toxin-antitoxin, mixture of a poisonous substance, or toxin, with an antitoxin, or antibody, in such proportion that a large percentage of the toxin is neutralized by the antitoxin. Although formerly used to immunize an individual against disease, toxin-antitoxin mixtures have been largely supplanted by toxoids. See immunity.

antitoxin, any of a group of antibodies formed in the body as a response to the introduction of poisonous products, or toxins. By introducing small amounts of a specific toxin into the healthy body, it is possible to stimulate the production of antitoxin so that the body's defenses are already established against invasion by the bacteria or other organisms that produce the toxin. See immunity.

Antibody formed in the body in reaction to a bacterial toxin, which it can neutralize. People who have recovered from bacterial diseases often develop specific antitoxins that give them immunity against recurrence. Injecting an animal (usually a horse) with increasing doses of toxin produces a high concentration of antitoxin in the blood. The resulting highly concentrated preparation of antitoxins is called an antiserum. The first antitoxin developed (1890) was specific to diphtheria; today, antitoxins are also used to treat botulism, dysentery, gas gangrene, and tetanus.

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