Splenectomy protects aged mice from injury after experimental stroke

A novel nutritional inflammation index for predicting mortality in acute ischemic stroke patients: insights into advanced lung cancer inflammation index from the Medical Information Mart for Intensive Care-IV database

Objective

This investigation aimed to delineate the association between the advanced lung cancer inflammation index (ALI) and all-cause mortality (ACM) in individuals experiencing acute ischemic stroke (AIS).

Methods

Drawing on information from the Medical Information Mart for Intensive Care (MIMIC)-IV database, release 2.2, covering the years 2012 to 2019, this research assessed the advanced lung cancer inflammation index (ALI) by factoring in body mass index (BMI), serum albumin levels (ALB), and the neutrophil-to-lymphocyte ratio (NLR). Patients with AIS were identified using codes from the International Classification of Diseases (ICD). To address potential confounding factors, a 1:1 propensity score matching (PSM) method was utilized. The investigation identified the pivotal ALI level impacting patient survival using maximally selected rank statistics. It then examined the effects on short- and long-term ACM through multivariate Cox proportional hazards regression models and Kaplan-Meier (K-M) survival analysis. Additionally, restricted cubic spline (RCS) methods were applied to delve into the linear or nonlinear nature of the relationship between ALI and ACM, with further insights gained from interaction and subgroup analyses.

Results

The cohort comprised 838 AIS patients. Post-PSM, analysis involved 199 matched patient pairs. Adjusted Cox proportional hazard models indicated a significant association of low ALI (<10.38) with increased in-hospital ACM, both before (HR: 1.98; 95% CI: 1.36-2.88; p < 0.001) and after PSM (HR: 2.16; 95% CI: 1.32-3.52; p = 0.002). Associations of low ALI with elevated risk were consistent across ICU, 30 days, 90 days, and 1 year ACM pre- and post-PSM. Subsequent RCS analysis post-PSM underscored a negative nonlinear relationship between ALI and ACM over both short and long terms, without significant interaction effects across different subgroups for ACM.

Conclusion

In this retrospective cohort study, by utilizing a nationally representative sample of United States patients with AIS, our analysis elucidates a negative correlation between the ALI and ACM in individuals with AIS, underscoring the utility of ALI as a novel, efficacious, and accessible inflammatory biomarker for prognosticating ACM. These results carry profound implications for public health policy and practice. A deeper comprehension of these associations can empower public health practitioners and researchers to devise more targeted interventions and policies, aimed specifically at catering to the distinct needs of the AIS patient population, thereby enhancing their health outcomes. The further research in other races/ethnicity is urgent, particularly before applying these findings in clinical practice.

Mechanisms of inflammation after ischemic stroke in brain-peripheral crosstalk

Stroke is a devastating disease with high morbidity, disability, and mortality, among which ischemic stroke is more common. However, there is still a lack of effective methods to improve the prognosis and reduce the incidence of its complications. At present, there is evidence that peripheral organs are involved in the inflammatory response after stroke. Moreover, the interaction between central and peripheral inflammation includes the activation of resident and peripheral immune cells, as well as the activation of inflammation-related signaling pathways, which all play an important role in the pathophysiology of stroke. In this review, we discuss the mechanisms of inflammatory response after ischemic stroke, as well as the interactions through circulatory pathways between peripheral organs (such as the gut, heart, lung and spleen) and the brain to mediate and regulate inflammation after ischemic stroke. We also propose the potential role of meningeal lymphatic vessels (MLVs)-cervical lymph nodes (CLNs) as a brain-peripheral crosstalk lymphatic pathway in ischemic stroke. In addition, we also summarize the mechanisms of anti-inflammatory drugs in the treatment of ischemic stroke.

Age-Related Alterations in Immune Function and Inflammation: Focus on Ischemic Stroke

The aging of the global population poses significant scientific challenges. Moreover, the biological process of aging is the most significant risk factor for most chronic illnesses; therefore, understanding the molecular and cellular mechanisms underlying these aging-related challenges is crucial for extending the healthy lifespan of older individuals. Preventing brain aging remains a priority public health goal, and integrative and comprehensive aging analyses have revealed that immunosenescence is a potential cause of age-related brain damage and disease (e.g., stroke). Importantly, the neuroinflammatory and immune systems present two-way contact and thus can affect each other. Emerging evidence supports the numerous effects of immunosenescence- and inflammation-mediated immunity in neurologically injured brains. In this study, we briefly outline how aging alters the pathophysiology and transcriptional amplitude in patients who experienced stroke and then discuss how the immune system and its cellular components and molecular mechanisms are affected by age after stroke. Finally, we highlight emerging interventions with the potential to slow down or reduce aging and prevent stroke onset.

Effect of Cyclosporin H on ischemic injury and neutrophil infiltration in cerebral infarct model of rats via PET imaging

BACKGROUND

Brain ischemia-reperfusion injury is a complex process, and neuroinflammation is an important secondary contributing pathological event. Neutrophils play major roles in ischemic neuroinflammation. Once activated, neutrophils express formyl peptide receptors (FPRs), which are special receptors of a class of chemoattractants and may be potential targets to regulate the activity of neutrophils and control cerebral ischemic injury. This study was aimed to explore the ameliorating effect of Cyclosporin H (CsH), a potent FPR antagonist, on brain ischemic injury by inhibiting the activation and migration of neutrophils, and improving cerebral blood flow.

METHODS

We employed a middle cerebral artery occlusion (MCAO) Model on rats and performed behavioral, morphological, and microPET imaging assays to investigate the potential restoring efficacy of CsH on cerebral ischemic damages. Peptide N-cinnamoyl-F-(D)L-F-(D)L-F (cFLFLF), an antagonist to the neutrophil FPR with a high binding affinity, was used for imaging neutrophil distribution.

RESULTS

We found that CsH had similar effect with edaravone on improving the neurobehavioral deficient symptoms after cerebral ischemia-reperfusion, and treatment with CsH also alleviated ischemic cerebral infarction. Compared with the MCAO Model group, [18F]FDG uptake ratios of the CsH and edaravone treatment groups were significantly higher. The CsH-treated groups also showed significant increases in [18F]FDG uptake at 144 h when compared with that of 24 h. This result indicates that like edaravone, treatment with both doses of CsH promoted the recovery of blood supply after cerebral ischemic event. Moreover, MCAO-induced cerebral ischemia significantly increased the radiouptake of [68Ga]Ga-cFLFLF at 72 h after ischemia-reperfusion operation. Compared with MCAO Model group, radiouptake values of [68Ga]-cFLFLF in both doses of CsH and edaravone groups were all decreased significantly. These results showed that both doses of CsH resulted in a similar therapeutic effect with edaravone on inhibiting neutrophil infiltration in cerebral infarction.

CONCLUSION

Potent FPR antagonist CsH is promisingly beneficial in attenuating neuroinflammation and improving neurobehavioral function against cerebral infarction. Therefore, FPR may become a novel target for regulating neuroinflammation and improving prognosis for ischemic cerebrovascular disorders.

Peripheral MC1R Activation Modulates Immune Responses and is Neuroprotective in a Mouse Model of Parkinson's Disease

BACKGROUND

Melanocortin 1 receptor (MC1R) is a key pigmentation gene, and loss-of-function of MC1R variants that produce red hair may be associated with Parkinson's disease (PD). We previously reported compromised dopaminergic neuron survival in Mc1r mutant mice and dopaminergic neuroprotective effects of local injection of a MC1R agonist to the brain or a systemically administered MC1R agonist with appreciable central nervous system (CNS) permeability. Beyond melanocytes and dopaminergic neurons, MC1R is expressed in other peripheral tissues and cell types, including immune cells. The present study investigates the impact of NDP-MSH, a synthetic melanocortin receptor (MCR) agonist that does not cross BBB, on the immune system and the nigrostriatal dopaminergic system in mouse model of PD.

METHODS

C57BL/6 mice were treated systemically with MPTP.HCl (20 mg/kg) and LPS (1 mg/kg) from day 1 to day 4 and NDP-MSH (400 µg/kg) or vehicle from day 1 to day 12 following which the mice were sacrificed. Peripheral and CNS immune cells were phenotyped and inflammatory markers were measured. The nigrostriatal dopaminergic system was assessed behaviorally, chemically, immunologically, and pathologically. To understand the role of regulatory T cells (Tregs) in this model, CD25 monoclonal antibody was used to deplete CD25 + Tregs.

RESULTS

Systemic NDP-MSH administration significantly attenuated striatal dopamine depletion and nigral dopaminergic neuron loss induced by MPTP + LPS. It improved the behavioral outcomes in the pole test. Mc1r mutant mice injected with NDP-MSH in the MPTP and LPS paradigm showed no changes in striatal dopamine levels suggesting that the NDP-MSH acts through the MC1R pathway. Although no NDP-MSH was detected in the brain, peripheral, NDP-MSH attenuated neuroinflammation as observed by diminished microglial activation in the nigral region, along with reduced TNF-α and IL1β levels in the ventral midbrain. Depletion of Tregs was associated with diminished neuroprotective effects of NDP-MSH.

CONCLUSIONS

Our study demonstrates that peripherally acting NDP-MSH confers protection on dopaminergic nigrostriatal neurons and reduces hyperactivated microglia. NDP-MSH modulates peripheral immune responses, and Tregs may be involved in the neuroprotective effect of NDP-MSH.

