Splenic responses in ischemic stroke: new insights into stroke pathology

Impact of peripheral immune cells in experimental neonatal hypoxia-ischemia: A systematic review and meta-analysis

Infiltration of peripheral immune cells into the brain following neonatal hypoxia-ischemia (HI) contributes to increased neuroinflammation and brain injury. However, the specific roles of different immune cell types in neonatal brain injury remain poorly understood. Although existing evidence suggests a potential role for sexual dimorphism in HI outcomes, this aspect has been insufficiently investigated. In this systematic review and meta-analysis, we examined the brain infiltration of peripheral immune cells in rodents of both sexes following neonatal HI. A total of 25 studies were included. Our analysis revealed significant increases in the infiltration of various subtypes of leukocytes after HI, along with increased brain injury, cell death, and neuroinflammation, and reduced neuronal survival. Notably, males exhibited a greater degree of immune cell infiltration and more pronounced neuroinflammation compared to females. These findings suggest that infiltrating leukocytes contribute significantly to the pathophysiology of neonatal HI, with sexually dimorphic responses further influencing the outcomes. It is crucial that future research focuses on elucidating the specific roles of immune cell subtypes to better understand the mechanisms underlying brain damage after HI and identify novel therapeutic targets. Moreover, the observed sex differences highlight the need to consider sex as a key factor when developing strategies for the treatment of neonatal HI.

Prophylactic use of probiotics as an adjunctive treatment for ischemic stroke via the gut-spleen-brain axis

A growing body of research has focused on the role of spleen in orchestrating brain injury through the peripheral immune system following stroke, highlighting the brain-spleen axis as a potential target for mitigating neuronal damage during stroke. The gut microbiota plays a pivotal role in the bidirectional communication between the gut and the brain. Several studies have suggested that probiotic supplements hold promise as a strategic approach to maintaining a balanced intestinal microecology, reducing the apoptosis of intestinal epithelial cells, protecting the intestinal mucosal and blood-brain barrier (BBB), enhancing both intestinal and systemic immune functions, and thereby potentially affecting the pathogenesis and progression of ischemic stroke. In this study, we aimed to clarify the neuroprotective effects of supplementation with Lactobacillus, specifically Limosilactobacillus reuteri GMNL-89 (G89) and Lacticaseibacillus paracasei GMNL-133 (G133) on ischemic stroke and investigate how G89 and G133 modulate the communication mechanisms between the gut, brain, and spleen following ischemic stroke. We explored the neuroprotection and the underlying mechanisms of Lactobacillus supplementation in C57BL/6 mice subjected to permanent middle cerebral artery occlusion. Our results revealed that oral treatment with G89 or G133 alone, as well as oral administration combining G89 and G133, significantly decreased the infarct volume and improved the neurological function in mice with ischemic stroke. Moreover, G89 treatment alone preserved the tight junction integrity of gut barrier, while G133 alone and the combined treatment of G89 and G133 would significantly decreased the BBB permeability, and thereby significantly attenuated stroke-induced local and systemic inflammatory responses. Both G89 and G133 regulated cytotoxic T cells, and the balance between T helper 1 cells and T helper 2 cells in the spleen following ischemic stroke. Additionally, the combined administration of G89 and G133 improved the gut dysbiosis and significantly increased the concentration of short-chain fatty acids. In conclusion, our findings suggest that G89 and G133 may be used as nutrient supplements, holding promise as a prospective approach to combat ischemic stroke by modulating the gut-spleen-brain axis.

Buyang huanwu decoction alleviates stroke-induced immunosuppression in MCAO mice by reducing splenic T cell apoptosis triggered by AIM2 inflammasome

ETHNOPHARMACOLOGICAL RELEVANCE

Ischemic stroke is a serious disabling and fatal disease that places a heavy burden on the world. Stroke induces a state of systemic immunosuppression that is strongly associated with an increased risk of infection and severe outcomes. Buyang Huanwu Decoction (BYHWD) is an ancient Chinese traditional formula with a good clinical and experimental basis. However, the role of BYHWD on post-stroke immunomodulation, especially immunosuppression, is unclear.

AIM OF THE STUDY

The aim of this study was to investigate the pharmacological mechanism of BYHWD to alleviate ischemic stroke by analyzing splenic T cells apoptosis triggered by the AIM2 inflammasome activation cascade.

MATERIALS AND METHODS

An ischemic stroke model in C57BL/6 J mice was constructed using the MCAO method. The mNSS test and the hanging wire test were conducted to evaluate neurological impairment in mice. Histopathological damage was visualized by Nissl staining and HE staining. The protective effects of BYHWD on the spleen were determined by splenic index and spleen HE staining. The inhibition of AIM2 inflammasome cascade by BYHWD were explored through immunofluorescence (IF), flow cytometry, enzyme-linked immunosorbent assay (ELISA) and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Flow cytometry was used to assess the apoptosis of splenic T cells.

RESULTS

BYHWD significantly reduced infarct size, improved neurological function scores, and alleviated histopathological damage in middle cerebral artery occlusion (MCAO) mice. At the same time, BYHWD salvaged spleen atrophy. BYHWD significantly ameliorated apoptosis of splenic T lymphocytes. Key proteins and factors in the AIM2/IL-1β/FasL/Fas axis are effectively inhibited from expression after BYHWD treatment.

CONCLUSION

It is the first study to demonstrate that BYHWD can improve stroke-induced immunosuppression by down-regulating Fas-dependent splenic T-cell apoptosis triggered by peripheral AIM2 inflammasome-driven signaling cascade.

Role of intracranial bone marrow mesenchymal stem cells in stroke recovery: A focus on post-stroke inflammation and mitochondrial transfer

Stem cell therapy has become a hot research topic in the medical field in recent years, with enormous potential for treating a variety of diseases. In particular, bone marrow mesenchymal stem cells (BMSCs) have wide-ranging applications in the treatment of ischemic stroke, autoimmune diseases, tissue repair, and difficult-to-treat diseases. BMSCs can differentiate into multiple cell types and exhibit strong immunomodulatory properties. Although BMSCs can regulate the inflammatory response activated after stroke, the mechanism by which BMSCs regulate inflammation remains unclear and requires further study. Recently, stem cell therapy has emerged as a potentially effective approach for enhancing the recovery process following an ischemic stroke. For example, by regulating post-stroke inflammation and by transferring mitochondria to exert therapeutic effects. Therefore, this article reviews the therapeutic effects of intracranial BMSCs in regulating post-stroke inflammation and mitochondrial transfer in the treatment of stroke, providing a basis for further research.

Prospective randomized controlled trial on the safety and neuroprotective efficacy of remote administration of hypothermia over spleen during acute ischemic stroke with mechanical thrombectomy: rationale, design, and protocol

Background

Brain inflammation plays a key role in ischemia/reperfusion (I/R) injury and is the main cause of "ineffective or futile recanalization" after successful mechanical thrombectomy (MT) in acute ischemic stroke (AIS). One of the primary sources of inflammatory cells after AIS are derived from the spleen. As an innovative and potential neuroprotective strategy after stroke, Remote Administration of Hypothermia (RAH) temporarily suppresses immune activities in the spleen, reduces the release of inflammatory cells and cytokines into blood, and thus reversibly diminishes inflammatory injury in the brain.

