Immunization, the practice of inducing immunity (especially to infection) in a person or animal.

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immunization, the practice of inducing immunity (especially to infection) in a person or animal. This is usually achieved by vaccination, in which a vaccine (a preparation containing antigens) is used to stimulate the production of antibodies and therefore induce active immunity. The vaccine is usually administered by injection, and generally contains either live but attenuated organisms (reduced in virulence), or dead organisms which retain their ability to stimulate antibody production. Active immunity lasts many years. Passive immunity is induced by the administration of antibodies against a particular infection (passive immunization). Antibodies collected from humans are called immunoglobulins, and those from animals, antisera. Passive immunity lasts for only a few weeks.

 The earliest form of immunization was variolation, a type of inoculation against smallpox in which part of a scab from a smallpox sufferer was introduced into a scratch on the recipient's skin. The practice, developed in about the 5th century AD in India, was potentially very dangerous, since it involved the live smallpox virus, but it greatly reduced overall mortality from the disease. Variolation was not known in Europe until 1721, when Mary Montagu, the wife of the British ambassador to the Ottoman Empire, introduced it from Turkey. In 1796 Jenner successfully protected an 8-year-old boy from smallpox by inoculating him with the related but much less dangerous cowpox virus. In 1885 Pasteur adopted Jenner's principles to find a vaccine against rabies. Vaccines have subsequently been produced for other diseases and non-infectious agents, including diphtheria (by the German immunologist Emil von Behring in 1889) and snake venom (by Ehrlich in 1889). In 1890 von Behring and Kitasato first showed that immunity was due to antibodies that appeared in the blood a few days after immunization.

 In the richer countries of the world, mass immunization of children against major childhood diseases has been successful in reducing morbidity and mortality rates. In 1974 when the World Health Organization launched the Expanded Programme on Immunization, fewer than 5 per cent of children in developing countries were immunized. By 1991 four-fifths of the world's children were protected by immunization against diphtheria, whooping cough, tetanus, measles, polio, and tuberculosis, and WHO estimated that 2 million lives were being saved each year. None the less, there is still a heavy toll in preventable disease, with more than a million cases of measles, which is often fatal to malnourished children, for example. New goals for the 1990s are to eradicate neonatal tetanus and polio and to reduce measles by 90 per cent. WHO's global eradication of smallpox in 1977 through systematic immunization, and through tracking down the last carriers for treatment, has set a dramatic and encouraging precedent.

 

immunity, the ability of an organism to resist infection by means of the immune system. The immune system has two main parts: white blood cells, and antibodies circulating in the bloodstream. Antibodies are proteins produced by B-lymphocytes (a type of white blood cell) in response to exposure to antigens (antibody generators). Antigens can be micro-organisms, blood from transfusions, cells in transplanted tissues, and any other material not recognized as belonging to the body such as those that cause allergy. Antibodies are dormant until they attach to the specific antigens against which they are effective. They then become activated, and may directly destroy the antigen or 'label' it so that a white blood cell can engulf and destroy it. After the body has been exposed to an antigen, 'memory' ensures that a later exposure causes antibodies to be produced more quickly and in larger amounts than on the first occasion. This can produce immunity to a harmful antigen such as a virus, since it is eliminated before it has time to act. In addition, immunity also detects and eliminates the body's own abnormal cells and denatured proteins, which is a self-monitoring function called immunosurveillance.

 Cell-mediated immunity is the most reactive part of the immune system, and leads to the production of specific white blood cells (T-cells) in response to antigens. Humoral immunity, the second component, is responsible for the production of specific antibodies to the antigen. The components may act alone or in combination depending on the situation.

 Immunity may be induced by artificial means (see immunization). (See also immunology.)

 

 Ehrlich, Paul (1854-1915), German physician who founded chemotherapy and made important contributions to bacteriology, haematology, and immunology. As a student, he became interested in aniline dyes, using them for the first time to stain bacteria. He also employed a similar technique to identify the different types of white blood corpuscles and the corresponding leukaemias. From 1889, he investigated the principles of immunization and two years later devised a means of standardizing diphtheria toxin. In 1911 he introduced the arsenical drug arsphenamine as a treatment for syphilis. He shared the 1908 Nobel Prize for Physiology and Medicine with Elie Metchnikoff.

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 Jenner, Edward (1749-1823), British physician and naturalist, famous for his discovery of a vaccination against smallpox. After training under the surgeon John Hunter in London, Jenner set up in 1773 as a medical practitioner in Berkeley, Gloucestershire. Jenner observed that infection with the mild disease called cowpox made people immune to smallpox. In 1796 he performed the vaccination by inserting cowpox matter into two scratches made on the arm of a healthy 8-year-old boy. A few months later the boy was inoculated with smallpox, and the disease refused to take. By 1800 some 100,000 people had been immunized, and a dramatic ...

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