Summary
Highlights
While essential, inflammation can be problematic. Autoimmune diseases occur when inflammation attacks the body's own cells. Acute inflammation can become chronic and damaging to healthy tissues if it fails to stop after the initial insult is cleared.
Inflammation is the body's protective response to infections or injuries, involving the mobilization of defensive cells, limiting pathogen spread, elimination of pathogens, and initiation of tissue repair. It is most commonly observed in the skin and underlying tissues, presenting with redness, heat, swelling, and pain.
Acute inflammation begins when tissue-resident immune cells, like macrophages, encounter an inflammatory stimulus such as a pathogen, toxin, or injured cell. This triggers a signaling cascade, leading to the production of cytokines and other inflammatory mediators. These chemicals dilate blood vessels, increasing blood flow and permeability, resulting in redness, heat, and swelling as plasma fluid and immune cells accumulate.
The infiltration of blood components into injured tissue occurs in three phases: first, exudation of plasma fluid with antimicrobial mediators, platelets, and clotting factors to destroy microbes and stop bleeding. Second, infiltration of neutrophils, which are major phagocytes. Endothelial cells become adhesive, slowing down and guiding neutrophils to the site where they engulf bacteria, kill them with enzymes or toxic peroxides, and may release reactive oxygen species in an oxidative burst.
The third phase involves monocytes, which differentiate into macrophages. Macrophages remove pathogens, injured cells, and dying neutrophils via phagocytosis. Cleared macrophages are transported out of the tissue by the lymphatic system. Once the insult is resolved, immune cells switch from producing pro-inflammatory chemicals to anti-inflammatory mediators, many of which are synthesized from dietary omega-3 fatty acids, actively terminating the inflammation.
Failure to resolve inflammation leads to chronic inflammation, which continuously damages healthy tissues. Chronic inflammation is a contributing factor to various conditions, including cardiovascular diseases, asthma, diabetes, arthritis, and cancer.