Differential effects of physical and psychological stressors on immune functions of rats

To study the effects of different types or durations of stressors on immune functions, male Fischer rats were exposed to chronic physical (electric foot shock) or psychological (non-foot shock) stress induced in the communication box. Superoxide production by alveolar macrophages (AMs), mitogen-induced splenic lymphocyte proliferation, and splenic natural killer (NK) cell cytolysis were examined in vitro. Repeated exposure to physical stress suppressed superoxide production by AMs (-58%, p < 0.05 for opsonized zymosan (OZ) and -51%, p < 0.05 for phorbol 12-myristate 13-acetate (PMA)), although psychological stress suppressed superoxide production after 24 h of repeated exposures (-40%, p < 0.05 for OZ and -47%, p < 0.05 for PMA). Acute suppression of the blastic response of splenic lymphocytes was only found in the physical stress group (p < 0.05), although the chronic effects were only found in the psychological stress group (p < 0.05). NK cell activity was suppressed immediately after the acute physical stress (-30%, p < 0.05), but no effects were found in the psychological stress group. These results underline the importance of distinguishing between physical versus psychological stressors when examining the effects of stress on immune functions.