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Antibodies are proteins that play an

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integral role in the complex system of

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specific immunity. They bind to and

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inactivate foreign proteins called

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antigens. Each type of antibody binds to

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one kind of antigen molecule. B-cells are

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one of the two types of white blood

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cells that make antibodies. When a

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bacterial cell enters the bloodstream,

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proteins on its surface act as antigens

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and trigger a response by the immune

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system. These antigens will bind to the

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unique B cells that have the

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corresponding antibodies on their

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surfaces. These B cells now divide.

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Some continue to divide producing many

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plasma cells. Plasma cells secrete large

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quantities of antibodies into the

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bloodstream. This division of only the

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appropriate B cells is called clonal

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selection.