Systemic inflammation response index as a clinical outcome evaluating tool and prognostic indicator for hospitalized stroke patients: a systematic review and meta-analysis

BACKGROUND

Stroke, which is the main element of cerebrovascular disease (CVD), has become the foremost reason for death and disability on a global scale. The systemic inflammation response index (SIRI), a newly developed and comprehensive indicator, has demonstrated promise in forecasting clinical results for diverse ailments. Nevertheless, the uncertainty surrounding the assessment and prediction of clinical outcomes for stroke patients by SIRI persists, and the conflicting findings from the limited studies conducted on this matter further complicate the situation. Consequently, we performed a thorough systematic review and meta-analysis to explore the correlation between SIRI and the clinical results in individuals suffering from stroke.

METHODS

This research was registered in PROSPERO and carried out following the PRISMA guidelines. A thorough investigation was carried out on PubMed, Embase, the Cochrane Library, Web of Science, and Scopus databases. Furthermore, we conducted a manual search in Chinese databases, such as China national Knowledge Infrastructure (CNKI), WanFang, VIP, and China Biology Medicine (CBM). We assessed the potential for bias in the studies included by utilizing the Newcastle-Ottawa Scale (NOS) tool. Adverse clinical outcomes were the main focus of the study, with secondary endpoints including mortality, the predictive value of SIRI, SIRI values across various endpoints, and clinical parameters associated with subarachnoid hemorrhage (SAH) in relation to low and high SIRI group.

RESULTS

Following rigorous evaluation, a grand total of 22 investigations, encompassing a populace of 12,737 individuals, were considered suitable for incorporation in the final analysis. The findings from our meta-analysis indicate a strong and consistent correlation between elevated SIRI levels and adverse functional outcomes, irrespective of the method used to evaluate unfavorable outcomes. Furthermore, increased SIRI values have a strong correlation with mortality rates in both the short and long term. Besides, SIRI is a useful indicator of the severity of SAH. SIRI demonstrates strong predictive ability in identifying unfavorable outcomes and stroke-related pneumonia (SAP), as higher SIRI values are typically linked to negative endpoints. Nevertheless, the meta-analysis indicated that there was no significant increase in the risk of early neurological deterioration (END) and acute hydrocephalus (AHC) in high SIRI group when comparing to low SIRI.

CONCLUSION

This study could potentially pave the way for groundbreaking insights into the relationship between SIRI and stroke patient outcomes, as it appears to be the first meta-analysis to explore this association. Given the critical role of the inflammatory response in stroke recovery, closely monitoring patients with high SIRI levels could represent a promising strategy for mitigating brain damage post-stroke. Thus, further investigation into SIRI and its impact on clinical outcomes is essential. While our initial findings offer valuable insights into this area, continued research is necessary to fully elucidate the potential of SIRI, ideally through dynamic monitoring and large-scale, multi-center studies. Ultimately, this research has the potential to inform clinical decision-making and improve patient outcomes following stroke.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/ ; Identifier CRD42023405221.

CD13 facilitates immune cell migration and aggravates acute injury but promotes chronic post-stroke recovery

INTRODUCTION

Acute stroke leads to the activation of myeloid cells. These cells express adhesion molecules and transmigrate to the brain, thereby aggravating injury. Chronically after stroke, repair processes, including angiogenesis, are activated and enhance post-stroke recovery. Activated myeloid cells express CD13, which facilitates their migration into the site of injury. However, angiogenic blood vessels which play a role in recovery also express CD13. Overall, the specific contribution of CD13 to acute and chronic stroke outcomes is unknown.

METHODS

CD13 expression was estimated in both mice and humans after the ischemic stroke. Young (8-12 weeks) male wild-type and global CD13 knockout (KO) mice were used for this study. Mice underwent 60 min of middle cerebral artery occlusion (MCAO) followed by reperfusion. For acute studies, the mice were euthanized at either 24- or 72 h post-stroke. For chronic studies, the Y-maze, Barnes maze, and the open field were performed on day 7 and day 28 post-stroke. Mice were euthanized at day 30 post-stroke and the brains were collected for assessment of inflammation, white matter injury, tissue loss, and angiogenesis. Flow cytometry was performed on days 3 and 7 post-stroke to quantify infiltrated monocytes and neutrophils and CXCL12/CXCR4 signaling.

RESULTS

Brain CD13 expression and infiltrated CD13+ monocytes and neutrophils increased acutely after the stroke. The brain CD13+lectin+ blood vessels increased on day 15 after the stroke. Similarly, an increase in the percentage area CD13 was observed in human stroke patients at the subacute time after stroke. Deletion of CD13 resulted in reduced infarct volume and improved neurological recovery after acute stroke. However, CD13KO mice had significantly worse memory deficits, amplified gliosis, and white matter damage compared to wild-type animals at chronic time points. CD13-deficient mice had an increased percentage of CXCL12+cells but a reduced percentage of CXCR4+cells and decreased angiogenesis at day 30 post-stroke.

CONCLUSIONS

CD13 is involved in the trans-migration of monocytes and neutrophils after stroke, and acutely, led to decreased infarct size and improved behavioral outcomes. However, loss of CD13 led to reductions in post-stroke angiogenesis by reducing CXCL12/CXCR4 signaling.

Macrophage and monocyte subsets in response to ischemic stroke

Ischemic stroke is a leading cause of disability and mortality. Despite extensive efforts in stroke research, the only pharmacological treatment currently available is arterial recanalization, which has limited efficacy only in the acute phase of stroke. The neuroinflammatory response to stroke is believed to provide a wider time window than recanalization and has therefore been proposed as an attractive therapeutic target. In this review, we provide an overview of recent advances in the understanding of cellular and molecular responses of distinct macrophage populations following stroke, which may offer potential targets for therapeutic interventions. Specifically, we discuss the role of local responders in neuroinflammation, including the well-studied microglia as well as the emerging players, border-associated macrophages, and macrophages originating from the skull bone marrow. Additionally, we focus on the behavior of monocytes stemming from distant tissues such as the bone marrow and spleen. Finally, we highlight aging as a crucial factor modulating the immune response, which is often neglected in animal studies.

Human FcγRIIIa activation on splenic macrophages drives dengue pathogenesis in mice

Although dengue virus (DENV) infection typically causes asymptomatic disease, DENV-infected patients can experience severe complications. A risk factor for symptomatic disease is pre-existing anti-DENV IgG antibodies. Cellular assays suggested that these antibodies can enhance viral infection of Fcγ receptor (FcγR)-expressing myeloid cells. Recent studies, however, revealed more complex interactions between anti-DENV antibodies and specific FcγRs by demonstrating that modulation of the IgG Fc glycan correlates with disease severity. To investigate the in vivo mechanisms of antibody-mediated dengue pathogenesis, we developed a mouse model for dengue disease that recapitulates the unique complexity of human FcγRs. In in vivo mouse models of dengue disease, we discovered that the pathogenic activity of anti-DENV antibodies is exclusively mediated through engagement of FcγRIIIa on splenic macrophages, resulting in inflammatory sequelae and mortality. These findings highlight the importance of IgG-FcγRIIIa interactions in dengue, with important implications for the design of safer vaccination approaches and effective therapeutic strategies.

Bystanders or not? Microglia and lymphocytes in aging and stroke

As the average age of the world population increases, more people will face debilitating aging-associated conditions, including dementia and stroke. Not only does the incidence of these conditions increase with age, but the recovery afterward is often worse in older patients. Researchers and health professionals must unveil and understand the factors behind age-associated diseases to develop a therapy for older patients. Aging causes profound changes in the immune system including the activation of microglia in the brain. Activated microglia promote T lymphocyte transmigration leading to an increase in neuroinflammation, white matter damage, and cognitive impairment in both older humans and rodents. The presence of T and B lymphocytes is observed in the aged brain and correlates with worse stroke outcomes. Preclinical strategies in stroke target either microglia or the lymphocytes or the communications between them to promote functional recovery in aged subjects. In this review, we examine the role of the microglia and T and B lymphocytes in aging and how they contribute to cognitive impairment. Additionally, we provide an important update on the contribution of these cells and their interactions in preclinical aged stroke.

Peripheral MC1R activation modulates immune responses and is neuroprotective in a mouse model of Parkinson's disease

Background

Melanocortin 1 receptor (MC1R) is a key pigmentation gene, and loss-of-function of MC1R variants that produce red hair may be associated with Parkinson's disease (PD). We previously reported compromised dopaminergic neuron survival in Mc1r mutant mice and dopaminergic neuroprotective effects of local injection of a MC1R agonist to the brain or a systemically administered MC1R agonist with appreciable CNS permeability. Beyond melanocytes and dopaminergic neurons, MC1R is expressed in other peripheral tissues and cell types, including immune cells. The present study investigates the impact of NDP-MSH, a synthetic melanocortin receptor (MCR) agonist that does not cross BBB, on the immune system and the nigrostriatal dopaminergic system in mouse model of PD.

Methods

C57BL/6 mice were treated systemically with MPTP.HCl (20 mg/kg) and LPS (1 mg/kg) from day 1 to day 4 and NDP-MSH (400 μg/kg) or vehicle from day 1 to day 12 following which the mice were sacrificed. Peripheral and CNS immune cells were phenotyped and inflammatory markers were measured. The nigrostriatal dopaminergic system was assessed behaviorally, chemically, immunologically, and pathologically. To understand the role of regulatory T cells (Tregs) in this model, CD25 monoclonal antibody was used to deplete CD25+ Tregs.

