Early neutrophil infiltration is critical for inflammation-sensitized hypoxic-ischemic brain injury in newborns

Delving into the clinical impact of NETs in pediatric cancer

Pediatric cancer, a complex and heterogeneous group of diseases, continues to challenge medical research and treatment strategies. Despite advances in precision medicine and immunotherapy, certain aggressive subtypes of pediatric cancer are resistant to conventional therapies, requiring further exploration of potential therapeutic targets. Neutrophil extracellular traps (NETs), net-like structures released by neutrophils, have emerged as a potential player in the pediatric cancer landscape. However, our understanding of their role in pediatric oncology remains limited. This systematic review examines the current state of the NETs literature in pediatric cancer, focusing on the most frequent subtypes. The review reveals the scarcity of research in this area, highlighting the need for further investigation. The few studies available suggest that NETs may influence infection risk, treatment resistance and prognosis in certain pediatric malignancies. Although the field is still in its infancy, it holds great promise for advancing our understanding of pediatric cancer biology and potential therapeutic pathways. IMPACT: This review identifies a significant gap in research on neutrophil extracellular traps (NETs) in pediatric cancer. It provides a summary of existing studies and their promising findings and potential, as well as a comprehensive overview of current research on NETs in certain tumor types. It also emphasizes the lack of specific studies in pediatric cancer. The review encourages the prioritization of NET research in pediatric oncology, with the aim of improving prognosis and developing new treatments through increased understanding and targeted studies.

Hypoxic-Ischemic Encephalopathy: Pathogenesis and Promising Therapies

Hypoxic-ischemic encephalopathy (HIE) is a brain lesion caused by inadequate blood supply and oxygen deprivation, often occurring in neonates. It has emerged as a grave complication of neonatal asphyxia, leading to chronic neurological damage. Nevertheless, the precise pathophysiological mechanisms underlying HIE are not entirely understood. This paper aims to comprehensively elucidate the contributions of hypoxia-ischemia, reperfusion injury, inflammation, oxidative stress, mitochondrial dysfunction, excitotoxicity, ferroptosis, endoplasmic reticulum stress, and apoptosis to the onset and progression of HIE. Currently, hypothermia therapy stands as the sole standard treatment for neonatal HIE, albeit providing only partial neuroprotection. Drug therapy and stem cell therapy have been explored in the treatment of HIE, exhibiting certain neuroprotective effects. Employing drug therapy or stem cell therapy as adjunctive treatments to hypothermia therapy holds great significance. This article presents a systematic review of the pathogenesis and treatment strategies of HIE, with the goal of enhancing the effect of treatment and improving the quality of life for HIE patients.

Inflammatory and Hematologic Liver and Platelet (HALP) Scores in Hypothermia-Treated Hypoxic-Ischemic Encephalopathy (HIE)

OBJECTIVE

This study examined systemic inflammatory indices and "Hemoglobin, Albumin, Lymphocyte, Platelet (HALP) scores" in neonates with hypoxic-ischemic encephalopathy (HIE).

METHODS

A total of 43 neonates with moderate-to-severe HIE at 36 weeks' gestation were assessed. Systemic inflammatory markers were measured before HT commenced within 0-6 h after birth and between 60 and 72 h during and after therapy or before adjusting for hypothermia.

RESULTS

Platelet counts, hemoglobin levels, and platelet indices in the HIE group were significantly lower at both time points (p = 0.001). Both the neutrophil-to-lymphocyte ratio (NLR) and monocyte-to-lymphocyte ratio (MLR) decreased in the HIE group after hypothermia therapy (p = 0.001). Seizures, PVL, and kidney injuries were associated with higher HALP scores. The AUCs of NLR, PLR, MLR, SII, SIRI, and platelet, neutrophil, monocyte, and lymphocyte Index (PIV) showed significant sensitivity and specified HIE, with area under the curve (AUC) values of 0.654, 0.751, 0.766, 0.700, 0.722, and 0.749, respectively.

CONCLUSIONS

A significant difference in systemic inflammatory markers was found between the HIE and control groups after hypothermia treatment, with significant reductions in the MLR and NLR. These markers, particularly MLR, were significant predictors of adverse clinical outcomes including seizures, PVL, and kidney damage.

Experimental procedures for flow cytometry of wild-type mouse brain: a systematic review

Objective

The aim of this study was to systematically review the neuroimmunology literature to determine the average immune cell counts reported by flow cytometry in wild-type (WT) homogenized mouse brains.

Background

Mouse models of gene dysfunction are widely used to study age-associated neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. The importance of the neuroimmune system in these multifactorial disorders has become increasingly evident, and methods to quantify resident and infiltrating immune cells in the brain, including flow cytometry, are necessary. However, there appears to be no consensus on the best approach to perform flow cytometry or quantify/report immune cell counts. The development of more standardized methods would accelerate neuroimmune discovery and validation by meta-analysis.

