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

 So the research was incomplete, since nothing tells us how this gets us recovered. Further research needed that your doctors and hospital should initiate. NO EXCUSES!

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

• Justin N. Nguyen,
• Eric C. Mohan,
• Gargee Pandya,
• Uzma Ali,
• Chunfeng Tan,
• Julia K. Kofler,
• Linda Shapiro,
• Sean P. Marrelli &
• Anjali Chauhan 

Journal of Neuroinflammation volume 20, Article number: 232 (2023) Cite this article

• 108 Accesses

• Metrics details

Abstract

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.

Monocytes carrying GFAP detect glioma, brain metastasis and ischaemic stroke, and predict glioblastoma survival

 This would seem to be able to EXACTLY SPECIFY NEURONAL DEATH AT LEAST IN THE FIRST 48 HOURS. With that we could finally quantify the neurons killed off during the neuronal cascade of death. And with that we could beat over the head of stroke leadership that the neuronal cascade of death is worth preventing, because obviously nobody is listening to me.

Maybe your doctor will want you to create your own monocytes which means you will immediately post stroke be able to do sustained exercise. Which means 100% recovery within days. Now that is a BHAG(Big Hairy Audacious Goal, what is your doctor's plan to get there?

Training Monocytes by Physical Exercise

The latest here:

Monocytes carrying GFAP detect glioma, brain metastasis and ischaemic stroke, and predict glioblastoma survival

Wouter B L van den Bossche, Arnaud J P E Vincent, Cristina Teodosio, Jeroen Koets, Aladdin Taha, Anne Kleijn, Sandra de Bruin, Willem A Dik, Daniela Damasceno, Julia Almeida ... Show more

Brain Communications, Volume 3, Issue 1, 2021, fcaa215, https://doi.org/10.1093/braincomms/fcaa215

Published:

26 December 2020

Article history

Abstract

Diagnosis and monitoring of primary brain tumours, brain metastasis and acute ischaemic stroke all require invasive, burdensome and costly diagnostics, frequently lacking adequate sensitivity, particularly during disease monitoring. Monocytes are known to migrate to damaged tissues, where they act as tissue macrophages, continuously scavenging, phagocytizing and digesting apoptotic cells and other tissue debris. We hypothesize that upon completion of their tissue-cleaning task, these tissue macrophages might migrate via the lymph system to the bloodstream, where they can be detected and evaluated for their phagolysosomal contents. We discovered a blood monocyte subpopulation carrying the brain-specific glial fibrillary acidic protein in glioma patients and in patients with brain metastasis and evaluated the diagnostic potential of this finding. Blood samples were collected in a cross-sectional study before or during surgery from adult patients with brain lesions suspected of glioma. Together with blood samples from healthy controls, these samples were flowing cytometrically evaluated for intracellular glial fibrillary acidic protein in monocyte subsets. Acute ischaemic stroke patients were tested at multiple time points after onset to evaluate the presence of glial fibrillary acidic protein-carrying monocytes in other forms of brain tissue damage. Clinical data were collected retrospectively. High-grade gliomas (N = 145), brain metastasis (N = 21) and large stroke patients (>100 cm³) (N = 3 versus 6; multiple time points) had significantly increased frequencies of glial fibrillary acidic protein+CD16+ monocytes compared to healthy controls. Based on both a training and validation set, a cut-off value of 0.6% glial fibrillary acidic protein+CD16+ monocytes was established, with 81% sensitivity (95% CI 75–87%) and 85% specificity (95% CI 80–90%) for brain lesion detection. Acute ischaemic strokes of >100 cm³ reached >0.6% of glial fibrillary acidic protein+CD16+ monocytes within the first 2–8 h after hospitalization and subsided within 48 h. Glioblastoma patients with >20% glial fibrillary acidic protein+CD16+ non-classical monocytes had a significantly shorter median overall survival (8.1 versus 12.1 months). Our results and the available literature, support the hypothesis of a tissue-origin of these glial fibrillary acidic protein-carrying monocytes. Blood monocytes carrying glial fibrillary acidic protein have a high sensitivity and specificity for the detection of brain lesions and for glioblastoma patients with a decreased overall survival. Furthermore, their very rapid response to acute tissue damage identifies large areas of ischaemic tissue damage within 8 h after an ischaemic event. These studies are the first to report the clinical applicability for brain tissue damage detection through a minimally invasive diagnostic method, based on blood monocytes and not serum markers, with direct consequences for disease monitoring in future (therapeutic) studies and clinical decision making in glioma and acute ischaemic stroke patients.

Graphical Abstract

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Role of Immune Cells Migrating to the Ischemic Brain

I got nothing out of this that could help any survivor recover better. But since I'm not medically trained I obviously know nothing. 

