing those therapies. With a resounding failure to translate stroke therapies from the bench to the bedside, it is clearer than ever that inclusion of both sexes in stroke studies is essential for future clinical success. This Mini-Review examines sex differences in the immune response to experimental stroke and its implications for therapy development. © 2016 Wiley Periodicals, Inc.

B7-H1 Influences the Accumulation of Virus-Specific Tissue Resident Memory T Cells in the Central Nervous System

Therapies that target the PD-1/B7-H1 axis have revolutionized cancer treatment, yet precise knowledge of how this pathway provides benefit continues to evolve. Here, we report a novel role for the immune checkpoint ligand B7-H1 in the accumulation of tissue-resident memory CD8+ T-cells (TRM). After intracranial infection, Theiler's murine encephalomyelitis virus (TMEV) generates TRM that are maintained in the central nervous system (CNS) tissues of B7-H1WT animals. Although no differences in acute T-cell responses between B7-H1WT and B7-H1KO are observed, at long-term periods post-infection the maintenance of CD8+ TRM is diminished in B7-H1KO animals. This is accompanied by redistribution of the resident CD8+ population from primarily CD103+ TRM to a diminished population of TRM and a preponderance of non-specified PD-1+ CD103- CD8+ T-cells. T-cell transfer studies demonstrate that host B7-H1 is necessary for maintaining TRM and limiting accumulation of PD-1+ CD103- CD8+ T-cells. The lack of host B7-H1 results in compromised control of a heterologous virus re-challenge demonstrating a functional defect in TRM mediated virus control. This study reveals a new role for B7-H1 in TRM and pro-inflammatory PD-1+ CD103- CD8+ T-cell accumulation in the CNS and gives insight for using B7-H1/PD-1 blockade in modulating long-term T-cell protection.

Protective effect of autophagy in neural ischemia and hypoxia: Negative regulation of the Wnt/β-catenin pathway

Autophagy is a highly conserved process of self-digestion to promote cell survival in response to nutrient starvation and other metabolic stresses. However, whether ischemic-hypoxic (IH) injury-induced autophagy acts as a neuroprotective mechanism or leads to neuroinjury is a subject of debate. It is known that autophagy is regulated by signaling pathways, including the mammalian target of rapamycin pathway. However, in neural IH injury, whether other signaling pathways are involved in the regulation of autophagy remains to be fully elucidated. In the present study, using the autophagy agonist (rampycin), autophagy antagonist [3-methyl adenine (3-MA)] and lysosome antagonist (MHY1485), autophagy was intervened with at oxygen-glucose deprivation (OGD) 6 h, in order to elucidate the regulatory mechanisms of autophagy. Using immunocytochemistry and western blot analysis, the expression levels of stress-related proteins, such as hypoxia-inducible factor-1α (HIF-1α) (a key regulator in hypoxia) and cyclooxygenase 2 (COX2; inflammatory indicator), were analyzed. In addition, the upstream proteins (Wnt1 and Wnt3a), downstream proteins (Dvl2, β-catenin) and target proteins (C-myc and cyclin D) in the Wnt/β-catenin signaling pathway were examined by immunocytochemistry and western blot analysis. The present study revealed that autophagy was activated with the upregulation of autophagic flux in IH injury; it was demonstrated that autophagy had a protective role in IH injury. The Wnt/β-catenin pathway was involved in IH injury regulation, and the upstream proteins in the Wnt/β-catenin signaling pathway were upregulated, whereas downstream proteins were downregulated by the activity of autophagy accordingly.

Optimization of behavioural tests for the prediction of outcomes in mouse models of focal middle cerebral artery occlusion

Intraluminal middle cerebral artery occlusion (MCAO) is the most widely used model of stroke. We aimed to predict the outcome of MCAO using a combination of fine behavioural tests for the prediction of unsuccessful surgery in mice leading to no infarction, haemorrhage and unexpected death. MCAO was performed on adult mice under the guidance of laser-Doppler flowmetry (LDF) to warrant a decrease in regional cerebral blood flow (rCBF) in the MCA territory. Four outcomes of MCAO were defined according to histological analysis: infarction, no infarction, haemorrhage and unexpected death (death within 24h post-surgery). Fine behavioural tests including the rotarod, modified neurological severity score (mNSS), Clark general and Clark focal tests were performed separately at 6h, 12h and 24h post-stroke. A total of 94 mice were included in the analysis. The infarction rate associated with MCAO was 58.5% (55/94). After optimization of the timing and behavioural tests, we found that higher Clark focal (>17.5) or higher mNSS scores (>10) were markedly related to early death, whereas a lower mNSS score (<3.5) was indicative of a tendency to show no infarction at 6h post-stroke. After 24h post-stroke, there was a positive correlation between the infarct volume and Clark focal results. Behavioural tests could help to predict the outcomes in the MCAO mouse model.