Methods

There has not yet been a systematic review of 'neuroimmunology' by 'flow cytometry' via examination of the PROSPERO registry. A protocol for a systematic review was subsequently based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) using the Studies, Data, Methods, and Outcomes (SDMO) criteria. Literature searches were conducted in the Google Scholar and PubMed databases. From that search, 900 candidate studies were identified, and 437 studies were assessed for eligibility based on formal exclusion criteria.

Results

Out of the 437 studies reviewed, 58 were eligible for inclusion and comparative analysis. Each study assessed immune cell subsets within homogenized mouse brains and used flow cytometry. Nonetheless, there was considerable variability in the methods, data analysis, reporting, and results. Descriptive statistics have been presented on the study designs and results, including medians with interquartile ranges (IQRs) and overall means with standard deviations (SD) for specific immune cell counts and their relative proportions, within and between studies. A total of 58 studies reported the most abundant immune cells within the brains were TMEM119+ microglia, bulk CD4+ T cells, and bulk CD8+ T cells.

Conclusion

Experiments to conduct and report flow cytometry data, derived from WT homogenized mouse brains, would benefit from a more standardized approach. While within-study comparisons are valid, the variability in methods of counting of immune cell populations is too broad for meta-analysis. The inclusion of a minimal protocol with more detailed methods, controls, and standards could enable this nascent field to compare results across studies.

Role of Polymorphonuclear Myeloid-Derived Suppressor Cells and Neutrophils in Ischemic Stroke

Background Immune cells play a vital role in the pathology of ischemic stroke. Neutrophils and polymorphonuclear myeloid-derived suppressor cells share a similar phenotype and have attracted increasing attention in immune regulation research, yet their dynamics in ischemic stroke remain elusive. Methods and Results Mice were randomly divided into 2 groups and intraperitoneally treated with anti-Ly6G (lymphocyte antigen 6 complex locus G) monoclonal antibody or saline. Distal middle cerebral artery occlusion and transient middle cerebral artery occlusion were applied to induce experimental stroke, and mice mortality was recorded until 28 days after stroke. Green fluorescent nissl staining was used to measure infarct volume. Cylinder and foot fault tests were used to evaluate neurological deficits. Immunofluorescence staining was conducted to confirm Ly6G neutralization and detect activated neutrophils and CD11b⁺Ly6G⁺ cells. Fluorescence-activated cell sorting was performed to evaluate polymorphonuclear myeloid-derived suppressor cell accumulation in brains and spleens after stroke. Anti-Ly6G antibody successfully depleted Ly6G expression in mice cortex but did not alter cortical physiological vasculature. Prophylactic anti-Ly6G antibody treatment ameliorated ischemic stroke outcomes in the subacute phase. Moreover, using immunofluorescence staining, we found that anti-Ly6G antibody suppressed activated neutrophil infiltration into parenchyma and decreased neutrophil extracellular trap formation in penumbra after stroke. Additionally, prophylactic anti-Ly6G antibody treatment reduced polymorphonuclear myeloid-derived suppressor cell accumulation in the ischemic hemisphere. Conclusions Our study suggested a protective effect of prophylactic anti-Ly6G antibody administration against ischemic stroke by reducing activated neutrophil infiltration and neutrophil extracellular trap formation in parenchyma and suppressing polymorphonuclear myeloid-derived suppressor cell accumulation in the brain. This study may provide a novel therapeutic approach for ischemic stroke.

Irisin prevents hypoxic-ischemic brain damage in rats by inhibiting oxidative stress and protecting the blood-brain barrier

Hypoxic-ischemic encephalopathy (HIE) is associated with excessive inflammation, blood-brain barrier dysfunction, and oxidative stress. Irisin can reduce inflammation and ameliorate oxidative stress; however, its effects on hypoxic-ischemic brain damage in newborns are unknown. Newborn Sprague-Dawley rats were subjected to hypoxic-ischemic injury and irisin treatment. TUNEL staining assays, the albumin-Evans blue dye extravasation method, an antioxidants detection kit, quantitative reverse-transcriptase PCR, enzyme linked immunosorbent assay, Western blot analysis, immunohistochemistry, and electron microscopy were used to investigate the possible mechanisms underlying the prevention of HIE by irisin. We discovered that rats affected by HIE and administered irisin had lower levels of IL-6 (but not TNF-α or IL-1β) less oxidative stress, and enhanced blood-brain barrier integrity. Irisin can effectively attenuate brain damage by reducing oxidative stress and protecting the blood-brain barrier.

