Suppression of experimental autoimmune encephalomyelitis by restraint stress: sex differences.

We have recently reported that female Lewis rats exhibit significantly higher basal circadian levels of corticosterone (Cort) than male Lewis rats. The studies reported here were designed to explore whether male and female Lewis rats demonstrate a differential suppression of experimental autoimmune encephalomyelitis (EAE) following exposure to an identical regimen of repetitive restraint stress. Rats were restrained for 1 or 9 h/day beginning 5 days before myelin basic protein (MBP) challenge and extending through the recovery period (18 days post challenge). Both clinical signs and histopathological changes of EAE were more significantly suppressed in 9-h-stressed females relative to male Lewis rats. Investigation of the mechanism underlying the stress-induced suppression of EAE revealed that restraint stress did not alter the clinical course of EAE in rats challenged with MBP 68-88 encephalitogenic peptide, suggesting that restraint stress may affect processing and/or presentation of the MBP molecule. Stressed rats exhibited decreased interleukin-2 and interferon gamma production, and the frequency of MBP-reactive lymphocytes was reduced in comparison to non-stressed rats. Finally, repetitive restraint stress had no effect on blood-spinal cord permeability during EAE. The results presented here underscore the importance of such experimental variables as sex, strain, time of day, and the kinetics of immune response development.