Roles of programmed death protein 1/programmed death-ligand 1 in secondary brain injury after intracerebral hemorrhage in rats: selective modulation of microglia polarization to anti-inflammatory phenotype

Background

Microglia and its polarization play critical roles in intracerebral hemorrhage-induced secondary brain injury. Programmed death protein 1/programmed death-ligand 1 has been reported to regulate neuroimmune cell functions. Signal transducers and activators of transcription 1 participate in microglia polarization, and programmed death protein 1/programmed death-ligand 1 could regulate the activation of signal transducers and activators of transcription 1. We herein show the critical role of programmed death protein 1/programmed death-ligand 1 in the polarization of microglia during intracerebral hemorrhage-induced secondary brain injury in rat models.

Methods

An autologous blood intracerebral hemorrhage model was established in Sprague Dawley rats (weighing 250–300 g), and primary cultured microglia was exposed to oxyhemoglobin to mimic intracerebral hemorrhage in vitro. Specific siRNAs and pDNA for programmed death protein 1 and programmed death-ligand 1 were exploited both in vivo and in vitro.

Results

In the brain tissue around hematoma, the protein levels of programmed death protein 1 and programmed death-ligand 1 and the interaction between them, as well as the phosphorylation of signal transducers and activators of transcription 1, were higher than that of the sham group and collectively peaked at 24 h after intracerebral hemorrhage. Overexpression of programmed death protein 1 and programmed death-ligand 1 ameliorated intracerebral hemorrhage-induced secondary brain injury, including brain cell death, neuronal degeneration, and inflammation, while their knockdown induced an opposite effect. In addition, overexpression of programmed death protein 1 and programmed death-ligand 1 selectively promoted microglia polarization to anti-inflammation phenotype after intracerebral hemorrhage and inhibited the phosphorylation of signal transducers and activators of transcription 1, suggesting that intracerebral hemorrhage-induced increases in programmed death protein 1 and programmed death-ligand 1 maybe a self-help.

Conclusions

Enhancing the expressions of programmed death protein 1 and programmed death-ligand 1 may induce a selective modulation of microglia polarization to anti-inflammation phenotype for intracerebral hemorrhage treatment.

Programmed Death Ligand 1 Plays a Neuroprotective Role in Experimental Autoimmune Neuritis by Controlling Peripheral Nervous System Inflammation of Rats

Programmed death 1 (PD-1; CD279), a member of the CD28 family, is an inhibitory receptor on T cells and is responsible for T cell dysfunction in infectious diseases and cancers. The ligand for PD-1, programmed death ligand 1 (PD-L1; also known as B7-H1, CD274), is a member of the B7 family. The engagement of PD-1 with programmed death ligand can downregulate autoreactive T cells that participate in multiple autoimmune diseases. Experimental autoimmune neuritis (EAN) is an animal model of Guillain-Barré syndrome, and the pathogenesis of EAN is mediated principally through T cells and macrophages. In this study, we investigated the effects of PD-L1 in EAN rats. For preventative and therapeutic management, we administered PD-L1, which successfully decreased the severity of EAN; it alleviated the neurologic course of EAN, as well as inhibited the infiltration of inflammatory cells and demyelination of sciatic nerves. Our data revealed that PD-L1 treatment inhibited lymphocyte proliferation and altered T cell differentiation by inducing decreases in IFN-γ⁺CD4⁺ Th1 cells and IL-17⁺CD4⁺ Th17 cells and increases in IL-4⁺CD4⁺ Th2 cells and Foxp3⁺CD4⁺ regulatory T cells. The expression levels of p-STAT3 and Foxp3 were significantly different in PD-L1-treated groups compared with the control group. Additionally, PD-L1 regulated the expression of Foxp3 and p-STAT3 in EAN, probably by inhibiting PI3K/AKT/mTOR signaling expression. In summary, PD-L1 is a potentially useful agent for the treatment of EAN because of its anti-inflammatory and neuroprotective effects.