Results

Systemic NDP-MSH administration significantly attenuated striatal dopamine depletion and nigral dopaminergic neuron loss induced by MPTP+LPS. It improved the behavioral outcomes in the pole test. Mc1r mutant mice injected with NDP-MSH in the MPTP and LPS paradigm showed no changes in striatal dopamine levels suggesting that the NDP-MSH acts through the MC1R pathway. Although no NDP-MSH was detected in the brain, peripheral, NDP-MSH attenuated neuroinflammation as observed by diminished microglial activation in the nigral region, along with reduced TNF-α and IL1β levels in the ventral midbrain. Depletion of Tregs limited the neuroprotective effects of NDP-MSH.

Conclusions

Our study demonstrates that peripherally acting NDP-MSH confers protection on dopaminergic nigrostriatal neurons and reduces hyperactivated microglia. NDP-MSH modulates peripheral immune responses, and Tregs may be involved in the neuroprotective effect of NDP-MSH.

The age-dependent immune response to ischemic stroke

Stroke is a devastating cause of global morbidity and mortality. Ischemic brain injury triggers a profound local and systemic immune response that participates in stroke pathophysiology. In turn, this immune response has emerged as a potential therapeutic target. In order to maximize its therapeutic potential, it is critical to understand how the immune response to ischemic brain injury is affected by age - the strongest non-modifiable risk factor for stroke. The development of multi-omics and single-cell technologies has provided a more comprehensive characterization of transcriptional and cellular changes that occur during aging. In this review, we summarize recent advances in our understanding of how age-related immune alterations shape differential stroke outcomes in older versus younger organisms, highlighting studies in both experimental mouse models and patient cohorts. Wherever possible, we emphasize outstanding questions that present important avenues for future investigation with therapeutic value for the aging population.

Systemic inflammation response index as a prognostic predictor in patients with acute ischemic stroke: A propensity score matching analysis

Background

Acute ischemic stroke (AIS), the most common type of stroke, is a major cause of morbidity and mortality worldwide. A growing number of studies have demonstrated that inflammation is a critical mechanism in AIS. Being an easily available and effective inflammatory marker, the systemic inflammation response index (SIRI) shows a high association with mortality in patients with cancer and intracerebral hemorrhage. In this study, we evaluated the potential prognostic role of SIRI in critically ill patients with AIS.

Methods

Clinic data were extracted from the Medical Information Mart data for the Intensive Care IV (MIMIC-IV) database. The optimal cutoff value of SIRI was determined by X-tile software. The primary outcome was the 90-day all-cause mortality, and the secondary outcomes were 30-day and 1-year all-cause mortality of patients with AIS. Cox proportional hazards regression analyses were used to assess the association between SIRI levels and all-cause mortality, and survival curves were estimated using the Kaplan-Meier method. Furthermore, a 1:1 propensity score matching (PSM) method was performed to balance the influence of potential confounding factors.

Results

A total of 2,043 patients were included in our study. X-tile software indicated that the optimal cutoff value of the SIRI for 90-day mortality was 4.57. After PSM, 444 pairs of score-matched patients were generated. Cox proportional hazard model showed that after adjusting for possible confounders, high SIRI level (≥4.57) was independently associated with the 90-day all-cause mortality in the cohort before PSM (HR = 1.56, 95% CI: 1.30-1.89, p < 0.001) and the PSM subset (HR = 1.47, 95% CI: 1.16-1.86, p = 0.001). The survival curves showed that patients with SIRI ≥4.57 had a significantly lower 90-day survival rate in the cohort before PSM (56.7 vs. 77.3%, p < 0.001) and the PSM subset (61.0 vs. 71.8%, p = 0.001). Consistently, AIS patients with high SIRI levels (≥4.57) presented a significantly high risk of 30-day and 1-year all-cause mortality before and after PSM.

Conclusion

A higher SIRI (≥4.57) was associated with a higher risk of 90-day, 30-day, and 1-year mortality and was an independent risk factor of mortality in patients with acute ischemic stroke.

Neutrophil dynamics and inflammaging in acute ischemic stroke: A transcriptomic review

Stroke is among the leading causes of death and disability worldwide. Restoring blood flow through recanalization is currently the only acute treatment for cerebral ischemia. Unfortunately, many patients that achieve a complete recanalization fail to regain functional independence. Recent studies indicate that activation of peripheral immune cells, particularly neutrophils, may contribute to microcirculatory failure and futile recanalization. Stroke primarily affects the elderly population, and mortality after endovascular therapies is associated with advanced age. Previous analyses of differential gene expression across injury status and age identify ischemic stroke as a complex age-related disease. It also suggests robust interactions between stroke injury, aging, and inflammation on a cellular and molecular level. Understanding such interactions is crucial in developing effective protective treatments. The global stroke burden will continue to increase with a rapidly aging human population. Unfortunately, the mechanisms of age-dependent vulnerability are poorly defined. In this review, we will discuss how neutrophil-specific gene expression patterns may contribute to poor treatment responses in stroke patients. We will also discuss age-related transcriptional changes that may contribute to poor clinical outcomes and greater susceptibility to cerebrovascular diseases.

Aging Is Associated With Lower Neuroactive Steroids and Worsened Outcomes Following Cerebral Ischemia in Male Mice

Ischemic stroke is a leading cause of disability and death, and aging is the main nonmodifiable risk factor. Following ischemia, neuroactive steroids have been shown to play a key role in cerebroprotection. Thus, brain steroid concentrations at the time of injury as well as their regulation after stroke are key factors to consider. Here, we investigated the effects of age and cerebral ischemia on steroid levels, behavioral outcomes, and neuronal degeneration in 3- and 18-month-old C57BL/6JRj male mice. Ischemia was induced by middle cerebral artery occlusion for 1 hour followed by reperfusion (MCAO/R) and analyses were performed at 6 hours after MCAO. Extended steroid profiles established by gas chromatography coupled with tandem mass spectrometry revealed that (1) brain and plasma concentrations of the main 5α-reduced metabolites of progesterone, 11-deoxycorticosterone, and corticosterone were lower in old than in young mice; (2) after MCAO/R, brain concentrations of progesterone, 5α-dihydroprogesterone, and corticosterone increased in young mice; and (3) after MCAO/R, brain concentrations of 5α-reduced metabolites of progesterone, 3α5α-tetrahydrodeoxycorticosterone, and 3β5α-tetrahydrodeoxycorticosterone were lower in old than in young mice. After ischemia, old mice showed increased sensori-motor deficits and more degenerating neurons in the striatum than young mice. Altogether, these findings strongly suggest that the decreased capacity of old mice to metabolize steroids toward the 5α-reduction pathway comparatively to young mice may contribute to the worsening of their stroke outcomes.

Crosstalk between the aging intestinal microflora and the brain in ischemic stroke

Aging is an inevitable phenomenon experienced by animals and humans, and its intensity varies from one individual to another. Aging has been identified as a risk factor for neurodegenerative disorders by influencing the composition of the gut microbiota, microglia activity and cognitive performance. The microbiota-gut-brain axis is a two-way communication path between the gut microbes and the host brain. The aging intestinal microbiota communicates with the brain through secreted metabolites (neurotransmitters), and this phenomenon leads to the destruction of neuronal cells. Numerous external factors, such as living conditions and internal factors related to the age of the host, affect the condition of the intestinal microflora in the form of dysbiosis. Dysbiosis is defined as changes in the composition and function of the gut microflora that affect the pathogenesis, progress, and response to treatment of a disease entity. Dysbiosis occurs when changes in the composition and function of the microbiota exceed the ability of the microflora and its host to restore equilibrium. Dysbiosis leading to dysfunction of the microbiota-gut-brain axis regulates the development and functioning of the host’s nervous, immune, and metabolic systems. Dysbiosis, which causes disturbances in the microbiota-gut-brain axis, is seen with age and with the onset of stroke, and is closely related to the development of risk factors for stroke. The review presents and summarizes the basic elements of the microbiota-gut-brain axis to better understand age-related changes in signaling along the microbiota-gut-brain axis and its dysfunction after stroke. We focused on the relationship between the microbiota-gut-brain axis and aging, emphasizing that all elements of the microbiota-gut-brain axis are subject to age-related changes. We also discuss the interaction between microbiota, microglia and neurons in the aged individuals in the brain after ischemic stroke. Finally, we presented preclinical and clinical studies on the role of the aged microbiota-gut-brain axis in the development of risk factors for stroke and changes in the post-stroke microflora.

Mesenchymal stem cells exert renoprotection via extracellular vesicle-mediated modulation of M2 macrophages and spleen-kidney network

Adipose-derived mesenchymal stem cells (ASCs) have shown therapeutic potentials against refractory diseases. However, the detailed therapeutic mechanisms remain unclear. Here, we report the therapeutic actions of human ASCs in nephritis, focusing on cellular dynamics and multi-organ networks. Intravenously-administered ASCs accumulated in spleen but not kidneys. Nevertheless, ASCs increased M2 macrophages and Tregs in kidneys and drove strong renoprotection. Splenectomy abolished these therapeutic effects. ASC-derived extracellular vesicles (EVs) were transferred to M2 macrophages, which entered the bloodstream from spleen. EVs induced the transcriptomic signatures of hyperpolarization and PGE2 stimulation in M2 macrophages and ameliorated glomerulonephritis. ASCs, ASC-derived EVs, and EV-transferred M2 macrophages enhanced Treg induction. These findings suggest that EV transfer from spleen-accumulated ASCs to M2 macrophages and subsequent modulation of renal immune-environment underlie the renoprotective effects of ASCs. Our results provide insights into the therapeutic actions of ASCs, focusing on EV-mediated modulation of macrophages and the spleen-kidney immune network.

