Lesson 3

Interactive Part 1.6

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When we zoom in even closer, we see that there are bumps
on the surface of the cell wall. These bumps are made of protein and are called antigens. The immune system identifies these antigens as things that don't belong in the body.
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Antigens are proteins that stick out from the bacterial cell wall and can be recognized as "nonself." All cells contain thousands of different proteins, but not all proteins are antigens.