Sex differences and the role of PPAR alpha in experimental stroke

Males and females respond differently to stroke. Moreover, females often experience worse long-term stroke outcomes. Fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARα) agonist has been shown to improve stroke outcome and resolve neuroinflammation in male mice. The present study compares the effect of pretreatment with fenofibrate versus vehicle control in male and female mice during experimental stroke. Mice were treated with low-dose fenofibrate 30 min before and once a day for three additional days after stroke onset. We observed a reduction in infarct volume in male mice 96 h post-stroke with low-dose fenofibrate pretreatment that was due to increase of an M2 macrophage phenotype in the brain and an increase in regulatory cells in the periphery. These outcomes were not replicated in females, likely due to the lower PPARα expression in cells and tissues in females vs males. We conclude that PPARα agonist treatment prior to stroke is neuroprotective in males but not females. These findings indicate PPARα as a probable mechanism of sex difference in stroke outcome and support the need for representation of females in stroke therapy research.

Are Microglial Cells the Regulators of Lymphocyte Responses in the CNS?

The infiltration of immune cells in the central nervous system is a common hallmark in different neuroinflammatory conditions. Accumulating evidence indicates that resident glial cells can establish a cross-talk with infiltrated immune cells, including T-cells, regulating their recruitment, activation and function within the CNS. Although the healthy CNS has been thought to be devoid of professional dendritic cells (DCs), numerous studies have reported the presence of a population of DCs in specific locations such as the meninges, choroid plexuses and the perivascular space. Moreover, the infiltration of DC precursors during neuroinflammatory situations has been proposed, suggesting a putative role of these cells in the regulation of lymphocyte activity within the CNS. On the other hand, under specific circumstances, microglial cells are able to acquire a phenotype of DC expressing a wide range of molecules that equip these cells with all the necessary machinery for communication with T-cells. In this review, we summarize the current knowledge on the expression of molecules involved in the cross-talk with T-cells in both microglial cells and DCs and discuss the potential contribution of each of these cell populations on the control of lymphocyte function within the CNS.

PD-L1 Monoclonal Antibody Treats Ischemic Stroke by Controlling Central Nervous System Inflammation

BACKGROUND AND PURPOSE

Both pathogenic and regulatory immune processes are involved in the middle cerebral artery occlusion (MCAO) model of experimental stroke, including interactions involving the programmed death 1 (PD-1) receptor and its 2 ligands, PD-L1 and PD-L2. Although PD-1 reduced stroke severity, PD-L1 and PD-L2 appeared to play pathogenic roles, suggesting the use of anti-PD-L monoclonal antibody therapy for MCAO.

METHODS

Male C57BL/6 mice were treated with a single dose of anti-PD-L1 monoclonal antibody 4 hours after MCAO and evaluated for clinical, histological and immunologic changes after 96 hours of reperfusion.

RESULTS

Blockade of the PD-L1 checkpoint using a single injection of 200 μg anti-PD-L1 monoclonal antibody given intravenously 4 hours after occlusion significantly reduced MCAO infarct volumes and improved neurological outcomes after 96 hours of reperfusion. Treatment partially reversed splenic atrophy and decreased central nervous system infiltrating immune cells concomitant with enhanced appearance of CD8(+) regulatory T cells in the lesioned central nervous system hemisphere.

CONCLUSIONS

This study demonstrates for the first time the beneficial therapeutic effects of PD-L1 checkpoint blockade on MCAO, thus validating proposed mechanisms obtained in our previous studies using PD-1- and PD-L-deficient mice. These results provide strong support for the use of available humanized anti-PD-L1 antibodies for treatment of human stroke subjects.

Differential induction of PD-1/PD-L1 in Neuroimmune cells by drug of abuse

Interaction of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) plays a critical role in regulating the delicate balance between protective immunity and tolerance. Human neuroimmune cells express very low or undetectable levels of PD-1/PD-L1 in normal physiological condition.We seek to examine if exposure of these cells to drug of abuse such as methamphetamine (METH) alters the profile of PD-1/PD-L1 levels, thereby dampens the innate immune response of the host cells. Thus, we assessed the changes in the levels of PD-1/PD-L1 in primary human macrophages, brain endothelial cells (hBECs), astrocytes, microglia, and neurons after exposure to METH. We observed that stimulation of these neuroimmune cells by METH responded differentially to PD-1/PD-L1 expression. Stimulation of macrophage culture with 50 μM of METH exhibited immediate gradual upregulation of PD-L1, while increase in PD-1 took 2-4 hours later than PD-L1. The response of hBECs to PD-1/PD-L1 induction occurred at 24 hours, while increase of PD-1/PD-L1 levels in neurons and microglia was immediate following METH exposure. We found that astrocytes expressed moderate levels of endogenous PD-1/PD-L1, which was diminished by METH exposure. Our findings show a differential expression of PD-1/PD-L1 in neuroimmune cells in response to METH stimulation, suggesting that PD-1/PD-L1 interplay in these cell types could orchestrate the intercellular interactive communication for neuronal death or protection in the brain environment.

