Some parameters of conditioned immunosuppression: species difference and CS-US delay.

Three experiments were conducted in which an illness-inducing immunosuppressant, cyclophosphamide (an unconditioned stimulus, US) was associated with a previously presented saccharin solution conditioned stimulus (CS). In each experiment, reexposure to the CS produced a conditioned suppression of the plaque-forming-cell response in the experimental groups. Experiment I demonstrated this result with Fisher 344 rats. Experiment II replicated the effect with Balb/c mice. In Experiment III conditioned immunosuppression was demonstrated when mice received CS-US delays as long as 6 hours. No evidence of a delay gradient was present in either the behavioral or the immunologic data. These parallel findings offer no support for the idea of a dissociation between the taste aversion and conditioned immunosuppression processes.