Neutrophil Extracellular Traps Release following Hypoxic-Ischemic Brain Injury in Newborn Rats Treated with Therapeutic Hypothermia

The peripheral immune system plays a critical role in neuroinflammation of the central nervous system after an insult. Hypoxic-ischemic encephalopathy (HIE) induces a strong neuroinflammatory response in neonates, which is often associated with exacerbated outcomes. In adult models of ischemic stroke, neutrophils infiltrate injured brain tissue immediately after an ischemic insult and aggravate inflammation via various mechanisms, including neutrophil extracellular trap (NETs) formation. In this study, we used a neonatal model of experimental hypoxic-ischemic (HI) brain injury and demonstrated that circulating neutrophils were rapidly activated in neonatal blood. We observed an increased infiltration of neutrophils in the brain after exposure to HI. After treatment with either normothermia (NT) or therapeutic hypothermia (TH), we observed a significantly enhanced expression level of the NETosis marker Citrullinated H3 (Cit-H3), which was significantly more pronounced in animals treated with TH than in those treated with NT. NETs and NLR family pyrin domain containing 3 (NLRP-3) inflammasome assembly are closely linked in adult models of ischemic brain injury. In this study, we observed an increase in the activation of the NLRP-3 inflammasome at the time points analyzed, particularly immediately after TH, when we observed a significant increase in NETs structures in the brain. Together, these results suggest the important pathological functions of early arriving neutrophils and NETosis following neonatal HI, particularly after TH treatment, which is a promising starting point for the development of potential new therapeutic targets for neonatal HIE.

[Prognosis of late-life depression: clinical and immunological features]

OBJECTIVE

To study the outcomes of depression at a late age during a 3-year prospective follow-up in patients with various immunophenotypes.

MATERIAL AND METHODS

A cohort of patients with depressive disorders who were treated in a gerontopsychiatric hospital and re-examined after 1 and 3 years. The group with immunophenotype A (with increased activity of leukocyte elastase (LE) and complex depressions, comorbid with anxiety and senesto-hypochondriac disorders) included 20 people: 6 men (30%) and 14 women (70%), median age was 68 years. A depressive episode (DE) was diagnosed in 13 patients (65%) with recurrent depressive disorder (RDD) and in 7 patients (35%) with bipolar affective disorder (BAD). The group with immunophenotype B (with reduced activity of LE and prolonged apathetic-adynamic depression) included 31 people: 10 men (32.3%) and 21 women (67.7%), the median age was 68 years. DE was diagnosed in 20 patients (64.5%) with RDD, 9 patients (29%) with BAD, and in 2 patients (6.5%) with a single DE. The patients were examined using clinical, psychometric, immunological and clinical- follow-up methods (after 1 and 3 years).

RESULTS

More favorable course of the disease with the formation of high-quality remission was observed in patients with immunophenotype A (95% of cases after 1 and 3 years; χ2=10.44; p=0.001 and χ2=11.97; p=0.001, respectively). In patients with immunophenotype B, an unfavorable course of the disease prevailed (83.9 and 87.1% of cases after 1 and 3 years) with the formation of low-quality remissions (with residual depressive disorders, the development of repeated depressive phases and chronification of depression).

CONCLUSION

The study revealed the relationship between clinical and biological features and the course of late-life depression.

Stem Cell Therapy for Acute/Subacute Ischemic Stroke with a Focus on Intraarterial Stem Cell Transplantation: From Basic Research to Clinical Trials

Stem cell therapy for ischemic stroke holds great promise for the treatment of neurological impairment and has moved from the laboratory into early clinical trials. The mechanism of action of stem cell therapy includes the bystander effect and cell replacement. The bystander effect plays an important role in the acute to subacute phase, and cell replacement plays an important role in the subacute to chronic phase. Intraarterial (IA) transplantation is less invasive than intraparenchymal transplantation and can provide more cells in the affected brain region than intravenous transplantation. However, transplanted cell migration was reported to be insufficient, and few transplanted cells were retained in the brain for an extended period. Therefore, the bystander effect was considered the main mechanism of action of IA stem cell transplantation. In most clinical trials, IA transplantation was performed during the acute and subacute phases. Although clinical trials of IA transplantation demonstrated safety, they did not demonstrate satisfactory efficacy in improving patient outcomes. To increase efficacy, increased migration of transplanted cells and production of long surviving and effective stem cells would be crucial. Given the lack of knowledge on this subject, we review and summarize the mechanisms of action of transplanted stem cells and recent advancements in preclinical and clinical studies to provide information and guidance for further advancement of acute/subacute phase IA stem cell transplantation therapy for ischemic stroke.

Bioinformatics-based analysis reveals IDR-1018-mediated ceRNA regulation network for protective effect on hypoxia-ischemic brain injury in neonatal mice

Activation of an innate immune response serves as a key, contributing factor in perinatal brain injury. The current study sought to evaluate the clinical significance of innate defense regulatory peptide 1018 (IDR-1018)-derived peptide mediating ceRNA regulation network as a biomarker in neonatal mice with hypoxic-ischemic brain damage (HIBD). Firstly, bioinformatics analyses were performed to screen the HIBD-related candidate genes, miRNAs, and lncRNAs. The StarBase, miRDB, and LncBase databases were retrieved to obtain the lncRNA-miRNA-mRNA network, which revealed the ceRNA regulatory network mediated by IDR-1018. Subsequently, RT-qPCR was adopted to determine the expression patterns of MIAT, miR-7a-5p, and Plp2 in neonatal mice with HIBD after treatment with IDR-1018. Moreover, the relationship among mRNA, miRNA, and lncRNA in primary hippocampal neurons was verified by means of dual-luciferase reporter assay and RIP assay. Initial findings demonstrated that Plp2, mmu-miR-7a-5p, and three lncRNAs (MIAT, XIST, and 1700020I14RIK) were related to HIBD. Moreover, IDR-1018 could relieve HIBD in neonatal mice. Plp2 and MIAT were down-regulated, while mmu-miR-7a-5p was up-regulated in the striatum, hippocampus, and cortical tissues of the neonatal mice with HIBD, whereas treatment with the IDR-1018 could revere these trends. Additionally, MIAT acted as a ceRNA of miR-7a-5p to elevate Plp2 expression. In conclusion, our findings highlighted that IDR-1018 relieved HIBD in neonatal mice via the MIAT/miR-7a-5p/Plp2 axis.