Upregulation of Programmed Death-1 and Its Ligand in Cardiac Injury Models: Interaction with GADD153

Purpose

Programmed Death-1 (PD-1) and its ligand, PD-L1, are regulators of immune/ inflammatory mechanisms. We explored the potential involvement of PD-1/PD-L1 pathway in the inflammatory response and tissue damage in cardiac injury models.

Experimental Design

Ischemic-reperfused and cryoinjured hearts were processed for flow cytometry and immunohistochemical studies for determination of cardiac PD-1 and PD-L1 in the context of assessment of the growth arrest- and DNA damage-inducible protein 153 (GADD153) which regulates both inflammation and cell death. Further, we explored the potential ability of injured cardiac cells to influence proliferation of T lymphocytes.

Results

The isolated ischemic-reperfused hearts displayed marked increases in expression of PD-1 and PD-L1 in cardiomyocytes; however, immunofluorescent studies indicate that PD-1 and PD-L1 are not primarily co-expressed on the same cardiomyocytes. Upregulation of PD-1/PD-L1 was associated with a) marked increases in GADD153 and interleukin (IL)-17 but a mild increase in IL-10 and b) disruption of mitochondrial membrane potential (ψ_m) as well as apoptotic and necrotic cell death. Importantly, while isotype matching treatment did not affect the aforementioned changes, treatment with the PD-L1 blocking antibody reversed those effects in association with marked cardioprotection. Further, ischemic-reperfused cardiac cells reduced proliferation of T lymphocytes, an effect partially reversed by PD-L1 antibody. Subsequent studies using the cryoinjury model of myocardial infarction revealed significant increases in PD-1, PD-L1, GADD153 and IL-17 positive cells in association with significant apoptosis/necrosis.

Conclusions

The data suggest that upregulation of PD-1/PD-L1 pathway in cardiac injury models mediates tissue damage likely through a paracrine mechanism. Importantly, inhibition of T cell proliferation by ischemic-reperfused cardiac cells is consistent with the negative immunoregulatory role of PD-1/PD-L1 pathway, likely reflecting an endogenous cardiac mechanism to curtail the deleterious impact of infiltrating immune cells to the damaged myocardium. The balance of these countervailing effects determines the extent of cardiac injury.

Liver myeloid-derived suppressor cells expand in response to liver metastases in mice and inhibit the anti-tumor efficacy of anti-CEA CAR-T

Chimeric antigen receptor-modified T cell (CAR-T) technology, a promising immunotherapeutic tool, has not been applied specifically to treat liver metastases (LM). While CAR-T delivery to LM can be optimized by regional intrahepatic infusion, we propose that liver CD11b+Gr-1+ myeloid-derived suppressor cells (L-MDSC) will inhibit the efficacy of CAR-T in the intrahepatic space. We studied anti-CEA CAR-T in a murine model of CEA+ LM and identified mechanisms through which L-MDSC expand and inhibit CAR-T function. We established CEA+ LM in mice and studied purified L-MDSC and responses to treatment with intrahepatic anti-CEA CAR-T infusions. L-MDSC expanded threefold in response to LM, and their expansion was dependent on GM-CSF, which was produced by tumor cells. L-MDSC utilized PD-L1 to suppress anti-tumor responses through engagement of PD-1 on CAR-T. GM-CSF, in cooperation with STAT3, promoted L-MDSC PD-L1 expression. CAR-T efficacy was rescued when mice received CAR-T in combination with MDSC depletion, GM-CSF neutralization to prevent MDSC expansion, or PD-L1 blockade. As L-MDSC suppressed anti-CEA CAR-T, infusion of anti-CEA CAR-T in tandem with agents targeting L-MDSC is a rational strategy for future clinical trials.

Splenectomy reduces infarct volume and neuroinflammation in male but not female mice in experimental stroke

The peripheral immune response contributes to neurodegeneration after stroke yet little is known about how this process differs between males and females. The current study demonstrates that splenectomy prior to experimental stroke eliminates sex differences in infarct volume and activated brain monocytes/microglia. In the periphery of both sexes, activated T cells correlate directly with stroke outcome while monocytes are reduced by splenectomy only in males. This study provides new information about the sex specific mechanisms of the peripheral immune response in neurodegeneration after stroke and demonstrates the need for representation of both sexes in basic and clinical stroke research.

