Moderate stress protects female mice against bacterial infection of the bladder by eliciting uroepithelial shedding.

We have previously shown (M. Aronson, O. Medalia, D. Amichay, and O. Nativ, Infect. Immun. 56:1615-1617, 1988) that shedding of viable uroepithelial cells (elicited by invading microorganisms) constitutes an antimicrobial defense mechanism. The present study deals with two different stress-involving procedures, in which increased uroepithelial shedding rendered female mice resistant to vesical infection. Moderate stress was induced in female mice by exposing the animals either to constant illumination for 96 h or to 37 degrees C heat for 24 h. In both cases, the rate of infection was considerably reduced as a result of increased epithelial shedding (P < 0.0001). Stress was manifested by both reduced thymic weight and increased blood corticosterone levels. Shedding was also elicited by intraperitoneal injection of norepinephrine together with hydrocortisone or by intravesical injection of corticosterone. Constant illumination as well as heat enormously facilitated the migration of polymorphonuclear cells into the bladder following the action of chemotactic stimuli. Male mice subjected to identical stress-generating conditions did not display considerable epithelial shedding or increased migration of polymorphonuclear cells, and they were not protected from intravesical infection.