Rationale for the Use of Cord Blood in Hypoxic-Ischaemic Encephalopathy

Hypoxic-ischaemic encephalopathy (HIE) is a severe complication of asphyxia at birth. Therapeutic hypothermia, the standard method for HIE prevention, is effective in only 50% of the cases. As the understanding of the immunological basis of these changes increases, experiments have begun with the use of cord blood (CB) because of its neuroprotective properties. Mechanisms for the neuroprotective effects of CB stem cells include antiapoptotic and anti-inflammatory actions, stimulation of angiogenesis, production of trophic factors, and mitochondrial donation. In several animal models of HIE, CB decreased oxidative stress, cell death markers, CD4+ T cell infiltration, and microglial activation; restored normal brain metabolic activity; promoted neurogenesis; improved myelination; and increased the proportion of mature oligodendrocytes, neuron numbers in the motor cortex and somatosensory cortex, and brain weight. These observations translate into motor strength, limb function, gait, and cognitive function and behaviour. In humans, the efficacy and safety of CB administration were reported in a few early clinical studies which confirmed the feasibility and safety of this intervention for up to 10 years. The results of these studies showed an improvement in the developmental outcomes over hypothermia. Two phase-2 clinical studies are ongoing under the United States regulations, namely one controlled study and one blinded study.

Temporal Characterization of Microglia-Associated Pro- and Anti-Inflammatory Genes in a Neonatal Inflammation-Sensitized Hypoxic-Ischemic Brain Injury Model

Hypoxic-ischemic encephalopathy (HIE) mainly affects preterm and term newborns, leading to a high risk of brain damage. Coexisting infection/inflammation and birth asphyxia are key factors associated with intracerebral increase of proinflammatory cytokines linked to HIE. Microglia are key mediators of inflammation during perinatal brain injury, characterized by their phenotypic plasticity, which may facilitate their participation in both the progression and resolution of injury-induced inflammation. The purpose of this study was to investigate the temporal expression of genes associated with pro- and anti-inflammatory cytokines as well as the nucleotide-binding domain, leucine-rich repeat protein (NLRP-3) inflammasome from microglia cells. For this purpose, we used our established neonatal rat model of inflammation-sensitized hypoxic-ischemic (HI) brain injury in seven-day-old rats. We assessed gene expression profiles of 11 cytokines and for NLRP-3 using real-time PCR from sorted CD11b/c microglia of brain samples at different time points (3.5 h after LPS injection and 0, 5, 24, 48, and 72 hours post HI) following different treatments: vehicle, E. coli lipopolysaccharide (LPS), vehicle/HI, and LPS/HI. Our results showed that microglia are early key mediators of the inflammatory response and exacerbate the inflammatory response following HI, polarizing into a predominant proinflammatory M1 phenotype in the early hours post HI. The brains only exposed to HI showed a delay in the expression of proinflammatory cytokines. We also demonstrated that NLRP-3 plays a role in the inflammatory resolution with a high expression after HI insult. The combination of both, a preinfection/inflammation condition and hypoxia-ischemia, resulted in a higher proinflammatory cytokine storm, highlighting the significant contribution of acute inflammation sensitizing prior to a hypoxic insult on the severity of perinatal brain damage.

Monocytes promote acute neuroinflammation and become pathological microglia in neonatal hypoxic-ischemic brain injury

Rationale: Monocytes belong to the mononuclear phagocyte system and are immune responders to tissue injury and infection. There were also reports of monocytes transforming to microglia-like cells. Here we explore the roles of monocytes in microglia ontogeny and the pathogenesis of neonatal cerebral hypoxic-ischemic (HI) brain injury in mice. Methods: We used three genetic methods to track the development of monocytes, including CX3CR1GFP/+; CCR2RFP/+ reporter mice, adoptive transfer of GFP+ monocytes, and fate-mapping with CCR2-CreER mice, in neonatal mouse brains with or without lipopolysaccharide (LPS, 0.3 mg/kg)-sensitized Vannucci HI. We also used genetic (CCR2RFP/ RFP, CCR2 knockout) and pharmacological methods (RS102895, a CCR2 antagonist) to test the roles of monocytic influx in LPS/HI brain injury. Results: CCR2+ monocytes entered the late-embryonic brains via choroid plexus, but rapidly became CX3CR1+ amoeboid microglial cells (AMCs). The influx of CCR2+ monocytes declined after birth, but recurred after HI or LPS-sensitized HI (LPS/HI) brain injury, particularly in the hippocampus. The CCR2-CreER-based fate-mapping showed that CCR2+ monocytes became CD68+ TNFα+ macrophages within 4 d after LPS/HI, and maintained as TNFα+ MHCII+ macrophages or persisted as Tmem119+ Sall1+ P2RY12+ ramified microglia for at least five months after injury. Genetic deletion of the chemokine receptor CCR2 markedly diminished monocytic influx, the expression of pro- and anti-inflammatory cytokines, and brain damage. Post-LPS/HI application of RS102895 also reduced inflammatory responses and brain damage, leading to better cognitive functions. Conclusion: These results suggest that monocytes promote acute inflammatory responses and may become pathological microglia long after the neonatal LPS/HI insult. Further, blocking the influx of monocytes may be a potential therapy for neonatal brain injury.