The renoprotective effects of adipose-derived mesenchymal stem cells (ASCs) are enhanced through the transfer of EVs predominantly to M2 macrophages in the spleen, providing insights into therapeutic avenues for ASCs.

CD11bhigh B Cells Increase after Stroke and Regulate Microglia

Recent studies have highlighted the deleterious contributions of B cells to post-stroke recovery and cognitive decline. Different B cell subsets have been proposed on the basis of expression levels of transcription factors (e.g., T-bet) as well as specific surface proteins. CD11b (α-chain of integrin) is expressed by several immune cell types and is involved in regulation of cell motility, phagocytosis, and other essential functions of host immunity. Although B cells express CD11b, the CD11b^high subset of B cells has not been well characterized, especially in immune dysregulation seen with aging and after stroke. Here, we investigate the role of CD11b^high B cells in immune responses after stroke in young and aged mice. We evaluated the ability of CD11b^high B cells to influence pro- and anti-inflammatory phenotypes of young and aged microglia (MG). We hypothesized that CD11b^high B cells accumulate in the brain and contribute to neuroinflammation in aging and after stroke. We found that CD11b^high B cells are a heterogeneous subpopulation of B cells predominantly present in naive aged mice. Their frequency increases in the brain after stroke in young and aged mice. Importantly, CD11b^high B cells regulate MG phenotype and increase MG phagocytosis in both ex vivo and in vivo settings, likely by production of regulatory cytokines (e.g., TNF-α). As both APCs and adaptive immune cells with long-term memory function, B cells are uniquely positioned to regulate acute and chronic phases of the post-stroke immune response, and their influence is subset specific.

High-fat diet activates splenic NOD1 and enhances neutrophil recruitment and neutrophil extracellular traps release in the spleen of ApoE-deficient mice

In the course of atherogenesis, the spleen plays an important role in the regulation of extramedullary hematopoiesis, and in the control of circulating immune cells, which contributes to plaque progression. Here, we have investigated the role of splenic nucleotide-binding oligomerization domain 1 (NOD1) in the recruitment of circulating immune cells, as well as the involvement of this immune organ in extramedullary hematopoiesis in mice fed on a high-fat high-cholesterol diet (HFD). Under HFD conditions, the absence of NOD1 enhances the mobilization of immune cells, mainly neutrophils, from the bone marrow to the blood. To determine the effect of NOD1-dependent mobilization of immune cells under pro-atherogenic conditions, Apoe^−/− and Apoe^−/−Nod1^−/− mice fed on HFD for 4 weeks were used. Splenic NOD1 from Apoe^−/− mice was activated after feeding HFD as inferred by the phosphorylation of the NOD1 downstream targets RIPK2 and TAK1. Moreover, this activation was accompanied by the release of neutrophil extracellular traps (NETs), as determined by the increase in the expression of peptidyl arginine deiminase 4, and the identification of citrullinated histone H3 in this organ. This formation of NETs was significantly reduced in Apoe^−/−Nod1^−/− mice. Indeed, the presence of Ly6G⁺ cells and the lipidic content in the spleen of mice deficient in Apoe and Nod1 was reduced when compared to the Apoe^−/− counterparts, which suggests that the mobilization and activation of circulating immune cells are altered in the absence of NOD1. Furthermore, confirming previous studies, Apoe^−/−Nod1^−/− mice showed a reduced atherogenic disease, and diminished recruitment of neutrophils in the spleen, compared to Apoe^−/− mice. However, splenic artery ligation reduced the atherogenic burden in Apoe^−/− mice an effect that, unexpectedly was lost in Apoe^−/−Nod1^−/− mice. Together, these results suggest that neutrophil accumulation and activity in the spleen are driven in part by NOD1 activation in mice fed on HFD, contributing in this way to regulating atherogenic progression.

Aging Microbiota-Gut-Brain Axis in Stroke Risk and Outcome

The microbiota-gut-brain-axis (MGBA) is a bidirectional communication network between gut microbes and their host. Many environmental and host-related factors affect the gut microbiota. Dysbiosis is defined as compositional and functional alterations of the gut microbiota that contribute to the pathogenesis, progression and treatment responses to disease. Dysbiosis occurs when perturbations of microbiota composition and function exceed the ability of microbiota and its host to restore a symbiotic state. Dysbiosis leads to dysfunctional signaling of the MGBA, which regulates the development and the function of the host's immune, metabolic, and nervous systems. Dysbiosis-induced dysfunction of the MGBA is seen with aging and stroke, and is linked to the development of common stroke risk factors such as obesity, diabetes, and atherosclerosis. Changes in the gut microbiota are also seen in response to stroke, and may impair recovery after injury. This review will begin with an overview of the tools used to study the MGBA with a discussion on limitations and potential experimental confounders. Relevant MGBA components are introduced and summarized for a better understanding of age-related changes in MGBA signaling and its dysfunction after stroke. We will then focus on the relationship between the MGBA and aging, highlighting that all components of the MGBA undergo age-related alterations that can be influenced by or even driven by the gut microbiota. In the final section, the current clinical and preclinical evidence for the role of MGBA signaling in the development of stroke risk factors such as obesity, diabetes, hypertension, and frailty are summarized, as well as microbiota changes with stroke in experimental and clinical populations. We conclude by describing the current understanding of microbiota-based therapies for stroke including the use of pre-/pro-biotics and supplementations with bacterial metabolites. Ongoing progress in this new frontier of biomedical sciences will lead to an improved understanding of the MGBA's impact on human health and disease.

The "Dialogue" Between Central and Peripheral Immunity After Ischemic Stroke: Focus on Spleen

The immune response generated by the body after the incidence of ischemic stroke, runs through the comprehensive process of aftermath. During this process of ischemic stroke, the central neuroinflammation and peripheral immune response seriously affect the prognosis of patients, which has been the focus of research in recent years. As this research scenario progressed, the "dialogue" between central nervous inflammation and peripheral immune response after ischemic stroke has become more closely related. It's worth noting that the spleen, as an important peripheral immune organ, plays a pivotal role in this dialogue. Multiple mechanisms have previously been reported for brain-spleen crosstalk after ischemic stroke. Further, neuroinflammation in the brain can affect the peripheral immune state by activating/inhibiting spleen function. However, the activation of the peripheral immune inflammatory response can work reversibly in the spleen. It further affects intracerebral neuroinflammation through the injured blood-brain barrier. Therefore, paying close attention to the role of spleen as the pivot between central and peripheral immunity in ischemic stroke may help to provide a new target for immune intervention in the treatment of ischemic stroke. In the present review, we reviewed the important role of spleen in central neuroinflammation and peripheral immune response after ischemic stroke. We summarized the relevant studies and reports on spleen as the target of immune intervention which can provide new ideas for the clinical treatment of ischemic stroke.

Age-related immune alterations and cerebrovascular inflammation

Aging is associated with chronic systemic inflammation, which contributes to the development of many age-related diseases, including vascular disease. The world's population is aging, leading to an increasing prevalence of both stroke and vascular dementia. The inflammatory response to ischemic stroke is critical to both stroke pathophysiology and recovery. Age is a predictor of poor outcomes after stroke. The immune response to stroke is altered in aged individuals, which contributes to the disparate outcomes between young and aged patients. In this review, we describe the current knowledge of the effects of aging on the immune system and the cerebral vasculature and how these changes alter the immune response to stroke and vascular dementia in animal and human studies. Potential implications of these age-related immune alterations on chronic inflammation in vascular disease outcome are highlighted.

Immune suppression reversal of the spleen: a promising strategy for improving the survival rate of sepsis in rats

Evidence suggests that immune dysfunction exerts a central role in the morbidity and mortality of sepsis. As the spleen is the largest lymphatic tissue in the body, its influence on immune regulation during sepsis should be explored. In this study, we analysed the immune alterations of the spleen of septic rats and the effects of splenectomy at 6 h, 12 h, and 24 h following caecal ligation and puncture (CLP). Results showed declines in CD4⁺ T cells and elevations in lymphocyte apoptosis, the percentage of Treg cells, and inflammatory cytokine levels (TNF-α, IL-6, and IL-10) in the spleens of CLP-induced septic rats. Moreover, splenectomy improved the survival of septic rats and bacterial clearance from peripheral blood. CLP-induced apoptosis of lymphocytes and the decreased CD4⁺ T cell percentage in the peripheral blood could be reversed in splenectomy-treated rats. Splenectomy greatly decreased the number of white blood cells, lymphocytes, monocytes, neutrophils, and serum concentration of TNF-α and IL-10 after CLP. Moreover, splenectomy alleviated pathologic damage to the liver and lungs and weakened expression of CD163. These novel findings demonstrate that immune disorders of the spleen are important pathogenic factors during the course of severe sepsis. Splenectomy could alleviate apoptosis and reduction of lymphocytes induced by sepsis, and lower the level of inflammation in the body. Reversing the immune suppression of the spleen may be a novel strategy to improve sepsis survival.

Neuronal CD200 Signaling Is Protective in the Acute Phase of Ischemic Stroke

BACKGROUND AND PURPOSE

CD200 (cluster of differentiation 200), a highly glycosylated protein primarily expressed on neurons in the central nervous system, binds with its receptor CD200R to form an endogenous inhibitory signal against immune responses. However, little is known about the effect of neuronal CD200 signaling in cerebral ischemia. The aim of this study was to investigate how neuronal CD200 signaling impacts poststroke inflammation and the ischemic injury.

