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. 2010 Feb 3;87(5):779–789. doi: 10.1189/jlb.1109766

Inflammatory mechanisms in ischemic stroke: role of inflammatory cells

Rong Jin *, Guojun Yang †, Guohong Li *,1
PMCID: PMC2858674  PMID: 20130219

Abstract

Inflammation plays an important role in the pathogenesis of ischemic stroke and other forms of ischemic brain injury. Experimentally and clinically, the brain responds to ischemic injury with an acute and prolonged inflammatory process, characterized by rapid activation of resident cells (mainly microglia), production of proinflammatory mediators, and infiltration of various types of inflammatory cells (including neutrophils, different subtypes of T cells, monocyte/macrophages, and other cells) into the ischemic brain tissue. These cellular events collaboratively contribute to ischemic brain injury. Despite intense investigation, there are still numerous controversies concerning the time course of the recruitment of inflammatory cells in the brain and their pathogenic roles in ischemic brain injury. In this review, we provide an overview of the time-dependent recruitment of different inflammatory cells following focal cerebral I/R. We discuss how these cells contribute to ischemic brain injury and highlight certain recent findings and currently unanswered questions about inflammatory cells in the pathophysiology of ischemic stroke.

Keywords: inflammation, leukocytes, brain ischemia

Introduction

Stroke is the third leading cause of death and the most frequent cause of permanent disability worldwide [1], and inflammation appears to play an important role in the pathogenesis of ischemic stroke and other forms of ischemic brain injury. Clinically, the susceptibility of the patients to stroke and the subsequent prognosis are influenced by systemic inflammatory processes [2, 3]. Stroke patients with systemic inflammation exhibit clinically poorer outcomes [4,5,6]. Experimentally, focal cerebral ischemia induces a time-dependent recruitment and activation of inflammatory cells, including neutrophils, T cells, and monocytes/macrophages, and inhibiting the inflammatory response, decreases infarct size and improves neurological deficit in experimental stroke [7, 8]. Although anti-inflammatory approaches have proven successful in animal models [9,10,11], attempts to translate this into clinical application have been unsuccessful [12, 13], likely as a result of the heterogeneity in mechanisms underlying postischemic brain inflammation and the uncertain time window at which inflammation could be targeted in the human disease situation [13]. Thus, a comprehensive understanding of the time-dependent recruitment of inflammatory cells following focal cerebral I/R and how these cells differentially (and synergistically) contribute to ischemic brain injury is a prerequisite for developing effective therapeutic interventions for the treatment of acute ischemic stroke by targeting inflammatory pathways in a time-dependent manner.

Despite intense investigation, there are still numerous controversies concerning the time course of the recruitment of inflammatory cells in the brain and their pathogenic roles in ischemic brain injury. In the present review, we provide an overview of the time-dependent recruitment of different inflammatory cells following focal cerebral I/R. This review focuses on the potential contribution of these cells to ischemic brain injury and highlights recent findings and currently open questions regarding inflammatory cells in the pathophysiology of ischemic stroke.

EXPERIMENTAL STROKE MODELS AND LEUKOCYTE RECRUITMENT

Ischemic stroke results from transient or permanent reduction in regional cerebral blood flow. In humans, ischemic stroke occurs most often in the area perfused by the MCA [14]. Studies in animal models of stroke have provided an invaluable contribution to our current understanding of the pathophysiology of ischemic stroke [15]. One of the most relevant stroke models involves transient or permanent MCAO in the rats and mice [14, 15]. Rats are one of the most suitable species for stroke study because of the pathogenetic similarities of strokes in rats and humans [16]. In recent years, the importance of mouse MCAO models has increased rapidly with the development of transgenic or knockout techniques for a targeted single gene [15]. Currently, there are three main categories of transient MCAO: intraluminal MCAO with thread or wire filaments (the most widely used model in the literature); abluminal application of potent vasoconstrictor endothelin-1 to the MCA; and thromboembolic models, including photochemically induced thrombotic MCAO and the introduction of emboli into the cerebral circulation. The details of the design and operation of these animal stroke models have been described elsewhere [14, 15]. The results of the comparisons between transient and permanent MCAO models in rats and mice are summarized in Table 1.

TABLE 1.

Comparison of Transient and Permanent MCAO Stroke Models in Rats and Mice

Transient MCAO Permanent MCAO References
Reperfusion With MCA reperfusion after a defined period of focal cerebral ischemia. Without reperfusion. [14, 15]
Ischemic damage Lesions primarily in the ipsilateral cortex and striatum but also shown in hippocampus. Lesions primarily in the ipsilateral cortex but also shown in striatum. Lesion size in the cortex comparable with or larger than transient MCAO. [8,9,10, 15]
Leukocyte infiltration Inducing adhesion and infiltration of a large number of leukocytes in the ischemic brain tissue. Although inducing a significant amount of leukocyte rolling and adhesion in pial venules, only a small number of leukocytes infiltrated into ischemic tissue. [8,9,10, 15]
Antileukocyte (including antiadhesion molecule) therapy Immunoblocking or genetic deletion of a number of adhesion molecules (e.g., CD11b/CD18, ICAM-1, P-selectin) effectively reduces ischemic brain injury. Less effective. [9,10,11, 17,18,19,20,21]
Clinical relevance Generally appreciated, as most cases of human ischemic stroke have spontaneous or tPA-induced reperfusion. Limited, as human ischemic stroke is seldom permanent. [14, 15]
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Emerging data indicate that transient MCAO models may better mimic the pathophysiology of human stroke compared with permanent occlusion models in rats and mice (Table 1). In human stroke, cerebral vessel occlusion is seldom permanent, as most cases of human ischemic stroke have spontaneous or thrombolytic therapy-induced reperfusion [14, 15]. Leukocyte infiltration into the ischemic brain in transient MCAO models is more prominent, and antileukocyte strategies (including antiadhesion molecule strategies) have generally proven to be more effective in animal stroke models of transient but not permanent ischemia [8, 15]. For this reason, experimental studies about leukocyte recruitment and ischemic brain injury are now performed mostly using transient cerebral I/R models in rats and mice [8, 15].

TIME-DEPENDENT RECRUITMENT OF INFLAMMATORY CELLS DURING CEREBRAL I/R

The brain’s inflammatory responses to postischemia are characterized by a rapid activation of resident cells (mainly microglial cells), followed by the infiltration of circulating inflammatory cells, including granulocytes (neutrophils), T cells, monocyte/macrophages, and other cells in the ischemic brain region, as demonstrated in animal models [22,23,24,25] and in stroke patients [26,27,28,29]. In the acute phase (minutes to hours) of ischemic stroke, ROS and proinflammatory mediators (cytokines and chemokines) are released rapidly from injured tissue [22, 23]. These mediators induce the expression of the adhesion molecules on cerebral ECs and on leukocytes and thus, promote the adhesion and transendothelial migration of circulating leukocytes [8]. In the subacute phase (hours to days), infiltrating leukocytes release cytokines and chemokines, especially excessive production of ROS and induction/activation of MMP (mainly MMP-9), which amplify the brain-inflammatory responses further by causing more extensive activation of resident cells and infiltration of leukocytes, eventually leading to disruption of the BBB, brain edema, neuronal death, and hemorrhagic transformation [22, 23] (Fig. 1). However, many of these proinflammatory factors have a dual role at early and late stages of stroke. For instance, regardless of the cellular origin, MMP-9 has been shown to affect early ischemic brain damage detrimentally but promote brain regeneration and neurovascular remodeling in the later repair phase [22]. Thus, a thorough understanding of the time course of events leading to inflammation in ischemic brain injury is critical [23].

Figure 1.

Figure 1.

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Potential inflammatory pathways that respond to cerebral I/R. Mac-1 is a β2-integrin (CD11b/CD18); PSGL-1 actually functions as a ligand for E-/P-/L-selectins.

Resident microglia and blood-derived macrophages

Microglial cells, the resident macrophages of the brain, are activated rapidly in response to brain injury [30, 31]. Experimental data have shown that resident microglia are activated within minutes of ischemia onset and produce a plethora of proinflammatory mediators, including IL-1β and TNF-α, which exacerbate tissue damage [32,33,34] but may also protect the brain against ischemic and excitotoxic injury [35,36,37]. Postischemic microglial proliferation peaks at 48–72 h after focal cerebral ischemia and may last for several weeks after initial injury [38, 39]. In contrast to the rapid resident microglia response, blood-derived leukocytes are recruited to the brain tissue, usually with a delay of hours to a few days [24, 25, 40].

However, reactive microglia are morphologically and functionally similar to blood-derived monocyte/macrophages [24, 25]. To date, it has been difficult to distinguish these cells in the brain, as there is a lack of discriminating cellular markers [24, 41]. Blood-derived macrophages are able to acquire a ramified morphology indistinguishable from resident microglia, and reactive resident microglia can develop into a phagocytic phenotype indistinguishable from infiltrating macrophages. Fortunately, the use of chimeric mice with the GFP bone marrow provides a powerful tool to distinguish their roles and contributions in ischemic brain injury [24, 25, 41]. Most current data have shown that blood-derived macrophages are recruited into the ischemic brain tissue, most abundantly at Days 3–7 after stroke (but not significant prior to 3 days after cerebral ischemia) [41,42,43,44]. Schilling et al. [24, 41, 42] show that resident microglial activation precedes and predominates over blood-derived macrophage infiltration after transient MCAO in a chimeric mouse model. These studies demonstrated that neutrophils are the first blood-derived leukocytes seen at Day 1 in the damaged brain, whereas blood-derived macrophages (GFP-positive) were rarely observed at Day 2 but reached peak numbers at Day 7 and decreased thereafter. In contrast, resident microglial cells (GFP-negative) are already activated rapidly at Day 1 after focal cerebral ischemia. Intriguingly, even at Days 4 and 7, most macrophage-like cells remain GFP-negative, indicating that they are resident microglia-derived; however, in mouse models of transient MCAO [45] and permanent MCAO [25], others demonstrate that blood-derived macrophages (Iba1-positive) are infiltrated into the brain 24–48 h after focal cerebral ischemia, but the number of the infiltrating macrophages remains much lower than activated resident microglia. Together, most current data support the hypothesis that the vast majority of macrophage-like cells in the ischemic brain represents activated resident microglia, especially during the first few days following cerebral I/R injury.