Role of Immune Cells Migrating to the Ischemic Brain

Anna M. Planas

Originally published27 Aug 2018Stroke. 2018;49:2261-2267

The central nervous system and the immune system are tightly interconnected through complex communicating networks.¹ Immune cells are distributed in specific central nervous system compartments. Microglia are the innate immune cells resident in the brain parenchyma. Macrophages surround the blood vessels and also line the leptomeninges and the choroid plexus together with dendritic cells and lymphocytes, among other immune cells, where they play immunosurveillance functions. Therefore, the immune system keeps a close watch on brain function and reacts when brain homeostasis is lost because of injuries or diseases. Sterile organ damage may turn immune cells into harmful agents and for this reason they are regarded as targets for therapeutic intervention in acute stroke.² Stroke induces strong inflammatory reactions involving the local production of cytokines, such as TNF-α (tumor necrosis factor-α) by various brain cells, including human neurons,³ activation of glial and endothelial cells, blood-brain barrier damage, and infiltration of different types of leukocytes after an orchestrated time course.⁴ Given the variety of leukocyte subsets trafficking to the ischemic brain tissue, this review will focus on neutrophils, monocyte/macrophages, and T and NK (natural killer) lymphocytes. For further information, the readers are addressed to previous reviews on dendritic cells⁵ and B lymphocytes.⁶ The different immune cells are considered separately in the next sections, but leukocyte infiltration surely comprises intercellular crosstalks by mechanisms that are not entirely known.

Neutrophils

Neutrophils are among the first cells attracted to the brain after ischemic stroke where they are detected in the microvessels within the first hour⁷ and peak at 1 to 3 days.^4,7,8 Neutrophils are short-lived innate immune cells containing different types of granules with antimicrobial pro-oxidant and proteolytic enzymes that can damage the tissues. Accordingly, neutrophils are regarded as detrimental following compelling evidence associating these cells with blood-brain barrier breakdown and brain injury.^7,9 Also, higher blood neutrophil counts are associated with larger infarct volumes in acute ischemic stroke patients.¹⁰ Nevertheless, the pathogenic role of neutrophils in ischemic stroke is still not conclusive. For instance, there are conflicting results in the literature on the potential benefit of neutrophil depletion in experimental ischemia models.^9,11 Furthermore, we lack entire demonstration that neutrophils reach the ischemic tissue before substantial neuronal death has occurred.¹¹ Nonetheless, neutrophils can exert detrimental effects already from the vessel wall. Adhesion of neutrophils to the inflamed endothelium after ischemia/reperfusion is involved in the no-reflow phenomenon, obstructing blood flow in precapillary arterioles, postcapillary venules, and the capillary bed.^7,12 In addition, neutrophils in the vessel lumen and at perivascular locations can damage the blood-brain barrier by releasing proteolytic enzymes and pro-oxidant molecules (Figure).⁹ Moreover, neutrophils can produce NETs (neutrophil extracellular traps) promoting clot formation.¹³ NETs can precipitate thrombotic events and impair tPA (tissue-type plasminogen activator)-induced thrombolysis.¹⁴ In turn, thrombolysis may exacerbate detrimental effects of neutrophils because tPA promotes neutrophil transmigration to the reperfused tissue by proteolytic activation of plasmin and matrix metalloproteinases.¹⁵ These effects might contribute to explain why neutrophilia and high neutrophil-to-lymphocyte ratio are associated with the risk of hemorrhagic transformation in ischemic stroke patients treated with tPA.¹⁶ After permanent middle cerebral artery occlusion (MCAo) in mice, we observed the formation of intravascular NETs and found NETs in perivascular locations and in the brain parenchyma.¹⁷

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Figure. Schematic representation of leukocyte infiltration to the ischemic brain tissue. Neutrophils are attracted to the activated endothelium and reach perivascular spaces after extravasation from intracerebral venules and leptomeningeal vessels. Activated neutrophils are prothrombotic and can damage the blood-brain barrier (BBB). The presence of neutrophils in the brain parenchyma is observed only under certain circumstances, but the conditions determining that neutrophils remain in perivascular spaces or reach the parenchyma are still poorly defined. Attracted by certain chemokines, immature proinflammatory monocytes infiltrate the ischemic tissue where they mature to macrophages, acquire signs of alternative polarization, and seem to be involved in tissue repair. Current experimental evidence suggests that lymphocytes, in particular T cells and γδ T cells, play detrimental roles in the acute phase of stroke by promoting thromboinflammation and tissue damage. Natural killer (NK) cells are attracted to the ischemic tissue, but their function is not fully clear. RBC indicates red blood cells.