Methods

This single-center, prospective, randomized controlled study (RCT) is proposed for AIS patients with anterior circulation large vessel occlusion (LVO). Subjects will be randomly assigned to either the control or intervention groups in a 1:1 ratio (n = 40). Participants allocated to the intervention group will receive RAH on the abdomen above the spleen prior to recanalization until 6 h after thrombectomy. All enrolled patients will receive standard stroke Guideline care. The main adverse events associated with RAH are focal cold intolerance and abdominal pain. The primary outcome will assess safety as it pertains to RAH application. The secondary outcomes include the efficacy of RAH on spleen, determined by spleen volumes, blood inflammatory factor (cells and cytokines), and on brain injury, determined by infarction volumes and poststroke functional outcomes.

Discussion

This study aims to examine the safety and preliminary effectiveness of RAH over the spleen during endovascular therapy in AIS patients. The results of this study are expected to facilitate larger randomized clinical trials and hopefully prove RAH administration confers adjuvant neuroprotective properties in AIS treated with MT.

Clinical trial registration

https://www.chictr.org.cn/. Identifier ChiCTR 2300077052.

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.

The Involvement of Immune Cells Between Ischemic Stroke and Gut Microbiota

Ischemic stroke, a disease with high mortality and disability rate worldwide, currently has no effective treatment. The systemic inflammation response to the ischemic stroke, followed by immunosuppression in focal neurologic deficits and other inflammatory damage, reduces the circulating immune cell counts and multiorgan infectious complications such as intestinal and gut dysfunction dysbiosis. Evidence showed that microbiota dysbiosis plays a role in neuroinflammation and peripheral immune response after stroke, changing the lymphocyte populations. Multiple immune cells, including lymphocytes, engage in complex and dynamic immune responses in all stages of stroke and may be a pivotal moderator in the bidirectional immunomodulation between ischemic stroke and gut microbiota. This review discusses the role of lymphocytes and other immune cells, the immunological processes in the bidirectional immunomodulation between gut microbiota and ischemic stroke, and its potential as a therapeutic strategy for ischemic stroke.

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.

GPR55 Inactivation Diminishes Splenic Responses and Improves Neurological Outcomes in the Mouse Ischemia/Reperfusion Stroke Model

Although strokes are frequent and severe, treatment options are scarce. Plasminogen activators, the only FDA-approved agents for clot treatment (tissue plasminogen activators (tPAs)), are used in a limited patient group. Moreover, there are few approaches for handling the brain's inflammatory reactions to a stroke. The orphan G protein-coupled receptor 55 (GPR55)'s connection to inflammatory processes has been recently reported; however, its role in stroke remains to be discovered. Post-stroke neuroinflammation involves the central nervous system (CNS)'s resident microglia activation and the infiltration of leukocytes from circulation into the brain. Additionally, splenic responses have been shown to be detrimental to stroke recovery. While lymphocytes enter the brain in small numbers, they regularly emerge as a very influential leukocyte subset that causes secondary inflammatory cerebral damage. However, an understanding of how this limited lymphocyte presence profoundly impacts stroke outcomes remains largely unclear. In this study, a mouse model for transient middle cerebral artery occlusion (tMCAO) was used to mimic ischemia followed by a reperfusion (IS/R) stroke. GPR55 inactivation, with a potent GPR55-specific antagonist, ML-193, starting 6 h after tMCAO or the absence of the GPR55 in mice (GPR55 knock out (GPR55ko)) resulted in a reduced infarction volume, improved neurological outcomes, and decreased splenic responses. The inhibition of GPR55 with ML-193 diminished CD4+T-cell spleen egress and attenuated CD4+T-cell brain infiltration. Additionally, ML-193 treatment resulted in an augmented number of regulatory T cells (Tregs) in the brain post-tMCAO. Our report offers documentation and the functional evaluation of GPR55 in the brain-spleen axis and lays the foundation for refining therapeutics for patients after ischemic attacks.

Chemical profiling of Shengmai injection, tissue distribution and pharmacokinetic characteristics of ginsenosides after intravenous dosing Shengmai injection in rats with cerebral ischemia

ETHNOPHARMACOLOGICAL RELEVANCE

Shengmai injection (SMI), consisting of Panax ginseng, Fructus schisandrae, and Radix ophiopogonis, has been widely used in the treatment of cardiovascular and cerebrovascular diseases.

AIM OF THE STUDY

This study aimed to uncover the chemical profile of SMI, tissue distribution and pharmacokinetic characteristics of the main compounds after administration by combing UPLC-LTQ-Orbitrap-MS and UPLC-QQQ-MS.

MATERIALS AND METHODS

UPLC-LTQ-Orbitrap-MS method was firstly established for the chemical profiling analysis of SMI. Then UPLC-QQQ-MS method was used to quantitatively analyze the contents of the main identified compounds in SMI and in the different tissues after intravenous dosing SMI in rats with cerebral ischemia. Finally, a new method was developed for the pharmacokinetic study of ginsenosides with considerable exposure.

RESULTS

A total of 59 compounds were identified in SMI, including 25 ginsenosides, 25 lignans, four ophiopogon saponins, and five flavonoids. Among them, 26 compounds were confirmed by the standard substance. By UPLC-QQQ-MS, 23 chemical compounds were then quantitatively identified with their contents in SMI. Ginsenosides, as the main active compounds from Panax ginseng, showed the highest contents in SMI. Fifteen compounds including ginsenosides and Schisandrol were further found to have considerable exposure in different tissues. A rapid, sensitive, and specified method was then developed for simultaneously detecting the seven ginsenosides in the plasma and had good method validation. Pharmacokinetic evaluation showed that PPD type ginsenosides (Rd, Rb1, Rc) were all exhibited at higher levels of exposure in the plasma and had a much slower elimination rate, whereas PPT type ginsenosides (Re, Rg1, Rf, Rg2) underwent fast elimination.

CONCLUSION

This study systematically revealed the ingredients of SMI and their tissue distribution. The pharmacokinetic characteristics of ginsenosides were also discovered. The findings provide a helpful reference for the pharmacological, toxicological, and clinical research on SMI.

HMGB1 Promotes Accelerated Fracture Healing in Traumatic Brain Injury through PINK1/Parkin-Mediated Mitochondrial Autophagy

We aimed to investigate the mechanism of high mobility group box 1 (HMGB1) in the accelerated fracture healing process during Traumatic brain injury (TBI). The lateral ventricles of mice in the TBI model group were injected with adenovirus-packaged short hairpin RNA (shRNA)-HMGB1 or overexpressing (ov)-HMGB1 vector. We found HMGB1 levels were higher in bone tissue at the fracture end of TBI combined with fracture model mice. Compared with the TBI combined with fracture model mice, the mice in the ov-HMGB1 group healed faster and the expression levels of mitochondrial autophagy-related proteins were higher. Compared to the ov-HMGB1 group, mice in the ov-HMGB1 + autophagy inhibitor cyclosporin A (CsA) and ov-HMGB1 + shRNA-phosphatase and tensin homolog-induced kinase 1 (PINK1) groups showed slower healing and lower expression of mitochondrial autophagy-associated proteins. The expression of osteocalcin (OCN), SOX9, and bone morphogenetic protein (BMP)-2 in bone tissue at the fracture end of the ov-HMGB1 + shRNA-PINK1 group was lower than that in the ov-HMGB1 group. The mRNA expression levels of chondrogenic differentiation markers in bone tissue at the fracture end of the ov-HMGB1 + shRNA-PINK1 group were lower than those in the ov-HMGB1 group. Fracture healing was accelerated during TBI, especially when HMGB1 was highly expressed, and HMGB1 promote accelerated fracture healing during TBI through PINK1/Parkin-mediated mitochondrial autophagy.