Neutrophils

Of the various types of leukocytes, neutrophils are among the first to infiltrate ischemic brain (30 min to a few hours of focal cerebral ischemia), peak earlier (Days 1–3), and then disappear or decrease rapidly with time [8, 23]. However, the infiltrating neutrophils may remain more than 3 days or longer in the ischemic brain after focal cerebral I/R, but most likely, their existence is largely masked after 3 days by large-scale accumulation of activated microglia/macrophages in the inflammatory site [46]. In the rat model of endothelin-1-induced cerebral ischemia, Weston et al. [46] observed that neutrophil infiltration into the brain increases at 1 day, peaks at 3 days, and although reduced, continues through 7 and 15 days after cerebral ischemia.

A recent study seems to challenge the current view, as it provides evidence demonstrating that the recruitment of other inflammatory cells may precede neutrophil infiltration in response to cerebral ischemia [47]. In a mouse transient MCAO model, flow cytometric analysis of cell samples isolated from the ischemic brains shows that the majority of leukocyte cells in the ischemic hemisphere at 3 days after MCAO includes neutrophils [47], which is consistent with most reports in the literature [43, 48, 49]. However, an interesting observation is that the infiltration of other inflammatory cells, including macrophages, lymphocytes, and DCs, in the ischemic hemisphere precedes the neutrophilic influx [47].

T lymphocytes

Earlier studies suggest that lymphocyte recruitment into the brain is involved in the later stages of ischemic brain injury [50,51,52]. In a rat model of the photochemically induced focal ischemia, immunocytochemistry reveals that numerous T cells infiltrated the border zone around the infarct by Day 3, and the number of infiltrating T cells increased further between Days 3 and 7 [50]. In a mouse model of transient MCAO, flow cytometeric examination of the inflammatory cell infiltration in the ischemic brain reveals that (CD3+) T cells increased relatively late (3–4 days) postischemia, whereas activated (CD11b+) microglia/macrophages and (Ly6G+) neutrophils increased significantly at earlier times postischemia [52]. However, more recent studies in rodent models demonstrate that T cells accumulate in the ischemic brain within the first 24 h after focal cerebral I/R and may influence the evolution of tissue inflammation and injury prior to their appearance in the extravascular brain compartment [40, 53]. In recent years, increasing research efforts have been devoted to the roles of specific T cell subtypes in ischemic stroke. There are many subtypes of lymphocytes, and several subtypes of T cells have been implicated in the pathogenesis of ischemic stroke [8, 40]. However, the time course of the recruitment of different subtypes of T cells into the ischemic brain remains largely undetermined.

Other inflammatory cells

In addition to the above leukocytes, several other types of inflammatory cells such as DCs and MCs have been implicated recently in ischemic brain injury. These inflammatory cells are considered as early responders to act in the first-line defense in response to cerebral ischemia. In a mouse model of transient MCAO, Felger et al. [54] show that DCs accumulated in the ischemic hemisphere at 24 h after focal cerebral ischemia, particularly in the border region of the infarct where T cells accrued. MCs in the brain are typically located perivascularly and contain potent, fast-acting vasoactive and proteolytic substances. In a rat model of transient MCAO, Strbian et al. [55] show that brain MCs regulate early brain swelling and neutrophil accumulation at 4 h after ischemia.

In summary, our current knowledge about the time-dependent infiltration of inflammatory cells into the brain is based on immunohistochemistry and especially on flow cytometry of brain samples [47, 52]. However, there are important limitations of these approaches. For flow cytometric analysis, there is a need to isolate cells from brain tissue using enzymatic digestion ex vivo. The surface antigens for specific types of inflammatory cells may be modulated after the enzymatic digestion. In addition, immunohistochemistry and flow cytometry cannot examine dynamic alteration in the same animal as a result of a nonsurvival procedure. Similarly, our current knowledge about adhesive interactions of inflammatory cells with cerebral microcirculation after cerebral I/R is based on optical imaging technologies (especially on intravital microscopy), which allow for observation and quantification of cell adhesion to the walls of intact cerebral microvessels [8, 40]. There are important limitations of these approaches, including the need to examine microvessels on or near the brain surface, labeling the total leukocyte population, and being unable to assess early and late adhesive events in the same animal as a result of a nonsurvival procedure. Of note, there are many inconsistencies in the literature about the time course of the recruitment of various inflammatory cells in the brain following focal cerebral ischemia, even in the very same experimental animal models [47, 52] (Fig. 2).

Figure 2.

Figure 2.

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Schematic showing a time-dependent recruitment of inflammatory cells into the brain following focal cerebral ischemia in mice. The figure, adapted from (A) ref. [52] and (B) ref. [47] with permission. Note that a transient 60-min MCAO model in C57Bl6 mice was used in both reports.

With improvements in imaging technology and labeling methods, such as positron emission tomography/single photon emission tomography and functional MRI, it has now become possible to examine accurately inflammatory cell trafficking and the molecular activity (e.g., MPO and oxidative activity) noninvasively in ischemic brain parenchyma in living animals. Advanced imaging techniques and experimental approaches will provide the opportunity to visualize and assess more directly the dynamic profiles of specific inflammatory cell trafficking, adhesive interactions, and molecular activity of these inflammatory cells with cerebral microcirculation and with each other in the brains of living animals at early and late stages of cerebral I/R. The application of such imaging technologies and approaches should help to address some important unanswered questions about how these cells contribute to ischemic brain injury differentially and collaboratively.

ROLE OF ACTIVATED MICROGLIA/MACROPHAGES IN CEREBRAL I/R DAMAGE

Resident microglial cells are major inflammatory cells in the brain that are among the first cells to respond to brain injury, and multiple lines of evidence have shown that activated microglia play a dual role in ischemic stroke. Microglia exert neurotoxic functions through the production of ROS via NADPH oxidase [56], cytokines (IL-1β, IL-6, TNF-α) [30, 31], and MMP-9 [57]. These events precede leukocyte infiltration into the brain and may play a crucial role in mediating the initial increase in BBB permeability and the early infiltration of circulating leukocytes into the brain [56,57,58]. Microglia activation potentiates damage to BBB integrity, whereas inhibition of microglial activation may protect the brain after ischemic stroke by improving BBB viability and integrity in vivo and in vitro [58].

In contrast, activated microglia also appear to play a neuroprotective role after cerebral ischemia [59,60,61,62]. Production of neurotoxic and neuroprotective factors emphasizes the complex role of resident microglia in the process of tissue damage, neuronal survival, and regeneration in the response to cerebral ischemia. The protective role of microglia is possibly mediated by their ability to eliminate excess excitotoxins in the extracellular space, in part through phagocytosis of infiltrating neutrophils [39]. Further, accumulating evidence indicates that microglia can produce various neurotrophic factors such as neurotrophins and growth factors (fibroblast growth factor, TGF-β1), which are involved in neuronal survival and brain tissue repair in cases of brain injury [59,60,61,62]. Intriguingly, recent work [63] has identified a neuroprotective role for microglia-derived TNF in cerebral ischemia through TNF-p55R in mice.

Experimentally, TNF has neuroprotective and neurotoxic effects. Although TNF can be produced by microglia and infiltrating leukocytes in the brain, the neuroprotective effects of TNF appear to be attributed to microglia- but not leukocyte-derived TNF. These findings may have clinical relevance and potential applications. TNF is implicated in ischemic stroke and trauma in humans [64], where similar to the mouse [65, 66], it is produced by microglia and infiltrating leukocytes [67]. In addition, abundant evidence indicates a neuroprotective role of proliferating microglial cells in cerebral ischemia in vivo [38, 39]. Selective ablation of proliferating microglial cells exacerbates ischemic brain injury associated with a decrease in insulin-like growth factor-1 and an increase in cytokines (IL-1β, IL-6, TNF-α) [38].

As discussed above, activated microglia are morphologically and functionally indistinguishable from blood-derived monocyte/macrophages in the brain. Thus, it has been difficult to determine their distinct contribution to the pathogenesis of ischemic stroke. Nevertheless, the difference of the time course of their recruitment in the brain suggests that they contribute to ischemic brain injury in different time-dependent manners. Experimental studies using GFP bone marrow chimera mice indicate that blood-derived macrophage infiltration into the brain occurs at a later time after focal cerebral I/R [24, 25, 41]. These studies have revealed significant differences in terms of the ratio and contribution of resident microglia versus exogenous infiltrating macrophages to early postischemic cerebral injury. Resident microglia dominate over blood-derived macrophages during the first 3–4 days of cerebral I/R [24, 25, 41]. In the absence of blood-derived monocytes, brain microglia is able to differentiate into macrophages [56].

Regardless of their origin, activated microglia/macrophages seem to be critical in the clearance of infiltrating neutrophils after cerebral I/R. As discussed above, neutrophil infiltration occurs in the first 3 days after cerebral I/R, and thereafter, macrophage-like cells replace them as the dominant inflammatory cells in the ischemic site. The major pathway for clearance of infiltrating neutrophils and their potentially cytotoxic substances from the inflammatory sites is apoptosis followed by engulfment by activated microglia/macrophages [68,69,70,71]. Macrophages can resolve neutrophils and therefore, reduce neuronal injury by triggering neutrophil apoptosis, engulfing them, and thereby preventing the release of cytotoxic substances into the surrounding tissue [68, 69]. Induction of apoptosis and phagocytosis of apoptotic neutrophils by reactive microglia/macrophages is a critical step in the resolution of the inflammatory response and in preventing further exacerbation of the ischemic injury [69, 71]. In a rat model of endothelin-1-induced cerebral ischemia, Weston et al. [46, 72] demonstrate that large-scale emigration of neutrophils into the ischemic region occurs during the first day and peaks at 3 days after cerebral ischemia. Double immunostaining clearly shows that macrophages (stained by ED-1) engulf neutrophils (stained by anti-polymorphonuclear neutrophil sera) in the brain and that this engulfment of invading neutrophils increases with time (50% of neutrophils in the brain are engulfed at 3 days and 85% at 15 days) [46]. Nevertheless, it is unclear whether the “ED-1-stained cells” in the brain represent activated resident microglia or/and infiltrating macrophages.

