Download At the heart of the immune response is the ability to distinguish

At the heart of the immune response is the ability to distinguish between self and nonself
Markers of Self
At the heart of the immune response is the ability to distinguish between self and nonself.
Every body cell carries distinctive molecules that distinguish it as "self." Normally the body's defenses
do not attack tissues that carry a self marker; rather, immune cells coexist peaceably with other body
cells in a state known as self-tolerance.
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At the heart of the immune response is the ability to distinguish between self and nonself
Markers of Non-Self
Foreign molecules, too, carry distinctive markers, characteristic shapes called epitopes that protrude
from their surfaces.
One of the remarkable things about the immune system is its ability to recognize many millions of
distinctive non-self molecules, and to respond by producing molecules such as these antibodies—and
also cells—that can match and counteract each one of the non-self molecules.
Any substance capable of triggering an immune response is known as an antigen. An antigen can be a
bacterium or a virus, or even a portion or product of one of these organisms. Tissues or cells from
another individual also act as antigens; that's why transplanted tissues are rejected as foreign.
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