antibody defined in 1951 year

antibody - antibody;
antibody - A protein produced in a vertebrate animal when a certain kind of substance (an antigen) which is normally foreign to its body fluids gains access to them; the antibody combines chemically with the antigen. Antibodies tend to be highly specific, in that they combine only with antigens of a particular kind. Antigens are large molecules, mostly proteins or carbohydrates; and the specificity of their reaction is due to the structure of certain small areas on the surface of these molecules. These active areas evoke antibodies carrying matching structures that in turn combine only with the specific active areas. Importance of antibody formation is as defence mechanism against invasion by parasites, particularly by bacteria and viruses. Antibodies at present seem to be peculiar to vertebrates. When parasites or their poisonous products enter the tissues the animal produces antibodies, which circulate dissolved in the body fluids. This antibody production is stimulated by antigens forming part of, or produced by, the parasites. A given parasite is likely to bear several antigens, some peculiar to its species or strain, and therefore to evoke several sorts of antibodies equally specific. In some cases different pathogens have the same antigen, so that immunity to one confers immunity to another, e.g. vaccinia and smallpox. The combination of antibody with antigen kills or immobilizes parasites, or makes them more susceptible to phagocytes or makes their poison innocuous. Antibodies are formed by a complex system involving lymphocytes, plasma cells and perhaps macrophages; and once produced they are found mainly in the blood, and may persist there long after disappearance of the antigen, conferring immunity to a new infection by the same sort of parasite. A new infection also induces a much more rapid production of the specific antibodies than the first infection; this is called a secondary response. Immunity to disease from vaccination or inoculation is due to antibodies. Antibodies cannot be formed until late in embryonic development. Substances quite unconnected with parasites can act as antigens when injected, e.g. almost any foreign protein, and the specificity of the reaction provides an extraordinarily sensitive test for different proteins. Grafting of foreign tissues also leads to the production of antibodies against their antigens.

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