ROLE OF NEUTROPHIL INFILTRATION IN CEREBRAL I/R DAMAGE

Despite intense investigation, the exact role of neutrophils in the pathogenesis of ischemic stroke remains under debate. Most experimental and clinical studies support the importance of neutrophil infiltration in ischemic stroke. In animal models of focal cerebral I/R, recruitment of neutrophils in the ischemic brain occurs within 30 min to a few hours and peaks in the first 3 days [8, 23]. Genetic deficiency or antibody blockade of leukocyte adhesion molecules (e.g., ICAM-1, CD11b/CD18, P-selectin) [8,9,10,11, 17,18,19,20,21, 49] has been shown to reduce infarct volume, brain edema, neurological deficits, and mortality in animal models of ischemic stroke. These protective effects appear to be more effective in the transient but not permanent MCAO models in rats and mice. Clinical studies have confirmed that neutrophils accumulate intensively in the regions of human cerebral infarction, and this accumulation is correlated with the severity of the brain tissue damage and poor neurological outcome after ischemic stroke [28, 29, 73]. Furthermore, total leukocyte and neutrophil counts are increased in the first 3 days after symptom onset in stroke patients, and this is associated with larger final infarct volumes (on CT and MRI) and increased stroke severity [27, 29]. A number of potential mechanisms may explain how activation and accumulation of neutrophils contribute to the pathogenesis of ischemic stroke. These mechanisms include: excessive production of ROS, such as superoxide and hypochlorous acid via NADPH oxidase and MPO, respectively; release of a variety of proinflammatory cytokines (IL-1β, IL-6, TNF-α) and chemokines (MCP-1, MIP-1α, IL-8); release of elastase and MMPs (mainly MMP-9); and enhancing expression of leukocyte β2-integrins (Mac-1, LFA-1) and adhesion molecules (PSGL-1, L-selectin). By these mechanisms, infiltrating neutrophils amplify a cerebral inflammatory response that may exacerbate ischemic brain injury further [8, 22, 23] (Fig. 1). Nevertheless, the pathogenic role of neutrophils in ischemic stroke remains uncertain, and some studies fail to demonstrate a clear correlation between neutrophil infiltration and infarct formation [74,75,76,77,78,79].

Recent studies suggest that neutrophil infiltration may play a more prominent role in the pathogenesis of ischemic stroke in individuals with elevated systemic inflammation. In stroke patients with prior infection, total leukocyte and neutrophil counts and the extent of leukocyte-platelet adhesion and activation are elevated in the circulation [29, 80, 81]. Recent experimental studies have shown that systemic inflammation exacerbates neutrophil infiltration in the brain and thus, alters the kinetics of the BBB tight junction disruption after experimental stroke in mice [4, 82]. These studies clearly demonstrate that infiltrating neutrophils are the primary source of increased (fivefold) MMP-9 activity in the ischemic brain of IL-1β-challenged mice at 4, 8, or 24 h after MCAO. A transformation from transient to sustained BBB disruption caused by enhanced neutrophil-derived neurovascular MMP-9 is a critical mechanism underlying the exacerbation of ischemic brain injury by systemic inflammation, mediated through conversion of a transient to a sustained disruption of the tight junction protein, claudin-5, and markedly exacerbated disruption of the cerebrovascular basal lamina protein, collagen-IV [82]. These molecular mechanisms may contribute to the poor clinical outcome in stroke patients presenting with antecedent infection. Stroke patients presenting with an elevated systemic inflammatory status may be at increased risk of MMP-9-mediated neurovascular proteolysis and hemorrhagic transformation [83], particularly when recombinant tPA is administered for thrombolytic therapy, as tPA is known to promotes neutrophil degranulation and MMP-9 release [84, 85]. In this regard, it is critical to better understand the exact roles of neutrophils in the pathogenesis of ischemic stroke under clinically relevant conditions that are linked to an elevated systemic inflammatory status, such as prior infection, atherosclerosis, type 2 diabetes, obesity, and rheumatoid arthritis.

ROLE OF DIFFERENT SUBTYPES OF T LYMPHOCYTES IN CEREBRAL I/R DAMAGE

In recent years, considerable research efforts have been devoted to understanding the roles of lymphocytes in ischemic brain injury. Several subtypes of T cells have been implicated in the pathogenesis of ischemic stroke, and accumulating evidence indicates that different subtypes of T cells play differential roles in response to cerebral I/R injury.

CD4+ and CD8+ T cells

Experimental evidence indicates that in the vascular bed of other organs (e.g., intestine, liver, and kidney), CD4+ and CD8+ T cells contribute importantly to the pathogenesis of I/R injury [86,87,88]. Recent work has shown that CD4+ and CD8+ T cells are major contributors to brain inflammation in a mouse model of transient MCAO. Studies using intravital video microscopy show that Rag1(−/−), CD4+ T cell(−/−), CD8+ T cell(−/−), and IFN-γ(−/−) mice have comparable, significant reductions in cerebral I/R-induced leukocyte and platelet adhesion in cerebral microcirculation, compared with wild-type mice after exposure to focal cerebral I/R [40]. Futhermore, data indicate that CD4+ and CD8+ T cells contribute to the inflammatory and thrombogenic responses, brain infarction, and neurological deficit associated with experimental stroke [40]. Moreover, experimental studies have shown that CD4+ TH1 cells may play a key role in the pathogenesis of stroke through releasing proinflammatory cytokines, including IL-2, IL-12, IFN-γ, and TNF-α, whereas CD4+ TH2 cells may play a protective role through anti-inflammatory cytokines such as IL-4, IL-5, IL-10, and IL-13 [89]. It is important to note that some of these cytokines, especially IFN-γ, are known to be critical in prevention of infections, which are a leading cause of death in stroke patients, especially in the postacute phase of stroke [90], which results mainly from immunodepression caused by depletion of circulating T cell and NK cell populations and therefore, the antibacterial cytokine IFN-γ in the early reperfusion period [90]. Therefore, treatment of stroke patients by targeting T cells must be designed carefully to evaluate and reduce deleterious and enhance protective actions of specific T cell subtypes.

Treg cells

Treg cells come in many forms, including CD4+CD25+ forkhead box p3+ T cells (Tregs) and other subsets. Treg cells play a key part in controlling immune responses under physiological conditions and in various systemic and CNS inflammatory diseases [91,92,93]. Experimental data have shown that Treg cells are capable of modulating effector T cell function and secreting anti-inflammatory cytokines (IL-10, TGF-β) [94, 95]. These actions enable Treg cells to be pivotal players in the fields of self-tolerance, immunologic homeostasis, and damage control at the site of inflammation [96]. More recently, an elegant study by Liesz et al. [97] reveals that the Treg cells are key cerebroprotective immunomodulators in acute experimental stroke in mice. They found that Treg cells prevent secondary infarct growth by counteracting excessive production of proinflammatory cytokines and by modulating invasion and/or activation of lymphocytes and microglia in the ischemic brain. Depletion of Treg cells increases delayed brain damage profoundly and deteriorates functional outcome, and Treg cells antagonize enhanced TNF-α and IFN-γ production, which induce delayed inflammatory brain damage. Also, Treg cell-derived secretion of IL-10 is the key mediator of cerebroprotection via suppression of deleterious cerebral cytokine (TNF-α, IFN-γ) production. Absence of Treg cells augmented postischemic activation of resident and infiltrating inflammatory cells including microglia and T cells, the main sources of cerebral TNF-α and IFN-γ [97, 98], respectively. TNF-α expression is elevated early after ischemia in the brain, where it is generated predominantly by microglia. Whereas IFN-γ is almost absent in normal brain tissue, its expression increases at a later time-point after cerebral ischemia than does TNF-α expression, and its expression is strongly induced after Treg cell depletion. Taken together, these findings reveal a previously unknown role of the Treg cells as cerebroprotective immunomodulators after stroke, thus potentially providing new insights into the endogenous adaptive immune response after acute brain ischemia.

γδT cells

γδT cells represent a small subset of T cells that possesses a distinct TCR on their surface. A majority of T cells has a TCR composed of two glycoprotein chains, called α and β TCR chains. In contrast, in γδT cells, the TCR is made up of one γ-chain and one δ-chain. This group of T cells is usually much less common than αβT cells [99]. The conditions that lead to responses of γδT cells are not fully understood, and current concepts of γδT cells as “first line of defense”, “regulatory cells”, or “bridge between innate and adaptive responses” [99] only address facets of their complex behavior. A recent study by Shibata et al. [100] demonstrates that resident γδT cells control early infiltration of neutrophils in the peritoneal cavity of mice after Escherichia coli infection. They indicate that a rapid and transient production of IL-17 after i.p. infection with E. coli precedes the influx of neutrophils. Flow cytometric analysis of intracellular cytokine demonstrates that the γδT cell population is the major source of IL-17. Neutralization of IL-17 results in a reduced infiltration of neutrophils and impaired bacterial clearance. Mice depleted of γδT cells by anti-TCR-γδ mAb treatment have diminished IL-17 production and reduced neutrophil infiltration after E. coli infection [100]. More recently, an elegant study by Shichita et al. [101] reveals a pivotal role of cerebral IL-17-producing γδT cells in the delayed phase of ischemic brain injury. In a mouse model of transient MCAO, they demonstrate that the infiltration of T cells into the brain as well as the production of cytokines IL-17 and IL-23 play pivotal roles in the evolution of brain infarction and accompanying neurological deficits. Blockade of T cell infiltration into the brain by the immunosuppressant FTY720 reduced cerebral I/R damage. The expression of IL-23 (most likely derived from activated microglia/macrophages) [102, 103] increases on Day 1 after I/R, whereas IL-17 levels are elevated after Day 3, and this induction of IL-17 was dependent on IL-23. Immunohistochemistry shows that γδT cells are localized in the infarct boundary zones at 4 days after cerebral I/R. Intracellular cytokine staining confirms that γδT cells are a major source of IL-17. Further, gene knockouts demonstrate that IL-23 functions in the immediate stage of cerebral I/R injury, whereas IL-17 is an important role in the delayed phase of cerebral I/R injury, during which apoptotic neuronal death occurs in the penumbra. A significant reduction in infarct volume is observed in TCR-γδ knockout mice, as well as in mice treated with TCR-γδ-specific antibody [100]. These findings reveal a previously unknown role of the γδT cells in the pathogenesis of ischemic stroke. Therefore, the γδT cells could be a novel, therapeutic target for limiting the inflammatory events that amplify the initial damage during cerebral I/R.

