Antibody is a protein produced by the white blood cells that help the white blood cells destroy bacteria. Antibodies react with the antigens and inactivate or destroy them. A large number of antibodies are produced in the blood which are targeted against various types of antigens. Antigens are foreign molecules, cells, bacteria, viruses and fungi which enter the body usually as disease causing microorganisms. Antibodies are the integral part of the defense mechanism of human body. They are also involved in immunity against diseases.