Peripheral immune cells and perinatal brain injury: a double-edged sword?

Perinatal brain injury is the leading cause of neurological mortality and morbidity in childhood ranging from motor and cognitive impairment to behavioural and neuropsychiatric disorders. Various noxious stimuli, including perinatal inflammation, chronic and acute hypoxia, hyperoxia, stress and drug exposure contribute to the pathogenesis. Among a variety of pathological phenomena, the unique developing immune system plays an important role in the understanding of mechanisms of injury to the immature brain. Neuroinflammation following a perinatal insult largely contributes to evolution of damage to resident brain cells, but may also be beneficial for repair activities. The present review will focus on the role of peripheral immune cells and discuss processes involved in neuroinflammation under two frequent perinatal conditions, systemic infection/inflammation associated with encephalopathy of prematurity (EoP) and hypoxia/ischaemia in the context of neonatal encephalopathy (NE) and stroke at term. Different immune cell subsets in perinatal brain injury including their infiltration routes will be reviewed and critical aspects such as sex differences and maturational stage will be discussed. Interactions with existing regenerative therapies such as stem cells and also potentials to develop novel immunomodulatory targets are considered. IMPACT: Comprehensive summary of current knowledge on the role of different immune cell subsets in perinatal brain injury including discussion of critical aspects to be considered for development of immunomodulatory therapies.

Multiple Roles of Peripheral Immune System in Modulating Ischemia/Hypoxia-Induced Neuroinflammation

Given combined efforts of neuroscience and immunology, increasing evidence has revealed the critical roles of the immune system in regulating homeostasis and disorders of the central nervous system (CNS). Microglia have long been considered as the only immune cell type in parenchyma, while at the interface between CNS and the peripheral (meninges, choroid plexus, and perivascular space), embryonically originated border-associated macrophages (BAMs) and multiple surveilling leukocytes capable of migrating into and out of the brain have been identified to function in the healthy brain. Hypoxia-induced neuroinflammation is the key pathological procedure that can be detected in healthy people at high altitude or in various neurodegenerative diseases, during which a very thin line between a beneficial response of the peripheral immune system in maintaining brain homeostasis and a pathological role in exacerbating neuroinflammation has been revealed. Here, we are going to focus on the role of the peripheral immune system and its crosstalk with CNS in the healthy brain and especially in hypobaric or ischemic hypoxia-associated neuroinflammation.

The role of lymphocytes in neonatal encephalopathy

Neonatal encephalopathy is a syndrome characterised by abnormal neurological function often caused by a hypoxic insult during childbirth. Triggers such as hypoxia-ischaemia result in the release of cytokines and chemokines inducing the infiltration of neutrophils, natural killer cells, B cells, T cells and innate T cells into the brain. However, the role of these cells in the development of the brain injury is poorly understood. We review the mechanisms by which lymphocytes contribute to brain damage in NE. NK, T and innate T cells release proinflammatory cytokines contributing to the neurodegeneration in the secondary and tertiary phase of injury, whereas B cells and regulatory T cells produce IL-10 protecting the brain in NE. Targeting lymphocytes may have therapeutic potential in the treatment of NE in terms of management of inflammation and brain damage, particularly in the tertiary or persistent phases.

Classical complement pathway inhibition reduces brain damage in a hypoxic ischemic encephalopathy animal model

Perinatal hypoxic ischemic encephalopathy (HIE) remains a major contributor of infant death and long-term disability worldwide. The role played by the complement system in this ischemia-reperfusion injury remains poorly understood. In order to better understand the role of complement activation and other modifiable mechanisms of injury in HIE, we tested the dual-targeting anti-inflammatory peptide, RLS-0071 in an animal model of HIE. Using the well-established HIE rat pup model we measured the effects of RLS-0071 during the acute stages of the brain injury and on long-term neurocognitive outcomes. Rat pups subject to hypoxia-ischemia insult received one of 4 interventions including normothermia, hypothermia and RLS-0071 with and without hypothermia. We measured histopathological effects, brain C1q levels and neuroimaging at day 1 and 21 after the injury. A subset of animals was followed into adolescence and evaluated for neurocognitive function. On histological evaluation, RLS-0071 showed neuronal protection in combination with hypothermia (P = 0.048) in addition to reducing C1q levels in the brain at 1hr (P = 0.01) and at 8 hr in combination with hypothermia (P = 0.005). MRI neuroimaging demonstrated that RLS-0071 in combination with hypothermia reduced lesion volume at 24 hours (P<0.05) as well as decreased T2 signal at day 21 in combination with hypothermia (P<0.01). RLS-0071 alone or in combination with hypothermia improved both short-term and long-term memory. These findings suggest that modulation by RLS-0071 can potentially decrease brain damage resulting from HIE.

