The Influence of Conditioning on Immune Responses

Abstract

This chapter discusses the influence of conditioning on immune responses. Conditioned alterations of immunologic reactivity provide dramatic evidence of functional relationships between the brain and the immune system. In one or another study, the acquisition and extinction of the conditioned suppression or enhancement of antibody-and cell-mediated immune responses have been documented. Conditioning processes have also been implicated in the development of tolerance to an immunomodulating agent. The physiological mediation of conditioned alterations in immune function is not yet known. Some have explicitly or implicitly assumed that the conditioned suppression of immunologic reactivity is the direct result of stress-induced responses. The available data provide no support for stress-induced elevations in adrenocortical steroids as the mediator of conditioned alterations in immune function. Conditioned immunosuppressive responses occur when conditioned animals are reexposed to the corticosterone before and after immunization. Such effects could imply that the mechanisms do not involve antigen-induced immunologic or neuroendocrine changes; they could also indicate that different mechanisms are involved when conditioning is superimposed on a resting or on an antigen-activated system. Also, there are differences in the site of action of different immunomodulating agents, and the same immunomodulating drug may have different effects on an activated or nonactivated immune system.