Immune system

The immune system is the system of specialised cells and organs that protect an organism from outside biological influences. In a broad sense, almost every organ has a protective function (e.g., the skin). When the immune system is functioning properly, it protects the body against bacteria and viral infections, destroying cancer cells and foreign substances. If the immune system weakens, its ability to defend the body also weakens, allowing pathogens, including viruses that cause common colds and flu, to grow and flourish in the body. The immune system also performs surveillance of tumor cells, and immune suppression has been reported to increase the risk of certain types of cancer.

Disorders of the human immune system

The most important function of the human immune system occurs at the cellular level of the blood and tissues. The lymphatic and blood circulation systems are highways for specialized white blood cells to travel round the body.White blood cells include B cells, T cells, natural killer cells, and macrophages. Each has a different responsibility, but all function together with the primary objective of recognizing, attacking and destroying bacteria, viruses, cancer cells, and all substances seen as foreign. Without this coordinated effort, a person would not be able to survive more than a few days, before succumbing to overwhelming infection.

Related Topics:
Lymphatic - Blood circulation - White blood cell - B cells - T cells - Natural killer cells - Macrophages - Bacteria - Viruses - Cancer cells

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Infections set off an alarm that alerts the immune system to bring out its defensive weapons. Natural killer cells and macrophages rush to the scene to gobble up and digest infected cells. If the first line of defense fails to control the threat, antibodies, produced by the B cells, upon the order of T helper cells, are custom-designed to hone in on the invader.

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Many disorders of the human immune system fall into two broad categories that are characterized by:

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• Attenuated immune response: There are 'congenital' (inborn) and 'acquired' forms of immunodeficiency, characterized by an attenuated response. Chronic granulomatous disease, in which phagocytes have trouble destroying pathogens, is an example of the former, while AIDS ("Acquired Immune Deficiency Syndrome"), an infectious disease caused by the HIV virus that destroys CD4⁺ T cells, is an example of the latter. Immunosuppressive medication intentionally induces an immunodeficiency in order to prevent rejection of transplanted organs.
• Overzealous immune response: On the other end of the scale, an overactive immune system figures in a number of other disorders, particularly autoimmune disorders such as lupus erythematosus, type I diabetes (sometimes called "juvenile onset diabetes"), multiple sclerosis, psoriasis, and rheumatoid arthritis. In these, the immune system fails to properly distinguish between self and non-self, and attacks a part of the patient's own body. Other examples of overzealous immune responses in disease include hypersensitivities, such as allergies and asthma.

Many factors can also contribute to the general weakening of the immune system:

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• Poor eating habits, and alcohol abuse;
• Drug use (particularly the use of anti-cancer drugs, corticosteroids, and antibiotics);
• Radiation;
• Exposure to environmental toxins, chemical, cigarette smoke, polluted air; and
• Stress (research show that psychological stress can greatly increase your susceptibility to colds, and other viral diseases).

The body's immunity also begins to wear down as a person gets older.

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