METHODS

CD200 tma1^lf/fl:Thy1CreER mice were treated with tamoxifen to induce conditional gene knockout (ICKO) of neuronal CD200. The mice were subjected to a 60-minute transient middle cerebral artery occlusion. Stroke outcomes, apoptotic cell death, immune cell infiltration, microglia activation, and other inflammatory profiles were evaluated at 3 and 7 days after stroke.

RESULTS

Infarct volumes were significantly larger, and behavioral deficits more severe in ICKO versus control mice at 3 days after middle cerebral artery occlusion. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay also revealed a significant increase in apoptotic neuronal death in CD200 ICKO mice. An enhancement in lymphocytic infiltration and microglial proinflammatory responses were revealed by flow cytometry at 3 and 7 days after stroke in ICKO mice, accompanied by an increased microglial phagocytosis activity. Plasma proinflammatory cytokine (TNFα [tumor necrosis factor alpha] and IL [interleukin]-1β) levels significantly increased at 3 days, and IL-1β/IL-6 levels increased at 7 days in ICKO versus control animals. ICKO led to significantly lower baseline level of CD200 both in brain and plasma.

CONCLUSIONS

Neuronal CD200 inhibits proinflammatory responses and is protective against stroke injury.

Inhibition of exosome release augments neuroinflammation following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a severe stroke subtype without effective pharmacological treatment. Following ICH, peripheral leukocytes infiltrate into the brain and contribute to neuroinflammation and brain edema. However, the intercellular machinery controlling the initiation and propagation of leukocyte infiltration remains elusive. Exosomes are small extracellular vesicles released from donor cells and bridge intercellular communication. In this study, we investigated the effects of inhibition of exosome release on neuroinflammation and ICH injury. Using a mouse model of ICH induced by collagenase injection, we found that ICH induced an increase of exosome level in the brain. Inhibition of exosome release using GW4869 augmented neurological deficits and brain edema after ICH. The exacerbation of ICH injury was accompanied by increased barrier disruption and brain infiltration of leukocytes. The detrimental effects of GW4869 were ablated in ICH mice receiving antibody depletion of Gr-1⁺ myeloid cells. Extracted exosomes from the ICH brains suppressed the production of inflammatory factors by splenocytes. Additionally, exosomes extracted from brain tissues of donor ICH mice reduced ICH injury in recipient mice. These results demonstrate that inhibition of exosome release augments neuroinflammation and ICH injury. The impact of exosomes released from the ICH brain on the immune system deserves further investigation.

Quantitative and Correlational Analysis of Brain and Spleen Immune Cellular Responses Following Cerebral Ischemia

Stroke is a multiphasic process, and the initial ischemic phase of neuronal damage is followed by secondary innate and adaptive responses that unfold over days after stroke, offer a longer time frame of intervention, and represent a novel therapeutic target. Therefore, revealing the distinct functions of immune cells in both brain and periphery is important for identification of immunotherapeutic targets for stroke to extend the treatment time window. In this paper an examination of the cellular dynamics of the immune response in the central nervous system (CNS) and periphery provoked by cerebral ischemia is provided. New data is presented for the number of immune cells in brain and spleen of mice during the 7 days following middle cerebral artery occlusion (MCAO). A novel analysis of the correlation among various cell types in the brain and spleen following stroke is presented. It is found that the infiltrated macrophages in the ischemic hemisphere positively correlate with neutrophils which implies their synergic effect in migrating into the brain after stroke onset. It is noted that during infiltration of adaptive immune cells, the number of neutrophils correlate positively with T cells, which suggests neutrophils contribute to T cell infiltration in the stroked brain. Furthermore, the correlation among neurological deficit and various immune cells suggests that microglia and splenic adaptive immune cells (T and B cells) are protective while infiltrating peripheral myeloid cells (macrophage and neutrophils) worsen stroke outcome. Comprehension of such immune responses post cerebral ischemia is crucial for differentiating the drivers of outcomes and also predicting the stroke outcome.

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

Stroke causes systemic immunosuppression. T lymphocytes are involved in infarct size in the early stages of stroke. However, the phenotypes of T lymphocytes and their functions in peripheral immune organs and the brain have not been well analyzed in the acute and chronic phases of stroke. Here, we investigated pathological phenotypic alterations in the systemic immune response, especially changes in T lymphocytes, from one day to six months after ischemic stroke in mice. Impairment in thymocyte numbers, development, proliferation, and apoptosis were observed for up to two weeks. The number of mature T cells in the spleen and blood decreased and showed reduced interferon-γ production. Increased numbers of CD4^-CD8^-CD3⁺ double-negative T cells were observed in the mouse brain during the early stages of stroke, whereas interleukin (IL)-10⁺Foxp3⁺ regulatory T lymphocytes increased from two weeks during the chronic phase. These phenotypes correlated with body weight and neurological severity scores. The recovery of T lymphocyte numbers and increases in IL-10⁺Foxp3⁺ regulatory T lymphocytes may be important for long-term neurological outcomes. Dynamic changes in T lymphocytes between the acute and chronic phases may play different roles in pathogenesis and recovery. This study provides fundamental information regarding the T lymphocyte alterations from the brain to the peripheral immune organs following stroke.

Potential caveats of putative microglia-specific markers for assessment of age-related cerebrovascular neuroinflammation

BACKGROUND

The ability to distinguish resident microglia from infiltrating myeloid cells by flow cytometry-based surface phenotyping is an important technique for examining age-related neuroinflammation. The most commonly used surface markers for the identification of microglia include CD45 (low-intermediate expression), CD11b, Tmem119, and P2RY12.

METHODS

In this study, we examined changes in expression levels of these putative microglia markers in in vivo animal models of stroke, cerebral amyloid angiopathy (CAA), and aging as well as in an ex vivo LPS-induced inflammation model.

RESULTS

We demonstrate that Tmem119 and P2RY12 expression is evident within both CD45^int and CD45^high myeloid populations in models of stroke, CAA, and aging. Interestingly, LPS stimulation of FACS-sorted adult microglia suggested that these brain-resident myeloid cells can upregulate CD45 and downregulate Tmem119 and P2RY12, making them indistinguishable from peripherally derived myeloid populations. Importantly, our findings show that these changes in the molecular signatures of microglia can occur without a contribution from the other brain-resident or peripherally sourced immune cells.

CONCLUSION

We recommend future studies approach microglia identification by flow cytometry with caution, particularly in the absence of the use of a combination of markers validated for the specific neuroinflammation model of interest. The subpopulation of resident microglia residing within the "infiltrating myeloid" population, albeit small, may be functionally important in maintaining immune vigilance in the brain thus should not be overlooked in neuroimmunological studies.

Microglia depletion increase brain injury after acute ischemic stroke in aged mice

Microglia are one of the first responders to ischemic injury. Aged microglia acquire a senescent phenotype and produce more inflammatory cytokines after stroke. Depletion of microglia in young mice worsens post-ischemic damage by increasing inflammation. However, young mice do not have dysfunctional microglia. Hence, we hypothesized that depletion of microglia in older mice will contribute to improved early recovery after ischemic stroke injury. Aged (18-19 month) mice were fed with either control chow diet (CD) or PLX5622 chow diet (PLXD) for 21 days. On day 22, a 60-min middle cerebral artery occlusion (MCAo) surgery or sham surgery was performed. Twenty-four and 72 h after stroke immunohistochemistry and flow cytometry were performed. AFS98, a monoclonal antibody against CSF1R was used to specifically deplete brain macrophages by injection into the right hemisphere. Two days after AFS98 injections, mice underwent one-hour MCAo. Twenty-four hours later mice were euthanized and flow cytometry was performed. An increase in infarct volume (p < 0.05) was seen in the PLXD versus CD after stroke in aged mice at 24 and 72 h. An increase (p < 0.05) in infiltrating monocytes was observed after microglial depletion in aged stroke mice suggesting a differential monocyte response. An increase in astrocyte numbers was evident in the PLXD sham mice compared to CD sham, reflecting the off-target effects of PLX5622 treatment. In conclusion, PLX5622 and AFS98 treatment depleted microglia in aged animals but resulted in increased neuroinflammation after ischemic stroke.

A key role of gut microbiota-vagus nerve/spleen axis in sleep deprivation-mediated aggravation of systemic inflammation after LPS administration

AIMS

Sleep deprivation (SD) correlates with exacerbated systemic inflammation after sepsis. However, the underlying mechanisms remain unclear. This study aimed to evaluate the roles and mechanisms of SD in inflammatory organ injury after lipopolysaccharide (LPS) administration.

MAIN METHODS

Mice were intraperitoneally injected with LPS followed by 3 consecutive days of SD. The pseudo germ-free (PGF) mice received fecal microbiota transplant by being gavaged with supernatant from fecal suspension of septic mice with or without SD. The subdiaphragmatic vagotomy (SDV) or splenectomy was performed 14 days prior to LPS injection or antibiotics administration.

