Time-dependent effects of isolation on lymphocyte and adrenocortical activity

Individual housing of previously group-housed animals was found to result in time-dependent changes in mitogen-induced lymphocyte proliferation and plasma corticosterone concentrations. During the first week of isolation, both B and T lymphocyte responses were depressed. However, within 2 weeks at least a 2-fold enhancement was observed. The increased lymphocyte response was still present after 35 days of isolation. Within the first day of isolation and continuing for 2 weeks, plasma corticosterone levels were found to be significantly decreased in isolated animals compared to those of continuously housed animals. No significant differences in steroid levels were observed by 35 days. These data demonstrate that isolation is accompanied by a depressed adrenocortical activity and suggest that the immunosuppression associated with short-term exposure is mediated by factors other than corticosterone.