Research progress on the regulation and mechanism of borneol on the blood-brain barrier in pathological states: a narrative review focused on ischemic stroke and cerebral glioma

Background and Objective

The blood-brain barrier (BBB) serves as a dynamic, selective shield, safeguarding the central nervous system (CNS) by separating the brain from circulating blood, preserving its microenvironment, and ensuring stability. However, in the presence of brain pathology, drug delivery across the BBB and blood-tumor barrier (BTB) becomes challenging, hindering effective treatments. Borneol exhibits promise in bidirectionally modulating the BBB under pathological conditions, suggesting at potential clinical applications for related diseases. Our primary goal in this review is to investigate borneol's potential clinical utility in bidirectionally regulating the BBB under pathological conditions.

Methods

The PubMed database, CNKI (China National Knowledge Infrastructure), Wanfang Data were searched to retrieve articles on animal experiments and cell-based research published from January 1, 2003, to May 1, 2023, using the following medical subject headings (MeSH) terms: borneol, blood-brain barrier, ischemic stroke, cerebral gliomas, anti-inflammatory. The search was limited to articles published in English and Chinese. In total, 86 articles were deemed eligible for inclusion in this study.

Key Content and Findings

The breakdown of the BBB is a key pathological process in ischemic stroke and cerebral glioma. When used alone, the lipophilic properties of borneol can reduce the permeability of the BBB and restore its normal function, thereby repairing brain damage and protecting brain tissue. Its specific protective effects may be related to inflammatory regulation mechanisms. The anti-inflammatory and protective effects of borneol can be used to improve and treat lesions caused by ischemic stroke and cerebral glioma. Furthermore, when combined with other drugs, borneol can accelerate the opening of the BBB, improve permeability through physiological processes, and enhance drug penetration and distribution in the brain without causing pathological damage to the brain.

Conclusions

This review summarizes the mechanisms by which borneol regulates the BBB and BTB in ischemic stroke and cerebral glioma, and discusses the potential clinical applications of borneol in the treatment of these diseases. It is believed that in the future, as research methods are refined, more effective and targeted therapies for cerebral glioma and ischemic stroke will be explored related to the protective mechanism of the BBB under pathological conditions with borneol alone or in combination with other drugs.

Human Wharton's jelly mesenchymal stem cells derived-exosomes enriched by miR-124 promote an anti-fibrotic response in an experimental model of liver fibrosis

BACKGROUND

Liver fibrosis is a significant challenge to global health that results in organ failure through inflammation and the release of fibrotic biomarkers. Due to the lack of effective treatments for liver fibrosis, anti-fibrotic and anti-inflammatory therapies are being developed. Since there has been an association between aberrant expression of miR-124 and liver disease progression, we investigated whether delivery of miR-124 through human Wharton's jelly mesenchymal stem cells derived-exosomes (hWJMSC-Exo) can improve liver fibrosis.

METHODS

We established a 6-week carbon tetrachloride (CCl4)-induced mouse model of liver fibrosis, then we administered hWJMSC-Exo and miR-124-3p-enriched exosomes (ExomiR-124) for three weeks. The extent of fibrosis and inflammation was assessed by histology, biochemistry, Real-time PCR, immunohistochemistry, and Enzyme-linked immunoassays (ELISA). The inflammatory status of the spleen was also investigated using flow cytometry.

RESULTS

Based on the gene and protein expression measurement of IL-6, IL-17, TGF-β, STAT3, α-SMA, and COL1, In vivo administration of Exo and ExomiR-124 effectively reduce collagen accumulation and inhibition of inflammation. Regarding histopathology findings, the therapeutic effect of ExomiR-124 against liver fibrosis was significantly greater than hWJMSC-Exo. In addition, we found that Exo and ExomiR-124 was capable of phenotype switching of splenic monocytes from inflammatory Ly6C^hi to restorative Ly6C^lo.

CONCLUSIONS

MSC-derived exosomes demonstrated anti-inflammatory effect via different aspects. Aside from the therapeutic approach, enrichment of exosomes as a nanocarrier by miR-124 revealed the down-regulation of STAT3, which plays a crucial role in liver fibrosis. The anti-inflammatory and anti-fibrotic properties of ExomiR-124 could be a promising option in liver fibrosis combination therapies.

The potential risk factors of early-onset post-stroke depression from immuno-inflammatory perspective

Background

Mounting evidence strongly uncovered that peripheral immuno-inflammatory response induced by acute stroke is associated with the appearance of post-stroke depression (PSD), but the mechanism remains unclear.

Methods

103 stroke patients were assessed at 2 weeks after onset using Diagnostic and Statistical Manual of Mental Disorders, 5th edition and then divided into PSD and non-PSD groups. Polymorphisms of inflammatory molecules (interleukin [IL]-1β, IL-6, IL-10, IL-18, tumor necrosis factor-α [TNF-α], interferon-γ [IFN-γ] and C-reactive protein [CRP]), complete blood count parameters, splenic attenuation (SA) and splenic volume (SV) on unenhanced chest computed tomography, demographic and other clinical characteristics were obtained. Binary logistic regression model was used to analyze the associations between inflammation-related factors and the occurrence of PSD at 2 weeks after stroke.

Results

49 patients were diagnosed with PSD at 2 weeks after onset (early-onset PSD). The C/T genotypes of CRP rs2794520 and rs1205 were less in PSD group than non-PSD group (both adjusted odds ratio = 3.364; 95%CI: 1.039-10.898; p = 0.043). For CRP rs3091244, the frequency of G allele was higher (80.61% vs. 13.89%) while the frequency of A allele was lower (6.12% vs. 71.30%) in PSD patients than non-PSD patients (χ² = 104.380; p<0.001). SA of PSD patients was lower than that of non-PSD patients in the presence of CRP rs2794520 C/T genotype and rs1205 C/T genotype (both t = 2.122; p = 0.039). Peripheral monocyte count was less in PSD group than non-PSD group (adjusted odds ratio = 0.057; 95%CI: 0.005-0.686; p = 0.024).

Conclusions

CRP polymorphisms, SA based on CRP genotype, and peripheral monocytes are associated with the risk of early-onset PSD, suggesting peripheral immuno-inflammatory activities elicited by stroke in its aetiology.

Peripheral Organ Injury After Stroke

Stroke is a disease with high incidence, mortality and disability rates. It is also the main cause of adult disability in developed countries. Stroke is often caused by small emboli on the inner wall of the blood vessels supplying the brain, which can lead to arterial embolism, and can also be caused by cerebrovascular or thrombotic bleeding. With the exception of recombinant tissue plasminogen activator (rt-PA), which is a thrombolytic drug used to recanalize the occluded artery, most treatments have been demonstrated to be ineffective. Stroke can also induce peripheral organ damage. Most stroke patients have different degrees of injury to one or more organs, including the lung, heart, kidney, spleen, gastrointestinal tract and so on. In the acute phase of stroke, severe inflammation occurs in the brain, but there is strong immunosuppression in the peripheral organs, which greatly increases the risk of peripheral organ infection and aggravates organ damage. Nonneurological complications of stroke can affect treatment and prognosis, may cause serious short-term and long-term consequences and are associated with prolonged hospitalization and increased mortality. Many of these complications are preventable, and their adverse effects can be effectively mitigated by early detection and appropriate treatment with various medical measures. This article reviews the pathophysiological mechanism, clinical manifestations and treatment of peripheral organ injury after stroke.

