Enhancement of rat lymphocyte proliferation after prolonged exposure to stress

Rats exposed to 5 weeks of isolation, water scheduling (daily consumption restricted to 30 min), and their combination demonstrated significantly enhanced splenic lymphocyte proliferative responses to phytohemagglutinin (PHA) compared to those of group-housed animals (five per cage) maintained under standard vivarium conditions. The increased response found with the combination treatment was of the same magnitude as that found with each stressor alone. Blood lymphocyte responses were similarly increased after 5 weeks of isolation. When animals were exposed to the combination treatment for 12 weeks, both blood and splenic lymphocyte responses were found to be enhanced by greater than 2- and 3-fold, respectively. At the time of sacrifice no changes were found in total white blood cell numbers or plasma corticosterone levels with any of these treatments. These data suggest that prolonged exposure to a stressor results in an enhancement of immune cell activity.