Protein molecule produced in the blood by lymphocytes in response to the presence of foreign or invading substances (antigens); such substances include the proteins carried on the surface of infecting micro-organisms. Antibody production is only one aspect of immunity in vertebrates.
Each antibody acts against only one kind of antigen, and combines with it to form a ‘complex’. This action may render antigens harmless, or it may destroy micro-organisms by setting off chemical changes that cause them to self-destruct.
Each bacterial or viral infection will bring about the manufacture of a specific antibody, which will then fight the disease. Many diseases can only be contracted once because antibodies remain in the blood after the infection has passed, preventing any further invasion. Vaccination boosts a person's resistance by causing the production of antibodies specific to particular infections.
Large quantities of specific antibodies can now be obtained by the monoclonal technique (see monoclonal antibody).
In 1989 a Cambridge University team developed genetically engineered bacteria to make a small part of an antibody (single domain antibodies) which bind to invaders such as toxins, bacteria, and viruses. Since they are smaller, they penetrate tissues more easily, and are potentially more effective in clearing organs of toxins. They can be produced more quickly, using fewer laboratory mice, and unlike conventional antibodies, they also disable viruses. In addition, single domain antibodies can be used to highlight other molecules, such as hormones in pregnancy testing.
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