Effects of corticosterone on innate and humoral immune functions and oxidative stress in barn owl nestlings

Abstract

SUMMARYThe costs of coping with stressful situations are traded-off against other functions such as immune responses. This trade-off may explain why corticosterone secretion reduces immune reactions. Corticosterone differentially affects various immunity components. However, which component is suppressed varies between studies. It remains unclear whether the trade-off in energy, nutrition, autoimmunity or oxidative stress accounts for differential immunosuppression. In this study, we investigated whether corticosterone differentially affects the constitutive innate and humoral acquired immunity. We used barn owl nestlings, implanting 50% with a corticosterone-releasing pellet and the other 50% with a placebo pellet. To measure the effect on humoral immunity we vaccinated 50% of the corticosterone-nestlings and 50% of the placebo-nestlings with the antigens 'Tetravac' and the other 50% were injected with PBS. To assess the costs of elevated corticosterone, we measured body mass and resistance to oxidative stress. Administration of corticosterone increased corticosterone levels whereas vaccination induced the production of antibodies. Corticosterone reduced the production of antibodies, but it did not significantly affect the constitutive innate immunity. Corticosterone reduced body growth and resistance to oxidative stress. Under stressful conditions barn owl nestlings seem to keep the constitutive innate immunity, whereas elevated corticosterone levels negatively affected inducible immune responses. We found evidence that mounting a humoral immune reaction is not costly in terms of growth, but reduces the resistance to oxidative stress independently of corticosterone administration. We suggest that humoral immunity is suppressed because the risk of immunopathologies may be disproportionately high when mounting an antibody response under stressful situations.

Feather corticosterone content in predatory birds in relation to body condition and hepatic metal concentration

“…In the present study, significant differences in feather CORT content between species were most evident between buzzard and sparrowhawk (both Accipitriformes species) whereas feather CORT concentrations did not differ significantly between barn owls, kestrels and tawny owls. This is consistent with reports that baseline and stress-induced levels of plasma CORT are similar in barn owls and kestrels (Almasi et al, 2012(Almasi et al, , 2013Meijer and Schwabl, 1989;Müller et al, 2009;Stier et al, 2009;Strasser and Heath, 2011).…”

Relationships between metabolic status, corticosterone secretion and maintenance of innate and adaptive humoral immunities in fasted re-fed mallards

“…Nevertheless, a negative, weak but significant, relationship was observed between plasma corticosterone and NAbs. However, barn owl chicks (Tyto alba) implanted with exogenous corticosterone maintained plasma NAbs (constitutive innate immunity) at levels similar to those observed in sham-implanted chicks (Stier et al, 2009). Overall, in the current study, the variations in the two branches of the immune system do not seem to be causally driven by corticosterone secretions.…”

“…However, humoral immunity did not significantly covary with natural corticosterone concentrations in breeding barn swallows (Hirundo rustica) (Saino et al, 2002). Moreover, while the administration of exogenous corticosterone did not affect T cell-mediated immunity (CMI) of captive common eiders or constitutive innate immunity of wild barn owl nestlings (Tyto alba) (Stier et al, 2009), it did suppress humoral immunity of both species, further suggesting that corticosterone can selectively suppress different immune components. Therefore, it is still unclear whether naturally elevated corticosterone levels would induce immunosuppression, and the relationships between corticosterone and the different arms of the immune system need to be clarified.…”

Effects of early developmental conditions on innate immunity are only evident under favourable adult conditions in zebra finches

“…Correspondingly, prolonged fasting resulted in increased corticosterone and decreased NAb levels in female mallards (Bourgeon et al 2010). Yet, administering corticosterone did not alter innate immune capacity in barn owl (Tyto alba) nestlings (Stier et al 2009), while brood size manipulation produced no effect on corticosterone in nestlings of the spotless starling (Sturnus unicolor; Gil et al 2008), and have not been measured in zebra finches. However, as we only measured two components of the innate immune system, we cannot rule out that other branches of (innate) immunity were differently affected.…”