KEY FINDINGS

Post-septic SD increased the plasma levels of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α), reduced IL-10 plasma level, increased spleen weight, and promoted inflammatory injury of the lung, liver and kidney. The relative abundance of Proteobacteria and its subgroups were increased after post-septic SD. PGF mice transplanted with fecal bacteria from septic mice subjected to SD developed splenomegaly, systemic inflammation, organ inflammation and damage as their donors did. Intriguingly, SDV abolished the aggravated effects of SD on splenomegaly and inflammatory organ injury in septic mice received SD or in PGF mice transplanted with fecal bacteria from septic mice subjected to SD. Furthermore, splenectomy also abrogated the increase in IL-6 and TNF-α plasma levels and the decrease in IL-10 plasma level in PGF mice transplanted with fecal bacteria from septic mice subjected to SD.

SIGNIFICANCE

Gut microbiota-vagus nerve axis and gut microbiota-spleen axis play key roles in modulating systemic inflammation induced by SD after LPS administration.

Spleen is not required for therapeutic effects of 4OH-GTS-21, a selective α7 nAChR agonist, in the sub-acute phase of ischemic stroke in rats

Acute ischemic stroke (AIS) causes both central and peripheral inflammation, while activation of α7 nicotinic acetylcholine receptors (nAChRs) provides both central and peripheral anti-inflammatory and anti-apoptotic effects. Here, we provide evidence that 4OH-GTS-21, a selective α7 agonist, produces its therapeutic effects via primarily central sites of action because 4OH-GTS-21 was found equally effective in splenectomized and non-spenectomized rats in the sub-acute phase of ischemic stroke (≤1 week). However, the spleen may boost the therapeutic efficacy of 4OH-GTS-21 in certain behavioral tasks as our data also indicated. In our tests, AIS was modeled by transient middle cerebral artery occlusion (tMCAO). Splenectomy was done 2 weeks before tMCAO. We determined that: 1) Daily 4OH-GTS-21 treatments for 7 days after tMCAO significantly reduced neurological deficits and brain injury in both splenectomized and non-spelenectomized rats demonstrating that the spleen is not required for therapeutic benefits of 4OH-GTS-21; 2) The effects of 4OH-GTS-21 in the adhesive sticker removal test were significantly weaker in splenectomized animals suggesting that the spleen boosts the efficacy of 4OH-GTS-21 in the first week after tMCAO; and 3) Ischemic brain injury was not significantly affected by splenectomy in both vehicle-treated and 4OH-GTS-21-treated animals. These data support the hypothesis that the therapeutic efficacy of sub-chronic (≤1 week) 4OH-GTS-21 primarily originates from central sites of action. These results validate brain availability as a critical factor for developing novel α7 ligands for AIS.

Contribution of Extramedullary Hematopoiesis to Atherosclerosis. The Spleen as a Neglected Hub of Inflammatory Cells

Cardiovascular diseases (CVDs) incidence is becoming higher. This fact is promoted by metabolic disorders such as obesity, and aging. Atherosclerosis is the underlying cause of most of these pathologies. It is a chronic inflammatory disease that begins with the progressive accumulation of lipids and fibrotic materials in the blood-vessel wall, which leads to massive leukocyte recruitment. Rupture of the fibrous cap of the atherogenic cusps is responsible for tissue ischemic events, among them myocardial infarction. Extramedullary hematopoiesis (EMH), or blood cell production outside the bone marrow (BM), occurs when the normal production of these cells is impaired (chronic hematological and genetic disorders, leukemia, etc.) or is altered by metabolic disorders, such as hypercholesterolemia, or after myocardial infarction. Recent studies indicate that the main EMH tissues (spleen, liver, adipose and lymph nodes) complement the hematopoietic function of the BM, producing circulating inflammatory cells that infiltrate into the atheroma. Indeed, the spleen, which is a secondary lymphopoietic organ with high metabolic activity, contains a reservoir of myeloid progenitors and monocytes, constituting an important source of inflammatory cells to the atherosclerotic lesion. Furthermore, the spleen also plays an important role in lipid homeostasis and immune-cell selection. Interestingly, clinical evidence from splenectomized subjects shows that they are more susceptible to developing pathologies, such as dyslipidemia and atherosclerosis due to the loss of immune selection. Although CVDs represent the leading cause of death worldwide, the mechanisms involving the spleen-atherosclerosis-heart axis cross-talk remain poorly characterized.

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

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

Sex differences in T cell immune responses, gut permeability and outcome after ischemic stroke in aged mice

INTRODUCTION

Stroke is a disease that presents with well-known sex differences. While women account for more stroke deaths, recent data show that after adjusting for age and pre-stroke functional status, mortality is higher in men. Immune responses are key determinants of stroke outcome and may differ by sex. This study examined sex differences in central and peripheral T cell immune responses, systemic effects on gut permeability and microbiota diversity and behavioral outcomes after stroke in aged mice. We hypothesized that there are sex differences in the immune response to stroke in aged animals.

METHODS

C57BL/6CR mice (20-22 months) were subjected to 60 min middle cerebral artery occlusion, or sham surgery. T cells were quantified in brain and blood at 3, 7 and 15 days (d) post-stroke by flow cytometry. Peripheral effects on gut permeability and microbiota diversity, as well as neurological function were assessed up to 14 d, and at 21 d (cognitive function) post-stroke. Brain glial fibrillary acidic protein (GFAP) expression was evaluated at 42 d post-stroke.

RESULTS AND DISCUSSION

Mortality (50% vs 14%, p < 0.05) and hemorrhagic transformation (44% vs 0%) were significantly higher in males than in females. No difference in infarct size at 3d were observed. Peripherally, stroke induced greater gut permeability of FITC-dextran in males at d3 (p < 0.05), and non-reversible alterations in microbiota diversity in males. Following the sub-acute phase, both sexes demonstrated a time-dependent increase of CD4⁺ and CD8⁺ T cells in the brain, with significantly higher levels of CD8⁺ T cells and Regulatory T cells in males at d15 (p < 0.01). Aged males demonstrated greater neurological deficits up to d5 and impaired sensorimotor function up to d15 when assessed by the corner asymmetry test (p < 0.001 and p < 0.01, respectively). A trend in greater cognitive decline was observed at d21 in males. Increased GFAP expression in the ischemic hemisphere, indicating astroglial activation and gliosis, was demonstrated in both males and females 42d post-stroke. Our findings indicate that despite a similar initial ischemic brain injury, aged male mice experience greater peripheral effects on the gut and ongoing central neuroinflammation past the sub-acute phase after stroke.

Immune responses to stroke: mechanisms, modulation, and therapeutic potential

Stroke is the second leading cause of death worldwide and a leading cause of disability. Most strokes are caused by occlusion of a major cerebral artery, and substantial advances have been made in elucidating how ischemia damages the brain. In particular, increasing evidence points to a double-edged role of the immune system in stroke pathophysiology. In the acute phase, innate immune cells invade brain and meninges and contribute to ischemic damage, but may also be protective. At the same time, danger signals released into the circulation by damaged brain cells lead to activation of systemic immunity, followed by profound immunodepression that promotes life-threatening infections. In the chronic phase, antigen presentation initiates an adaptive immune response targeted to the brain, which may underlie neuropsychiatric sequelae, a considerable cause of poststroke morbidity. Here, we briefly review these pathogenic processes and assess the potential therapeutic value of targeting immunity in human stroke.

Growth differentiation factor-11 supplementation improves survival and promotes recovery after ischemic stroke in aged mice

Growth differentiation factor (GDF) 11 levels decline with aging. The age-related loss of GDF 11 has been implicated in the pathogenesis of a variety of age-related diseases. GDF11 supplementation reversed cardiac hypertrophy, bone loss, and pulmonary dysfunction in old mice, suggesting that GDF11 has a rejuvenating effect. Less is known about the potential of GDF11 to improve recovery after an acute injury, such as stroke, in aged mice. GDF11/8 levels were assessed in young and aged male mice and in postmortem human brain samples. Aged mice were subjected to a transient middle cerebral artery occlusion (MCAo). Five days after MCAo, mice received and bromodeoxyuridine / 5-Bromo-2'-deoxyuridine (BrdU) and either recombinant GDF11 or vehicle for five days and were assessed for recovery for one month following stroke. MRI was used to determine cerebrospinal fluid (CSF) volume, corpus callosum (CC) area, and brain atrophy at 30 days post-stroke. Immunohistochemistry was used to assess gliosis, neurogenesis, angiogenesis and synaptic density. Lower GDF11/8 levels were found with age in both mice and humans (p<0.05). GDF11 supplementation reduced mortality and improved sensorimotor deficits after stroke. Treatment also reduced brain atrophy and gliosis, increased angiogenesis, improved white matter integrity, and reduced inflammation after stroke. GDF11 may have a role in brain repair after ischemic injury.

Impaired Collateral Flow in Pial Arterioles of Aged Rats During Ischemic Stroke

Cerebral collateral circulation and age are critical factors in determining outcome from acute ischemic stroke. Aging may lead to rarefaction of cerebral collaterals, and thereby accelerate ischemic injury by reducing penumbral blood flow. Dynamic changes in pial collaterals after onset of cerebral ischemia may vary with age but have not been extensively studied. Here, laser speckle contrast imaging (LSCI) and two-photon laser scanning microscopy (TPLSM) were combined to monitor cerebral pial collaterals between the anterior cerebral artery (ACA) and the middle cerebral artery (MCA) in young adult and aged male Sprague Dawley rats during distal middle cerebral artery occlusion (dMCAo). Histological analysis showed that aged rats had significantly greater volumes of ischemic damage than young rats. LSCI showed that cerebral collateral perfusion declined over time after stroke in aged and young rats, and that this decline was significantly greater in aged rats. TPLSM demonstrated that pial arterioles narrowed faster after dMCAo in aged rats compared to young adult rats. Notably, while arteriole vessel narrowing was comparable 4.5 h after ischemic onset in aged and young adult rats, red blood cell velocity was stable in young adults but declined over time in aged rats. Overall, red blood cell flux through pial arterioles was significantly reduced at all time-points after 90 min post-dMCAo in aged rats relative to young adult rats. Thus, collateral failure is more severe in aged rats with significantly impaired pial collateral dynamics (reduced diameter, red blood cell velocity, and red blood cell flux) relative to young adult rats.

