Laminin peptide ameliorates brain injury by inhibiting leukocyte accumulation in a rat model of transient focal cerebral ischemia

Granulocyte colony-stimulating factor and stromal cell-derived factor-1 combination therapy: A more effective treatment for cerebral ischemic stroke

BACKGROUND

Drugs that promote angiogenesis include statins, recombinant human granulocyte colony-stimulating factor, and stromal cell-derived factor-1. Low doses of atorvastatin could significantly increase the vascular expressions of endothelial growth factor, and the number of peripheral blood endothelial progenitor cells (EPCs), thus improving angiogenesis and local blood flow. G-CSF is an EPC-mobilization agent used in ischemia studies for targeting angiogenesis after cerebral ischemia via EPCs. In previous clinical trials, consistent conclusions have not been reached about the effectiveness of G-CSF on ischemic stroke. Therefore, the therapeutic effect of G-CSF and its combination with other medicines need further experimental verification. It is known that atorvastatin, rhG-CSF, and SDF-1 are considered the most promising neuroprotective candidates, but a comprehensive comparison of their effects is lacking.

AIMS

To compare the effects of atorvastatin, stromal cell-derived factor-1, and recombinant human granulocyte colony-stimulating factor on ischemic stroke.

METHODS

Adult male Sprague-Dawley rats were randomly allocated to three groups: normal, sham-operated, and middle cerebral artery occlusion operated. Middle cerebral artery occlusion operated rats were further allocated into saline, atorvastatin, recombinant human granulocyte colony-stimulating factor, and recombinant human granulocyte colony-stimulating factor + stromal cell-derived factor-1 groups. Neurological function evaluation, cerebral infarction and the blood-brain barrier integrity analysis, identification of angiogenic factors, assessment of angiogenesis, expression of growth-associated protein-43, neuroglobin, glial cell-derived neurotrophic factor, and cleaved caspase 3, were performed.

RESULTS

Compared with atorvastatin or recombinant human granulocyte colony-stimulating factor alone, recombinant human granulocyte colony-stimulating factor + stromal cell-derived factor-1 treatment improved neurological performance, reduced cerebral infarction and blood-brain barrier disruption after stroke, and increased the content of stromal cell-derived factor-1, vascular endothelial growth factor, monocyte chemotactic protein 1, and basic fibroblast growth factor in peripheral blood. In addition, recombinant human granulocyte colony-stimulating factor + stromal cell-derived factor-1 promoted greater angiogenesis than atorvastatin or recombinant human granulocyte colony-stimulating factor alone and increased the expression of growth-associated protein-43, neuroglobin, and glial cell-derived neurotrophic factor, while decreasing the levels of cleaved caspase 3 in the brain after ischemic stroke.

CONCLUSIONS

Combination therapy with recombinant human granulocyte colony-stimulating factor and stromal cell-derived factor-1 is more effective than atorvastatin or recombinant human granulocyte colony-stimulating factor alone in protecting against stroke-induced damage and could be an optimal therapeutic strategy for stroke.

Laminins and their receptors in the CNS

Laminin, an extracellular matrix protein, is widely expressed in the central nervous system (CNS). By interacting with integrin and non-integrin receptors, laminin exerts a large variety of important functions in the CNS in both physiological and pathological conditions. Due to the existence of many laminin isoforms and their differential expression in various cell types in the CNS, the exact functions of each individual laminin molecule in CNS development and homeostasis remain largely unclear. In this review, we first briefly introduce the structure and biochemistry of laminins and their receptors. Next, the dynamic expression of laminins and their receptors in the CNS during both development and in adulthood is summarized in a cell-type-specific manner, which allows appreciation of their functional redundancy/compensation. Furthermore, we discuss the biological functions of laminins and their receptors in CNS development, blood-brain barrier (BBB) maintenance, neurodegeneration, stroke, and neuroinflammation. Last, key challenges and potential future research directions are summarized and discussed. Our goals are to provide a synthetic review to stimulate future studies and promote the formation of new ideas/hypotheses and new lines of research in this field.

