Chronic restraint attenuates the immunosuppressive response induced by novel aversive stimuli.

The exposure to a novel aversive event, such as foot shock, induced a decrease in the percentage of T lymphocytes and a clear reduction in the delayed-type hypersensitivity reaction (DTH). This immunosuppressive response to an acute stressor was absent in rats that were previously exposed to a chronic immobilization stress regime (2 h daily during 7 consecutive days), but was still present in animals with prior exposure to only one or three restraint sessions. No stress effect was observed in other immunologic parameters, such as the percentage of B lymphocytes or the hemagglutinin titer, in any of the experimental treatments. The possible involvement of central adaptive mechanisms in the attenuation of the immunosuppressive response induced by an acute stress is discussed.