Antibodies are proteins that play an

integral role in the complex system of

specific immunity. They bind to and

inactivate foreign proteins called

antigens. Each type of antibody binds to

one kind of antigen molecule. B-cells are

one of the two types of white blood

cells that make antibodies. When a

bacterial cell enters the bloodstream,

proteins on its surface act as antigens

and trigger a response by the immune

system. These antigens will bind to the

unique B cells that have the

corresponding antibodies on their

surfaces. These B cells now divide.

Some continue to divide producing many

plasma cells. Plasma cells secrete large

quantities of antibodies into the

bloodstream. This division of only the

appropriate B cells is called clonal

selection.