Hapten

A part of an antigen or a low molecular weight substance that does not induce antibody production by itself, but does cause a visible reaction such as a precipitation reaction with the corresponding antibody. For example, polysaccharides obtained from the capsule of pneumonia bacteria do not produce antibodies against it when inoculated into a rabbit, but they do cause a precipitation reaction with antibodies obtained by inoculating a rabbit with pneumonia bacteria. There are also substances that have no antibody production ability and do not cause precipitation reactions or other reactions with the corresponding antibodies, but which inhibit the reaction between antibodies and antigens; these are called simple haptens. For example, partial hydrolysis products of the above polysaccharides inhibit the precipitation reaction between rabbit anti-pneumonia bacteria serum and pneumonia bacteria or polysaccharides.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

抗原の一部あるいは低分子物質で，単独では抗体産生を誘起しないが，対応する抗体とは沈降反応などの目に見える反応を起こす物質．たとえば，肺炎菌の莢(きょう)膜から得た多糖体は，ウサギに接種してもそれに対する抗体は産生されないが，肺炎菌をウサギに接種して得た抗体とは沈降反応を起こす．また，抗体産生能もなく，対応する抗体と沈降反応などの反応も起こさないが，抗体と抗原との反応を阻害する物質があり，単純ハプテン(simple hapten)と名づけられる．たとえば，上記の多糖類の部分分解物は，ウサギの抗肺炎菌血清と肺炎菌，あるいは多糖体との沈降反応を阻害する．

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