There is also some controversy on whether neutrophils actually reach the ischemic brain parenchyma at all. An elegant study by Enzmann et al¹⁸ noticed the massive accumulation of neutrophils in perivascular spaces surrounding venules within the ischemic tissue after ischemia/reperfusion in mice. Most neutrophils remained perivascular, and only a few were detected in the brain parenchyma.¹⁸ This is an important observation because it highlights that perivascular spaces are a niche for neutrophils where they accumulate after transient MCAo. We also detected neutrophils in perivascular locations and leptomeningeal spaces in the mouse after permanent MCAo.¹⁷ These results suggest that, besides extravasating from intracerebral venules, neutrophils extravasate from leptomeningeal vessels and migrate from the subpial space along the vessels penetrating the cortex.¹⁷ However, our study¹⁷ and previous studies⁷ found neutrophils in the ischemic brain parenchyma using models of permanent MCAo. Ischemic conditions involving severe endothelial damage, vessel rupture, and microbleeds or hemorrhagic transformation, are expected to facilitate the presence of neutrophils in the brain parenchyma. Other conditions, such as high blood glucose, also promote neutrophil infiltration.¹⁹ A recent study²⁰ analyzed the postmortem brain of 16 ischemic stroke patients and confirmed the presence of neutrophils in the leptomeninges and perivascular spaces, but neutrophils were rare in the infarcted parenchyma with the exception of 1 patient deceased 3 days after stroke with no signs of infection. Interestingly, the time to death of this series of patients was 1 day in 2 cases, 3 days in the case above mentioned, and then times ranged from 8 days to 240 days poststroke.²⁰ Neutrophils display a specific time-window of attraction to the damaged tissues after acute injuries, and they have a short life in tissues. Therefore, the time to death of ischemic stroke patients is critical to look for the presence of neutrophils in the brain parenchyma. More studies of human tissue within the first days poststroke are necessary to understand under which conditions neutrophils might gain access to the infarcted brain parenchyma.
Despite many advances, there are aspects of neutrophil behavior in stroke that are still difficult to interpret. For instance, neutrophils with anti-inflammatory and repair phenotypes were found in the ischemic brain tissue of experimental animals,²¹ neutrophils of ischemic stroke patients show a reduced oxidative burst and NET formation,²² and microglia surrounding blood vessels phagocyte neutrophils.²³ The possibility that neutrophils were passive bystanders under some circumstances but active players in others depending on specific features of the ischemic lesion needs further consideration.

Monocyte/Macrophages

After brain ischemia, microglia acquire a reactive morphology resembling macrophages. Classically, immunohistochemical studies have described the presence of reactive microglia/macrophages peaking at ≈4 days postischemia in rats or mice, but it was not possible to distinguish whether these cells derived from resident microglia or they infiltrated from the periphery. Nowadays, flow cytometry, cell type-specific fluorescent reporter mice, adoptive transfer of fluorescent cells, generation of chimeras, and recently identified specific microglia markers, allow differentiating resident reactive microglia from infiltrating macrophages. Monocyte infiltration is detected within the first 24 hours postischemia, peak at 4 days, and some of these cells persist for weeks and acquire features of tissue macrophages. Immature CCR2⁺Ly6C^hi proinflammatory monocytes are the subset of monocytes first attracted to the ischemic brain tissue.^24–26 These cells might be released by the bone marrow, but a study reported that monocytes reaching the ischemic brain originate in the spleen.²⁵
Infiltrating macrophages were classically associated with inflammation and brain damage after ischemic stroke. In mice, monocyte infiltration is largely dependent on CCR2 (C-C motif chemokine receptor type 2), the receptor of the chemokine CCL2 (C-C motif chemokine ligand 2), also known as MCP1 (monocyte chemoattractant protein 1). To investigate the role of monocytes, several studies used CCR2-deficient mice or CCR2 inhibitors, with the limitation that besides the subset of Ly6C^hi monocytes other cells, like some T cells, also express CCR2. CCR2-deficiency reduced the ischemic brain lesions in mice.²⁷ Challenging this view, CCR2 drug inhibitors exacerbated the brain lesion.²⁸ Furthermore, anti-CCR2 blocking antibodies impaired spontaneous long-term functional recovery,²⁹ depletion of monocytes/macrophages worsened the ischemic lesion,³⁰ and infiltrating macrophages prevented hemorrhagic transformation of the ischemic lesion.²⁴ By systemic injection of fluorescent monocytes after brain ischemia, we observed fluorescent cells in the subpial space, and along the vessels penetrating the cortex,²⁶ supporting the view that a subset of infiltrating macrophages establish persistent interactions with the blood vessels (Figure).
The phenotype of activated macrophages depends on the environmental stimuli. The M1 and M2 phenotypes are prototypical states of macrophage polarization achieved in culture after exposure to certain cytokines. The M1 phenotype is proinflammatory whereas the M2 phenotype promotes resolution of inflammation and repair. Macrophages infiltrating the ischemic tissue, including the Ly6C^lo population and some of the Ly6C^hi monocytes, acquire features of alternatively polarized M2 macrophages during the first week postischemia.^26,28–30 Studies of human ischemic infarcts reported that macrophages initially showed proinflammatory features that with lesion maturation transformed into anti-inflammatory phenotypes.²⁰ Interestingly, a study noticed that after ischemia in mice, the expression of M2 markers increased within the first week but then decreased, whereas proinflammatory markers persisted and predominated at week 2, suggesting a long-lasting inflammatory status.³¹
The factors that contribute to the time-dependent changes in macrophage phenotypes in the ischemic brain tissue are not entirely identified. Increased anaerobic glycolysis and activation of the hypoxia-inducible factor-1 are associated with proinflammatory M1 phenotypes, whereas energy production in M2 phenotypes rather relies on fatty acid oxidation.³² In M1 activated macrophages, arginine metabolism occurs through inducible nitric oxide synthase leading to generation of reactive oxygen and nitrogen species that damage proteins, lipids, and DNA. In contrast, M2 macrophages metabolize arginine through arginase-1 generating polyamines involved in cell division and collagen synthesis, among other functions.³² However, under pathological conditions 1 single phenotypic feature may not be sufficient to attribute any specific phenotype to the cells. Likely, cellular metabolic adaptations to ischemia and reperfusion together with the cytokine environment and phagocytic activity have an impact on the phenotype and function of macrophages and microglia.

