Pre-exposure to the unconditioned or conditioned stimulus does not affect learned immunosuppression in rats

In order to analyze the effects of pre-exposure to either the unconditioned (US) or conditioned stimulus (CS) on learned immunosuppression, we employed an established conditioned taste aversion (CTA) paradigm in rats. In our model, a sweet-tasting drinking solution (saccharin) serves as CS and injection of the immunosuppressive drug cyclosporine A (CsA) is used as US. The conditioned response is reflected by a pronounced CTA and diminished cytokine production by anti-CD3 stimulated splenic T cells. In the present study, experimental animals were exposed either to the US or the CS three times prior to the acquisition phase. On the behavioral level, we found a significantly diminished CTA when animals were pre-exposed to the US or the CS before acquisition. In contrast, US or CS pre-exposure did not affect the behaviorally conditioned suppression of interleukin (IL)-2 production. From the clinical perspective, our data may suggest that conditioning paradigms could be systemically integrated as supportive therapeutic interventions in patients that are already on immunosuppressive therapy or have had previous contact to the gustatory stimulus. Such supportive therapies to pharmacological regimens could not only help to reduce the amount of medication needed and, thus, unwanted toxic side effects, but may also maximize the therapeutic outcome.