The immune system plays a vital role in preventing or limiting infection. When a body comes in contact with harmful bacteria, viruses, or other substances that can cause illness, its immune system kicks into action. Fundamentally, the immune system is designed to recognize “self” from “nonself.” That is, it should be able to distinguish between cells that are part of the body’s own tissues (self) and substances that come from substances outside it (nonself), which can include bacteria and other pathogens, as well as toxins. These nonself substances are “invaders,” and the immune system must differentiate them from cells and tissues of the body so that it can mount an appropriate response. Immunocompromise impedes the body from mounting such a response.
Figure
29.1
In June 1987, a small group of strangers gathered in a San Francisco storefront to document the lives they feared history would neglect. Their goal was to create a memorial for those who had died of AIDS, and to thereby help people understand the devastation. The quilt grew over time and is shown on the National Mall in Washington, DC. (credit: Carol M. Highsmith Archive, Library of Congress, Prints and Photographs Division, Public Domain)