Radioimmunoassay for Type A Toxin of Clostridium botulinum

A preparation of pure type A toxin ofClostridium botulinum was labeled with131 I in the presence of chloramine-T and carrier-free isotope. The radioactive toxin (131 I Tox) was used in a radioimmunoassay procedure similar to that of Berson and Yalow. Dilutions of antibody to the toxin, capable of binding 50% of the added131 I Tox, were mixed with a sample of the labeled toxin and various concentrations of unlabeled toxin (‚Cold’ Tox). When concentration of Cold Tox were plotted against the ratio131 I bound/131 I not bound, a standard curve was established that could be used to estimate the concentration of Cold Tox in a test mixture. This assay was sensitive to as little as 100 mouse minimum lethal dose and was highly specific for the serological type of the toxin used.