Loss of Endothelial Laminin α5 Exacerbates Hemorrhagic Brain Injury

Endothelial cells make laminin-411 and laminin-511. Although laminin-411 is well studied, the role of laminin-511 remains largely unknown due to the embryonic lethality of lama5^-/- mutants. In this study, we generated endothelium-specific lama5 conditional knockout (α5-TKO) mice and investigated the biological functions of endothelial lama5 in blood-brain barrier (BBB) maintenance under homeostatic conditions and the pathogenesis of intracerebral hemorrhage (ICH). First, the BBB integrity of α5-TKO mice was measured under homeostatic conditions. Next, ICH was induced in α5-TKO mice and their littermate controls using the collagenase model. Various parameters, including injury volume, neuronal death, neurological score, brain edema, BBB integrity, inflammatory cell infiltration, and gliosis, were examined at various time points after injury. Under homeostatic conditions, comparable levels of IgG or exogenous tracers were detected in α5-TKO and control mice. Additionally, no differences in tight junction expression, pericyte coverage, and astrocyte polarity were found in these mice. After ICH, α5-TKO mice displayed enlarged injury volume, increased neuronal death, elevated BBB permeability, exacerbated infiltration of inflammatory cells (leukocytes, neutrophils, and mononuclear cells), aggravated gliosis, unchanged brain edema, and worse neurological function, compared to the controls. These findings suggest that endothelial lama5 is dispensable for BBB maintenance under homeostatic conditions but plays a beneficial role in ICH.

A Novel Therapeutic Peptide as a Partial Agonist of RANKL in Ischemic Stroke

The enhanced receptor activator of nuclear factor-κB (NFκB) ligand (RANKL) and its receptor (RANK) signal have been reported to attenuate ischemic brain injury through inhibition of Toll-like receptor (TLR) 4-mediated inflammation. However, augmentation of the RANKL/RANK signal also accelerates osteoporosis, which is a potential problem in clinical use of RANKL. Therefore, we developed novel peptides, microglial healing peptides (MHPs), which were based on the DE and/or EF loop of RANKL. Among them, MHP1 was the most effective inhibitor of TLR4-induced inflammations in microglia/macrophages. The effects depended on RANK, as confirmed by knockdown experiments. In contrast to RANKL, MHP1 did not stimulate osteoclast differentiation. Unexpectedly, MHP1 inhibited RANKL-induced osteoclast differentiation. These findings suggested that MHP1 was a partial agonist of RANKL, and administration of MHP1 attenuated ischemic injury by decreasing inflammation. MHP1 could be a novel therapeutic agent for treating ischemic stroke.

Regulation of Integrin α6 Recycling by Calcium-independent Phospholipase A2 (iPLA2) to Promote Microglia Chemotaxis on Laminin

Microglia are the immune effector cells that are activated in response to pathological changes in the central nervous system. Microglial activation is accompanied by the alteration of integrin expression on the microglia surface. However, changes of integrin expression upon chemoattractant (ADP) stimulation still remain unknown. In this study, we investigated whether ADP induces the alteration of integrin species on the cell surface, leading to changes in chemotactic ability on different extracellular matrix proteins. Flow cytometry scans and on-cell Western assays showed that ADP stimulation induced a significant increase of α6 integrin-GFP, but not α5, on the surface of microglia cells. Microglia also showed a greater motility increase on laminin than fibronectin after ADP stimulation. Time lapse microscopy and integrin endocytosis assay revealed the essential role of calcium-independent phospholipase A₂ activity for the recycling of α6 integrin-GFP from the endosomal recycling complex to the plasma membrane. Lack of calcium-independent phospholipase A₂ activity caused a reduced rate of focal adhesion formation on laminin at the leading edge. Our results suggest that the alteration of integrin-mediated adhesion may regulate the extent of microglial infiltration into the site of damage by controlling their chemotactic ability.

