Biology for Nonbiologists by Frank R. Spellman

Author:Frank R. Spellman
Language: eng
Format: epub
Publisher: Government Institutes
Published: 2007-07-14T16:00:00+00:00

INDIGENOUS AND FOREIGN CELLS

The key to a healthy immune system is its remarkable ability to distinguish between the body’s indigenous and foreign cells. The body’s immune defenses normally coexist peacefully with cells that carry distinctive indigenous marker molecules. But when immune defenders encounter cells or organisms carrying markers that say, “foreign,” they quickly launch an attack.

Anything that can trigger this immune response is called an antigen. An antigen can be a microbe such as a virus, or even a part of a microbe. Tissues or cells from another person (except an identical twin) also carry non-self markers and act as antigens. This explains why tissue transplants may be rejected.

In abnormal situations, the immune system can mistake indigenous for foreign and launch an attack against the body’s own cells or tissues. The result is called an autoimmune disease. Some forms of arthritis and diabetes are autoimmune diseases. In other cases, the immune system responds to a seemingly harmless foreign substance such as ragweed pollen. The result is an allergy, and this kind of antigen is called an allergen.

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