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The ammonium sulfate coprecipitation technique of Farr was applied in a study of the purified enterotoxins of Staphylococcus aureus. Ammonium sulfate coprecipitation of iodine-131-labeled enterotoxins A, B, and C, with the use of a 1.6 m concentration of (NH(4))(2)SO(4), revealed differences in the antigen-binding capacity of normal and immune rabbit sera for the enterotoxins. The coprecipitation technique provided a quantitative test for detecting antibody to enterotoxin that was more sensitive than agar-gel diffusion methods. Antigen-binding tests suggested the presence of similar antigenic determinant groups in all three toxins. Measurable antigenbinding capacities for enterotoxins A, B, and C were detected in sera of normal human subjects and became elevated in several subjects accidently exposed to enterotoxin.
Gruber et al. (1969) studied this question.