ROLE OF OTHER INFLAMMATORY CELLS IN CEREBRAL I/R DAMAGE

DCs

DCs are immune cells that form part of the mammalian immune system and constitute key elements in the control of immune activation or immune tolerance [104]. Their main function is to process antigen material and present it on the surface to other cells of the immune system, thus functioning as effective APCs [105]. There are at least two major lineages of DCs [106]: mDCs, which respond to bacteria and fungi, releasing IL-12, and pDCs, which release IFN-α upon viral infection. Both lineages are detected as DCPs in blood, patrolling through the circulation and invading the tissue in response to a local infection or other inflammatory situation. mDCs and/or pDCs appear to play a role in several proinflammatory diseases, especially atherosclerosis [104, 107]. In multiple sclerosis, mDCs invade the human brain, subsequently triggering cerebral inflammation [108].

Several clinical and experimental studies suggest the potential importance of DCs in cerebral inflammation and tissue injury during ischemic stroke [54, 109, 110]. Using flow cytometeric analysis of blood samples, Yilmaz et al. [109] found that acute stroke leads to a significant but transient decrease in circulating DCPs within 24 h after symptom onset in stroke patients, and patients with large stroke size in CT scan have significantly lower mDCP, pDCP, and total DCPs than those with smaller stroke. Follow-up analysis shows a significant recovery of circulating DCP in the first 2–4 days after stroke. Double immunohistochemical staining demonstrates colocalization of mDCs and T cells and a high expression of HLA-DR close to mDCs observed, suggesting that mDCs are mature and able to activate T cells in the infarcted brain [109]. Thus, circulating DCPs may be recruited into the infarcted brain and thereby trigger cerebral immune/inflammatory reactions in the brain. This view is also supported by previous findings that have shown that DCs are present in the ischemic brain in a rat model of permanent MCAO [110]. Immunohistochemistry showed that numbers of DCs are low in nonischemic (sham) brains but are elevated in the ischemic hemispheres at 1 h (11-fold increase) and increase further in the 6-day observation period with an 84-fold increase at 6 days after MCAO. Activated DCs expressing MHC-II remain elevated at 6 days after MCAO in the ischemic versus nonischemic hemispheres [110]. More recently, Gelderblom et al. [47] demonstrate that DCs are increased by 20-fold on Day 3 and 12-fold on Day 7 and thus, constituted a substantial proportion of infiltrating cells. DCs exhibit a significant up-regulation of MHC-II, and the increase of DCs is even more pronounced if only MHCII high-expressing DCs are analyzed (100-fold increase). To date, there is no direct experimental evidence showing the correlation between the increase of DC numbers and brain infarction in cerebral ischemia. Nevertheless, these previous observations may constitute a basis for further studies about DCs in the pathogenesis of ischemic stroke.

MCs

MCs reside in a variety of locations in the brain of different species, including humans, where they appear to be concentrated in the diencephalic parenchyma, thalamus, and cerebral cortex [111, 112]. Their subendothelial and perivascular location at the boundary between the intravascular and extravascular milieus and their ability to respond rapidly to blood- and tissue-borne stimuli via release of potent vasodilatory, proteolytic, fibrinolytic, and proinflammatory mediators render MCs with a unique status to act in the first-line defense in various pathologies [55]. Experimental evidence indicates an emerging role of mast cells in cerebral ischemic injury and hemorrhage [55]. In experimental cerebral I/R, MCs regulate BBB permeability, brain edema formation, and the intensity of local neutrophil infiltration [55]. Strbian et al. [113] demonstrate that cerebral MCs regulate early ischemic brain swelling and neutrophil accumulation in a rat model of transient MCAO. Pharmacological MC-blocking (sodium cromoglycate) leads to a 39% decrease in brain swelling, and compound 48/80 (MC-degranulating agent) elevates it by 89%. Early ischemic BBB leakage and postischemic neutrophil infiltration are significantly lower in MC-deficient rats than in the wild-type. In addition, MCs appear to play a role in the tPA-mediated cerebral hemorrhages after experimental ischemic stroke and to be involved in the expansion of hematoma and edema following intracerebral hemorrhage [113, 114]. MC stabilization was reported to reduce hemorrhagic transformation and mortality after administration of thrombolytics in experimental ischemic stroke [114]. Thus, MC stabilization may provide an adjuvant therapy in treatment of acute ischemic stroke in patients.

ANTI-INFLAMMATORY THERAPY

The pathologic processes after ischemic stroke can be separated into acute (within hours), subacute (hours to days), and chronic (days to months) phases [115, 116]. Clinical and experimental data show an acute and prolonged inflammatory response in the brain after stroke, and leukocyte recruitment is a hallmark feature of the prolonged inflammatory response that occurs over hours to days after cerebral ischemia [117, 118]. Experimental stroke studies demonstrate that reperfusion represents an especially vulnerable period for the brain [8,9,10,11], as it provides the potential benefits of restoring blood flow to an ischemic region and simultaneously opens the flood gates for a massive influx of activated leukocytes into ischemic tissue. Thereby, the subacute reperfusion period after a stroke is considered more amenable to treatment than acute neurotoxicity [116,117,118]. It is hypothesized that stroke outcomes may be improved by antileukocyte strategies (including antiadhesion molecule strategies), which are targeted specifically to the reperfusion period. This hypothesis is supported by numerous experimental findings [8, 15]. As discussed above, inhibition of leukocyte infiltration into the ischemic brain via antiadhesion molecules (e.g., CD11b/CD18, ICAM-1, P-selectin) has been shown to reduce infarct size, edema, and neurological deficits in transient MCAO stroke models in rats and mice [9,10,11, 17,18,19,20,21, 72], but the benefits do not extend to permanent MCAO [9, 10]. Further, experimental studies demonstrate that antileukocyte strategies may extend the therapeutic time window of tPA reperfusion therapy in acute stroke [8, 15]. For example, in a rat thromboembolic stroke model, UK-279276 treatment reduces infarct size only in combination with tPA and prolongs the efficacy “time window” for tPA from 2 h to 4 h [11]. UK-279276 is a recombinant glycoprotein and is a selective antagonist of the CD11b integrin of Mac-1 (CD11b/CD18) and has been shown to reduce neutrophil infiltration and infarct volume in the transient MCAO model in rats when administered within 4 h after onset of ischemia [119]. These results raise the question of whether antileukocyte strategies provide an effective therapy for stroke patients.

Clinically, several drugs that target neutrophil recruitment have been developed as potential therapies for ischemic stroke. Three such drugs were tested in clinical trials: a mAb to ICAM-1 (Enlimomab, R6.5) [12], a humanized antibody to the CD11b/CD18 (Hu23F2G or LeukArrest) [13], and the UK-279276 [120]. All clinical trials with these drugs have been unsuccessful as a result of lack of neuroprotective efficacy and side-effects such as leukopenia and immunosuppression. These clinical outcomes further intensify the debate over the role of neutrophils in ischemic stroke [74,75,76,77,78,79] and raise the question of whether inflammation in general and neutrophils in particular may serve as useful therapeutic targets in treatment of human stroke.

Despite intense investigation, it remains unclear why anti-inflammatory therapy succeeded in animal models but not in clinical application. Can animal models truly replicate human stroke? The main limitations of the most current animal studies include at least the following: limited clinical relevance of the experiments in animal stroke models that are performed in young and healthy animals and normal physiological conditions and targeting single-cell type (mainly neutrophils) and single adhesion molecule (e.g., ICAM-1 or CD11b/CD18). It is widely acknowledged that no single animal model replicates human stroke perfectly, and the current animal models do not replicate the complexities of human stroke. Nevertheless, animal models can provide mechanistic insights that have correlated quite well with clinical findings in terms of the pathophysiology of stroke [15].

In addition to neutrophils, in recent years, considerable research has been devoted to understanding the roles of other cell types, in particular, T lymphocyte subtypes in ischemic brain injury. Many relevant questions remain largely unanswerable, at least at present; for example, how different inflammatory cells work together in the brain after stroke (in temporal and spatial domains with different time-dependent manners) and whether (and how) these cells function in a common pathway contributing to the pathogenesis of ischemic stroke. There are no definitive answers to questions such as these, because of the complexity and multiplicity of the mechanisms by which inflammatory cells contribute to ischemic brain damage. Not only do different types of inflammatory cells contribute differentially to the pathogenesis of ischemic stroke, but also, the same cell type may play different roles in different stages of ischemic stroke. Moreover, the same molecule produced by different cells (e.g., microglia- and leukocyte-derived TNF-α) may play different roles [63, 64]. Nevertheless, oxidative stress might serve as a common pathway for different inflammatory cells [56]. Oxidative stress is an important mediator of tissue injury in acute ischemic stroke. During ischemic stroke, ROS are generated by various types of inflammatory cells and trigger the expression of a number of proinflammatory genes, including cytokines and adhesion molecules, which play an important role in leukocyte-endothelium interactions and secondary brain damage after cerebral ischemia. These proinflammatory genes are regulated by oxidant-sensitive transcription factors (e.g., NF-κB) [56].

CONCLUSIONS

Emerging data suggest that inflammatory cells play complex and multiphasic roles after ischemic stroke, and most of the cell types display beneficial and adverse effects. There is a growing body of evidence that inflammatory cell infiltration is predominantly deleterious in the early phase after ischemic stroke. Antileukocyte strategies (including antiadhesion molecule strategies) reduce ischemic brain injury in animal models; however, attempts to translate experimental findings into clinical therapies have been unsuccessful. Most likely, targeting a single cell type or single adhesion molecule is not a feasible way to treat human stroke. Many relevant questions remain to be answered; for example, how different inflammatory cells work together in the brain after stroke; whether (and how) these cells contribute to the pathogenesis of ischemic stroke via a common pathway; and how to evaluate and reduce deleterious and enhance protective actions of specific types of inflammatory cells. By addressing these questions, future research might provide novel, alternative stroke mechanisms and develop new therapeutic directions for ischemic stroke. Future efforts should be directed toward defining the time-dependent interactions between inflammatory cells and their interactions with cerebral vasculature with advanced brain imaging technologies and other approaches in animal models and human stroke patients. Future basic research should be performed under clinical relevant conditions linked to elevated inflammatory states, such as prior infection, atherosclerosis, and type 2 diabetes. More sophisticated therapies with pleiotropic beneficial effects and more sophisticated targeting of potential inflammatory cells (and molecules) will increase the likelihood of successful clinical translation [116].