Lymphocytes

T Cells

Severe stroke reduces the numbers of lymphocytes in the circulation and lymphoid organs.³³ In contrast, T-cell numbers increase in the ischemic brain within the first 24 hours and can persist for long times.⁴ During the first hours after ischemia/reperfusion, T cells facilitate adhesion of platelets and leukocytes to the vascular endothelium³⁴ causing a phenomenon called thromboinflammation³⁵ by which molecular and cellular players in thrombosis and coagulation promote proinflammatory pathways exacerbating the brain lesion.³⁶ However, the interaction of T cells with platelets may also have hemostatic effects preventing hemorrhagic transformation after severe ischemic stroke.³⁷ T cells are found in subpial and cortical vessels and infiltrating the ischemic lesion.^38,39 In addition, the choroid plexus is a gateway for T cells migrating to the periphery of cortical infarction.⁴⁰ Importantly, CD8⁺ cytotoxic T cells were detected in human ischemic infarcts.²⁰ Also, ischemic stroke patients show increased frequency of CD4⁺CD28^null cells in blood associated with stroke severity and serum levels of proinflammatory cytokines.⁴¹ CD4⁺CD28^null T cells are an interesting subset of T cells because they have enhanced effector functions, are associated with senescent T cells, and expand under inflammatory conditions.⁴² At later phases, CD4⁺ cells accumulate in the brain of mice peaking at day 14 and persisting at day 30 after ischemia/reperfusion.⁴³ Furthermore, emerging evidence suggests that antigen-mediated T-cell responses take place in subacute or chronic stages after stroke and may worsen stroke outcome.^43–47 However, in central nervous system trauma, protective autoimmunity mediated by T-cell responses is involved in promoting recovery.⁴⁸ Overall, T cells seem to play innate functions and interact with players in thrombosis and hemostasis in the acute phase of stroke, whereas at later stages they exert adaptive functions that could affect stroke outcome in the long term.

γδ T Cells

Subsets of unconventional innate T cells with invariant T-cell receptor could play a role in acute ischemic brain damage. Growing evidence supports that γδ T cells are pathogenic in experimental brain ischemia/reperfusion by secreting IL (interleukin)-17 and exacerbating the inflammatory response.^49–51 Moreover, IL-17A⁺ lymphocytes were detected in the postmortem brain of stroke patients.⁵⁰ Interestingly, γδ T cells are abundant in the gut from where they seem to traffic to the leptomeninges after brain ischemia.⁵² T helper 17 cells (Th17) and γδ T cells increase in the blood of stroke patients in association with increased levels of IL-17A, IL-23, IL-6, and IL-1β.⁵³ In spite of the fact that IL-17 producing cells are a small subset of cells, they seem to play a prominent role in orchestrating the inflammatory response in acute stroke and exacerbating the lesion (Figure).

Regulatory Lymphocytes

Regulatory lymphocytes exert immunomodulatory and immunosuppressor functions. Several lines of evidence support beneficial effects of regulatory T cells (Treg)⁵⁴ and regulatory B cells⁵⁵ in experimental brain ischemia. However, other studies found acute detrimental effects of Treg in brain ischemia/reperfusion⁵⁶ as previously reviewed.⁵⁷ Although the number of Treg found in the ischemic brain parenchyma during the first days poststroke is low, Treg strongly accumulate in the ischemic lesion 15 days poststroke where potentially they could inhibit autoimmune responses.⁴³ Increased apoptosis of Tregs, loss of Tregs in peripheral blood, and impaired suppressive function of the remaining Treg population has been reported in ischemic stroke patients.^53,58,59 However, other studies reported upregulation of Tregs in stroke patients in spite that decreased Treg function was observed, particularly in female patients.⁶⁰ Notably, an increased proportion of Treg cells was reported in the spleen of mice 4 days after transient MCAo.⁶¹