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.

Splenic Rhythms and Postprandial Dynamics in Physiology, Portal Hypertension, and Functional Hyposplenism: A Review

BACKGROUND

Before the discovery of immunological and haematological functions of the spleen, it had for centuries been considered to be a digestive organ of variable size with a role in the portal vein system and nutritional metabolism. In the 19th and 20th centuries, volume changes in the spleen related to nutrition were studied using plethysmographic measurements. Rhythmical and regulatory functions of the spleen were demonstrated in the haemodynamics of the splanchnic region and were described as a "hepatolienal pendulum," a "Windkessel function," or a "pressure compensation." These studies were mainly published in German-speaking countries and have not, as far as is known, been discussed in the English-speaking world so far.

SUMMARY

This review explores the historical development of the rhythmical regulatory function of the spleen in the splanchnic region. Older studies and results are followed up in the modern literature, wherever possible, up to the present. The clinical relevance is illustrated with portal hypertension (with congestive or hyperdynamic splenomegaly), coeliac disease, and chronic inflammatory bowel diseases (with functional hyposplenism). Key Message: The spleen's rhythmical regulatory function in nutrition is based on an autonomous rhythm comprising cycles of contractions and dilations of the spleen of around 1 min. These cycles can be influenced by sympathetically mediated single contractions with a release of pooled blood or by portal vein congestion. After food ingestion, the spleen responds either with contraction according to a vasomotor reaction or postprandial congestion with significant increases in volume. The spleen's rhythmical function is lost in the clinical picture of portal hypertension or in coeliac disease and chronic inflammatory bowel diseases. In the aforementioned gastrointestinal diseases, we recommend taking more account of the haemodynamics between the spleen, liver, and intestine. New innovative techniques for recording splenograms are required which, besides elastographic measurements of spleen stiffness, could offer an important tool for early detection, diagnosis, and therapeutic evaluation.

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.

A systemic immune challenge to model hospital-acquired infections independently regulates immune responses after pediatric traumatic brain injury

Background

Traumatic brain injury (TBI) is a major cause of disability in young children, yet the factors contributing to poor outcomes in this population are not well understood. TBI patients are highly susceptible to nosocomial infections, which are mostly acquired within the first week of hospitalization, and such infections may modify TBI pathobiology and recovery. In this study, we hypothesized that a peripheral immune challenge such as lipopolysaccharide (LPS)—mimicking a hospital-acquired infection—would worsen outcomes after experimental pediatric TBI, by perpetuating the inflammatory immune response.

Methods

Three-week-old male mice received either a moderate controlled cortical impact or sham surgery, followed by a single LPS dose (1 mg/kg i.p.) or vehicle (0.9% saline) at 4 days post-surgery, then analysis at 5 or 8 days post-injury (i.e., 1 or 4 days post-LPS).

Results

LPS-treated mice exhibited a time-dependent reduction in general activity and social investigation, and increased anxiety, alongside substantial body weight loss, indicating transient sickness behaviors. Spleen-to-body weight ratios were also increased in LPS-treated mice, indicative of persistent activation of adaptive immunity at 4 days post-LPS. TBI + LPS mice showed an impaired trajectory of weight gain post-LPS, reflecting a synergistic effect of TBI and the LPS-induced immune challenge. Flow cytometry analysis demonstrated innate immune cell activation in blood, brain, and spleen post-LPS; however, this was not potentiated by TBI. Cytokine protein levels in serum, and gene expression levels in the brain, were altered in response to LPS but not TBI across the time course. Immunofluorescence analysis of brain sections revealed increased glia reactivity due to injury, but no additive effect of LPS was observed.

Conclusions

Together, we found that a transient, infection-like systemic challenge had widespread effects on the brain and immune system, but these were not synergistic with prior TBI in pediatric mice. These findings provide novel insight into the potential influence of a secondary immune challenge to the injured pediatric brain, with future studies needed to elucidate the chronic effects of this two-hit insult.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02114-1.

Systematic Study of the Immune Components after Ischemic Stroke Using CyTOF Techniques

Stroke induces a robust inflammatory response. However, it still lacks a systematic view of the various immune cell types due to the limited numbers of fluorophore used in the traditional FACS technique. In our current study, we utilized the novel technique mass cytometry (CyTOF) to analyze multiple immune cell types. We detected these immune cells from the ischemic brain, peripheral blood, spleen, and bone marrow at different time courses after stroke. Our data showed (1) dynamic changes in the immune cell numbers in the ischemic brain and peripheral organs. (2) The expression levels of cell surface markers indicate the inflammation response status after stroke. Interestingly, CD62L, a key adhesion molecule, regulates the migration of leukocytes from blood vessels into secondary lymphoid tissues and peripheral tissues. (3) A strong leukocyte network across the brain and peripheral immune organs was identified using the R program at day 1 after ischemia, suggesting that the peripheral immune cells dramatically migrated into the ischemic areas after stroke. This study provides a systematic, wide view of the immune components in the brain and peripheral organs for a deep understanding of the immune response after ischemic stroke.

Remote ischemic preconditioning-induced neuroprotection in cerebral ischemia-reperfusion injury: Preclinical evidence and mechanisms

Remote ischemic preconditioning (RIPC) is an intrinsic protective phenomenon in which 3 to 4 interspersed cycles of non-fatal regional ischemia followed by reperfusion to the remote tissues protect the vital organs including brain, heart and kidney against sustained ischemia-reperfusion-induced injury. There is growing preclinical evidence supporting the usefulness of RIPC in eliciting neuroprotection against focal and global cerebral ischemia-reperfusion injury. Scientists have explored the involvement of HIF-1α, oxidative stress, apoptotic pathway, Lcn-2, platelets-derived microparticles, splenic response, adenosine A₁ receptors, adenosine monophosphate activated protein kinase and neurogenic pathway in mediating RIPC-induced neuroprotection. The present review discusses the early and late phases of neuroprotection induced by RIPC against cerebral ischemic injury in animals along with the various possible mechanisms.

Post-stroke infections associated with spleen volume reduction: A pilot study

BACKGROUND

Spleen volume reduction followed by re-expansion has been described in acute ischemic stroke in both animal and human studies. Splenic contraction might be partially due to sympathetic hyperactivity and might be accompanied by release of splenocytes in the peripheral circulation, leading to immunodepression.

AIMS

To investigate whether spleen volume changes in the first week after stroke are associated with post-stroke infections, changes in lymphocytes count and autonomic dysfunction.

METHODS

In patients with acute ischemic stroke, spleen sizes were calculated from abdominal CT images on day one and day seven. Spleen size reduction was defined as > 10% spleen size reduction between day one and day seven. Post stroke infections were diagnosed during the first seven days after stroke onset using the modified criteria of the US Center of Disease Control and Prevention. We assessed the time course of leukocyte subsets and analysed pulse rate variability (PRV) indices.

RESULTS

Post-stroke infections occurred in six out of 11 patients (55%) with spleen size reduction versus in five out of 27 patients (19%) without spleen size reduction (p = 0,047). Spleen size reduction was associated with a drop in lymphocytes and several lymphocyte subsets from admission to day one, and a higher NIHSS at admission and at day three (p = 0,028 and p = 0,006 respectively). No correlations could be found between spleen volume change and PRV parameters.

CONCLUSION

Post-stroke infections and a drop in lymphocytes and several lymphocyte subsets are associated with spleen volume reduction in acute ischemic stroke.

