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Published on Aug 2, 2007
How the Body Works The Development of Immunity
When an antigen enters the body, it stimulates B-lymphocytes in the blood to produce antibodies, specific to that antigen, which attack and destroy it. After the initial attack, the number of specific antibodies in the blood falls slowly, over several weeks, but the body "remembers" their structure, and can produce them at short notice. Subsequent invasion by the same antigen is, therefore, rapidly halted and specific immunity is acquired. When a second antigen is encountered, the B-lymphocytes must produce a new antibody, since the first antibody is specific only to the first antigen. The second antibody continues to circulate in the bloodstream and immunity to the second antigen is acquired.