NK Cells

NK innate lymphocytes show a rapid and transient increase in the ischemic brain tissue.^4,8 A study reported no benefits of depleting NK cells in permanent or transient MCAo.⁴⁴ In contrast, another study suggested pathogenic actions of NK cells by promoting inflammation and neuronal cytotoxicity.⁶² This study reported infiltration of NK cells in the ischemic brain tissue of humans and mice where NK cell numbers peaked as soon as 3 hours postischemia and then declined.⁶² Interestingly, the β2-nACh-R (nicotinic acetylcholine) receptor seems to be involved in the NK cell decline observed in the ischemic tissue from 3 hours postischemia.⁶³ Induced-persistence of NK cells in the ischemic tissue achieved by interfering with this cholinergic receptor did not modify lesion size but increased systemic IFNγ (interferon γ), protected from bacterial infection, and enhanced poststroke survival.⁶³ More studies are needed to validate the putative capacity of brain infiltrating NK cells to prevent poststroke infection, the role of central acetylcholine in this process, as well as the suggested rapid pathogenic effect of NK cells worsening the acute ischemic brain lesion.

Therapeutic Intervention

Strategies designed to prevent negative actions of leukocytes have been taken to the clinic in acute ischemic stroke patients but with no success to date.⁶⁴ Several studies with drugs blocking the action of neutrophils were investigated.^11,64 As an example, the ASTIN trial (Acute Stroke Therapy by Inhibition of Neutrophils) investigated a compound known as UK-279 276, a recombinant neutrophil inhibitory factor that selectively binds the CD11b integrin of macrophage-1 antigen (CD11b/CD18).⁶⁵ The treatment did not improve recovery above placebo. This trial followed encouraging results of a few preclinical studies with UK-279 276 in experimental models of brain ischemia/reperfusion.⁶⁶ However, only a fifth of patients in the ASTIN trial received tPA.⁶⁵
Monocyte/macrophages may acutely exacerbate the inflammatory responses, but experimental studies have identified their involvement in resolution of inflammation, vascular protection, and recovery of function,^24,27–29 possibly linked to the phagocytic and vasculoprotective roles of these cells. These protective actions of monocytes are in line with the beneficial effects of administration of autologous bone marrow–derived mononuclear cells (MNC) after experimental ischemic stroke.⁶⁷ MNC contain myeloid and lymphoid cells, as well as hematopoietic and mesenchymal stem cells. MNC administration 24 hours after MCAo improved functional recovery, reduced lesion size and proinflammatory cytokines, and enhanced vessel density and neurogenesis,⁶⁸ and these benefits were long lasting.⁶⁹ Furthermore, MNC reduced blood-brain barrier permeability and decreased the severity of hemorrhagic transformation after tPA in an embolic stroke model.⁷⁰ However, MNC therapy did not improve outcome in hypertensive rats.⁷¹ MNC reach the periphery of brain infarction soon after administration,⁶⁸ and then the cells seem to differentiate into smooth muscle cells and endothelial cells, incorporate into vessel walls, and enhance the growth of leptomeningeal anastomoses, the circle of Willis, and basilar arteries.⁶⁹ Phase I trials administering MNC to ischemic stroke patients have shown safety, but the clinical efficacy of this cell therapy awaits demonstration.⁷²
Anti-inflammatory treatments, such as minocycline, have not been successful in the clinic.⁶⁴ Experimental evidences, including a cross-laboratory preclinical study in mouse models of brain ischemia,⁷³ support the therapeutic potential of the IL-1Ra (IL-1β receptor antagonist). A recent clinical trial with subcutaneous administration of IL-1Ra showed safety and reduction of plasma IL-6.⁷⁴ However, the analysis excluded a major clinical benefit of the treatment, and negative effects potentially attributable to interactions of IL-1Ra with tPA became apparent.⁷⁴
Experimental studies support damaging effects of T lymphocytes in the acute phase of stroke. Accordingly, fingolimod, a drug approved for remitting-relapsing multiple sclerosis that sequesters lymphocytes in the lymph nodes preventing lymphocyte access to the inflamed tissues, showed beneficial effects in preclinical studies and small clinical trials in acute ischemic stroke patients, including patients receiving thrombolysis.⁶⁴ By acting on S1P1 (sphingosine-1-phosphate receptor 1), fingolimod induces sustained lymphopenia, but current data do not show higher incidence of poststroke infection in patients receiving fingolimod. Fingolimod also acts on endothelial S1P1 receptor increasing vascular barrier function that might contribute to the observed benefits of this drug in ischemic stroke. Given that the benefits of fingolimod seem to be mediated by S1P1, whereas certain side effects are dependent on other S1P receptors, selective S1P1 agonists were studied in experimental stroke showing reduced lesion size after ischemia/reperfusion in mice.⁷⁵ In contrast to the benefits of blocking T-cell trafficking, systemic administration of regulatory T lymphocytes in rodent models of ischemic stroke reduced infarct size, ameliorated the neurological functions,⁷⁶ and reduced hemorrhagic transformation after tPA.⁷⁷
Leukocyte recruitment to inflammatory sites is attenuated by blocking α4β1 integrin (VLA-4 [very late antigen-4]) with natalizumab, an antibody in clinical use for multiple sclerosis treatment. Blockade of VLA-4 with CD49d antibody was investigated in a multicentric preclinical study in mice using 2 different models of cerebral ischemia.⁷⁸ CD49d antibody attenuated leukocyte infiltration and reduced infarct volume in small cortical lesions but not in large infarctions. Natalizumab was investigated in ischemic stroke patients in the ACTION trial (Effect of Natalizumab on Infarct Volume in Acute Ischemic Stroke).⁷⁹ Natalizumab did not meet the primary end point of the study, but secondary and exploratory end points suggested improvement of clinical outcomes,^64,79 encouraging the second ACTION2 trial. This phase-IIb trial was recently completed and the notes released by the sponsor (Biogen) state that natalizumab did not improve clinical outcomes compared with placebo.