RNA sequencing reveals novel macrophage transcriptome favoring neurovascular plasticity after ischemic stroke

Blood monocytes/macrophages infiltrate the brain after ischemic stroke and critically influence brain injury and regeneration. We investigated stroke-induced transcriptomic changes of monocytes/macrophages by RNA sequencing profiling, using a mouse model of permanent focal cerebral ischemia. Compared to non-ischemic conditions, brain ischemia induced only moderate genomic changes in blood monocytes, but triggered robust genomic reprogramming in monocytes/macrophages invading the brain. Surprisingly, functional enrichment analysis of the transcriptome of brain macrophages revealed significant overrepresentation of biological processes linked to neurovascular remodeling, such as angiogenesis and axonal regeneration, as early as five days after stroke, suggesting a previously underappreciated role for macrophages in initiating post-stroke brain repair. Upstream Regulator analysis predicted peroxisome proliferator-activated receptor gamma (PPARγ) as a master regulator driving the transcriptional reprogramming in post-stroke brain macrophages. Importantly, myeloid cell-specific PPARγ knockout (mKO) mice demonstrated lower post-stroke angiogenesis and neurogenesis than wild-type mice, which correlated significantly with the exacerbation of post-stroke neurological deficits in mKO mice. Collectively, our findings reveal a novel repair-enhancing transcriptome in brain macrophages during post-stroke neurovascular remodeling. As a master switch controlling genomic reprogramming, PPARγ is a rational therapeutic target for promoting and maintaining beneficial macrophage functions, facilitating neurorestoration, and improving long-term functional recovery after ischemic stroke.

Postprandial dynamics of splenic volume in healthy volunteers

Throughout the history of medicine, many functions have been attributed to the spleen and numerous researchers have focused on a postulated digestive function. Beginning in 1825, systematic animal studies showed evidence for a postprandial increase in splenic volume (SV) with a peak 30 min to five hours after food intake. Since the introduction of imaging techniques, two studies have been conducted on humans, revealing a decrease in SV 30 to 45 min postprandially. The aim of this study was to examine possible postprandial changes in SV over a period of seven hours. The ethics-approved, randomized crossover study included 10 healthy volunteers, who received a standardized meal (3,600 kJ) on one study day and fasted on the other. Sonographic measurements were obtained at six measurement points on each day. Thirty minutes after the meal, SV increased significantly by 38.2 ± 51.2 cm3 (17.3%; p = .04) compared to the baseline measurement and decreased gradually afterward. In males, SV 30 min after the meal was 70.2 ± 21.6 cm3 higher (p = .002) compared to the fasting condition and 60 min later it was still significantly increased. The apparent SV increase after food intake is discussed in relation to hemodynamic changes in the splanchnic region. It seems plausible that the spleen has a rhythmic and regulative function within the portal system, something which warrants further research and should be taken more into account in nutritional physiology.

Macrophages reprogram after ischemic stroke and promote efferocytosis and inflammation resolution in the mouse brain

AIMS

Blood-borne monocytes/macrophages infiltrate the brain in massive numbers after ischemic stroke, but their impact on poststroke brain injury and recovery remains elusive. This study examined the transcriptomic changes in monocytes/macrophages after ischemic stroke and the functional implications of these changes, particularly with regards to the contribution of these cells to the phagocytic clearance of dead/dying cells (efferocytosis) in the poststroke brain.

METHODS

We performed whole-genome RNA sequencing on the monocyte/macrophage population sorted from mouse brain and peripheral blood 5 days after permanent focal cerebral ischemia. In addition, the spatial and temporal profiles of macrophage efferocytosis were examined in vivo by immunohistochemistry 3-7 days after brain ischemia.

RESULTS

Robust transcriptomic changes occurred in monocytes/macrophages upon infiltrating the poststroke brain. Functional enrichment analysis revealed a transcriptome of brain macrophages that strongly favored efferocytic activity. A large number of efferocytosis-related genes were upregulated in brain macrophages, the products of which are essential components involved in various steps of efferocytosis, such as chemotaxis, recognition of dead cells, engulfment, and processing of phagosomes. The efferocytic activity of brain macrophages were verified by immunohistochemistry, wherein Iba1-labeled microglia/macrophages effectively cleared apoptotic neurons in the infarct during the subacute stage after brain ischemia. We also identified PPARγ and STAT6 as potential upstream regulators that shaped this proefferocytic and inflammation-resolving transcriptome of macrophages in the poststroke brain.

CONCLUSION

Macrophages play a crucial role in the phagocytic clearance of dead neurons after ischemic stroke and promote the resolution of inflammation in the brain. Molecular therapies that enhance macrophage efferocytic capability may be promising treatments for ischemic stroke by facilitating inflammation resolution, brain repair, and recovery of neurological functions.

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.

Circulating factors in young blood as potential therapeutic agents for age-related neurodegenerative and neurovascular diseases

Recent animal studies on heterochronic parabiosis (a technique combining the blood circulation of two animals) have revealed that young blood has a powerful rejuvenating effect on brain aging. Circulating factors, especially growth differentiation factor 11 (GDF11) and C-C motif chemokine 11 (CCL11), may play a key role in this effect, which inspires hope for novel approaches to treating age-related cerebral diseases in humans, such as neurodegenerative and neurovascular diseases. Recently, attempts have begun to translate these astonishing and exciting findings from mice to humans and from bench to bedside. However, increasing reports have shown contradictory data, questioning the capacity of these circulating factors to reverse age-related brain dysfunction. In this review, we summarize the current research on the role of young blood, as well as the circulating factors GDF11 and CCL11, in the aging brain and age-related cerebral diseases. We highlight recent controversies, discuss related challenges and provide a future outlook.

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.

Accessing neuroinflammation sites: Monocyte/neutrophil-mediated drug delivery for cerebral ischemia

Cerebral ischemia (CI) results from inadequate blood flow to the brain. The difficulty of delivering therapeutic molecules to lesions resulting from CI hinders the effective treatment of this disease. The inflammatory response following CI offers a unique opportunity for drug delivery to the ischemic brain and targeted cells because of the recruitment of leukocytes to the stroke core and penumbra. In the present study, neutrophils and monocytes were explored as cell carriers after selectively carrying cRGD liposomes, which effectively transmigrated the blood-brain barrier, infiltrated the cerebral parenchyma, and delivered therapeutic molecules to the injured sites and target cells. Our results showed the successful comigration of liposomes with neutrophils/monocytes and that both monocytes and neutrophils were important for successful delivery. Enhanced protection against ischemic injury was achieved in the CI/reperfusion model. The strategy presented here shows potential in the treatment of CI and other diseases related to inflammation.