Microglia-leucocyte axis in cerebral ischaemia and inflammation in the developing brain

Development of the Central Nervous System (CNS) is reliant on the proper function of numerous intricately orchestrated mechanisms that mature independently, including constant communication between the CNS and the peripheral immune system. This review summarizes experimental knowledge of how cerebral ischaemia in infants and children alters physiological communication between leucocytes, brain immune cells, microglia and the neurovascular unit (NVU)-the "microglia-leucocyte axis"-and contributes to acute and long-term brain injury. We outline physiological development of CNS barriers in relation to microglial and leucocyte maturation and the plethora of mechanisms by which microglia and peripheral leucocytes communicate during postnatal period, including receptor-mediated and intracellular inflammatory signalling, lipids, soluble factors and extracellular vesicles. We focus on the "microglia-leucocyte axis" in rodent models of most common ischaemic brain diseases in the at-term infants, hypoxic-ischaemic encephalopathy (HIE) and focal arterial stroke and discuss commonalities and distinctions of immune-neurovascular mechanisms in neonatal and childhood stroke compared to stroke in adults. Given that hypoxic and ischaemic brain damage involve Toll-like receptor (TLR) activation, we discuss the modulatory role of viral and bacterial TLR2/3/4-mediated infection in HIE, perinatal and childhood stroke. Furthermore, we provide perspective of the dynamics and contribution of the axis in cerebral ischaemia depending on the CNS maturational stage at the time of insult, and modulation independently and in consort by individual axis components and in a sex dependent ways. Improved understanding on how to modify crosstalk between microglia and leucocytes will aid in developing age-appropriate therapies for infants and children who suffered cerebral ischaemia.

Change and predictive ability of circulating immunoregulatory lymphocytes in long-term outcomes of acute ischemic stroke

Lymphocytes play an important role in the immune response after stroke. However, our knowledge of the circulating lymphocytes in ischemic stroke is limited. Herein, we collected the blood samples of clinical ischemic stroke patients to detect the change of lymphocytes from admission to 3 months after ischemic stroke by flow cytometry. A total of 87 healthy controls and 210 patients were enrolled, and the percentages of circulating T cells, CD4⁺ T cells, CD8⁺ T cells, double negative T cells (DNTs), CD4⁺ regulatory T cells (Tregs), CD8⁺ Tregs, B cells and regulatory B cells (Bregs) were measured. Among patients, B cells, Bregs and CD8⁺ Tregs increased significantly, while CD4⁺ Tregs dropped and soon reversed after ischemic stroke. CD4⁺ Tregs, CD8⁺ Tregs, and DNTs also showed high correlations with the infarct volume and neurological scores of patients. Moreover, these lymphocytes enhanced the predictive ability of long-term prognosis of neurological scores when added to basic clinical information. The percentage of CD4⁺ Tregs within lymphocytes showed high correlations with both acute and long-term neurological outcomes, which exhibited a great independent predictive ability. These findings suggest that CD4⁺ Tregs can be a biomarker to predict stroke outcomes and improve existing therapeutic strategies of immunoregulatory lymphocytes.

Haematological issues in neonates with neonatal encephalopathy treated with hypothermia

Neonatal encephalopathy (NE) is associated with abnormality of neurological function and involves multiorgan dysfunction. There are long-term complications such as cerebral palsy and developmental delay. Cardiac, renal, neurological and other organ dysfunctions are well described. Haematological dysfunction is relatively common and includes anaemia, thrombocytopenia, monocyte and neutrophil activation, hypofibrinogenemia and coagulopathy. There is a lack of consensus definitions of hematological parameters and optimal levels for intervention due to the lack of interventional studies in term neonates and the lack of knowledge of the optimal values during therapeutic hypothermia. However, derangements in hematological values are also associated with neurodevelopmental outcomes. This article outlines the different hematological complications associated with NE and therapeutic hypothermia and suggests a framework for management.

