The use of radioactive isotopes in immunological investigations. 6. Some observations on precipitin inhibition tests and on antibody valence

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Abstract
Using I131 labelled antigen or inhibitor, a quantitative study was made of the iodinated protein antigen-antibody precipitin reaction in the presence of the specific inhibitor, 3,5-diiodotyrosine. Addition of inhibitor usually caused a fall in the antibody: antigen ratio of the precipitate due apparently to the inhibitor reducing the concn. of free or effective antibody. Some of these precipitin tests were carried out with mixtures containing 5% deuterium oxide. This made it possible for detns. to be made of the amount of supernatant soln., and hence the amt. of free inhibitor, in the unwashed precipitates. The amt. of combined inhibitor in the precipitates was small and sometimes immeasurable; at most, it was equivalent to one molecule of 3,5-diiodotyrosine per 20 molecules of antibody in the precipitate. The results were discussed in relation to antibody valence, and it is suggested that they support the view that the precipitating antibodies studied are univalent.