The role of Interleukin-33 in the modulation of splenic T-cell immune responses after experimental ischemic stroke

The splenic T-cell immune response to stroke has been identified as an important role in the progression of brain injury following ischemic stroke. Interleukin (IL)-33 as a novel cytokine of IL-1 family has been found to be protective for ischemic brain injury. Here, we determined the contribution of IL-33 to the T-cell immune responses in the spleen after experimental ischemic stroke. Mice were subjected to 30 min of middle cerebral artery occlusion (MCAO) for ischemic stroke induction. Recombinant mouse IL-33 (100 μg/kg) was pre-treated intraperitoneally at 30 min prior to MCAO, then the percentages of T cell subsets, related cytokines and transcription factors in the spleen tissues were measured. Intraperitoneal IL-33 pre-treatment may attenuate neurological deficit scores and infarct volumes after MCAO, which was accompanied by reduced IFN-γ⁺ T cells and increased Foxp3⁺ T cells in the spleen tissues. Meanwhile, IL-33 pre-treatment could decrease the production of IFN-γ and increase the secretion of IL-4, IL-10 and TGF-β from the spleen at 24 h after MCAO. Additionally, the mRNA level of the transcription factor T-bet was downregulated by IL-33, and the levels of GATA-3 and Foxp3 mRNA were upregulated. These results showed that the long-term protective mechanism of IL-33 in ischemic stroke may be partly associated to its modulation role for splenic T-cell immune responses through inhibiting Th1 response and promoting Treg response, suggesting that IL-33 may be a candidate treatment for human stroke via modulating the peripheral immune system following stroke.

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.

The peripheral immune response after stroke-A double edge sword for blood-brain barrier integrity

The blood‐brain barrier (BBB) is a highly regulated interface that separates the peripheral circulation and the brain. It plays a vital role in regulating the trafficking of solutes, fluid, and cells at the blood‐brain interface and maintaining the homeostasis of brain microenvironment for normal neuronal activity. Growing evidence has led to the realization that ischemic stroke elicits profound immune responses in the circulation and the activation of multiple subsets of immune cells, which in turn affect both the early disruption and the later repair of the BBB after stroke. Distinct phenotypes or subsets of peripheral immune cells along with diverse intracellular mechanisms contribute to the dynamic changes of BBB integrity after stroke. This review focuses on the interaction between the peripheral immune cells and the BBB after ischemic stroke. Understanding their reciprocal interaction may generate new directions for stroke research and may also drive the innovation of easy accessible immune modulatory treatment strategies targeting BBB in the pursuit of better stroke recovery.

The evolving role of neuro-immune interaction in brain repair after cerebral ischemic stroke

Stroke is the world's leading cause of disability with limited brain repair treatments which effectively improve long-term neurological deficits. The neuroinflammatory responses persist into the late repair phase of stroke and participate in all brain repair elements, including neurogenesis, angiogenesis, synaptogenesis, remyelination and axonal sprouting, shedding new light on post-stroke brain recovery. Resident brain glial cells, such as astrocytes not only contribute to neuroinflammation after stroke, but also secrete a wide range of trophic factors that can promote post-stroke brain repair. Alternatively, activated microglia, monocytes, and neutrophils in the innate immune system, traditionally considered as major damaging factors after stroke, have been suggested to be extensively involved in brain repair after stroke. The adaptive immune system may also have its bright side during the late regenerative phase, affecting the immune suppressive regulatory T cells and B cells. This review summarizes the recent findings in the evolving role of neuroinflammation in multiple post-stroke brain repair mechanisms and poses unanswered questions that may generate new directions for future research and give rise to novel therapeutic targets to improve stroke recovery.

Interleukin 15 blockade protects the brain from cerebral ischemia-reperfusion injury

Acute ischemic stroke is followed by a complex interplay between the brain and the immune system in which ischemia-reperfusion leads to a detrimental inflammatory response that causes brain injury. In the brain, IL-15 is expressed by astrocytes, neurons and microglia. Previous study showed that ischemia-reperfusion induces expression of IL-15 by astrocytes. Transgenic over-expression of IL-15 in astrocytes aggravates ischemia-reperfusion brain damage by increasing the levels and promoting the effector functions of CD8⁺ T and NK cells. Treatment of neonatal rats with IL-15 neutralizing antibody before hypoxia-ischemia induction reduces the infarct volume. However, as stroke-induced inflammatory responses differ between neonate and adult brain, the effects of IL-15 blockade on the injury and immune response arising from stroke in adult animals has remained unclear. In this study, we examined the effect of post-ischemia/reperfusion IL-15 blockade on the pathophysiology of cerebral ischemia-reperfusion in adult mice. Using a cerebral ischemia-reperfusion model, we compared infarct size and the infiltrating immune cells in the brain of wild type (WT) mice and Il15^-/- mice lacking NK and memory CD8⁺ T cells. We also evaluated the effects of IL-15 neutralizing antibody treatment on brain infarct volume, motor function, and the status of brain-infiltrating immune cells in WT mice. Il15^-/- mice show a smaller infarct volume and lower numbers of activated brain-infiltrating NK, CD8⁺ T, and CD4⁺ T cells compared to WT mice after cerebral ischemia-reperfusion. Post-ischemia/reperfusion IL-15 blockade reduces infarct size and improves motor and locomotor activity. Furthermore, IL-15 blockade reduces the effector function of NK, CD8⁺ T, and CD4⁺ T cells in the ischemia-reperfusion brain of WT mice. Ablation of IL-15 responses after cerebral ischemia-reperfusion ameliorates brain injury in adult mice. Therefore, targeting IL-15 is a potential effective therapy for ischemic stroke.

11C-DPA-713 Versus 18F-GE-180: A Preclinical Comparison of Translocator Protein 18 kDa PET Tracers to Visualize Acute and Chronic Neuroinflammation in a Mouse Model of Ischemic Stroke

Neuroinflammation plays a key role in neuronal injury after ischemic stroke. PET imaging of translocator protein 18 kDa (TSPO) permits longitudinal, noninvasive visualization of neuroinflammation in both preclinical and clinical settings. Many TSPO tracers have been developed, however, it is unclear which tracer is the most sensitive and accurate for monitoring the in vivo spatiotemporal dynamics of neuroinflammation across applications. Hence, there is a need for head-to-head comparisons of promising TSPO PET tracers across different disease states. Accordingly, the aim of this study was to directly compare 2 promising second-generation TSPO tracers, ¹¹C-DPA-713 and ¹⁸F-GE-180, for the first time at acute and chronic time points after ischemic stroke. Methods: After distal middle cerebral artery occlusion or sham surgery, mice underwent consecutive PET/CT imaging with ¹¹C-DPA-713 and ¹⁸F-GE-180 at 2, 6, and 28 d after stroke. T2-weighted MR images were acquired to enable delineation of ipsilateral (infarct) and contralateral brain regions of interest (ROIs). PET/CT images were analyzed by calculating percentage injected dose per gram in MR-guided ROIs. SUV ratios were determined using the contralateral thalamus (SUV_Th) as a pseudoreference region. Ex vivo autoradiography and immunohistochemistry were performed to verify in vivo findings. Results: Significantly increased tracer uptake was observed in the ipsilateral compared with contralateral ROI (SUV_Th, 50-60 min summed data) at acute and chronic time points using ¹¹C-DPA-713 and ¹⁸F-GE-180. Ex vivo autoradiography confirmed in vivo findings demonstrating increased TSPO tracer uptake in infarcted versus contralateral brain tissue. Importantly, a significant correlation was identified between microglial/macrophage activation (cluster of differentiation 68 immunostaining) and ¹¹C-DPA-713- PET signal, which was not evident with ¹⁸F-GE-180. No significant correlations were observed between TSPO PET and activated astrocytes (glial fibrillary acidic protein immunostaining). Conclusion: ¹¹C-DPA-713 and ¹⁸F-GE-180 PET enable detection of neuroinflammation at acute and chronic time points after cerebral ischemia in mice. ¹¹C-DPA-713 PET reflects the extent of microglial activation in infarcted distal middle cerebral artery occlusion mouse brain tissue more accurately than ¹⁸F-GE-180 and appears to be slightly more sensitive. These results highlight the potential of ¹¹C-DPA-713 for tracking microglial activation in vivo after stroke and warrant further investigation in both preclinical and clinical settings.

