Nonspecific hypersensitivity: false-positive responses with the use of Freund's complete adjuvant

While conducting a guinea pig sensitization protocol, using the maximization test, it was discovered, at challenge, that the test animals were more responsive to the vehicle (acetone) than they were to the proprietary test material. During rechallenge, conducted to clarify the specific immune status of the test animals, it was determined that they were also hyperreactive to an alternate vehicle (diethyl phthalate), to which they were naïve. This bizarre set of data is presented and it is suggested that this type of response is the prototype for the presence of false-positive responses experienced by toxicologists using this test. The test conditions imposed on the immune system by the maximization test that could result in these anomalous results are discussed. These data suggest that investigators need cautiously to interpret data that are produced by the injection of Freund's complete adjuvant (FCA).