AUTHORSHIP

The concept, design, and writing of the manuscript: Guohong Li; the literature search and discussion of the manuscript: Rong Jin and Guojun Yang, who equally contributed to this work.

ACKNOWLEDGMENTS

The work was supported by the National Institutes of Health grant HL087990 (G.L.) and by a Scientist Development grant (0530166N) from American Heart Association (G.L.). We give special thanks to Dr. Michael Wyss for critical review of this manuscript.

Footnotes

Abbreviations: BBB=blood-brain barrier, CT=computed tomography, DC=dendritic cell, DCP=DC precursor, EC=endothelial cell, I/R=ischemia and reperfusion, LFA-1=lymphocyte function associated antigen 1, Mac-1=leucocyte integrin CD11B/CD18, MC=mast cell, MCA=middle cerebral artery, MCAO=MCA occlusion, mDC=myeloid DC, MMP=matrix metalloproteinase, MPO=myeloperoxidase, MRI=magnetic resonance imaging, pDC=plasmacytoid DC, PSGL-1=P-selectin glycoprotein ligand-1, ROS=reactive oxygen species, tPA=tissue plasminogen activator, Treg cell=T regulatory cell

References

  1. Donnan G A, Fisher M, Macleod M, Davis S M. Stroke. Lancet. 2008;371:1612–1623. doi: 10.1016/S0140-6736(08)60694-7. [DOI] [PubMed] [Google Scholar]
  2. Emsley H C, Hopkins S J. Acute ischaemic stroke and infection: recent and emerging concepts. Lancet Neurol. 2008;7:341–353. doi: 10.1016/S1474-4422(08)70061-9. [DOI] [PubMed] [Google Scholar]
  3. McColl B W, Allan S M, Rothwell N J. Systemic infection, inflammation and acute ischemic stroke. Neuroscience. 2009;158:1049–1061. doi: 10.1016/j.neuroscience.2008.08.019. [DOI] [PubMed] [Google Scholar]
  4. McColl B W, Rothwell N J, Allan S M. Systemic inflammatory stimulus potentiates the acute phase and CXC chemokine responses to experimental stroke and exacerbates brain damage via interleukin-1- and neutrophil-dependent mechanisms. J Neurosci. 2007;27:4403–4412. doi: 10.1523/JNEUROSCI.5376-06.2007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Elkind M S, Cheng J, Rundek T, Boden-Albala B, Sacco R L. Leukocyte count predicts outcome after ischemic stroke: the Northern Manhattan Stroke Study. J Stroke Cerebrovasc Dis. 2004;13:220–227. doi: 10.1016/j.jstrokecerebrovasdis.2004.07.004. [DOI] [PubMed] [Google Scholar]
  6. Baird T A, Parsons M W, Barber P A, Butcher K S, Desmond P M, Tress B M, Colman P G, Jerums G, Chambers B R, Davis S M. The influence of diabetes mellitus and hyperglycemia on stroke incidence and outcome. J Clin Neurosci. 2002;9:618–626. doi: 10.1054/jocn.2002.1081. [DOI] [PubMed] [Google Scholar]
  7. Wang X. Investigational anti-inflammatory agents for the treatment of ischemic brain injury. Expert Opin Investig Drugs. 2005;14:393–409. doi: 10.1517/13543784.14.4.393. [DOI] [PubMed] [Google Scholar]
  8. Yilmaz G, Granger D N. Cell adhesion molecules and ischemic stroke. Neurol Res. 2008;30:783–793. doi: 10.1179/174313208X341085. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Zhang R L, Chopp M, Jiang N, Tang W X, Prostak J, Manning A M, Anderson D C. Anti-intercellular adhesion molecule-1 reduces ischemic cell damage after transient but not permanent middle cerebral artery occlusion in the Wistar rat. Stroke. 1995;26:1438–1443. doi: 10.1161/01.str.26.8.1438. [DOI] [PubMed] [Google Scholar]
  10. Prestigiacomo C J, Kim S C, Liao H, Yan S F, Pinsky D J. CD18-mediated neutrophil recruitment contributes to the pathogenesis of reperfused but not nonreperfused stroke. Stroke. 1999;30:1110–1117. doi: 10.1161/01.str.30.5.1110. [DOI] [PubMed] [Google Scholar]
  11. Zhang L, Zhang Z G, Zhang R L, Lu M, Krams M, Chopp M. Effects of a selective CD11b/CD18 antagonist and recombinant human tissue plasminogen activator treatment alone and in combination in a rat embolic model of stroke. Stroke. 2003;34:1790–1795. doi: 10.1161/01.STR.0000077016.55891.2E. [DOI] [PubMed] [Google Scholar]
  12. Enlimomab Acute Stroke Trial Investigators Use of anti-ICAM-1 therapy in ischemic strokes: results of the Enlimomab Acute Stroke Trial. Neurology. 2001;57:1428–1434. doi: 10.1212/wnl.57.8.1428. [DOI] [PubMed] [Google Scholar]
  13. Becker K J. Anti-leukocyte antibodies: LeukArrest (Hu23F2G) and Enlimomab (R6.5) in acute stroke. Curr Med Res Opin. 2002;18:s18–s22. doi: 10.1185/030079902125000688. [DOI] [PubMed] [Google Scholar]
  14. Mhairi Macrae I. New models of focal cerebral ischemia. Br J Clin Pharmacol. 1992;34:302–308. doi: 10.1111/j.1365-2125.1992.tb05634.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Lo E H. Experimental models, neurovascular mechanisms and translational issues in stroke research. Br J Pharmacol. 2008;153, S1:S396–S405. doi: 10.1038/sj.bjp.0707626. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Yamori Y, Horie R, Handa H, Sato M, Fukase M. Pathogenetic similarity of strokes in stroke-prone spontaneously hypertensive rats and humans. Stroke. 1976;7:46–53. doi: 10.1161/01.str.7.1.46. [DOI] [PubMed] [Google Scholar]
  17. Kitagawa K, Matsumoto M, Mabuchi T, Yagita Y, Ohtsuki T, Hori M, Yanagihara T. Deficiency of intercellular adhesion molecule 1 attenuates microcirculatory disturbance and infarction size in focal cerebral ischemia. J Cereb Blood Flow Metab. 1998;18:1336–1345. doi: 10.1097/00004647-199812000-00008. [DOI] [PubMed] [Google Scholar]
  18. Soriano S G, Coxon A, Wang Y F, Frosch M P, Lipton S A, Hickey P R, Mayadas T N. Mice deficient in MAC-1 (CD11B/CD18) are less susceptible to cerebral ischemia/reperfusion injury. Stroke. 1999;30:134–139. doi: 10.1161/01.str.30.1.134. [DOI] [PubMed] [Google Scholar]
  19. Chopp M, Zhang R L, Chen H, Li Y, Jiang N, Rusche J R. Postischemic administration of an anti-Mac-1 antibody reduces ischemic cell damage after transient middle cerebral artery occlusion in rats. Stroke. 1994;25:869–875. doi: 10.1161/01.str.25.4.869. [DOI] [PubMed] [Google Scholar]
  20. Ishikawa M, Stokes K Y, Zhang J H, Nanda A, Granger D N. Cerebral microvascular responses to hypercholesterolemia: roles of NADPH oxidase and P-selectin. Circ Res. 2004;94:239–244. doi: 10.1161/01.RES.0000111524.05779.60. [DOI] [PubMed] [Google Scholar]
  21. Ishikawa M, Cooper D, Arumugam T V, Zhang J H, Nanda A, Granger D N. Platelet-leukocyte-endothelial cell interactions after middle cerebral artery occlusion and reperfusion. J Cereb Blood Flow Metab. 2004;24:907–915. doi: 10.1097/01.WCB.0000132690.96836.7F. [DOI] [PubMed] [Google Scholar]
  22. Amantea D, Nappi G, Bernardi G, Bagetta G, Corasaniti M T. Post-ischemic brain damage: pathophysiology and role of inflammatory mediators. FEBS J. 2009;276:13–26. doi: 10.1111/j.1742-4658.2008.06766.x. [DOI] [PubMed] [Google Scholar]
  23. Kriz J. Inflammation in ischemic brain injury: timing is important. Crit Rev Neurobiol. 2006;18:145–157. doi: 10.1615/critrevneurobiol.v18.i1-2.150. [DOI] [PubMed] [Google Scholar]
  24. Schilling M, Besselmann M, Leonhard C, Mueller M, Ringelstein E B, Kiefer R. Microglial activation precedes and predominates over macrophage infiltration in transient focal cerebral ischemia: a study in green fluorescent protein transgenic bone marrow chimeric mice. Exp Neurol. 2003;183:25–33. doi: 10.1016/s0014-4886(03)00082-7. [DOI] [PubMed] [Google Scholar]
  25. Tanaka R, Komine-Kobayashi M, Mochizuki H, Yamada M, Furuya T, Migita M, Shimada T, Mizuno Y, Urabe T. Migration of enhanced green fluorescent protein expressing bone marrow-derived microglia/macrophage into the mouse brain following permanent focal ischemia. Neuroscience. 2003;117:531–539. doi: 10.1016/s0306-4522(02)00954-5. [DOI] [PubMed] [Google Scholar]
  26. Lindsberg P J, Carpén O, Paetau A, Karjalainen-Lindsberg M L, Kaste M. Endothelial ICAM-1 expression associated with inflammatory cell response in human ischemic stroke. Circulation. 1996;94:939–945. doi: 10.1161/01.cir.94.5.939. [DOI] [PubMed] [Google Scholar]
  27. Gerhard A, Neumaier B, Elitok E, Glatting G, Ries V, Tomczak R, Ludolph A C, Reske S N. In vivo imaging of activated microglia using [11C]PK11195 and positron emission tomography in patients after ischemic stroke. Neuroreport. 2000;11:2957–2960. doi: 10.1097/00001756-200009110-00025. [DOI] [PubMed] [Google Scholar]
