Page 167 - Read Online

Liu et al. Neuroinflammation in ischemic stroke

consumption, and/or diabetes mellitus. [1] cells. Additionally, stroke induces the deleterious
[19]
antigen-specific autoreactive responses, but it also
Ischemic stroke is caused by arterial embolism and has beneficial effects. The ischemic brain can
[20]
in situ small vessel diseases. Embolism in brain act through the autonomic nervous system to have
results in oxygen and glucose deprivation, leading suppressive effect that can induce intercurrent
to brain damage and neurologic deficit. The cellular infections and contribute to the morbidity and mortality
and molecular mechanisms underlying ischemic after stroke. [21-23] Therefore, immune system-mediated
stroke-induced brain damage have been extensively inflammation is critically involved in determining
investigated. Excitotoxicity, oxidative stress, and the fate of the brain following ischemic stroke. [24-26]
inflammation have been considered as major Understanding the mechanisms underlying role of
contributors to ischemic neuronal injury. Cerebral neuroinflammation in ischemic stroke would provide
[2]
ischemia induces large release of glutamate that important targets for the development of therapy in
causes over-activation of NMDA receptors and ischemic stroke.
large inflow of Ca , leading to excitotoxicity-induced
2+
cell death. [3-7] The process of ischemia-reperfusion The aim of this review is to offer an overview of the
induces the production of superoxide and nitric oxide current knowledge about the immune system and the
from damaged neurons and astrocytes and depletes neuroinflammatory processes in ischemic stroke. We
glutathione, a primary antioxidant to protect against focus on how the neuroinflammatory processes are
reactive oxygen species-mediated DNA damage. [8-10] triggered by ischemic stroke, and how microglia cells
Inflammation occurs after ischemia-reperfusion injury, play a role in neuroinflammation after ischemic stroke.
which is caused by the dying cells and debris in the
absence of microbes. [11,12] NEUROINFLAMMATION

There is an increasing evidence to showing complex Neuroinflammation, an inflammatory response in the
role of the immune system in the pathophysiological brain, occurs in a variety of acute brain diseases. [27,28]
changes that occur following ischemic stroke. The non-diseased brain is separated by the blood brain
[13]
For example, brain injury activates neutrophils barrier (BBB) from periphery. [29] The BBB prevents
and macrophage/microglia, as well as the lectin immune cells that are in the blood from entering
[14]
pathway of complement activation and the toll-like brain tissue. [30] Brain is an independent immune-
receptors (TLRs) that are the sensors in the innate privileged organ with the innate. Neuroinflammation
immune system, [15,16] which leads to amplification of is regulated by the production of reactive oxygen
the inflammatory cascades. The immune system is species (ROS), cytokines and chemokines. [31] Once
closely involved in all the stages of ischemic stroke- neuroinflammation happens, it enhances the release
induced brain damage and tissue repair by the of several cytokines in the brain. [32,33] It also involves
parenchymal processes. [17,18] When activated, the the reaction of innate immune cells (i.e. the microglia)
adaptive immune system is intervened by lymphocyte in the parenchyma, the infiltration of myeloid cells
populations that include T - B cells and regulatory T and the adaptive immune cells (i.e. lymphocytes). [34]
But the own innate immune system of brain operates
mainly dependent on microglia, astrocyte and the
expression of TLRs on these glia as well as the
release of interleukins. [35,36]
Microglia is an innate immune cell that is well-
characterized as the resident macrophage of
the brain. Astrocyte is important mediator of
[37]
homeostasis in the brain. These two cells are key
[38]
players in the multicellular response to central nervous
system (CNS) trauma and disease, including the
immune reactions. [39,40] TLRs, the well-defined pattern
recognition receptors of the immune system, can
[41]
initiate an immune response upon exposure to harmful
microorganisms and play a key role in macrophage
[42]
activation. Neuronal TLR’s play a central role in
Figure 1: Stroke is comprised of ischemic stroke (85%) and
hemorrhagic stroke (15%) (intracerebral hemorrhage and connecting the interactions between the immune
[42]
subarachnoid hemorrhage) system and the nervous system. Interleukin’s act as
Neuroimmunology and Neuroinflammation ¦ Volume 4 ¦ August 28, 2017 159