Effects of stress on immunocompetence and oxidative stress in nestling barn owls

Corticosterone, a glucocorticoid released during stressful situations, is commonly thought to cause immunosuppression. However, several authors demonstrated an opposite effect of stress, namely an enhancement of the immune response. It is likely that different parts of the immune system react differently to a challenge because of its complex network of regulation. In the present study I looked at the effect of moderately elevated plasma concentrations of the stress hormone corticosterone on some components of the innate and acquired immune system and on the susceptibility to oxidative stress in barn owl nestlings. Chicks were either implanted with a corticosterone releasing or a placebo pellet as controls. During the following weeks, the reaction of the constitutive innate immune system was measured as well as the ability of the humoral acquired immunity to react to a Tetravac injection with the synthesis of specific antibodies.

As expected, chicks with an elevated corticosterone level showed a reduced production of antibodies compared with the control nestlings. In contrast, the constitutive innate immune response was increased in corticosterone implanted chicks, which may be a compensatory response. Additionally, the elevated concentrations of circulating corticosterone were causing a transitory loss of body mass and a higher susceptibility to oxidative stress.

The moderately elevated plasma corticosterone levels enable barn owl nestlings to cope with stressful situations, but the long-lasting consequences may be severe. Possible benefits like a reduced risk of autoimmune responses or energy reallocations trade-off with costs including an increased risk of viral infections, detrimental effects of a lowered resistance to oxidative stress and the loss of body mass.