Ischemic postconditioning diminishes matrix metalloproteinase 9 expression and attenuates loss of the extracellular matrix proteins in rats following middle cerebral artery occlusion and reperfusion

AIMS

Ischemic postconditioning (IPostC) has been proved to have neuroprotective effects for cerebral ischemia, but the underlying mechanism remains elusive. This study aimed at validating the neuroprotective effects of IPostC and investigating whether the neuroprotection of IPostC is associated with matrix metalloproteinase 9 (MMP9) and the extracellular matrix proteins, laminin and fibronectin, following cerebral ischemia/reperfusion in rats.

METHODS

The rats in middle cerebral artery occlusion (MCAO) group underwent MCAO and reperfusion, and the animals in MCAO + IPostC group were treated by occluding bilateral common carotid arteries for 10 seconds and then reperfusing for 10 seconds for five episodes at the beginning of MCAO. Apoptosis was detected with terminal deoxynucleotidyl transferase dUTP nick end labeling staining. The expression of MMP9, laminin, and fibronectin was measured with immunofluorescence and enzyme-linked immunosorbent assay.

RESULTS

IPostC reduced brain edema and infarct volume and improved the neurological function. Furthermore, IPostC decreased cell apoptosis compared with the MCAO group. Compared to the MCAO group, IPostC treatment reduced MMP9 expression. Moreover, the results showed that the expression of laminin and fibronectin significantly increased in the MCAO + IPostC group compared to the MCAO group.

CONCLUSION

These findings indicated that diminishment of MMP9 expression and the attenuation of degradation of laminin and fibronectin may be involved in the protective mechanisms of postconditioning against cerebral ischemia/reperfusion injury.

Neuroprotective effects of laminin and its KDI domain

Successful treatment of neurodegenerative diseases and CNS trauma are the most intractable problems in modern medicine. Numerous reports have shown the strong role that laminins have on the survival, regeneration and development of various types of cells, including neural cells. It would be desirable to take advantage of laminin activities for therapeutic purposes. However, there are at least ten laminin variants and the trimeric molecules are of the order of 800,000 molecular weight. Furthermore, human laminins are not available in quantity. Therefore, we and others have taken the approach of determining which domains of the laminin molecules are functional in the CNS, and whether short peptides from these regions exhibit biological activities with the intent of testing their potential for therapeutic use. Understanding the role of laminins and their small biologically active peptide domains, such as the KDI (lysine–aspartic acid–isoleucine) peptide from γ1 laminin, in neuronal development, CNS trauma (spinal cord injury and stroke) and neurodegenerative disorders (amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease) may help to develop clinically applicable methods to treat the presently untreatable CNS diseases and trauma even in the near future.

Spatial and temporal distribution of laminins in permanent focal ischemic brain damage of the adult rat

Laminins are extracellular matrix glycoproteins with multiple functions in the central nervous system, including maintenance of the blood-brain barrier. Because ischemic brain damage results in rapid degradation of extracellular matrix, we used immunocytochemistry on rat central nervous system after permanent focal ischemia to identify laminins involved in pathophysiology of stroke. At 24 hr after stroke, laminin-1 is transiently expressed by neurons inside the ischemic core, but from 2-3 days to 28 days it is expressed only in basement membrane structures. During the first 24 hr, alpha1, alpha5, beta1, and gamma1 laminins are transiently expressed in neurons within the ischemic core as an acute reaction of the brain to ischemia. Rapid induction of gamma1 laminin but no other laminin in reactive astrocytes surrounding the ischemic core is clear at 24 hr, and importantly, expression of gamma1 laminin in astrocytes surrounding the ischemic core intensifies during the first days and persists up to 28 days after stroke. At 2-3 days, gamma1 laminin immunoreactive barrier of reactive astrocytes is already fully formed, isolating the ischemic area from the healthy brain. Similar to gamma1 laminin, its KDI domain localizes in reactive astrocytes isolating the ischemic core. Results indicate that gamma1 laminin and its KDI domain are rapidly induced in glial cells after stroke and their expression persists, forming a molecular barrier between the healthy and the damaged brain. Thus, gamma1 laminin is involved in pathology of stroke and is likely to serve a protective function, considering its potent neuroprotective role after spinal cord injury and in neurodegenerative disorders.