Splenectomy Fails to Provide Long-Term Protection Against Ischemic Stroke

Splenectomy before or immediately after stroke provides early brain protection. This study aims to explore the effect of splenectomy on long-term neurological recovery after stroke, which is currently lacking in the field. Adult male rats were randomized into splenectomy or sham groups and then subjected to 90 min of middle cerebral artery occlusion (MCAO). Spleen was removed right upon reperfusion or 3d after MCAO. Infarct volume, neurological functions, and peripheral immune cell populations were assessed up to 28d after stroke. The results show that delayed removal of spleen did not reduce brain tissue loss and showed no effect on sensorimotor function (Rotarod, beam balance, forelimb placing, grid walk, and adhesive removal tests) or cognitive function (Morris water maze). Spleen removal immediately upon reperfusion, although significantly reduced the infarct size and immune cell infiltration 3d after MCAO, also failed to promote long-term recovery. Flow cytometry analysis demonstrated that immediate splenectomy after MCAO resulted in a prolonged decrease in the percentage of CD3⁺CD4⁺ and CD3⁺CD8⁺ T cells in total lymphocytes as compared to non-splenectomy MCAO rats. In contrast, the percentage of CD3^-CD45RA⁺ B cells was significantly elevated after splenectomy. As a result, the ratio of T/B cells was significantly reduced in stroke rats with splenectomy. In conclusion, delayed splenectomy failed to provide long-term protection to the ischemic brain or improve functional recovery. The acute neuroprotective effect achieved by early splenectomy after stroke cannot last for long term. This loss of neuroprotection might be related to the prolonged disturbance in the T cell to B cell ratio.

Splenic responses play an important role in remote ischemic preconditioning-mediated neuroprotection against stroke

Background

Remote ischemic preconditioning (RIPC) of a limb has been reported to protect against ischemic stroke. Our previous results demonstrated that the RIPC-mediated neuroprotection is associated with alterations in circulating immune cell populations. Here, we evaluated the effect of the spleen, the largest reservoir of immune cells, on RIPC-mediated neuroprotection against stroke.

Methods

Noninvasive RIPC was achieved by four repeated cycles of 5-min blood flow constriction in the hindlimbs using a tourniquet. The blood and spleens were collected before and 1 h and 3 days after preconditioning to analyze the effect of RIPC on the spleen and the correlation between splenic and peripheral lymphocytes. Moreover, spleen weight and splenic lymphocytes were compared in stroke rats with or without RIPC. Finally, splenectomy was made 1 day or 2 weeks before RIPC and 90-min middle cerebral artery occlusion (MCAO). The infarct areas and deficits were assessed. Blood was collected 1 h after RIPC and 3 days after MCAO to explore the impact of splenectomy on RIPC-induced neuroprotection and immune changes. The contralateral and ipsilateral hemispheres were collected 3 days after MCAO to detect the infiltration of immune cells after RIPC and splenectomy.

Results

Flow cytometry analysis demonstrated that the RIPC promptly increased the percentages of CD3⁺CD8⁺ cytotoxic T (Tc) cells in the spleen with a relatively delayed elevation in CD3⁺CD161⁺ natural killer T (NKT) and CD3⁻CD45RA⁺ B lymphocytes. The percentages of circulating lymphocytes are positively correlated with the percentages of splenic lymphocytes in normal rats. Interestingly, RIPC resulted in negative correlations between the percentages of splenic and circulating T lymphocytes, while the correlation between splenic and circulating B lymphocytes remained positive. For animals subjected to RIPC followed by MCAO, RIPC increased splenic volume with an expansion of splenic lymphocytes 3 days after MCAO. Furthermore, the removal of the spleen 1 day or 2 weeks before RIPC and MCAO reduced the protective effect of RIPC on ischemic brain injury and reversed the effects of RIPC on circulating immune cell composition. RIPC significantly reduced brain infiltration of Tc and NKT cells. Prior splenectomy showed no effect on immune cell infiltration after RIPC and stroke.

Conclusion

These results reveal an immunomodulatory effect of the spleen, effecting mainly the spleen-derived lymphocytes, during RIPC-afforded neuroprotection against cerebral ischemia.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1190-9) contains supplementary material, which is available to authorized users.

The spleen as a neuroimmune interface after spinal cord injury

Traumatic spinal cord injury (SCI) causes widespread damage to neurons, glia and endothelia located throughout the spinal parenchyma. In response to the injury, resident and blood-derived leukocytes orchestrate an intraspinal inflammatory response that propagates secondary neuropathology and also promotes tissue repair. SCI also negatively affects autonomic control over peripheral immune organs, notably the spleen. The spleen is the largest secondary lymphoid organ in mammals, with major roles in blood filtration and host defense. Splenic function is carefully regulated by neuroendocrine mechanisms that ensure that the immune responses to infection or injury are proportionate to the initiating stimulus, and can be terminated when the stimulus is cleared. After SCI, control over the viscera, including endocrine and lymphoid tissues is lost due to damage to spinal autonomic (sympathetic) circuitry. This review begins by examining the normal structure and function of the spleen including patterns of innervation and the role played by the nervous system in regulating spleen function. We then describe how after SCI, loss of proper neural control over splenic function leads to systems-wide neuropathology, immune suppression and autoimmunity. We conclude by discussing opportunities for targeting the spleen to restore immune homeostasis, reduce morbidity and mortality, and improve functional recovery after SCI.

Association Between Splenic Contraction and the Systemic Inflammatory Response After Acute Ischemic Stroke Varies with Age and Race

Animal models have demonstrated the deleterious contribution of splenic immunocytes on secondary brain injury after stroke. While previous work has demonstrated splenic contraction (SC) in patients with acute ischemic stroke (AIS) and intracranial hemorrhage (ICH), no clinical studies have examined the relationship between the systemic inflammatory response syndrome (SIRS) with SC in stroke patients. This is a retrospective analysis of a previous prospective observational study where daily spleen sizes were evaluated in 178 acute stroke patients. Spleen contraction was based on previously established normograms of healthy volunteers from the same study. SC from the first 24 h of stroke onset was evaluated against criteria for SIRS for the first 5 days of admission after AIS. Ninety-one patients had verified AIS without concurrent infection at admission. SIRS was not associated with SC at admission. African-American patients with early SIRS had higher odds of having SC. Older patients with persistent SIRS at 72 h had lower odds of SC. At 48 h, there was significantly higher lymphocytosis and lower neutrophils present in patients with SC. Patients with SIRS at 72 h were more likely to have worse discharge mRS. This study provides evidence for an association among SC and SIRS in African-American patients suggesting that spleen changes could be a biomarker for detecting SIRS in this population. Our data also indicate a counter association between SC and a lack of SIRS in patients older than 75. Further studies are needed to ascertain how age affects this association.

