When your body suffers an injury or infection, inflammation is a normal part of the healing process. We are most familiar with short term (or acute) inflammation, such as when we get a cut and the skin swells up, turns red, and hurts. This effect usually goes away in a few hours.
Inflammation in your body’s cells or tissues may cause you to feel hot or lose function, or you may have no outward symptoms at all.
If inflammation fails to resolve itself and becomes chronic, it could contribute to further tissue injury and disease. Chronic inflammation can persist for months or years and is a contributing factor to more than half of deaths worldwide.
A review of scientific literature conducted by NIEHS-funded researchers affiliated with the National Toxicology Program found the environment plays a role in inflammation, which is associated with such diseases as:
Tissue inflammation may result from exposure to factors such as:
source: The National Institute of Environmental Health Sciences (NIEHS)
Inflammation is your body’s response to an illness, injury or something that doesn’t belong in your body (like germs or toxic chemicals). Inflammation is a normal and important process that allows your body to heal. Fever, for example, is how you know your body’s inflammatory system is working correctly when you’re ill. But inflammation can harm you if it occurs in healthy tissues or goes on for too long.
When an invader (like a virus) tries to enter your body, or you get injured, your immune system sends out its first responders. These are inflammatory cells and cytokines (cytokines (substances that stimulate more inflammatory cells). These cells begin an inflammatory response to trap germs or toxins and start healing injured tissue. Inflammation can cause pain, swelling or discoloration. These are signs your body is healing itself. Normal inflammation should be mild, and pain shouldn’t be extreme.
But inflammation can also affect parts of your body you can’t see. Inflammatory responses that occur behind the scenes can help you heal, but other times, they can harm your health.
What’s the difference between acute and chronic inflammation?
There are two main types of inflammation: acute and chronic. Acute inflammation is sudden and temporary, while chronic inflammation can go on for months or years.
Acute inflammation
This is your immune system’s response to a sudden injury or illness. Inflammatory cells travel to the site of injury (like a cut on your finger) or infection and start the healing process.
Infections in different parts of your body can cause sudden, and usually short-lived, inflammation. For example, bacterial infections like strep throat and viral infections like the flu can cause throat inflammation. Other bacterial and viral infections can cause inflammation of your small intestine (enteritis).
Acute inflammation may last for a few hours to a few days, depending on your condition.
Chronic inflammation
This is when your body continues sending inflammatory cells even when there’s no danger. For example, in rheumatoid arthritis, inflammatory cells and substances attack joint tissues. This leads to inflammation that comes and goes and can cause severe damage to your joints.
With chronic inflammation, processes that normally protect your body end up hurting it. Chronic inflammation can last for months or years. You may have periods where it improves and other times when it gets worse.
Researchers have linked chronic inflammation to a wide range of conditions (inflammatory diseases).
source: Cleveland Clinic
Most of the features of acute inflammation continue as the inflammation becomes chronic, including the expansion of blood vessels (vasodilation), increase in blood flow, capillary permeability and migration of neutrophils into the infected tissue through the capillary wall (diapedesis). However, the composition of the white blood cells changes soon and the macrophages and lymphocytes begin to replace short-lived neutrophils. Thus the hallmarks of chronic inflammation are the infiltration of the primary inflammatory cells such as macrophages, lymphocytes, and plasma cells in the tissue site, producing inflammatory cytokines, growth factors, enzymes and hence contributing to the progression of tissue damage and secondary repair including fibrosis and granuloma formation, etc.[7][8][9][10]
In response to foreign or self-antigens, the tissue immune cells such as macrophages and dendritic cells release cytokines such as IL-1 and TNF-α. These cytokines induce the injury-site-endothelial cells to release Selectins and Integrins which stimulate chemotaxis and diapedesis of the circulating leukocytes. In addition to the recruitment of leukocytes, the tissue macrophages, and dendritic cells also play a role in the clearing of the antigen by phagocytosis, the release of cytokines and serving as antigen-presenting-cells to lymphocytes. Once the circulating leukocytes enter the local injury site, they are activated by various cytokines and chemokines secreted by the macrophages and dendritic cells. On activation, the leukocytes further release cytokines and mediators of inflammation. Neutrophils are the initial cells and most predominant in the acute phase of inflammation. Neutrophils contain granules rich with lysozyme, matrix metalloproteinases, myeloperoxidase which are released on the foreign or self-antigen leading to its destruction. Neutrophils also destroy the antigen by phagocytosis, the release of reactive oxygen species and cytokines such as IL-1, IL-6, and TNF-α. Lymphocytes including T-lymphocytes and B-lymphocytes are the next line of defense, and they play a crucial role in mediating inflammation by several complex mechanisms including secreting of cytokines, co-stimulation of lymphocytes, and production of antibodies and immune complexes. Circulating platelets can also play a role in inflammation by platelet aggregation, thrombus formation and degranulation releasing chemokines and inflammatory mediators.
source: Chronic Inflammation by Roma Pahwa; Amandeep Goyal; Ishwarlal Jialal. Last Update: August 7, 2023
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