Fibronectin and Laminin Increase in the Mouse Brain after Controlled Cortical Impact Injury

The complex environment of the traumatically injured brain exhibits aspects of inhibition and ongoing cell death together with attempts at repair and regeneration. Elucidating these events and exploiting those factors involved in endogenous repair and regeneration may aid in developing more effective treatments for traumatic brain injury. Two extracellular matrix proteins critical to neural development--fibronectin and laminin--may also play a protective or reparative role in the injury response. While both of these proteins have been found to increase following human brain injury,the presence of these proteins has not been studied in a clinically-relevant animal model of blunt head trauma. In this study, we examined the spatiotemporal profile of both fibronectin and laminin in the mouse brain following controlled cortical impact injury. Fibronectin and laminin reactivity was localized to the injury penumbra up to 14 days post-injury and was significantly higher than uninjured controls at 3 days post-injury. Upon examining the spatial relationship of fibronectin and laminin to support cells, we found macrophages/activated microglia prominently present in the fibronectin-rich tissue, consistent with a role for fibronectin in facilitating debris clearing. Furthermore, reactive astrocyte processes were found sheathing laminin positive vasculature, suggesting that laminin may play a role in repairing the blood-brain barrier. These and other hypothesized reparative roles for fibronectin and laminin after traumatic brain injury are discussed.

Cytokines regulate microglial adhesion to laminin and astrocyte extracellular matrix via protein kinase C-dependent activation of the alpha6beta1 integrin

Microglia are highly plastic cells that participate in inflammatory and injury responses within the CNS and that can migrate extensively after activation. Because astrocytes and their extracellular matrix (ECM) form a large part of the CNS parenchyma, we undertook to study the adhesive interactions between microglia and these substrates in vitro. In contrast to oligodendrocyte precursor cells, microglia formed only weak interactions with astrocytes and their ECM. On specific ECM substrates the microglia adhered strongly to fibronectin, vitronectin, and plastic but only weakly to laminin. Microglial adhesion to laminin was increased significantly by the proinflammatory cytokines TNF, IFN-alpha, and IFN-gamma but was decreased by TGF-beta1, with the TGF-beta1 effect being dominant over the other cytokines. Fluorescence-activated cell sorting (FACS) analysis and immunoprecipitation showed that microglia constitutively express the alpha6beta1 integrin, a well characterized laminin receptor, and that alpha6beta1 expression levels did not change after cytokine treatment. Function-blocking studies showed that microglial adhesion to laminin is mediated entirely by the alpha6beta1 integrin, strongly suggesting that the cytokine regulation of adhesion to laminin is mediated by changes in the activation state of alpha6beta1. Analysis of signaling pathways revealed that activation of alpha6beta1 is mediated by a PKC-dependent mechanism. In light of the evidence that laminin expression is upregulated after CNS injury, the findings suggest that cytokine regulation of microglial adhesion to laminin may play a fundamental role in determining the extent of microglial infiltration into and retention at the site of injury.

The role of leukocytes following cerebral ischemia: pathogenic variable or bystander reaction to emerging infarct?

