Introduction
Neuroinflammation is a process where the immune system is triggered by an inflammatory reaction such as injury, infection, exposure to a toxin, aging, or neurodegenerative disease. Certain biochemicals and cellular activities are initiated when the immune system is activated. This may result in physiological, biochemical, and behavioral outcomes. The central nervous system (CNS) is activated to protect the body against the danger posed to it. It is a natural process the innate immune system has developed for protection. The usual conditions are monitored by microglia, which help detect alterations that threaten disturbances to homeostasis (it is an automated process of the biological system which helps maintain stability).
During the phase of injury, infection, exposure to toxins, aging, or neurodegenerative condition, the microglia trigger inflammatory signals causing neuroinflammation. The central nervous system's response can be protective and harmful, as acute inflammation can be chronic and damaging.
What Is Meant by Neuroinflammation?
Neuroinflammation is the central nervous system's reaction to injury, pathological states, and the process of healing. The production of triggers neuroinflammation,
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Cytokines are small proteins which involved in cell signaling.
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Chemokines are small cytokines.
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Reactive oxygen is unstable oxygen molecules that react with other cell molecules.
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Secondary messengers are intracellular molecules used for signaling.
The aging process is the primary risk factor for many degenerative conditions, such as Alzheimer's disease and Parkinson's disease. The occurrence of Alzheimer's disease is one to every ten individuals aged 65 years and above. This condition worsens with aging. Most of the degenerative conditions related to aging cannot be treated, and they tend to progress irreversibly. These conditions are related to higher socioeconomic and personal costs.
How Does Acute Inflammation Differ From Chronic Inflammation?
Inflammation is essential in monitoring healing and injury repair to maintain proper working. Acute inflammation occurs suddenly and is characterized by redness, warmth, swelling, and pain around the injured tissue and joint, which is a responsive action to the injury. Acute inflammation along with the body helps to protect the affected person from bacteria present in the splinter (the sizeable foreign body that penetrates or is injected into the body). When this splinter is eliminated, the inflammatory response resolves in a few hours. Acute inflammation help to return to the normal homeostasis of the body.
Chronic inflammation, which is just opposite to acute inflammation, is related to the draining of the chronic disease associated with the cardiovascular system, brain, liver, aging, etc. Chronic inflammation is devastating as it worsens the functioning of many organs, whereas acute inflammation is considered reparative. In the brain, acute inflammation signifies reparative action called acute neuroinflammation, and in this case, chronic inflammation represents destruction called chronic neuroinflammation.
How Is Chronic Inflammation Targeted?
Alzheimer's disease is the most common chronic progressive degenerative condition which results in dementia; it is the loss of cognitive functioning, such as reasoning, remembering, and thinking which affects the person's daily activity. In the aging population, the number of people affected by dementia increases yearly, resulting in significant health, social, and economic issues. Even though there are many different research underway to develop therapeutic strategies to decrease the pace of disease progression, there are no disease-modifying therapies to treat Alzheimer's disease.
Scientists thought neuroinflammatory action is caused as a response to plaque and tangle, which is the primary pathology of Alzheimer's disease. So the doctors believed eliminating the plaque and tangles helped deal with neuroinflammation. But further studies discovered that neuroinflammation occurs before plaque and tangles, which is the common cause of nerve damage and death, and sympathetic dysfunction, which is the cause of cognitive decline.
What Are the Types of Neuroinflammation?
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Injury:
Traumatic brain injury results from a knock on the head with a huge impact. This can initiate degenerative mechanisms. The initiation of these pathways triggers the immune system to generate an inflammatory response. Due to head trauma, the immune system produces pro-cytokines which results in cell death and DNA (deoxyribonucleic acid) fragmentation which is caused due to worsening of the condition.
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Peripheral Immune Response:
The blood-brain barrier is formed to protect and prevent the brain from toxins that have a chance to enter the bloodstream. A physical wall of astrocytes is built between the bloodstream and the brain. This astrocyte junction regulates what should be passed through the barrier. Still, in case of any injury, it can get damaged, which results in the influx of T-cells, B-cells, and macrophages into the brain, worsening the inflammation.
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Infection:
Neuroinflammation can arise from infections caused by various microorganisms such as bacteria, viruses, fungi, protozoa, or parasites. The microorganisms can lead to conditions like encephalitis (inflammation of the brain) or meningitis (inflammation of the meninges covering the brain and spinal cord).
How Are Neuroinflammation and Neurodegenerative Disease Interlinked?
Neurodegenerative disease and neuroinflammation are always interlinked, where Alzheimer's disease, Parkinson's disease, and various types of sclerosis are associated with neuroinflammation. Neurodegradation is caused due to neuroinflammation, a characteristic feature of Alzheimer's disease.
Neuroinflammation is a significant component of Parkinson's disease, where inflammation in the gut triggers the initiation of the disease. This may result in brain inflammation, which destroys dopamine production, a central characteristic of this condition.
The blood-brain barrier gets damaged in the presence of inflammation, which allows the entry of B-cells and plasma cells into the central nervous system, where the myelin sheath covering the neurons gets damaged. This process is called demyelination which is a characteristic feature of sclerosis.
Aging and neurodegenerative disease can result in cognitive degradation, usually seen in old aged people, where both conditions are related to brain inflammation. Aging of the brain can enhance the level of pro-inflammatory cytokines and reduce the level of anti-inflammatory cytokines, where aging is alone associated with chronic neuroinflammation. The aging brain demonstrates a sign of an activated immune system, which links the aging brain and neuroinflammation.
Conclusion
The immune system is triggered due to neuroinflammatory reactions such as injury, aging, exposure to toxins, etc. During this phase, biochemicals and cellular activities will be released, triggered when the immune system is activated. Particular conditions such as Alzheimer's and Parkinson's disease, are associated with neuroinflammation. Aging and neurodegenerative disease result in cognitive decline, which cannot be prevented.
