Neuroendocrine regulation of immune processes: change in circulating corticosterone levels induced by the primary antibody response in mice.

The induction of antibody formation mediated significant changes in circulating corticosterone (CS) levels in mice. On the day of the peak plaque-forming cell (PFC) response to sheep red blood cells (SRBC) or to the trinitrophenyl (TNP) hapten, the 0800 h serum CS concentration was increased. This hormonal elevation was not observed in SRBC-immunized low responder animals which did not give a significant PFC response, thus suggesting a direct correlation between immune responsiveness and hormonal changes. A change in the circadian rhythm of CS was evident in immune animals injected with SRBC. Control animals injected with saline showed a regular circadian pattern of low CS level at 0800 h followed by a high level at 1600 h. In contrast, responding animals injected with SRBC were found to have a reversed CS pattern, i.e. the hormonal concentration was high at 0800 h and low at 1600 h, on the day of the peak PFC response. This reversal of the circadian CS pattern may have important immunoregulatory significance. The immunization-induced CS response could be significantly blocked by the administration of diazepam (DZM), an effect which implies the involvement of central hypothalamic-pituitary control of the response.