Data accumulated over the last 10 years have led to the popular hypothesis that neutrophils and other inflammatory cells play a prominent role in the neuropathology of cerebral ischemia. This hypothesis was derived from a large number of studies involving three general observations: (1) leukocytes, particularly neutrophils, are present in ischemic tissue at the approximate time that substantial neuronal death occurs; (2) neutropenia is sometimes associated with reduced ischemic damage; and (3) treatments that prevent leukocyte vascular adhesion and extravasation into the brain parenchyma can be neuroprotective. This review reexamines the literature to ascertain its support for a pathogenic role for neutrophils in ischemia-induced neuronal loss. To accomplish this goal, we employed several logical theorems of "cause-effect" relationships, as they pertain to leukocytes and ischemic brain damage. Since the majority of studies focused on neutrophils as the most likely pathogenic inflammatory cell, this review necessarily does so here. We reasoned that if neutrophils play an important pathogenic (i.e., cause-effect) role in the neuronal damage that follows a stroke, then one should expect to find clear evidence that: (1) neutrophils invade the ischemic area prior to terminal stage infarction, (2) greater numbers of early appearing neutrophils are accompanied by evidence of greater neuronal loss, and (3) dose-related inhibition of neutrophil trafficking or activity produces a corresponding decrease in the degree of brain damage following ischemia. This review of the literature reveals that the existing evidence does not readily support any of these predictions and that, therefore, it consistently falls short of establishing a clear cause-effect relationship between leukocyte recruitment and the pathogenesis of ischemia. While the available evidence does not necessarily rule out a potential pathogenic role of neutrophils and other leukocytes, it nevertheless does expose serious weaknesses in the existing studies intended to support that hypothesis. For this reason we also offer suggestions for additional experiments and the inclusion of control groups that, in the future, might provide more effective or conclusive tests of the hypothesis.

Elements of cerebral microvascular ischaemia

Although neuronal cells have long been thought to be the prime target of ischaemic insults, events which occur at the blood-vascular-parenchymal interface are necessary for the initiation of ischaemic tissue injury. This cascade of microvascular events includes fibrin accumulation, endothelium expression of leukocyte adhesion receptors, breakdown of the basal laminae with loss of astrocyte and endothelial cell contacts leading to blood-brain barrier disruption and consequently oedema formation and haemorrhagic transformation. Potential stroke treatments have been studied in the clinic and many have not been particularly successful, probably due to the delicate balance between improved outcome and adverse reactions as well as the window of opportunity for drug treatment after symptom onset. The only acute intervention trial demonstrating any benefit in patients was that of intravenous tissue plasminogen activator (tPA), administered within 3 h of the onset of symptoms of ischaemic stroke. Such treatment improved clinical outcome at 3 months, although there was an increased incidence of symptomatic haemorrhage [New Engl. J. Med. 333 (1995) 1581]. The recent progress made in defining the mechanisms involved in the initiation of ischaemic events, as described in this review, may lead to the identification of new strategies for intervention in the ischaemic cascade.

Immune abnormalities in aneurysmal subarachnoid haemorrhage patients: relation to delayed cerebral vasospasm

Peripheral blood CD3+, CD19+, CD4+, CD8+ and CD45RO+ mononuclear cell subsets, T-cell proliferative responses to combinations of coimmobilized OKT3 antibody and an ECM protein (collagen I, collagen IV, fibronectin or elastin), and T-cell adhesion to collagen IV, fibronectin and elastin were studied in patients with aneurysmal subarachnoid haemorrhage. No significant difference was found in the major lymphocyte subsets between subarachnoid haemorrhage patients receiving no dexamethasone for brain oedema treatment and healthy blood donors. Compared with the latter, both the dexamethasone-untreated and -treated subarachnoid haemorrhage patients showed decreased relative proliferative responses of circulating T cells to OKT3 combinations with collagen IV and fibronectin, and an increased PHA-activated T-cell adhesion to elastin. CD45RO+, CD4+ and CD19+ peripheral blood cell subsets, CD4+/CD8+ cell ratio, PHA-activated T-cell adhesion to fibronectin and collagen IV, and OKT3-triggered T-cell costimulatory responses to elastin, collagen IV and fibronectin were significantly higher in subarachnoid haemorrhage patients presenting with delayed cerebral vasospasm (DCV) than in their DCV-free counterparts. The DCV-related differences in circulating lymphocyte subsets showed no apparent relationship to the glucocorticoid treatment, whereas the differences in the other indices were confined to the dexamethasone-untreated subarachnoid haemorrhage patients. The above results suggest that the CD4+/CD8+ ratio and T cell-ECM interactions play a role in the emergence of subarachnoid haemorrhage/DCV and may represent potential targets for subarachnoid haemorrhage therapy.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Expression of nitric oxide synthase (NOS)-2 following permanent focal ischemia and the role of nitric oxide in infarct generation in male, female and NOS-2 gene-deficient mice

