Introduction
Impact of inflammatory cells on stroke
Microglia
Astrocytes
Endothelial cells and blood-brain barrier
Leukocytes
Cell type | Detrimental effects | Beneficial effects |
---|---|---|
Microglia/macrophages | Production of proinflammatory cytokines, including TNF and IL-1, reactive oxygen and nitrogen species, and proteases, such as MMPs. Brain microglia/macrophage phagocytose viable and functional neurons causing brain atrophy. | Resolution of inflammation (IL-10 and TGF-β release, production of arginase, and phagocytic activity). Late reparative processes by producing growth factors (IGF-1, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor), production of neurotrophic factors, facilitation of neurogenesis and plasticity, and scavenge and removal necrotic debris |
Astrocytes | Production of inflammatory mediators (e.g., TNF-α, IL-1, and MMPs). Edema formation, inhibition of axon regeneration and BBB disruption, glial scar formation, and glutamate release | Extracellular glutamate uptake, synthesis, and release of neurotrophic factors. Glial scar formation, BBB rebuilding, and neurovascular remodeling. |
Neutrophils | Microvessel obstruction, ROS production, and release of MMPs that contribute to BBB damage and exacerbate inflammation, stimulation of lipid peroxidation, release of proteolytic enzymes, damage of endothelial cell membrane, increase of BBB permeability, post-ischemic edema, no-reflow phenomenon | N2 phenotype: promote resolution of inflammation |
Dendritic cells | Up-regulation of MHC-II and co-stimulatory molecules that prompt the activation of lymphocytes | |
T Lymphocytes | Facilitate adhesion of platelets and leukocytes to the vascular endothelium causing thromboinflammation and promoting proinflammatory pathways | Interaction of T cells with platelets may also have hemostatic effects preventing hemorrhagic transformation after severe ischemic stroke |
Time-dependent entry of immune cells during ischemic stroke
Resident microglia and blood-derived macrophages
Neutrophils
T lymphocytes
Key pathological events and pathways fueling neuroinflammation
Oxidative stress
Cytokines
Chemokines
Excitotoxicity
Matrix metalloproteinases
Cyclooxygenase—an arachidonic acid metabolite
Transcriptional modifications
Mitogen-activated protein kinase (MAPK)
High-mobility group box protein family
Inflammatory mediators | Produced by | Beneficial | Detrimental | Reference |
---|---|---|---|---|
TNF-α | Macrophages, microglia, neurons | Overexpression of caspases, leukocyte adhesion molecules, and neurotrophic factors enhances endothelial cell dysfunction; modulates extracellular Ca2+ levels and neuronal plasticity; stimulates cerebral microvasculature repair, anti-apoptotic factors, and anti-oxidants; and induce ischemic tolerance | Increases or decreases infarct volume; blocks glutamate uptake, stimulate gliosis and release of neurotoxic mediators; enhance Ca2+ signaling in neurons and apoptosis of endothelial cells, edema formation, BBB disruption, prime endothelium for leukocyte adherence; and upregulate NF-ĸB activation | |
IL-6 | Macrophages, endothelial cells | Enhances post-stroke angiogenesis associated genes, induction IL-1ra | Endogenous pyrogen, attract T lymphocytes | |
IL-1α/β | Macrophages, microglia, endothelial cells | Enhances IL-1ra expression and promote survival factors | Increases infarct volume, acts as endogenous pyrogen, promote gliosis, increase neurotoxic mediators, enhance Ca2+ in neurons, induce edema formation and BBB disruption, prime endothelium for leukocyte adherence, upregulate MMP-9 | |
IL-12 | Macrophages, TH1 cells | Promote TH1 phenotype | Increases infarct volume | |
IL-8 | Endothelial cells, macrophages | Neutrophil chemoattractant | Increases infarct volume | |
MMPs | Microglia, astrocytes, leukocytes | Helps remove extracellular matrix; stimulates plasticity, recovery, and repair Clearance necrotic cell debris | Increases infarct volume, excitotoxicity, BBB disruption; promotes leukocyte adherence and transmigration; increases vasogenic edema and hemorrhagic transformation | |
iNOS | Endothelial cells, astrocytes, microglia, leukocytes | Promotes vasodilation, key effector molecule of ischemic preconditioning | Increases infarct volume, Induction of iron loss of cells, Inhibition enzymes DNA replication, stimulates expression of inflammatory mediators | |
IFN-γ | NK cells, T cells | Increases infarct volume, enhances inflammatory chemokine interferon inducible protein 10 (IP-10) and T-cell infiltration | ||
TGF-β | Astrocytes, microglia, macrophages | Reduces infarct volume, gliosis, and brain edema; decreases release ROS and apoptosis; prevent neutrophil adherence; Induces IL-1ra expression and angiogenesis, astrocytic TGF-β limit neuroinflammation | Enhance glial scar formation and β-amyloid precursor | |
IL-10 | Microglia, macrophages, Treg cells, endothelial cells | Decreases infarct volume, diminishes cytokines release and their receptors expression, prevents astrocytic activation, promotes neuronal and glial survival, reduces leukocyte adhesion | ||
HMGB-1 | Endothelial activation, enhances neuronal survival and neurite outgrowth | Increases infarct volume, vascular permeability, and inflammatory mediators, BBB disruption Activation of microglia, upregulates NF-ĸB expression | ||
CINC, MIP-1, MCP-1, fractalkine, MRF-1 | Microglia, infiltrating immune cells | Promote neuroblast migration, hematogenous cell recruitment, and functional repair; scavenge and repair necrotic tissue and angiogenesis | Enhance leukocyte and neutrophil infiltration, increase BBB disruption and cerebral edema, stimulate phagocytosis and apoptosis, increase cytokine secretion | |
ROS | Neurons, microglia, astrocytes, leukocytes | Enhances infarct volume, increased production of ROS, early ROS burst; initiates inflammatory response and lipid peroxidation; disrupts protein biochemistry | ||
NO | Neurons, macrophages, astrocytes, microglia, leukocytes, endothelial cells | Increases infarct volume, induces protein nitrosylation and iron loss of cells, inhibits enzymes for DNA replication, upregulates inflammatory mediators |