Both PD-1 ligands protect the kidney from ischemia reperfusion injury

Acute kidney injury (AKI) is a common problem in hospitalized patients that enhances morbidity and mortality and promotes the development of chronic and end-stage renal disease. Ischemia reperfusion injury (IRI) is one of the major causes of AKI and is characterized by uncontrolled renal inflammation and tubular epithelial cell death. Our recent studies demonstrated that regulatory T cells (Tregs) protect the kidney from ischemia reperfusion-induced inflammation and injury. Blockade of programmed death-1 (PD-1) on the surface of Tregs, prior to adoptive transfer, negates their ability to protect against ischemic kidney injury. The present study was designed to investigate the role of the known PD-1 ligands, PD-L1 and PD-L2, in kidney IRI. Administration of PD-L1 or PD-L2 blocking Abs prior to mild or moderate kidney IRI significantly exacerbated the loss of renal function, renal inflammation, and acute tubular necrosis compared with mice receiving isotype control Abs. Interestingly, blockade of both PD-1 ligands resulted in worse injury, dysfunction, and inflammation than did blocking either ligand alone. Genetic deficiency of either PD-1 ligand also exacerbated kidney dysfunction and acute tubular necrosis after subthreshold ischemia. Bone marrow chimeric studies revealed that PD-L1 expressed on non-bone marrow-derived cells is critical for this resistance to IRI. Finally, blockade of either PD-1 ligand negated the protective ability of adoptively transferred Tregs in IRI. These findings suggest that PD-L1 and PD-L2 are nonredundant aspects of the natural protective response to ischemic injury and may be novel therapeutic targets for AKI.

Different immunological mechanisms govern protection from experimental stroke in young and older mice with recombinant TCR ligand therapy

Stroke is a leading cause of death and disability in the United States. The lack of clinical success in stroke therapies can be attributed, in part, to inadequate basic research on aging rodents. The current study demonstrates that recombinant TCR ligand therapy uses different immunological mechanisms to protect young and older mice from experimental stroke. In young mice, RTL1000 therapy inhibited splenocyte efflux while reducing frequency of T cells and macrophages in the spleen. Older mice treated with RTL1000 exhibited a significant reduction in inflammatory cells in the brain and inhibition of splenic atrophy. Our data suggest age specific differences in immune response to stroke that allow unique targeting of stroke immunotherapies.

Antigen-specific immune reactions to ischemic stroke

Brain proteins are detected in the cerebrospinal fluid (CSF) and blood of stroke patients and their concentration is related to the extent of brain damage. Antibodies against brain antigens develop after stroke, suggesting a humoral immune response to the brain injury. Furthermore, induced immune tolerance is beneficial in animal models of cerebral ischemia. The presence of circulating T cells sensitized against brain antigens, and antigen presenting cells (APCs) carrying brain antigens in draining lymphoid tissue of stroke patients support the notion that stroke might induce antigen-specific immune responses. After stroke, brain proteins that are normally hidden from the periphery, inflammatory mediators, and danger signals can exit the brain through several efflux routes. They can reach the blood after leaking out of the damaged blood-brain barrier (BBB) or following the drainage of interstitial fluid to the dural venous sinus, or reach the cervical lymph nodes through the nasal lymphatics following CSF drainage along the arachnoid sheaths of nerves across the nasal submucosa. The route and mode of access of brain antigens to lymphoid tissue could influence the type of response. Central and peripheral tolerance prevents autoimmunity, but the actual mechanisms of tolerance to brain antigens released into the periphery in the presence of inflammation, danger signals, and APCs, are not fully characterized. Stroke does not systematically trigger autoimmunity, but under certain circumstances, such as pronounced systemic inflammation or infection, autoreactive T cells could escape the tolerance controls. Further investigation is needed to elucidate whether antigen-specific immune events could underlie neurological complications impairing recovery from stroke.

Regulation of Neuroinflammation through Programed Death-1/Programed Death Ligand Signaling in Neurological Disorders

Immune responses in the central nervous system (CNS), which involve both resident glial cells and infiltrating peripheral immune cells, play critical roles in the progress of brain injuries and neurodegeneration. To avoid inflammatory damage to the compromised brain, the immune cell activities in the CNS are controlled by a plethora of chemical mediators and signal transduction cascades, such as inhibitory signaling through programed death-1 (PD-1) and programed death ligand (PD-L) interactions. An increasing number of recent studies have highlighted the importance of PD-1/PD-L pathway in immune regulation in CNS disorders such as ischemic stroke, multiple sclerosis, and Alzheimer’s disease. Here, we review the current knowledge of the impact of PD-1/PD-L signaling on brain injury and neurodegeneration. An improved understanding of the function of PD-1/PD-L in the cross-talk between peripheral immune cells, CNS glial cells, and non-immune CNS cells is expected to shed further light on immunomodulation and help develop effective and safe immunotherapies for CNS disorders.