Considerable evidence implicates nitric oxide (NO) in the pathological events following cerebral ischemia and, depending on the enzyme/cell source, NO is considered to be either damaging or protective. As a role for the enzyme nitric oxide synthase (NOS)-2 in permanent focal ischemia is not clear, we examined its expression following permanent middle cerebral artery occlusion in mice. At 24 h after occlusion, NOS-2 was expressed in cells infiltrating the infarct, while at later times, there was also expression in astrocytes around the infarct. To reveal a role for NO derived from this source, we compared infarct size in male and female mice with littermates in which the NOS-2 gene was disrupted. No differences were found between gender and genotype at 24 h. At 72 h, the infarct was increased in male mice, but not in females or in either gender with the gene disruption. These results suggest that NOS-2 plays a role in the later development of the infarct in male mice. Female mice are protected either against the damaging effects of NO, or because NOS-2 expression/activity is modulated by steroids.

Deficiency of intercellular adhesion molecule 1 attenuates microcirculatory disturbance and infarction size in focal cerebral ischemia

Recent evidence has shown crucial roles for cell-adhesion molecules in inflammation-induced rolling, adhesion, and accumulation of neutrophils in tissue. Intercellular adhesion molecule-1 (ICAM-1) is one of these adhesion molecules. Previous studies have shown marked reduction in the size of infarction after focal cerebral ischemia by depletion of granulocytes and administration of the antibody against ICAM-1. In the present study we investigated the role of ICAM-1 in the size of ischemic lesions, accumulation of granulocytes, and microcirculatory compromise in focal cerebral ischemia by using ICAM-1-knockout mice. Ischemic lesions were significantly mitigated in knockout mice after permanent and transient focal ischemia, even though the number of granulocytes in the infarcted tissue was almost the same between knockout and wild-type mice. Depletion of granulocytes further decreased the size of ischemic lesions after transient focal ischemia in ICAM-1-knockout mice. Microcirculation was reduced after focal ischemia, but it was better preserved in the cerebral cortex of knockout mice than that of wild-type mice. The present study demonstrated that ICAM-1 played a role in microcirculatory failure and subsequent development and expansion of infarction after focal cerebral ischemia. However, it is highly unlikely that ICAM-1 played a key role in accumulation of granulocytes after focal cerebral ischemia.

Reperfusion injury after focal cerebral ischemia: the role of inflammation and the therapeutic horizon

Recent evidence indicates that thrombolysis may be an effective therapy for the treatment of acute ischemic stroke. However, the reperfusion of ischemic brain comes with a price. In clinical trials, patients treated with thrombolytic therapy have shown a 6% rate of intracerebral hemorrhage, which was balanced against a 30% improvement in functional outcome over controls. Destruction of the microvasculature and extension of the infarct area occur after cerebral reperfusion. We have reviewed the existing data indicating that an inflammatory response occurring after the reestablishment of circulation has a causative role in this reperfusion injury. The recruitment of neutrophils to the area of ischemia, the first step to inflammation, involves the coordinated appearance of multiple proteins. Intercellular adhesion molecule-1 and integrins are adhesion molecules that are up-regulated in endothelial cells and leukocytes. Tumor necrosis factor-alpha, interleukin-1, and platelet-activating factor also participate in leukocyte accumulation and subsequent activation. Therapies that interfere with the functions of these factors have shown promise in reducing reperfusion injury and infarct extension in the experimental setting. They may prove to be useful adjuncts to thrombolytic therapy in the treatment of acute ischemic stroke.