Behavioral influences on the immune system: stress and conditioning.

Several investigators have demonstrated that immune responses may be subject to classical conditioning processes. Conditioning effects in both cell-mediated and humoral immune responses have been reported. Strong evidence for behavioral effects on immune responses has been provided by studies of stress-induced immunosuppression. Stressors may increase morbidity due to infectious agents, depress antibody responses, inhibit lymphocyte reactions, and attenuate several other cell-mediated immune functions. In our studies, acute inescapable footshock inhibited natural killer cell (NK) activity in CD-1 and C57BL/6J mice, but not in DBA/2J mice. Genetic factors play a role in the immunological responses to stress. In contrast to the effects of acute stress, NK activity of mice exposed to chronic inescapable footshock was not reduced from control levels. Adaptive processes may be invoked during repeated stress exposure, thereby limiting the potentially damaging effects of the stressor.