Time phases of conditioned cellular immunosuppression in rats

Objective To understand the nature of the conditioned immunosuppression (CIS) and examine the time phase of CIS and conditioned taste aversion (CTA). Methods Cyclophosphamide was used as an unconditioned stimulus (UCS) and saccharin was used as the conditioned stimulus (CS). Both CTA and CIS as assessed by cell proliferation were examined by one re-exposure to CS at intervals of 5, 15, 30 days after two trials of CS-UCS pairing. Result CTA occurred and the level remained at the every interval testing. However, CIS occurred obviously only on the 5th day after conditioning. CIS was attenuated on the 15th day and disappeared on the 30th day after conditioning. Conclusion There was no association between the conditioned immunosuppression and the conditioned taste aversion. Both of them have their own modulation mechanism in the center nervous system.