Inflammation is an alarm signal of sorts that is triggered by invading pathogens or injury. It mobilizes the immune system to neutralize and kill the infection or promote tissue repair and healing. Although controlled inflammation is critical for surviving in a stressful world, when it is excessive or prolonged it can lead to health problems, and is a common driver of many chronic diseases.
Last Updated:March 6, 2022
What is inflammation?
Inflammation is a danger or alarm signal triggered by infection or injury that mobilizes the immune system to help fight off invading pathogens or initiate the repair of damaged or injured tissue. It was originally defined by observations of what occurs during the process, as described by the following Latin words:
Calor (heat) Dolor (pain) Rubor (redness) Tumor (swelling)
The pain, redness and swelling that occur with inflammation isn’t caused by the actual infection or injury, but the immune system’s reaction to them. When an inflammatory response is triggered, chemical messengers are released into the blood. This triggers an increase in the size of small blood vessels called capillaries, moving more blood into the damaged or infected region. Gaps also form in between the endothelial cells lining blood vessels, allowing blood plasma to leak into the surrounding tissues.
The local increase in blood flow and leakage of plasma into the damaged area in-turn causes skin in the area to feel warm to the touch and take on a darker, more reddish color. Increased volume of fluid in the damaged area causes swelling, which in turn causes pain by increasing the pressure on local nerve endings. Release of chemical messengers called cytokines also makes the surface of the endothelial cells lining blood vessels more “sticky”, allowing white blood cells to attach to the blood vessel wall.
After attaching to the blood vessel wall, white blood cells such as macrophages and neutrophils undergo a process called extravasation, where they squeeze in between the gaps in endothelial cells to move from the blood into the injured or damaged tissue. Macrophages and neutrophils in particular function as sort of first-responders, trafficking from the blood into the damaged or infected tissue to promote tissue repair or attack invading pathogens.
As the macrophages and neutrophils are waging war with the invading pathogen or helping to clear out damaged tissue, more chemical substances are released that can further enhance inflammation leading to collateral tissue damage and more pain and swelling.
What is chronic inflammation?
The inflammatory response is designed to be acute and self-limiting. As microbes are eliminated and tissue integrity is restored, local immune cells secrete anti-inflammatory cytokines that promote tissue regeneration and resolution of the inflammation.
Unlike acute inflammation, which may last days to weeks but eventually resolves, chronic inflammation is more of a slow, long-term type of inflammation that can last for months to years. While typically not as intense as acute inflammatory processes, chronic, low-grade inflammation does not tend to resolve and also is a contributing factor to the pathology of many diseases, including cancer, autoimmunity, cardiovascular disease, arthritis and joint diseases, and metabolic disorders.
Chronic inflammation can have many causes, including failure of the immune system to clear a pathogen or toxic substance from the body, or metabolic dysfunction that leads to an increase in toxic byproducts such as reactive oxygen species.
Unlike acute inflammation, which is more intense but self-limiting and short-lived, chronic inflammation can last for months or years, and is a contributing factor to many chronic diseases.
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