Neonatal encephalopathy: Focus on epidemiology and underexplored aspects of etiology

Neonatal Encephalopathy (NE) is a neurologic syndrome in term and near-term infants who have depressed consciousness, difficulty initiating and maintaining respiration, and often abnormal tone, reflexes and neonatal seizures in varying combinations. Moderate/severe NE affects 0.5-3/1000 live births in high-income countries, more in low- and middle-income countries, and carries high risk of mortality or disability, including cerebral palsy. Reduced blood flow and/or oxygenation around the time of birth, as with ruptured uterus, placental abruption or umbilical cord prolapse can cause NE. This subset of NE, with accompanying low Apgar scores and acidemia, is termed Hypoxic-Ischemic Encephalopathy. Other causes of NE that can present similarly, include infections, inflammation, toxins, metabolic disease, stroke, placental disease, and genetic disorders. Aberrant fetal growth and congenital anomalies are strongly associated with NE, suggesting a major role for maldevelopment. As new tools for differential diagnosis emerge, their application for prevention, individualized treatment and prognostication will require further systematic studies of etiology of NE.

Altered distributions and functions of natural killer T cells and γδ T cells in neonates with neonatal encephalopathy, in school-age children at follow-up, and in children with cerebral palsy

We enumerated conventional and innate lymphocyte populations in neonates with neonatal encephalopathy (NE), school-age children post-NE, children with cerebral palsy and age-matched controls. Using flow cytometry, we demonstrate alterations in circulating T, B and natural killer cell numbers. Invariant natural killer T cell and Vδ2⁺ γδ T cell numbers and frequencies were strikingly higher in neonates with NE, children post-NE and children with cerebral palsy compared to age-matched controls, whereas mucosal-associated invariant T cells and Vδ1 T cells were depleted from children with cerebral palsy. Upon stimulation ex vivo, T cells, natural killer cells and Vδ2 T cells from neonates with NE more readily produced inflammatory cytokines than their counterparts from healthy neonates, suggesting that they were previously primed or activated. Thus, innate and conventional lymphocytes are numerically and functionally altered in neonates with NE and these changes may persist into school-age.

Resolvin D1 ameliorates Inflammation-Mediated Blood-Brain Barrier Disruption After Subarachnoid Hemorrhage in rats by Modulating A20 and NLRP3 Inflammasome

Inflammation is typically related to dysfunction of the blood-brain barrier (BBB) that leads to early brain injury (EBI) after subarachnoid hemorrhage (SAH). Resolvin D1 (RVD1), a lipid mediator derived from docosahexaenoic acid, possesses anti-inflammatory and neuroprotective properties. This study investigated the effects and mechanisms of RVD1 in SAH. A Sprague-Dawley rat model of SAH was established through endovascular perforation. RVD1was injected through the femoral vein at 1 and 12 h after SAH induction. To further explore the potential neuroprotective mechanism, a formyl peptide receptor two antagonist (WRW4) was intracerebroventricularly administered 1 h after SAH induction. The expression of endogenous RVD1 was decreased whereas A20 and NLRP3 levels were increased after SAH. An exogenous RVD1 administration increased RVD1 concentration in brain tissue, and improved neurological function, neuroinflammation, BBB disruption, and brain edema. RVD1 treatment upregulated the expression of A20, occludin, claudin-5, and zona occludens-1, as well as downregulated nuclear factor-κBp65, NLRP3, matrix metallopeptidase 9, and intercellular cell adhesion molecule-1 expression. Furthermore, RVD1 inhibited microglial activation and neutrophil infiltration and promoted neutrophil apoptosis. However, the neuroprotective effects of RVD1 were abolished by WRW4. In summary, our findings reveal that RVD1 provides beneficial effects against inflammation-triggered BBB dysfunction after SAH by modulating A20 and NLRP3 inflammasome.

Neutrophil dynamics, plasticity and function in acute neurodegeneration following neonatal hypoxia-ischemia

Neonatal encephalopathy following hypoxia-ischemia (HI) is a major cause of long-term morbidity and mortality in children. Even though HI-induced neuroinflammation, involving infiltration of peripheral immune cells into the CNS has been associated with disease pathogenesis, the specific role of neutrophils is highly debated. Due to immaturity of the neonatal immune system, it has been assumed that neutrophils are less clinically relevant in neonatal HI-induced brain injury. In the present study, we demonstrate that neutrophils are rapidly activated in the neonatal brain after exposure to experimental HI, revealed by an enhanced proportion of CD86⁺ cells and an increased expression of CD11b compared to splenic and blood neutrophils. Furthermore, production of reactive oxygen species and the proportion of hyperactivated/aged (CXCR4⁺CD62L^-) cells was enhanced in brain compared to peripheral neutrophils. Delayed neutrophil depletion, initiated 12 h after HI resulted in reduced cellular neurodegeneration, associated with reduced micro- and astroglial activation. In the present study, we uncovered a new complex switch of the phenotype in brain neutrophils, which may offer new possibilities for the development of selective therapeutic approaches by modulation of neutrophils in the early post-hypoxic disease phase.