Final Remarks

Experimental studies support detrimental effects of certain types of leukocytes in acute ischemic stroke. However, to date, this knowledge has not been translated into clinical treatments. No doubt immunomodulatory interventions in the acute phase of stroke need fine-tuning and long-term experimental studies to ensure that repair processes in subacute and chronic phases are not disturbed and the neurological deficits are attenuated. Cell therapies based on administration of autologous MNC have shown promising results in preclinical studies by promoting functional recovery, but clinical efficacy remains to be demonstrated. Results of various experimental models of brain ischemia suggest the possibility that the putative pathogenic contribution of certain leukocytes to the acute ischemic lesion might differ depending on lesion severity, regions affected, and degree of reperfusion. Importantly, most of the studies described above were obtained in young healthy male mice in spite of the fact that aging, sex, and comorbidities influence the phenotype and function of immune cells. Identification of the ischemic conditions where leukocytes might have a meaningful contribution to the brain lesion, the relevant subsets of leukocytes, and the time-window for intervention, requires more investigation. Combining immunomodulatory strategies with reperfusion therapies offer the opportunity to attenuate negative responses of the immune system that might impair reperfusion at the microvascular bed or trigger detrimental effects on the brain tissue.

Acknowledgments

I acknowledge relevant studies used to prepare this article that could not be cited because of word count restriction.

Sources of Funding

Supported by the Spanish Ministerio de Economía y Competitividad (SAF2017-87459-R).

Disclosures

None.

Footnotes

Correspondence to Anna M. Planas, PhD, Institut d’Investigacions Biomèdiques de Barcelona (IIBB), Consejo Superior de Investigaciones Científicas (CSIC), Rosselló 161, Planta 6, 08036-Barcelona, Spain. Email anna.planas@iibb.csic.es

The Role of Monocytes in Ischemic Stroke Pathobiology: New Avenues to Explore

Someplace in here a smart person could figure out what further research is needed to make something useful out of this. But since we don't have anyone in our stroke associations with two functioning neurons the answers will not be coming from there.

The Role of Monocytes in Ischemic Stroke Pathobiology: New Avenues to Explore

Ayman ElAli^1,2* and Noëmie Jean LeBlanc²

• ¹Neuroscience Axis, CHU de Québec Research Center (CHUL), Québec City, QC, Canada
• ²Department of Psychiatry and Neuroscience, Faculty of Medicine, Laval University, Québec City, QC, Canada

Ischemic stroke accounts for the majority of stroke cases and constitutes a major cause of death and disability in the industrialized world. Inflammation has been reported to constitute a major component of ischemic stroke pathobiology. In the acute phase of ischemic stroke, microglia, the resident macrophages of the brain, are activated, followed by several infiltration waves of different circulating immune cells into the brain. Among these circulating immune cells, monocytes have been shown to play a particularly important role. Following their infiltration, monocytes differentiate into potent phagocytic cells, the monocyte-derived macrophages (MDMs), in the ischemic brain. Initially, the presence of these cells was considered as marker of an exacerbated inflammatory response that contributes to brain damage. However, the recent reports are suggesting a more complex and multiphasic roles of these cells in ischemic stroke pathobiology. Monocytes constitute a heterogeneous group of cells, which comprises two major subsets in rodent and three major subsets in human. In both species, two equivalent subsets exist, the pro-inflammatory subset and the anti-inflammatory subset. Recent data have demonstrated that ischemic stroke differentially regulate monocyte subsets, which directly affect ischemic stroke pathobiology and may have direct implications in ischemic stroke therapies. Here, we review the recent findings that addressed the role of different monocyte subsets in ischemic stroke pathobiology, and the implications on therapies.

Introduction

Stroke is the third leading cause of death and the first cause of disability in industrialized world. Ischemic stroke accounts for the majority of stroke cases, whereas the remaining stroke cases are hemorrhagic (Dirnagl et al., 1999). Regional blood supply disruption initiates the ischemic cascade that leads to neuronal death and rapid loss of neuronal function (Dirnagl et al., 1999). The ischemic cascade is characterized by the activation of several signaling pathways that compromise cell survival and function (Mehta et al., 2007). Ischemic stroke triggers blood-brain barrier (BBB) breakdown, thus contributing to the secondary progression of ischemic injury by increasing brain edema and exacerbating the inflammatory response in the sub-acute phase (hours to days after ischemic stroke onset; Dirnagl et al., 1999; Fagan et al., 2004). The severity of these early events reduces the capacity of neurons to recover in the chronic phase (days to weeks after ischemic stroke onset), thus significantly worsening stroke outcomes (Moskowitz et al., 2010).

