Immunomodulation by behavioural conditioning.
The contemporary surge in studies of behaviourally conditioned immunomodulation following Ader and Cohen (1975) was preceded by Pavlovian conditioning conducted in the Soviet Union during the 1920s and 1950s. Data from these studies provided a tenable hypothesis for immunomodification using classical conditioning processes. In particular a variant of Pavlovian conditioning, the conditioned taste aversion (CTA) paradigm, has proved very robust; here a novel gustatory experience (CS) is paired with an aversive physiological event (UCS) and subsequent gustatory avoidance of the CS alone is measured. Similar procedures have also been successfully applied to the conditioned alteration of cellular immune responses. Studies demonstrating behaviourally conditioned effects on the immune system are reviewed. More recently, conditioned immunoenhancement studies have demonstrated that taste aversion can induce a conditioned increase in the helper: suppressor T cell subset ratio in rats, and a depressed DTH response in mice. Mediating mechanisms for the conditioned effects are examined, in particular the roles of adrenocorticotropin (ACTH) and beta-endorphin (BEP), and the routes of communication between the CNS and immune system. Clinical applications of immunomodification may also be demonstrated by the potential therapeutic efficacy of both conditioned immunosuppression and immunoenhancement.