Placebo Effects in the Immune System.

Even though knowledge and systematic application of placebo responses in the immune system are sparse, this topic is of particular importance since it may aim at drug-dose reduction while maintaining therapeutic efficacy of treatment in clinical settings. Placebo responses in the immune system are inducible by associated learning paradigms, such as behaviorally conditioned immunosuppression. One established learning paradigm in both rats and humans is conditioned taste avoidance (CTA), where a novel taste as conditioned stimulus (CS) is paired with the administration of the immunosuppressive drug cyclosporine A (CsA) as unconditioned stimulus. By representing the CS alone at a later time point, the conditioned response is reflected by avoidance behavior toward the taste (CTA). Simultaneously, diminished cytokine production and proliferative capacity of T cells are observed, closely mimicking the pharmacological effects of CsA. This chapter provides an overview on placebo responses in the immune system and delineates actual approaches, translational aspects, and limitations of learning paradigms in clinical settings.