Inflammation plays a central role in ischemic stroke pathobiology (Jin et al., 2010). Following ischemic stroke, microglia, which are brain resident macrophages, are activated and circulating immune cells, such as monocytes, neutrophils and lymphocytes are recruited to injury site (Jin et al., 2010). Among these immune cells, monocytes that give rise to macrophages play a particularly important role (Chiba and Umegaki, 2013). Initially, the presence of monocytes at the injury site has been suggested to contribute to ischemic injury exacerbation in the acute phase (minutes to hours after ischemic stroke onset; Chen et al., 2003). However, the experimental approaches that aimed at depleting these cells in ischemic stroke animal models worsened ischemic injury by destabilizing brain microvasculature (Gliem et al., 2012). These reports outline the complex and multifaceted role of monocytes in ischemic stroke pathobiology. As such, this mini-review aims to summarize and discuss the recent findings that addressed the role of different monocyte subsets in ischemic stroke pathobiology, which may have direct implication on stroke therapies.

Training Monocytes by Physical Exercise

I'm sure your doctor knows how to train monocytes.

Training Monocytes by Physical Exercise

1. Elisa Avolio,
2. Gaia Spinetti,
3. Paolo Madeddu

+ Author Affiliations

1. From the Bristol Heart Institute, School of Clinical Sciences, University of Bristol, Bristol, United Kingdom (E.A., P.M.); and MultiMedica Research Institute, Milan, Italy (G.S.).

1. Correspondence to Paolo Madeddu, MD, Bristol Heart Institute, School of Clinical Sciences, University of Bristol, Upper Maudlin St, Bristol BS2 8HW, United Kingdom. E-mail mdprm@bristol.ac.uk

Peripheral artery disease is caused by obstructing atherosclerotic plaques that critically reduce blood flow during exercise. The disease affects ≈4% of people >40 years and 15% to 20% of subjects above 65 years of age. Critical limb ischemia, the most severe manifestation of peripheral artery disease, describes patients with chronic ischemic rest pain, or patients with ischemic skin lesions, either ulcers or gangrene. It requires foot amputation in 25% of cases within 1 year from the diagnosis. Revascularization therapies are indicated in critical limb ischemia patients, but they are often ineffective or unfeasible; and in the latter case, the reported amputation and mortality rates exceed 50%. Therefore, new therapeutic approaches are urgently needed.

See accompanying article on page 1862

Promotion of arteriogenesis, which refers to the enlargement and functionalization of preformed collateral arterioles, represents a promising therapeutic approach in critical limb ischemia patients. Several clinical studies have used the administration of growth factors (mostly basic fibroblast growth factor or vascular endothelial growth factor, either as protein or gene therapy) or stem and progenitor cells.¹ In addition, exercise rehabilitation programs have been shown to improve symptoms of claudication.^2,3 Mechanistic understanding of how physical exercise increases collateral artery formation is inadequate.

The new study from Schirmer et al⁴ shows that voluntary training confers mice with an improved capacity to recover from operatively induced limb ischemia when compared with sedentary controls. The positive outcome is associated with homing of inducible nitric oxide synthase (iNOS)-expressing mononuclear cells. The importance …

[Full Text of this Article]

From Hairballs to an Understanding of Transendothelial Migration of Monocytes in Atherosclerosis

If hairballs are listed in the full article I'm not paying for it. But ask your doctor for the explanation.
http://atvb.ahajournals.org/content/34/9/1809.extract?etoc

1. Mete Civelek,
2. Aldons J. Lusis

+ Author Affiliations

1. From the Departments of Medicine (M.C., A.J.L.), Microbiology, Immunology and Molecular Genetics, and Human Genetics (A.J.L.), University of California, Los Angeles.

1. Correspondence to Aldons J. Lusis, PhD, Division of Cardiology, Department of Medicine, A2-237 CHS, University of California, Los Angeles, Los Angeles, CA 90095. E-mail jlusis@mednet.ucla.edu

Key Words:

• Editorials
• leukocyte transmigration
• macrophage proliferation
• systems biology approach

In the current issue of ATVB, Shang et al provide compelling evidence for the involvement of LIM domain binding 2 (LDB2) in the transendothelial migration of monocytes in atherosclerosis.¹ The article is also of interest because of the systems analyses that led to its identification as a strong candidate.

