Intermittent but not continuous inescapable footshock stress and intracerebroventricular interleukin-1 similarly affect immune responses and immunocyte beta-endorphin concentrations in the rat

Both CNS- and immunocyte(lymphocytes, splenocytes)-derived beta-endorphin is involved in immune responses to stress. We show in the rat that stress-induced immunodepression (decrease of mitogen-induced lymphocyte proliferation and NK activity) is present only after the administration of a stress paradigm that increases immunocyte-derived beta-endorphin, while this is absent when the concentrations of the opioid are not modified. Interestingly, plasma corticosterone levels were similarly elevated after stresses whether or not they suppress immune responses, thus suggesting a pivotal role of the opioid. The increase of immunocyte beta-endorphin and immunosuppression are similarly present also after the intracerebroventricular administration of interleukin 1, thus suggesting a role for this cytokine in stress responses. The modifications of immunocyte beta-endorphin concentrations and immune responses induced by stress and interleukin 1 are not affected by indomethacin, adrenalectomy or hypophysectomy, whereas they are completely blocked by a CRH antagonist and depletion of the serotoninergic or catecholaminergic systems. In conclusion, our results suggest that immune responses to stress are not uniquely linked to an activation of the HPA axis.