Dynamic capillary stalls in reperfused ischemic penumbra contribute to injury: A hyperacute role for neutrophils in persistent traffic jams

Ever since the introduction of thrombolysis and the subsequent expansion of endovascular treatments for acute ischemic stroke, it remains to be identified why the actual outcomes are less favorable despite recanalization. Here, by high spatio-temporal resolution imaging of capillary circulation in mice, we introduce the pathological phenomenon of dynamic flow stalls in cerebral capillaries, occurring persistently in salvageable penumbra after reperfusion. These stalls, which are different from permanent cellular plugs of no-reflow, were temporarily and repetitively occurring in the capillary network, impairing the overall circulation like small focal traffic jams. In vivo microscopy in the ischemic penumbra revealed leukocytes traveling slowly through capillary lumen or getting stuck, while red blood cell flow was being disturbed in the neighboring segments under reperfused conditions. Stall dynamics could be modulated, by injection of an anti-Ly6G antibody specifically targeting neutrophils. Decreased number and duration of stalls were associated with improvement in penumbral blood flow within 2-24 h after reperfusion along with increased capillary oxygenation, decreased cellular damage and improved functional outcome. Thereby, dynamic microcirculatory stall phenomenon can be a contributing factor to ongoing penumbral injury and is a potential hyperacute mechanism adding on previous observations of detrimental effects of activated neutrophils in ischemic stroke.

Brain-targeted hypoxia-inducible factor stabilization reduces neonatal hypoxic-ischemic brain injury

Hypoxia-inducible factor-1α (HIF1α) is a major regulator of cellular adaptation to hypoxia and oxidative stress, and recent advances of prolyl-4-hydroxylase (P4H) inhibitors have produced powerful tools to stabilize HIF1α for clinical applications. However, whether HIF1α provokes or resists neonatal hypoxic-ischemic (HI) brain injury has not been established in previous studies. We hypothesize that systemic and brain-targeted HIF1α stabilization may have divergent effects. To test this notion, herein we compared the effects of GSK360A, a potent P4H inhibitor, in in-vitro oxygen-glucose deprivation (OGD) and in in-vivo neonatal HI via intracerebroventricular (ICV), intraperitoneal (IP), and intranasal (IN) drug-application routes. We found that GSK360A increased the erythropoietin (EPO), heme oxygenase-1 (HO1) and glucose transporter 1 (Glut1) transcripts, all HIF1α target-genes, and promoted the survival of neurons and oligodendrocytes after OGD. Neonatal HI insult stabilized HIF1α in the ipsilateral hemisphere for up to 24 h, and either ICV or IN delivery of GSK360A after HI increased the HIF1α target-gene transcripts and decreased brain damage. In contrast, IP-injection of GSK360A failed to reduce HI brain damage, but elevated the risk of mortality at high doses, which may relate to an increase of the kidney and plasma EPO, leukocytosis, and abundant vascular endothelial growth factor (VEGF) mRNAs in the brain. These results suggest that brain-targeted HIF1α-stabilization is a potential treatment of neonatal HI brain injury, while systemic P4H-inhibition may provoke unwanted adverse effects.

Midkine: The Who, What, Where, and When of a Promising Neurotrophic Therapy for Perinatal Brain Injury

Midkine (MK) is a small secreted heparin-binding protein highly expressed during embryonic/fetal development which, through interactions with multiple cell surface receptors promotes growth through effects on cell proliferation, migration, and differentiation. MK is upregulated in the adult central nervous system (CNS) after multiple types of experimental injury and has neuroprotective and neuroregenerative properties. The potential for MK as a therapy for developmental brain injury is largely unknown. This review discusses what is known of MK's expression and actions in the developing brain, areas for future research, and the potential for using MK as a therapeutic agent to ameliorate the effects of brain damage caused by insults such as birth-related hypoxia and inflammation.

Spleen participation in partial MHC class II construct neuroprotection in stroke

Pathological progression of stroke in the peripheral and central nervous systems (PNS and CNS) is characterized by multiple converging signalling pathways that exacerbate neuroinflammation-mediated secondary cell death. This creates a need for a novel type of immunotherapy capable of simultaneously lowering the synergistic inflammatory responses in the PNS and CNS, specifically the spleen and brain. Previously, we demonstrated that partial major histocompatibility complex (MHC) class II constructs can be administered subcutaneously to promote histological and behavioural effects that alleviate common symptoms found in a murine model of transient stroke. This MHC class II manipulates T cell cytokine expression in both PNS and CNS, resulting in dampened inflammation. In our long-standing efforts towards translational research, we recently demonstrated that a potent next generation mouse-based partial MHC class II construct named DRmQ (DRa1_L50Q -mMOG-35-55) similarly induces neuroprotection in stroke rats, replicating the therapeutic effects of the human homolog as DRhQ (DRa1_L50Q -human (h)MOG-35-55) in stroke mice. Our preclinical studies showed that DRmQ reduces motor deficits, infarct volume and peri-infarct cell loss by targeting inflammation in this second species. Moreover, we provided mechanistic support in both animal studies that partial MHC class II constructs effectively modulate the spleen, an organ which plays a critical role in modulating secondary cell death. Together, these preclinical studies satisfy testing the constructs in two stroke models, which is a major criterion of the Stroke Therapy Academic Industry Roundtable (STAIR) criteria and a key step in effectively translating this drug to the clinic. Additional translational studies, including dose-response and larger animal models may be warranted to bring MHC class II constructs closer to the clinic.