See accompanying article on page 2068

LDB2 was identified earlier as a key driver of atherosclerosis based on studies of gene expression profiles of tissues obtained from patients.² Using samples from the Stockholm Atherosclerosis Gene Expression (STAGE) study, the authors profiled gene expression of 5 atherosclerosis-relevant tissues from 114 patients undergoing coronary artery bypass grafting. The tissues collected were distal internal mammary artery, wall of the ascending aorta at the aortic root, anterior hepatic edge, skeletal muscle, and visceral fat. A total of 278 gene expression profiles were used in a coupled 2-way clustering analysis³ to identify 60 gene subnetworks in these tissues. Two of the gene clusters, one in atherosclerotic arterial wall (49 genes) and the other in visceral fat (59 genes), segregated the patients according to the extent of atherosclerosis as measured by quantitative coronary angiography. The authors further validated their findings using expression data obtained from carotid lesions isolated from patients undergoing carotid stenosis surgery. Clustering of data identified 8 gene subnetworks in carotid lesions, one of which segregated the patients according to the extent of atherosclerosis as measured by ultrasound-measured intima-media thickness. This cluster significantly overlapped with the 2 previously identified clusters from …

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Neutrophils Usher Monocytes Into Sites of Inflammation

Our researchers need to understand this if we truly want to prevent strokes and clean up after the damage.
Neutrophils Usher Monocytes Into Sites of Inflammation

One of the key processes of inflammation is the transmigration of circulating leukocytes across the endothelium. Among the leukocytes, neutrophils and monocytes are large phagocytes that can respond quickly to infection or injury. On sensing danger, neutrophils and monocytes adhere to the endothelium and transmigrate to the adjacent tissue via the coordinated activities of adhesion molecules, integrins, cytokines, and chemokines.¹ Once they accumulate, these myeloid cells participate in a myriad of immune inflammatory activities. The importance of this event cannot be understated, especially because the accumulation of leukocytes in tissue is a double-edged sword. On the one hand, coordinated leukocyte accumulation in injured or infected sites is required for effective pathogen elimination and tissue healing. On the other hand, uncontrolled accumulation is a defining feature of chronic diseases, such as atherosclerosis.² Understanding leukocyte migration is essential to understanding the immune system.

Article, see p 792

Neutrophils and monocytes do not accumulate all at once. In a typical acute inflammatory response, there is a well-defined sequence: neutrophils accumulate first; monocytes accumulate second. Among the monocytes, of which ≥2 subsets circulate in the mouse and human, there is yet another sequence: inflammatory murine Ly-6C^high monocytes accumulate first and reparative Ly-6C^low monocytes accumulate second.³ This temporal (neutrophil ––> Ly-6C^high monocyte ––> Ly-6C^low monocyte) hierarchy of accumulation is likely required for an effective innate response. The subsets, which have overlapping but also specialized functions, contribute sequentially to processes that involve pathogen elimination, efferocytosis, restoration of tissue integrity,
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All About Monocyte Migrations

Finally a better understanding of how plaque forms. I wonder if watermelon juice contains this stuff?
http://www.medicalnewstoday.com/releases/256585.php
LMU researchers led by Christian Weber have, for the first time, elucidated how cells that promote the development of atherosclerosis find their way to the blood vessel wall, where they stimulate the formation of obstructive deposits.

Atherosclerosis is one of the commonest causes of death in modern societies. The condition is characterized by the build-up of fatty deposits called atherosclerotic plaques on the inner surfaces of arteries, which restrict, and may eventually cut off, blood flow. The deposits can also be dislodged from their site of origin and may then block major vessels in the heart or the brain, leading to life-threatening myocardial infarction or stroke.

Monocytes, an important class of white blood cells, are known to contribute significantly to the development of atherosclerosis. They are actively recruited to atherosclerotic lesions, and promote plaque development by sustaining a chronic inflammatory reaction.

Inhibition of monocyte recruitment therefore offers a way of interrupting the build-up of plaques. However, one first needs to know how the monocytes are actually localized to the vessel wall. Professor Christian Weber and Dr. Maik Drechsler of the Institute for Prophylaxis and Epidemiology of Cardiovascular Disease at LMU, in collaboration with Oliver Söhnlein of LMU and a team at the Academic Medical Center in Amsterdam, have now shown that the receptor molecules CCR1 and CCR5 are crucially involved in the process by which monocytes are recruited to the vessel wall. This process is made up of a sequence of distinct steps, including adhesion of the endothelial cells that form the arterial wall, and their subsequent transmigration into the bloodstream by infiltration between neighboring endothelial cells, following activation of the receptors by binding of their respective ligands.

The new findings correct a commonly held view of the precise function of the CCR2 receptor in the recruitment of monocytes. "In contrast to what has been assumed so far, this receptor does not mediate the infiltration of monocytes into the vessel wall; instead, like another chemokine receptor, CXCR2, it controls their mobilization from the bone marrow into the bloodstream," says Oliver Söhnlein.

The receptor molecules CCR1 and CCR5 therefore present promising targets for the development of novel approaches to the treatment of atherosclerosis, using agents that inhibit their interaction with their respective binding partners, either directly or indirectly. (EMBO Molecular Medicine)