Our immune systems protect us from the threat of infection by microorganisms, such as bacteria and viruses, and parasites, such as worms. The immune system also protects us from certain cancers and helps to repair damaged tissues. We are born with certain built-in defence mechanisms, but much of our immunity is acquired as we are exposed to the organisms that cause disease.
This section begins with an overview of acquired immunodeficiency, one of the major disorders of the immune system. Acquired immunodeficiency is a condition, developing after birth, in which the immune system fails to function properly and is unable to combat microorganisms that invade the body. Such immunodeficiency develops for a variety of reasons. The most widely publicized form of acquired immunodeficiency is AIDS, which develops after infection with the human immunodeficiency virus (see HIV infection and AIDS).
A temporary, mild form of acquired immunodeficiency may appear after infection with other viruses, such as measles, and may also develop following certain drug treatments.
The second overview article covers autoimmune disorders, which occur when a person’s immune system functions abnormally and starts to attack the body’s own tissues, causing certain organs to become inflamed and damaged. Individual autoimmune disorders that affect more than one organ are covered next. Such disorders are most common in young adults and can lead to persistent poor health. Their causes are not fully understood, although genetic factors appear to play an important role. Overall, women are affected much more commonly and severely by autoimmune disorders.
Autoimmune disorders that affect specific organs or sites in the body are considered in the relevant sections of this guide. For example, rheumatoid arthritis, which primarily affects the joints, is dealt with in the musculoskeletal disorders section and Hashimoto’s thyroiditis (see Thyroiditis), which causes the underproduction of hormones from the thyroid gland, is covered in the section dealing with metabolic disorders. Immunodeficiency that is present from birth is covered in the section of the guide dealing with children’s disorders (see Congenital immunodeficiency).
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.