Markers of Non-Self

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.