  28. Price C J, Menon D K, Peters A M, Ballinger J R, Barber R W, Balan K K, Lynch A, Xuereb J H, Fryer T, Guadagno J V. Cerebral neutrophil recruitment, histology, and outcome in acute ischemic stroke: an imaging-based study. Stroke. 2004;35:1659–1664. doi: 10.1161/01.STR.0000130592.71028.92. [DOI] [PubMed] [Google Scholar]
  29. Buck B H, Liebeskind D S, Saver J L, Bang O Y, Yun S W, Starkman S, Ali L K, Kim D, Villablanca J P, Salamon N, Razinia T, Ovbiagele B. Early neutrophilia is associated with volume of ischemic tissue in acute stroke. Stroke. 2008;39:355–360. doi: 10.1161/STROKEAHA.107.490128. [DOI] [PubMed] [Google Scholar]
  30. Aloisi F. Immune function of microglia. Glia. 2001;36:165–179. doi: 10.1002/glia.1106. [DOI] [PubMed] [Google Scholar]
  31. Nakajima K, Kohsaka S. Microglia: activation and their significance in the central nervous system. J Biochem. 2001;130:169–175. doi: 10.1093/oxfordjournals.jbchem.a002969. [DOI] [PubMed] [Google Scholar]
  32. Banati R B, Gehrmann J, Schubert P, Kreutzberg G W. Cytotoxicity of microglia. Glia. 1993;7:111–118. doi: 10.1002/glia.440070117. [DOI] [PubMed] [Google Scholar]
  33. Barone F C, Arvin B, White R F, Miller A, Webb C L, Lysko P G, Feuerstein G Z. Tumor necrosis factor-α: a mediator of focal ischemic brain injury. Stroke. 1997;28:1233–1244. doi: 10.1161/01.str.28.6.1233. [DOI] [PubMed] [Google Scholar]
  34. Rothwell N, Allan S, Toulmond S. The role of interleukin 1 in acute neurodegeneration and stroke: pathophysiological and therapeutic implications. J Clin Invest. 1997;100:2648–2652. doi: 10.1172/JCI119808. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Mattson M P, Barger S W, Furukawa K, Bruce A J, Wyss-Coray T, Mark R J, Mucke L. Cellular signaling roles of TGFβ, TNF α and β APP in brain injury responses and Alzheimer’s disease. Brain Res Brain Res Rev. 1997;23:47–61. doi: 10.1016/s0165-0173(96)00014-8. [DOI] [PubMed] [Google Scholar]
  36. Raivich G, Bohatschek M, Kloss C U, Werner A, Jones L L, Kreutzberg G W. Neuroglial activation repertoire in the injured brain: graded response, molecular mechanisms and cues to physiological function. Brain Res Brain Res Rev. 1999;30:77–105. doi: 10.1016/s0165-0173(99)00007-7. [DOI] [PubMed] [Google Scholar]
  37. Hallenbeck J M. The many faces of tumor necrosis factor in stroke. Nat Med. 2002;8:1363–1368. doi: 10.1038/nm1202-1363. [DOI] [PubMed] [Google Scholar]
  38. Lalancette-Hébert M, Gowing G, Simard A, Weng Y C, Kriz J. Selective ablation of proliferating microglial cells exacerbates ischemic injury in the brain. J Neurosci. 2007;27:2596–2605. doi: 10.1523/JNEUROSCI.5360-06.2007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Denes A, Vidyasagar R, Feng J, Narvainen J, McColl B W, Kauppinen R A, Allan S M. Proliferating resident microglia after focal cerebral ischaemia in mice. J Cereb Blood Flow Metab. 2007;27:1941–1953. doi: 10.1038/sj.jcbfm.9600495. [DOI] [PubMed] [Google Scholar]
  40. Yilmaz G, Arumugam T V, Stokes K Y, Granger D N. Role of T lymphocytes and interferon-γ in ischemic stroke. Circulation. 2006;113:2105–2112. doi: 10.1161/CIRCULATIONAHA.105.593046. [DOI] [PubMed] [Google Scholar]
  41. Schilling M, Besselmann M, Muller M, Strecker J K, Ringelstein E B, Kiefer R. Predominant phagocytic activity of resident microglia over hematogenous macrophages following transient focal cerebral ischemia: an investigation using green fluorescent protein transgenic bone marrow chimeric mice. Exp Neurol. 2005;196:290–297. doi: 10.1016/j.expneurol.2005.08.004. [DOI] [PubMed] [Google Scholar]
  42. Schilling M, Strecker J K, Schäbitz W R, Ringelstein E B, Kiefer R. Effects of monocyte chemoattractant protein 1 on blood-borne cell recruitment after transient focal cerebral ischemia in mice. Neuroscience. 2009;161:806–812. doi: 10.1016/j.neuroscience.2009.04.025. [DOI] [PubMed] [Google Scholar]
  43. Breckwoldt M O, Chen J W, Stangenberg L, Aikawa E, Rodriguez E, Qiu S, Moskowitz M A, Weissleder R. Tracking the inflammatory response in stroke in vivo by sensing the enzyme myeloperoxidase. Proc Natl Acad Sci USA. 2008;105:18584–18589. doi: 10.1073/pnas.0803945105. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. Petry K G, Boiziau C, Dousset V, Brochet B. Magnetic resonance imaging of human brain macrophage infiltration. Neurotherapeutics. 2007;4:434–442. doi: 10.1016/j.nurt.2007.05.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Kokovay E, Li L, Cunningham L A. Angiogenic recruitment of pericytes from bone marrow after stroke. J Cereb Blood Flow Metab. 2006;26:545–555. doi: 10.1038/sj.jcbfm.9600214. [DOI] [PubMed] [Google Scholar]
  46. Weston R M, Jones N M, Jarrott B, Callaway J K. Inflammatory cell infiltration after endothelin-1-induced cerebral ischemia: histochemical and myeloperoxidase correlation with temporal changes in brain injury. J Cereb Blood Flow Metab. 2007;27:100–114. doi: 10.1038/sj.jcbfm.9600324. [DOI] [PubMed] [Google Scholar]
  47. Gelderblom M, Leypoldt F, Steinbach K, Behrens D, Choe C U, Siler D A, Arumugam T V, Orthey E, Gerloff C, Tolosa E, Magnus T. Temporal and spatial dynamics of cerebral immune cell accumulation in stroke. Stroke. 2009;40:1849–1857. doi: 10.1161/STROKEAHA.108.534503. [DOI] [PubMed] [Google Scholar]
  48. Jin G, Tsuji K, Xing C, Yang Y G, Wang X, Lo E H. CD47 gene knockout protects against transient focal cerebral ischemia in mice. Exp Neurol. 2009;217:165–170. doi: 10.1016/j.expneurol.2009.02.004. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Connolly E S, Jr, Winfree C J, Springer T A, Naka Y, Liao H, Yan S D, Stern D M, Solomon R A, Gutierrez-Ramos J C, Pinsky D J. Cerebral protection in homozygous null ICAM-1 mice after middle cerebral artery occlusion. Role of neutrophil adhesion in the pathogenesis of stroke. J Clin Invest. 1996;97:209–216. doi: 10.1172/JCI118392. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Jander S, Kraemer M, Schroeter M, Witte O W, Stoll G. Lymphocytic infiltration and expression of intercellular adhesion molecule-1 in photochemically induced ischemia of the rat cortex. J Cereb Blood Flow Metab. 1995;15:42–51. doi: 10.1038/jcbfm.1995.5. [DOI] [PubMed] [Google Scholar]
  51. Campanella M, Sciorati C, Tarozzo G, Beltramo M. Flow cytometric analysis of inflammatory cells in ischemic rat brain. Stroke. 2002;33:586–592. doi: 10.1161/hs0202.103399. [DOI] [PubMed] [Google Scholar]
  52. Stevens S L, Bao J, Hollis J, Lessov N S, Clark W M, Stenzel-Poore M P. The use of flow cytometry to evaluate temporal changes in inflammatory cells following focal cerebral ischemia in mice. Brain Res. 2002;932:110–119. doi: 10.1016/s0006-8993(02)02292-8. [DOI] [PubMed] [Google Scholar]
  53. Hurn P D, Subramanian S, Parker S M, Afentoulis M E, Kaler L J, Vandenbark A A, Offner H. T- and B-cell-deficient mice with experimental stroke have reduced lesion size and inflammation. J Cereb Blood Flow Metab. 2007;27:1798–1805. doi: 10.1038/sj.jcbfm.9600482. [DOI] [PMC free article] [PubMed] [Google Scholar]
  54. Felger J C, Abe T, Kaunzner U W, Gottfried-Balckmore A, Gal-Toth J, McEwen B S, Iadecola C, Bulloch K. Brain dendritic cells in ischemic stroke: time course, activation state, and origin. Brain Behav Immun. 2009 doi: 10.1016/j.bbi.2009.11.002. Epub ahead of print. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Strbian D, Kovanen P T, Karjalainen-Lindsberg M L, Tatlisumak T, Lindsberg P J. An emerging role of mast cells in cerebral ischemia and hemorrhage. Ann Med. 2009;1:1–13. doi: 10.1080/07853890902887303. [DOI] [PubMed] [Google Scholar]
  56. Pun P B, Lu J, Moochhala S. Involvement of ROS in BBB dysfunction. Free Radic Res. 2009;43:348–364. doi: 10.1080/10715760902751902. [DOI] [PubMed] [Google Scholar]
  57. del Zoppo G J, Milner R, Mabuchi T, Hung S, Wang X, Berg G I, Koziol J A. Microglial activation and matrix protease generation during focal cerebral ischemia. Stroke. 2007;38:646–651. doi: 10.1161/01.STR.0000254477.34231.cb. [DOI] [PubMed] [Google Scholar]
