inflammation, reaction of the body to injury or to infectious, allergic, or chemical irritation. The symptoms are redness, swelling, heat, and pain resulting from dilation of the blood vessels in the affected part with loss of plasma and leucocytes (white blood cells) into the tissues. White blood cells communicate with each other via cytokines, which are polypeptides released by cells of the immune system that regulate other cells. They are a broad class of soluble compounds that signal one cell type to another, particularly in response to foreign substances. Granulomas are most common in infectious diseases such as tuberculosis, leishmaniasis, and schistosomiasis, in which the body's defenses, unable to destroy the offending organisms, try to enclose them in a mass of inflammatory cells. Certain types of inflammation result in pus formation, as in an abscess. The leukocytes destroy harmful microorganisms and dead cells, preventing the spread of the irritation and permitting the injured tissue to repair itself.

Local reaction of living tissues to injury or illness, including burns, pneumonia, leprosy, tuberculosis, and rheumatoid arthritis. Its major signs are heat, redness, swelling, and pain. The process begins with brief contraction of nearby arterioles (see arteries). Dilation follows, flushing the capillaries with blood, from which fluid, plasma proteins, and leukocytes pass into the injured tissues, causing swelling as they attack the cause of injury. Initial acute inflammation can have any of four outcomes: resolution (return to normal), organization (new tissue buildup; see scar), suppuration (pus formation; see abscess), or chronic inflammation. Sometimes treatment—including antibiotics for bacteria, or surgical removal of an irritating foreign body—can eliminate the cause. If not, anti-inflammatory drugs (e.g., cortisone or aspirin) may be given, or simple remedies (e.g., hot or cold compresses) may be applied.

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