EMMPRIN/CD147 plays a detrimental role in clinical and experimental ischemic stroke

Background: Ischemic stroke is a devastating disease, often resulting in death or permanent neurological deficits. EMMPRIN/CD147 is a plasma membrane protein that induces the production of matrix metalloproteinases (MMPs), which contribute to secondary damage after stroke by disrupting the blood brain barrier (BBB) and facilitating peripheral leukocyte infiltration into the brain.

Results: CD147 surface expression increased significantly after stroke on infiltrating leukocytes, astrocytes and endothelial cells, but not on resident microglia. Inhibition of CD147 reduced MMP levels, decreased ischemic damage, and improved functional, cognitive and histological outcomes after experimental ischemic stroke in both young and aged mice. In stroke patients, high levels of serum CD147 24 hours after stroke predicted poor functional outcome at 12 months. Brain CD147 levels were correlated with MMP-9 and secondary hemorrhage in post-mortem samples from stroke patients.

Conclusions: Acute inhibition of CD147 decreases levels of MMP-9, limits tissue loss, and improves long-term cognitive outcomes following experimental stroke in aged mice. High serum CD147 correlates with poor outcomes in stroke patients. This study identifies CD147 as a novel, clinically relevant target in ischemic stroke.

Siponimod (BAF312) Treatment Reduces Brain Infiltration but Not Lesion Volume in Middle-Aged Mice in Experimental Stroke

Background and Purpose- The contribution of neuroinflammation and, in particular, the infiltration of the brain by lymphocytes is increasingly recognized as a substantial pathophysiological mechanism after stroke. The interaction of lymphocytes with endothelial cells and platelets, termed thromboinflammation, fosters microvascular dysfunction and secondary infarct growth. Siponimod is an S1PR (sphingosine-1-phosphate receptor) modulator, which blocks the egress of lymphocytes from lymphoid organs and has demonstrated beneficial effects in multiple sclerosis treatment. We investigated the effect of treatment with siponimod on stroke outcome in a mouse model of cerebral ischemia. Methods- Transient middle cerebral artery occlusion was induced in middle-aged wild-type mice. Animals were either treated with siponimod (3 mg/kg; intraperitoneal) or vehicle for 6 days. Stroke outcome was assessed by magnetic resonance imaging (spleen volume: prestroke, day 3, and day 7; infarct volume: days 1, 3, and 7) and behavioral tests (prestroke, day 2, and day 6). Immune cells of the peripheral blood and brain-infiltrating cells ipsilateral and contralateral were analyzed by VETScan and by flow cytometry. Results- Siponimod significantly induced lymphopenia on day 7 after transient middle cerebral artery occlusion and reduced T-lymphocyte accumulation in the central nervous system. No effect was detected for lesion size. Conclusions- For siponimod administered at 3 mg/kg in transient middle cerebral artery occlusion mouse model, our findings do not provide preclinical evidence for the use of S1PR1/5 modulators as neuroprotectant in stroke therapy.

CD147 as a key mediator of the spleen inflammatory response in mice after focal cerebral ischemia

Background

The splenic inflammatory response after cerebral ischemia has been implicated in secondary brain injury. We have recently reported that CD147 plays an important role in driving brain inflammation after ischemic stroke. In this study, we hypothesized that CD147 may play a role in the splenic inflammatory response after cerebral ischemia.

Methods

Transient (60 min) middle cerebral artery occlusion was induced in wild-type mice treated with an anti-CD147 antibody (αCD147) 1 h before ischemia onset. The splenic inflammatory response was evaluated at 4 and 24 h, representing the peak and early stage of splenic inflammatory activation in this model. Changes in mRNA and protein expression of CD147 and inflammatory markers were measured using RT-qPCR and western blot, respectively. Immune cells in the spleen and brain were measured using flow cytometry.

Results

CD147 expression was rapidly upregulated in the spleen at 4 and 24 h after ischemia onset. The splenic inflammatory response induced by cerebral ischemia was inhibited by αCD147 treatment as demonstrated by the reduced expression of cytokines (TNFα, IL-6, IL-1β) and monocyte chemoattractant protein-1 (MCP-1) in the spleen at 4 and 24 h after ischemia onset. Furthermore, reduced expression of Ly-6C and CCR2 coincided with a decrease in the number of Ly-6C^high MMs subset in the spleen at 4 h after ischemia onset. This suggests αCD147 treatment abrogates cerebral ischemia-induced inflammatory activation of splenic monocytes/macrophages (MMs). In addition, the experiment in splenectomized mice showed the spleen as the major source of infiltrated Ly-6C^high MMs subset in the ischemic brain and that brain infiltration of Ly-6C^high MMs was reduced by αCD147 treatment. These results reveal CD147 as a key mediator of the spleen’s inflammatory activation in response to cerebral ischemia.

Immune response mediates the cardiac damage after subarachnoid hemorrhage

Cardiac dysfunction is a common adverse effect of subarachnoid hemorrhage (SAH). Autopsy of SAH patients shows immunocyte infiltration into the heart. In this study, a SAH model of endovascular perforation was performed in adult male mice in order to test whether SAH causes cardiac dysfunction in non-primary cardiac disease young adult male mice and whether immune response mediates SAH induced cardiac and neurological deficit. Splenectomy was performed on a subpopulation of mice one week prior to induction of the SAH. Neurological functional tests, transthoracic Doppler echocardiography, immunofluorescent staining, and flow cytometry were performed to investigate neurological and cardiac function and immune/inflammatory effects of SAH in mice with or without splenectomy. We found that SAH significantly induces ventricular fibrillation and cardiac dysfunction identified by significantly reduced left ventricular ejection fraction, left ventricular fractional shortening, decreased heart rate, as well as increased macrophage and neutrophil infiltration into heart and inflammatory factor expression in the heart compared to sham control mice. SAH also induces neurological deficit, increases astrocyte and microglial activity, and inflammatory cell infiltration into brain as well as up-regulates inflammatory factor expression in the brain tissue. Splenectomy not only significantly improves neurological function, but also reduces cardiac dysfunction compared to SAH alone mice. Splenectomy in SAH mice significantly reduces inflammatory cell infiltration, and decreases NADPH oxidase-2 and macrophage chemokine protein-1 expression in heart and brain when compared to non-splenectomy SAH mice. Our data suggest that, SAH induces acute cardiac dysfunction in non-primary cardiac disease mice. Secondary immune response may play an important role in mediating brain-heart damage after SAH.

Inflammation as a mediator of arterial ageing

NEW FINDINGS

What is the topic of this review? This review summarizes and synthesizes what is known about the contribution of inflammation to age-related arterial dysfunction. What advances does it highlight? This review details observational evidence for the relationship of age-related inflammation and arterial dysfunction, insight from autoimmune inflammatory diseases and their effects on arterial function, interventional evidence linking inflammation and age-related arterial dysfunction, insight into age-related arterial inflammation from preclinical models and interventions to ameliorate age-related inflammation and arterial dysfunction.

ABSTRACT

Advanced age is a primary risk factor for cardiovascular disease, the leading cause of death in the industrialized world. Two major components of arterial ageing are stiffening of the large arteries and impaired endothelium-dependent dilatation in multiple vascular beds. These two alterations are major contributors to the development of overt cardiovascular disease. Increasing inflammation with advanced age is likely to play a role in this arterial dysfunction. The purpose of this review is to synthesize what is known about inflammation and its relationship to age-related arterial dysfunction. This review discusses both the initial observational evidence for the relationship of age-related inflammation and arterial dysfunction and the evidence that inflammatory autoimmune diseases are associated with a premature arterial ageing phenotype. We next discuss interventional and mechanistic evidence linking inflammation and age-related arterial dysfunction in older adults. We also attempt to summarize the relevant evidence from preclinical models. Lastly, we discuss interventions in both humans and animals that have been shown to ameliorate age-related arterial inflammation and dysfunction. The available evidence provides a strong basis for the role of inflammation in both large artery stiffening and impairment of endothelium-dependent dilatation; however, the specific inflammatory mediators, the initiating factors and the relative importance of the endothelium, smooth muscle cells, perivascular adipose tissue and immune cells in arterial inflammation are not well understood. With the expansion of the ageing population, ameliorating age-related arterial inflammation represents an important potential strategy for preserving vascular health in the elderly.

The impact of sex and age on T cell immunity and ischemic stroke outcomes

Sex differences are well-recognized in ischemic stroke, a disease mainly affecting the elderly. Stroke results in robust activation of central and peripheral immune responses which contributes to functional outcome. Aging is associated with increased low-grade chronic inflammation known as "inflammaging" that renders aged males and females more susceptible to poor outcomes after ischemic stroke. Despite the fact that sex differences are well-documented in immunity and inflammation, few studies have focused on sex differences in inflammatory responses after ischemic stroke and even fewer have been performed in the context of aging. The role of T cell responses in ischemic stroke have gained increasing attention over the past decade as data suggest a major role in the pathophysiology/recovery after ischemic injury. T cells offer an attractive therapeutic target due to their relatively delayed infiltration into the ischemic brain. This review will focus on T cell immune responses in ischemic stroke, highlighting studies examining the effects of aging and biological sex.