  58. Yenari M A, Xu L, Tang X N, Qiao Y, Giffard R G. Microglia potentiate damage to blood-brain barrier constituents: improvement by minocycline in vivo and in vitro. Stroke. 2006;37:1087–1093. doi: 10.1161/01.STR.0000206281.77178.ac. [DOI] [PubMed] [Google Scholar]
  59. Streit W J. Microglia as neuroprotective, immunocompetent cells of the CNS. Glia. 2002;40:133–139. doi: 10.1002/glia.10154. [DOI] [PubMed] [Google Scholar]
  60. Nakajima K, Kohsaka S. Microglia: neuroprotective and neurotrophic cells in the central nervous system. Curr Drug Targets Cardiovasc Haematol Disord. 2004;4:65–84. doi: 10.2174/1568006043481284. [DOI] [PubMed] [Google Scholar]
  61. Neumann J, Gunzer M, Gutzeit H O, Ullrich O, Reymann K G, Dinkel K. Microglia provide neuroprotection after ischemia. FASEB J. 2006;20:714–716. doi: 10.1096/fj.05-4882fje. [DOI] [PubMed] [Google Scholar]
  62. Kato H, Tanaka S, Oikawa T, Koike T, Takahashi A, Itoyama Y. Expression of microglial response factor-1 in microglia and macrophages following cerebral ischemia in the rat. Brain Res. 2000;882:206–211. doi: 10.1016/s0006-8993(00)02811-0. [DOI] [PubMed] [Google Scholar]
  63. Lambertsen K L, Clausen B H, Babcock A A, Gregersen R, Fenger C, Nielsen H H, Haugaard L S, Wirenfeldt M, Nielsen M, Dagnaes-Hansen F, Bluethmann H, Faergeman N J, Meldgaard M, Deierborg T, Finsen B. Microglia protect neurons against ischemia by synthesis of tumor necrosis factor. J Neurosci. 2009;29:1319–1330. doi: 10.1523/JNEUROSCI.5505-08.2009. [DOI] [PMC free article] [PubMed] [Google Scholar]
  64. Zaremba J, Losy J. Early TNF-α levels correlate with ischemic stroke severity. Acta Neurol Scand. 2001;104:288–295. doi: 10.1034/j.1600-0404.2001.00053.x. [DOI] [PubMed] [Google Scholar]
  65. Gregersen R, Lambertsen K, Finsen B. Microglia and macrophages are the major source of tumor necrosis factor in permanent middle cerebral artery occlusion in mice. J Cereb Blood Flow Metab. 2000;20:53–65. doi: 10.1097/00004647-200001000-00009. [DOI] [PubMed] [Google Scholar]
  66. Lambertsen K L, Meldgaard M, Ladeby R, Finsen B. A quantitative study of microglial-macrophage synthesis of tumor necrosis factor during acute and late focal cerebral ischemia in mice. J Cereb Blood Flow Metab. 2005;25:119–135. doi: 10.1038/sj.jcbfm.9600014. [DOI] [PubMed] [Google Scholar]
  67. Dziewulska D, Mossakowski M J. Cellular expression of tumor necrosis factor α and its receptors in human ischemic stroke. Clin Neuropathol. 2003;22:35–40. [PubMed] [Google Scholar]
  68. Meszaros A J, Reichner J S, Albina J E. Macrophage phagocytosis of wound neutrophils. J Leukoc Biol. 1999;65:35–42. doi: 10.1002/jlb.65.1.35. [DOI] [PubMed] [Google Scholar]
  69. Meszaros A J, Reichner J S, Albina J E. Macrophage-induced neutrophil apoptosis. J Immunol. 2000;165:435–441. doi: 10.4049/jimmunol.165.1.435. [DOI] [PubMed] [Google Scholar]
  70. Neumann J, Sauerzweig S, Rönicke R, Gunzer F, Dinkel K, Ullrich O, Gunzer M, Reymann K G. Microglia cells protect neurons by direct engulfment of invading neutrophil granulocytes: a new mechanism of CNS immune privilege. J Neurosci. 2008;28:5965–5975. doi: 10.1523/JNEUROSCI.0060-08.2008. [DOI] [PMC free article] [PubMed] [Google Scholar]
  71. Savill J. Apoptosis in resolution of inflammation. J Leukoc Biol. 1997;61:375–380. doi: 10.1002/jlb.61.4.375. [DOI] [PubMed] [Google Scholar]
  72. Weston R M, Jarrott B, Ishizuka Y, Callaway J K. AM-36 modulates the neutrophil inflammatory response and reduces breakdown of the blood brain barrier after endothelin-1 induced focal brain ischemia. Br J Pharmacol. 2006;149:712–723. doi: 10.1038/sj.bjp.0706918. [DOI] [PMC free article] [PubMed] [Google Scholar]
  73. Akopov S E, Simonian N A, Grigorian G S. Dynamics of polymorphonuclear leukocyte accumulation in acute cerebral infarction and their correlation with brain tissue damage. Stroke. 1996;27:1739–1743. doi: 10.1161/01.str.27.10.1739. [DOI] [PubMed] [Google Scholar]
  74. Beray-Berthat V, Palmier B, Plotkine M, Margaill I. Neutrophils do not contribute to infarction, oxidative stress, and no synthase activity in severe brain ischemia. Exp Neurol. 2003;182:446–454. doi: 10.1016/s0014-4886(03)00106-7. [DOI] [PubMed] [Google Scholar]
  75. Emerich D F, Dean R L, III, Bartus R T. The role of leukocytes following cerebral ischemia: pathogenic variable or bystander reaction to emerging infarct? Exp Neurol. 2002;173:168–181. doi: 10.1006/exnr.2001.7835. [DOI] [PubMed] [Google Scholar]
  76. Fassbender K, Ragoschke A, Kuhl S, Szabo K, Fatar M, Back W, Bertsch T, Kreisel S, Hennerici M. Inflammatory leukocyte infiltration in focal cerebral ischemia: unrelated to infarct size. Cerebrovasc Dis. 2002;13:198–203. doi: 10.1159/000047776. [DOI] [PubMed] [Google Scholar]
  77. Hayward N J, Elliott P J, Sawyer S D, Bronson R T, Bartus R T. Lack of evidence for neutrophil participation during infarct formation following focal cerebral ischemia in the rat. Exp Neurol. 1996;139:188–202. doi: 10.1006/exnr.1996.0093. [DOI] [PubMed] [Google Scholar]
  78. Soriano S G, Wang Y F, Wagner D D, Frenette P S. P- and E-selectin-deficient mice are susceptible to cerebral ischemia–reperfusion injury. Brain Res. 1999;835:360–364. doi: 10.1016/s0006-8993(99)01637-6. [DOI] [PubMed] [Google Scholar]
  79. Takeshima R, Kirsch J R, Koehler R C, Gomoll A W, Traystman R J. Monoclonal leukocyte antibody does not decrease the injury of transient focal cerebral ischemia in cats. Stroke. 1992;23:247–252. doi: 10.1161/01.str.23.2.247. [DOI] [PubMed] [Google Scholar]
  80. Emsley H C, Smith C J, Gavin C M, Georgiou R F, Vail A, Barberan E M, Hallenbeck J M, del Zoppo G J, Rothwell N J, Tyrrell P J, Hopkins S J. An early and sustained peripheral inflammatory response in acute ischaemic stroke: relationships with infection and atherosclerosis. J Neuroimmunol. 2003;139:93–101. doi: 10.1016/s0165-5728(03)00134-6. [DOI] [PubMed] [Google Scholar]
  81. Zeller J A, Lenz A, Eschenfelder C C, Zunker P, Deuschl G. Platelet-leukocyte interaction and platelet activation in acute stroke with and without preceding infection. Arterioscler Thromb Vasc Biol. 2005;25:1519–1523. doi: 10.1161/01.ATV.0000167524.69092.16. [DOI] [PubMed] [Google Scholar]
  82. McColl B W, Rothwell N J, Allan S M. Systemic inflammation alters the kinetics of cerebrovascular tight junction disruption after experimental stroke in mice. J Neurosci. 2008;28:9451–9462. doi: 10.1523/JNEUROSCI.2674-08.2008. [DOI] [PMC free article] [PubMed] [Google Scholar]
  83. Rosell A, Ortega-Aznar A, Alvarez-Sabín J, Fernández-Cadenas I, Ribó M, Molina C A, Lo E H, Montaner J. Increased brain expression of matrix metalloproteinase-9 after ischemic and hemorrhagic human stroke. Stroke. 2006;37:1399–1406. doi: 10.1161/01.STR.0000223001.06264.af. [DOI] [PubMed] [Google Scholar]
  84. Sumii T, Lo E H. Involvement of matrix metalloproteinase in thrombolysis-associated hemorrhagic transformation after embolic focal ischemia in rats. Stroke. 2002;33:831–836. doi: 10.1161/hs0302.104542. [DOI] [PubMed] [Google Scholar]
  85. Cuadrado E, Ortega L, Hernandez-Guillamon M, Penalba A, Fernandez-Cadenas I, Rosell A, Montaner J. Tissue plasminogen activator (t-PA) promotes neutrophil degranulation and MMP-9 release. J Leukoc Biol. 2008;84:207–214. doi: 10.1189/jlb.0907606. [DOI] [PubMed] [Google Scholar]
  86. Shigematsu T, Wolf R E, Granger D N. T-lymphocytes modulate the microvascular and inflammatory responses to intestinal ischemia-reperfusion. Microcirculation. 2002;9:99–109. doi: 10.1038/sj/mn/7800126. [DOI] [PubMed] [Google Scholar]
  87. Zwacka R M, Zhang Y, Halldorson J, Schlossberg H, Dudus L, Engelhardt J F. CD4(+) T-lymphocytes mediate ischemia/reperfusion-induced inflammatory responses in mouse liver. J Clin Invest. 1997;100:279–289. doi: 10.1172/JCI119533. [DOI] [PMC free article] [PubMed] [Google Scholar]
  88. Ysebaert D K, De Greef K E, Van Rompay A R, Vercauteren S, Persy V P, De Broe M E. T cells as mediators in renal ischemia/reperfusion injury. Kidney Int. 2004;66:491–496. doi: 10.1111/j.1523-1755.2004.761_4.x. [DOI] [PubMed] [Google Scholar]
