Bacterial Toxins and Toxoids as Vaccines
-Exotoxins of most pathogenic bacteria are highly antigenic; they stimulate the production of antibodies, (antitoxins) in animal or human body. These exotoxins are highly unstable and they lose toxicity during storage and are converted gradually into toxoids.

Toxoids retain the antigenic power but they are not toxic. Therefore, they can be used in producing immunity against corresponding toxins.

The transformation of toxins into toxoids is accelerated by heat, formaldehyde and other chemicals. Alum precipitated toxoids are highly antigenic. Toxoids have been used to develop immunity against several diseases including diphtheria, tetanus, gengrene, etc.