Distinct stressors and exogenous glucocorticoids promote immunomodulation in toads

Acute stressors effects followed by peaks in glucocorticoid levels, such as corticosterone, are generally immunostimulatory in mammals. However,  is this pattern also found in amphibians? In this study, we used distinct acute stressors (restraint with movement restriction and an immune challenge with LPS) and the transdermal application of corticosterone to evaluate their effects on the immune response of toads (Rhinella icterica). All protocols increased the plasma corticosterone levels and neutrophil to lymphocyte ratio. We also observed that the inflammatory response (measured as edema in response to phytohemagglutinin) and phagocytosis of blood leukocytes increased with the transdermal application of a high corticosterone dose. Contrary to predicted, we observed that phagocytosis of peritoneal leukocytes decreased in response to a low and high dose of corticosterone. An interesting result was that the protein immune response, measured as the plasma bacterial killing ability, was not changed by any protocols. In general, our results show that acute stressors and the acute application of corticosterone generate immune stimulation in toads. However, the stress and corticosterone-induced effects seem to be more complex, with opposite effects being observed. In addition, our results demonstrate that the cellular immune response seems more sensitive to stressors and corticosterone treatment. While the non-cellular response appears to be less sensitive and more robust, not being modulated by acute stressors and corticosterone application in toads. See the full article for more details: https://doi.org/10.1016/j.bbih.2021.100230