  89. Arumugam T V, Granger D N, Mattson M P. Stroke and T-cells. Neuromolecular Med. 2005;7:229–242. doi: 10.1385/NMM:7:3:229. [DOI] [PubMed] [Google Scholar]
  90. Prass K, Meisel C, Höflich C, Braun J, Halle E, Wolf T, Ruscher K, Victorov I V, Priller J, Dirnagl U, Volk H D, Meisel A. Stroke-induced immunodeficiency promotes spontaneous bacterial infections and is mediated by sympathetic activation reversal by poststroke T helper cell type 1-like immunostimulation. J Exp Med. 2003;198:725–736. doi: 10.1084/jem.20021098. [DOI] [PMC free article] [PubMed] [Google Scholar]
  91. McGeachy M J, Stephens L A, Anderton S M. Natural recovery and protection from autoimmune encephalomyelitis: contribution of CD4+CD25+ regulatory cells within the central nervous system. J Immunol. 2005;175:3025–3032. doi: 10.4049/jimmunol.175.5.3025. [DOI] [PubMed] [Google Scholar]
  92. Suri-Payer E, Fritzsching B. Regulatory T cells in experimental autoimmune disease. Springer Semin Immunopathol. 2006;28:3–16. doi: 10.1007/s00281-006-0021-8. [DOI] [PubMed] [Google Scholar]
  93. Sakaguchi S, Ono M, Setoguchi R, Yagi H, Hori S, Fehervari Z, Shimizu J, Takahashi T, Nomura T. Foxp3+ CD25+ CD4+ natural regulatory T cells in dominant self-tolerance and autoimmune disease. Immunol Rev. 2006;212:8–27. doi: 10.1111/j.0105-2896.2006.00427.x. [DOI] [PubMed] [Google Scholar]
  94. O'Connor R A, Anderton S M. Foxp3+ regulatory T cells in the control of experimental CNS autoimmune disease. J Neuroimmunol. 2008;193:1–11. doi: 10.1016/j.jneuroim.2007.11.016. [DOI] [PubMed] [Google Scholar]
  95. O'Garra A, Vieira P. Regulatory T cells and mechanisms of immune system control. Nat Med. 2004;10:801–805. doi: 10.1038/nm0804-801. [DOI] [PubMed] [Google Scholar]
  96. Tang Q, Bluestone J A. The Foxp3+ regulatory T cell: a jack of all trades, master of regulation. Nat Immunol. 2008;9:239–244. doi: 10.1038/ni1572. [DOI] [PMC free article] [PubMed] [Google Scholar]
  97. Liesz A, Suri-Payer E, Veltkamp C, Doerr H, Sommer C, Rivest S, Giese T, Veltkamp R. Regulatory T cells are key cerebroprotective immunomodulators in acute experimental stroke. Nat Med. 2009;15:138–139. doi: 10.1038/nm.1927. [DOI] [PubMed] [Google Scholar]
  98. Lambertsen K L, Gregersen R, Meldgaard M, Clausen B H, Heibøl E K, Ladeby R, Knudsen J, Frandsen A, Owens T, Finsen B. A role for interferon-γ in focal cerebral ischemia in mice. J Neuropathol Exp Neurol. 2004;63:942–955. doi: 10.1093/jnen/63.9.942. [DOI] [PubMed] [Google Scholar]
  99. Holtmeier W, Kabelitz D. γδ T cells link innate and adaptive immune responses. Chem Immunol Allergy. 2005;86:151–183. doi: 10.1159/000086659. [DOI] [PubMed] [Google Scholar]
  100. Shibata K, Yamada H, Hara H, Kishihara K, Yoshikai Y. Resident Vδ1+ γδ T cells control early infiltration of neutrophils after Escherichia coli infection via IL-17 production. J Immunol. 2007;178:4466–4472. doi: 10.4049/jimmunol.178.7.4466. [DOI] [PubMed] [Google Scholar]
  101. Shichita T, Sugiyama Y, Ooboshi H, Sugimori H, Nakagawa R, Takada I, Iwaki T, Okada Y, Iida M, Cua D J, Iwakura Y, Yoshimura A. Pivotal role of cerebral interleukin-17-producing γδT cells in the delayed phase of ischemic brain injury. Nat Med. 2009;15:946–950. doi: 10.1038/nm.1999. [DOI] [PubMed] [Google Scholar]
  102. Sonobe Y, Liang J, Jin S, Zhang G, Takeuchi H, Mizuno T, Suzumura A. Microglia express a functional receptor for interleukin-23. Biochem Biophys Res Commun. 2008;370:129–133. doi: 10.1016/j.bbrc.2008.03.059. [DOI] [PubMed] [Google Scholar]
  103. Becher B, Durell B G, Noelle R J. IL-23 produced by CNS-resident cells controls T cell encephalitogenicity during the effector phase of experimental autoimmune encephalomyelitis. J Clin Invest. 2003;112:1186–1191. doi: 10.1172/JCI19079. [DOI] [PMC free article] [PubMed] [Google Scholar]
  104. Yilmaz A, Lochno M, Traeg F, Cicha I, Reiss C, Stumpf C, Raaz D, Anger T, Amann K, Probst T. Emergence of dendritic cells in rupture-prone regions of vulnerable carotid plaques. Atherosclerosis. 2004;176:101–110. doi: 10.1016/j.atherosclerosis.2004.04.027. [DOI] [PubMed] [Google Scholar]
  105. Steinman R M, Banchereau J. Taking dendritic cells into medicine. Nature. 2007;449:419–426. doi: 10.1038/nature06175. [DOI] [PubMed] [Google Scholar]
  106. Liu Y J. Dendritic cell subsets and lineages, and their functions in innate and adaptive immunity. Cell. 2001;106:259–262. doi: 10.1016/s0092-8674(01)00456-1. [DOI] [PubMed] [Google Scholar]
  107. Niessner A, Sato K, Chaikof E L, Colmegna I, Goronzy J J, Weyand C M. Pathogen-sensing plasmacytoid dendritic cells stimulate cytotoxic T-cell function in the atherosclerotic plaque through interferon-α. Circulation. 2006;114:2482–2489. doi: 10.1161/CIRCULATIONAHA.106.642801. [DOI] [PubMed] [Google Scholar]
  108. Greter M, Heppner F L, Lemos M P, Odermatt B M, Goebels N, Laufer T, Noelle R J, Becher B. Dendritic cells permit immune invasion of the CNS in an animal model of multiple sclerosis. Nat Med. 2005;11:328–334. doi: 10.1038/nm1197. [DOI] [PubMed] [Google Scholar]
  109. Yilmaz A, Fuchs T, Dietel B, Altendorf R, Cicha I, Stumpf C, Schellinger P D, Blümcke I, Schwab S, Daniel W G, Garlichs C D, Kollmar R. Transient decrease in circulating dendritic cell precursors after acute stroke: potential recruitment into the brain. Clin Sci (Lond) 2009;118:147–157. doi: 10.1042/CS20090154. [DOI] [PubMed] [Google Scholar]
  110. Kostulas N, Li H L, Xiao B G, Huang Y M, Kostulas V, Link H. Dendritic cells are present in ischemic brain after permanent middle cerebral artery occlusion in the rat. Stroke. 2002;33:1129–1134. doi: 10.1161/hs0402.105379. [DOI] [PubMed] [Google Scholar]
  111. Silver R, Silverman A-J, Vitkovic L, Lederhendler I. Mast cells in the brain: evidence and functional significance. Trends Neurosci. 1996;19:25–31. doi: 10.1016/0166-2236(96)81863-7. [DOI] [PubMed] [Google Scholar]
  112. Theoharides T. Mast cells: the immune gate to the brain. Life Sci. 1990;46:607–617. doi: 10.1016/0024-3205(90)90129-f. [DOI] [PubMed] [Google Scholar]
  113. Strbian D, Karjalainen-Lindsberg M L, Tatlisumak T, Lindsberg P J. Cerebral mast cells regulate early ischemic brain swelling and neutrophil accumulation. J Cereb Blood Flow Metab. 2006;26:605–612. doi: 10.1038/sj.jcbfm.9600228. [DOI] [PubMed] [Google Scholar]
  114. Strbian D, Karjalainen-Lindsberg M L, Kovanen P T, Tatlisumak T, Lindsberg P J. Mast cell stabilization reduces hemorrhage formation and mortality after administration of thrombolytics in experimental ischemic stroke. Circulation. 2007;116:411–418. doi: 10.1161/CIRCULATIONAHA.106.655423. [DOI] [PubMed] [Google Scholar]
  115. Fagan S C, Hess D C, Hohnadel E J, Pollock D M, Ergul A. Targets for vascular protection after acute ischemic stroke. Stroke. 2004;35:2220–2225. doi: 10.1161/01.STR.0000138023.60272.9e. [DOI] [PubMed] [Google Scholar]
  116. Kleinig T J, Vink R. Suppression of inflammation in ischemic and hemorrhagic stroke: therapeutic options. Curr Opin Neurol. 2009;22:294–301. doi: 10.1097/wco.0b013e32832b4db3. [DOI] [PubMed] [Google Scholar]
  117. Barone F C, Feuerstein G Z. Inflammatory mediators and stroke: new opportunities for novel therapeutics. J Cereb Blood Flow Metab. 1999;19:819–834. doi: 10.1097/00004647-199908000-00001. [DOI] [PubMed] [Google Scholar]
  118. Tuttolomondo A, Di Sciacca R, Raimondo D, Renda C, Pinto A, Licata G. Inflammation as a therapeutic target in acute ischemic stroke treatment. Curr Top Med Chem. 2009;9:1240–1260. doi: 10.2174/156802609789869619. [DOI] [PubMed] [Google Scholar]
  119. Jiang N, Chopp M, Chahwala S. Neutrophil inhibitory factor treatment of focal cerebral ischemia in the rat. Brain Res. 1998;788:25–34. doi: 10.1016/s0006-8993(97)01503-5. [DOI] [PubMed] [Google Scholar]
  120. Krams M, Lees K R, Hacke W, Grieve A P, Orgogozo J-M, Ford G A, for the ASTIN Study Investigators Acute stroke therapy by inhibition of neutrophils (ASTIN): an adaptive dose-response study of UK-279,276 in acute ischemic stroke. Stroke. 2003;34:2543–2548. doi: 10.1161/01.STR.0000092527.33910.89. [DOI] [PubMed] [Google Scholar]

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