Nursing Markedly Protects Postpartum Mice From Stroke: Associated Central and Peripheral Neuroimmune Changes and a Role for Oxytocin

Recent studies demonstrate significant neuroimmune changes in postpartum females, a period that also carries an increased risk of stroke. Oxytocin, a major hormone upregulated in the brains of nursing mothers, has been shown to both modulate neuroinflammation and protect against stroke. In the present study we assessed whether and how nursing modulates the neuroimmune response and injury after stroke. We observed that postpartum nursing mice were markedly protected from 1 h of transient middle cerebral artery occlusion (MCAO) relative to either non-pregnant/non-postpartum or non-nursing (pups removed) postpartum females. Nursing mice also expressed reduced levels of pro-inflammatory cytokines, had decreased migration of blood leukocytes into the brain following MCAO, and displayed peripheral neuroimmune changes characterized by increased spleen weight and increased fraction of spleen monocytes. Intranasal oxytocin treatment in non-pregnant females in part recapitulated the protective and anti-inflammatory effects associated with nursing. In summary, the results of the present study demonstrate that nursing in the postpartum period provides relative protection against transient ischemic stroke associated with decreased brain leukocytes and increased splenic monocytes. These effects appear to be regulated, at least in part, by oxytocin.

The spleen may be an important target of stem cell therapy for stroke

Stroke is the most common cerebrovascular disease, the second leading cause of death behind heart disease and is a major cause of long-term disability worldwide. Currently, systemic immunomodulatory therapy based on intravenous cells is attracting attention. The immune response to acute stroke is a major factor in cerebral ischaemia (CI) pathobiology and outcomes. Over the past decade, the significant contribution of the spleen to ischaemic stroke has gained considerable attention in stroke research. The changes in the spleen after stroke are mainly reflected in morphology, immune cells and cytokines, and these changes are closely related to the stroke outcomes. Autonomic nervous system (ANS) activation, release of central nervous system (CNS) antigens and chemokine/chemokine receptor interactions have been documented to be essential for efficient brain-spleen cross-talk after stroke. In various experimental models, human umbilical cord blood cells (hUCBs), haematopoietic stem cells (HSCs), bone marrow stem cells (BMSCs), human amnion epithelial cells (hAECs), neural stem cells (NSCs) and multipotent adult progenitor cells (MAPCs) have been shown to reduce the neurological damage caused by stroke. The different effects of these cell types on the interleukin (IL)-10, interferon (IFN), and cholinergic anti-inflammatory pathways in the spleen after stroke may promote the development of new cell therapy targets and strategies. The spleen will become a potential target of various stem cell therapies for stroke represented by MAPC treatment.

IL-2mAb reduces demyelination after focal cerebral ischemia by suppressing CD8+ T cells

Aims

Demyelination, one of the major pathological changes of white matter injury, is closely related to T‐cell–mediated immune responses. Thus, we investigate the role of an IL‐2 monoclonal antibody (IL‐2mAb, JES6‐1) in combatting demyelination during the late phase of stroke.

Methods

IL‐2mAb or IgG isotype antibody (0.25 mg/kg) was injected intraperitoneally 2 and 48 hours after middle cerebral artery occlusion (MCAO) surgery. Infarct volume, peripheral immune cell infiltration, microglia activation, and myelin loss were measured by 2,3,5‐triphenyte trazoliumchloride staining, immunofluorescence staining, flow cytometry, and Western blot. Intraperitoneal CD8 neutralizing antibody (15 mg/kg) was injected 1 day before MCAO surgery to determine the role of CD8⁺ T cells on demyelinating lesions.

Results

IL‐2mAb treatment reduced brain infarct volume, attenuated demyelination, and improved long‐term sensorimotor functions up to 28 days after dMCAO. Brain infiltration of CD8⁺ T cells and peripheral activation of CD8⁺ T cells were both attenuated in IL‐2 mAb‐treated mice. The protection of IL‐2mAb on demyelination was abolished in mice depleted of CD8⁺ T cell 1 week after stroke.

Conclusions

IL‐2mAb preserved white matter integrity and improved long‐term sensorimotor functions following cerebral ischemic injury. The activation and brain infiltration of CD8⁺ T cells are detrimental for demyelination after stroke and may be the major target of IL‐2mAb posttreatment in the protection of white matter integrity after stroke.

Efficacy of leukemia inhibitory factor as a therapeutic for permanent large vessel stroke differs among aged male and female rats

Preclinical studies using rodent models of stroke have had difficulty in translating their results to human patients. One possible factor behind this inability is the lack of studies utilizing aged rodents of both sexes. Previously, this lab showed that leukemia inhibitory factor (LIF) promoted recovery after stroke through antioxidant enzyme upregulation. This study examined whether LIF promotes neuroprotection in aged rats of both sexes. LIF did not reduce tissue damage in aged animals, but LIF-treated female rats showed partial motor skill recovery. The LIF receptor (LIFR) showed membrane localization in young male and aged rats of both sexes after stroke. Although LIF increased neuronal LIFR expression in vitro, it did not increase LIFR in the aged brain. Levels of LIFR protein in brain tissue were significantly downregulated between young males and aged males/females at 72 h after stroke. These results demonstrated that low LIFR expression reduces the neuroprotective efficacy of LIF in aged rodents of both sexes. Furthermore, the ability of LIF to promote motor improvement is dependent upon sex in aged rodents.

NK cells in cerebral ischemia

As a vital cell type in immune system and infiltrating cells in ischemic brain, NK cells can bridge the crosstalk between immune system and nervous system in stroke setting. The mechanism of action of NK cells is complicated, involving direct and indirect actions. NK cells are closely associated with poststroke inflammation, immunodepression and infections. The excessive inflammatory response in ischemic brain is one of the important causes for aggravating cerebral ischemic injury. Besides the inflammation induced by ischemia itself, thrombolytic drug tissue plasminogen activator (tPA) administration could also induce deteriorative inflammation, which is unfavorable for stroke control and recovery. Regulating NK cells may has the potential to modulate the immune response, limiting the development of ischemic damage and getting better outcome. In addition, post-stroke immunosuppression may lead to infections which contribute to higher severity and mortality of ischemic stroke (IS). Targeting NK cells may help to find novel pathways for IS therapy, which can both ameliorate the infarction itself, but also reduce the infectious complications. NK cells may also link IS and related diseases, suggesting NK cells can be used as a diagnostic or prognostic biomarker for IS prevention and treatment.

Splenectomy modulates early immuno-inflammatory responses to trauma-hemorrhage and protects mice against secondary sepsis

In polytrauma patients, the impact of splenectomy is equivocal, ranging from negative to protective. We investigated the impact of splenectomy on immune responses in the 1^st-hit polytrauma alone and on survival in the post-traumatic sepsis (2^nd hit). Female BALB/c mice underwent polytrauma (1^st hit) consisting of either a) TH: femur fracture, hemorrhagic shock or b) TSH: splenectomy, femur fracture, hemorrhagic shock. Additionally, the polytrauma hit was followed by cecal ligation and puncture (CLP) 48 h later and compared to CLP alone. Splenectomy improved the 28-day survival in secondary sepsis to 92% (from 62%), while TH lowered it to 46% (p < 0.05). The improved survival was concurrent with lower release of inflammatory cytokines (IL-6, CXCL-1, MCP-1) and increase of C5a post-CLP. In the polytrauma hit alone, TSH induced stronger neutrophilia (1.9 fold) and lymphocytosis (1.7 fold) when compared to TH mice. Moreover, TSH resulted in a 41% rise of regulatory T-cells and reduced the median fluorescence intensity of MHC-2 on monocytes by 55% within 48 h (p < 0.05). Conversely, leukocyte phagocytic capacity was significantly increased by 4-fold after TSH despite a similar M1/M2 macrophage profile in both groups. Summarizing, splenectomy provoked both immuno-suppressive and immuno-stimulatory responses but was life-saving in secondary sepsis. Additionally, the polytrauma components in 2-hit models should be tested for their effects on outcome; the presumed end-effect of the 1^st hit solely based on the common immuno-inflammatory parameters could be misleading.

The splenic response to stroke: from rodents to stroke subjects

Background

Stroke is the fifth leading cause of death and the leading cause of long-term disability in the USA, costing $40.2 billion in direct and indirect costs. Globally, stroke is the second leading cause of death and has a higher prevalence in lower- and middle-income countries compared to high-income countries.

The role of the spleen in stroke has been studied in rodent models of stroke and is seen as a major contributor to increased secondary neural injury after stroke. Splenectomy 2 weeks prior to ischemic and hemorrhagic stroke in mice and rats shows decreased infarct volumes. Additionally, the spleen decreases in size following stroke in rodents. Pro-inflammatory mediators are also increased in the spleen and subsequently the brain after stroke. These data in preclinical models of stroke have led stroke neurologists to look at the splenic response in stroke subjects. The outcomes of these studies suggest the spleen is responding in a similar manner in stroke subjects as it is in animal models of stroke.

Conclusion

Animal models demonstrating the detrimental role of the spleen in stroke are providing strong evidence of how the spleen is responding during stroke in human subjects. This indicates treatments targeting the splenic immune response in animals could provide useful targets and treatments for stroke subjects.