Mesenchymal Stem Cells Overexpressing Interleukin-10 Promote Neuroprotection in Experimental Acute Ischemic Stroke

Interleukin (IL)-10 is a contributing factor to neuroprotection of mesenchymal stem cell (MSC) transplantation after ischemic stroke. Our aim was to increase therapeutic effects by combining MSCs and ex vivo IL-10 gene transfer with an adeno-associated virus (AAV) vector using a rat transient middle cerebral artery occlusion (MCAO) model. Sprague-Dawley rats underwent 90 min MCAO followed by intravenous administration of MSCs alone or IL-10 gene-transferred MSCs (MSC/IL-10) at 0 or 3 hr after ischemia reperfusion. Infarct lesions, neurological deficits, and immunological analyses were performed within 7 days after MCAO. 0-hr transplantation of MSCs alone and MSC/IL-10 significantly reduced infarct volumes and improved motor function. Conversely, 3-hr transplantation of MSC/IL-10, but not MSCs alone, significantly reduced infarct volumes (p < 0.01) and improved motor function (p < 0.01) compared with vehicle groups at 72 hr and 7 days after MCAO. Immunological analysis showed that MSC/IL-10 transplantation significantly inhibits microglial activation and pro-inflammatory cytokine expression compared with MSCs alone. Moreover, overexpressing IL-10 suppressed neuronal degeneration and improved survival of engrafted MSCs in the ischemic hemisphere. These results suggest that overexpressing IL-10 enhances the neuroprotective effects of MSC transplantation by anti-inflammatory modulation and thereby supports neuronal survival during the acute ischemic phase.

Multipotent Adult Progenitor Cells Enhance Recovery After Stroke by Modulating the Immune Response from the Spleen

Stem cell therapy modulates not only the local microenvironment of the brain but also the systemic immune responses. We explored the impact of human multipotent adult progenitor cells (MAPC) modulating splenic activation and peripheral immune responses after ischemic stroke. Hundred twenty-six Long-Evans adult male rats underwent middle cerebral artery occlusion. Twenty-four hours later, they received IV MAPC or saline treatment. At 3 days after infusion, RNA was isolated from the injured cortex and spleen for microarray analysis. Spleen mass, splenocyte phenotype, and releasing cytokines were measured. Serum cytokines, MAPC biodistribution, brain lesion sizes and neurofunctional deficits were compared in rats treated with MAPC or saline with and without spleens. Stroked animals treated with MAPC exhibited genes that more closely resembled animals with sham surgery. Gene categories downregulated by MAPC included leukocyte activation, antigen presentation, and immune effector processing, associated with the signaling pathways regulated by TNF-α, IL-1β, IL-6, and IFN-γ within the brain. MAPC treatment restored spleen mass reduction caused by stroke, elevated Treg cells within the spleen, increased IL-10 and decreased IL-1β released by splenocytes. MAPC reduced IL-6 and IL-1β and upregulated IL-10 serum levels. Compared with saline, MAPC enhance stroke recovery in rats with intact spleens but had no effects in rats without spleens. MAPC restores expression of multiple genes and pathways involved in immune and inflammatory responses after stroke. Immunomodulation of the splenic response by the intravenous administration of MAPC may create a more favorable environment for brain repair after stroke. Stem Cells 2017;35:1290-1302.

Is Immunomodulation a Principal Mechanism Underlying How Cell-Based Therapies Enhance Stroke Recovery?

Inflammation within the brain and in peripheral tissues contributes to brain injury following ischemic stroke. Therapeutic modulation of the inflammatory response has been actively pursued as a novel stroke treatment approach for decades, without success. In recent years, extensive studies support the high potential for cell-based therapies to become a new treatment modality for stroke and other neurological disorders. In this review, we explore different types of cellular therapies and discuss how they modulate central and peripheral inflammatory processes after stroke. Apart from identifying potential targets for cell therapy, we also discuss paracrine and immunomodulatory mechanisms of cell therapy.

Acute splenic responses in patients with ischemic stroke and intracerebral hemorrhage

Animal models provide evidence of spleen mediated post-stroke activation of the peripheral immune system. Translation of these findings to stroke patients requires estimation of pre-stroke spleen volume along with quantification of its day-to-day variation. We enrolled a cohort of 158 healthy volunteers and measured their spleen volume over the course of five consecutive days. We also enrolled a concurrent cohort of 158 stroke patients, measured initial spleen volume within 24 h of stroke symptom onset followed by daily assessments. Blood samples for cytokine analysis were collected from a subset of patients. Using data from healthy volunteers, we fit longitudinal quantile regression models to construct gender and body surface area based normograms of spleen volume. We quantified day-to-day variation and defined splenic contraction. Based on our criteria, approximately 40% of stroke patients experienced substantial post-stroke reduction in splenic volume. African Americans, older patients, and patients with past history of stroke have significantly higher odds of post-stroke splenic contraction. All measured cytokine levels were elevated in patients with splenic contraction, with significant differences for interferon gamma, interleukin 6, 10, 12, and 13. Our work provides reference standards for further work, validation of pre-clinical findings, and characterization of patients with post-stroke splenic contraction.

The spleen as an extramedullary source of inflammatory cells responding to acetaminophen-induced liver injury

Macrophages have been shown to play a role in acetaminophen (APAP)-induced hepatotoxicity, contributing to both pro- and anti-inflammatory processes. In these studies, we analyzed the role of the spleen as an extramedullary source of hepatic macrophages. APAP administration (300mg/kg, i.p.) to control mice resulted in an increase in CD11b(+) infiltrating Ly6G(+) granulocytic and Ly6G(-) monocytic cells in the spleen and the liver. The majority of the Ly6G(+) cells were also positive for the monocyte/macrophage activation marker, Ly6C, suggesting a myeloid derived suppressor cell (MDSC) phenotype. By comparison, Ly6G(-) cells consisted of 3 subpopulations expressing high, intermediate, and low levels of Ly6C. Splenectomy was associated with increases in mature (F4/80(+)) and immature (F4/80(-)) pro-inflammatory Ly6C(hi) macrophages and mature anti-inflammatory (Ly6C(lo)) macrophages in the liver after APAP; increases in MDSCs were also noted in the livers of splenectomized (SPX) mice after APAP. This was associated with increases in APAP-induced expression of chemokine receptors regulating pro-inflammatory (CCR2) and anti-inflammatory (CX3CR1) macrophage trafficking. In contrast, APAP-induced increases in pro-inflammatory galectin-3(+) macrophages were blunted in livers of SPX mice relative to control mice, along with hepatic expression of TNF-α, as well as the anti-inflammatory macrophage markers, FIZZ-1 and YM-1. These data demonstrate that multiple subpopulations of pro- and anti-inflammatory cells respond to APAP-induced injury, and that these cells originate from distinct hematopoietic reservoirs.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

Systemic inflammation as a therapeutic target in acute ischemic stroke

Acute systemic inflammatory reaction superimposed on chronic low-grade inflammation accompanies acute ischemic stroke. Elevated blood levels of systemic inflammatory markers such as IL-6 or C-reactive protein are associated with an unfavorable functional outcome and increased mortality after stroke. Animal studies have demonstrated a causal relationship between systemic inflammation and ischemic brain damage. The mechanisms linking systemic inflammation with poor outcome include increased neutrophil infiltration of cerebral cortex, disruption of the blood-brain barrier, impaired tissue reperfusion, increased platelet activation and microvascular coagulation and complement-dependent brain injury. Non-selective (e.g., by statins) or selective (e.g., by inhibition of IL-6) attenuation of systemic inflammation, enhancement of systemic anti-inflammatory response (e.g., by infusion of IL-1 receptor antagonist), prevention of infections that exacerbate systemic inflammation or inhibition of neuronal pathways triggering inflammatory reaction are potential therapeutic targets in stroke patients. This review discusses the relationship between systemic inflammation, cerebral ischemia and prognosis in the context of therapeutic strategies.