Effects of elevated corticosterone on humoral innate and antibody‐mediated immunity in southern leopard frog (Lithobates sphenocephalus) tadpoles

Abstract

As a free‐living larval stage of a vertebrate, tadpoles are good subjects for the study of the development of physiological systems and the study of evolutionarily conserved, context‐dependent responses to variable environments. While the basic components of innate and adaptive immune defenses in tadpoles are known, the impact of glucocorticoids on immune defenses in tadpoles is not well‐studied. We completed four experiments to assess effects of elevation of corticosterone on humoral innate defenses and antibody‐mediated immunity in southern leopard frog tadpoles (Lithobates sphenocephalus). To test humoral innate defense within the tadpoles exposed to short‐term and long‐term elevation of glucocorticoids, we exposed tadpoles to exogenous corticosterone for different lengths of time in each experiment (0–84 days). We used bacterial killing assays to assess humoral innate immune defense. To test antibody‐mediated immune responses, we again exposed tadpoles to exogenous corticosterone, while also exposing them to Aeromonas hydrophila. We used A. hydrophila ELISA comparing IgM and IgY responses among groups. Plasma from corticosterone‐dosed tadpoles killed more A. hydrophila than control tadpoles each following a short‐term (14 day) and long‐term (56 day) exposure to exogenous corticosterone. Conversely, corticosterone‐dosed tadpoles had significantly lower IgM and IgY against A. hydrophila after 12 weeks. Our fourth experiment revealed that the lower IgY response is a product of weaker, delayed isotype switching compared with controls. These results show that elevated corticosterone has differential effects on innate and acquired immunity in larval southern leopard frogs, consistent with patterns in more derived vertebrates and in adult frogs.

Introduction to the special issue: Ecoimmunology in ectotherms

“…Although less studied in ecoimmunology contexts, adaptive immunity is present in ectotherms, comprising antibodies, such as IgA, IgD, IgM, IgY, IgT, and IgX (Chen & Robert, 2011; Firdaus‐Nawi & Zamri‐Saad, 2016; Zimmerman, 2020). Confirming the presence of these different classes of antibodies, in this SI, Billig et al (2020) showed that the southern leopard frog ( Lithobates sphenocephalus ) tadpoles possess IgM and IgY antibodies that can be modulated by several hormones, including glucocorticoids. Also, in a study with fence lizards ( Sceloporus undulatus ), Tylan et al (2020) demonstrated IgM antibody production against fire ants, which is very useful for dealing with the ant's venom.…”

“…Short‐ and long‐term exogenous corticosterone administration promoted increased bacterial killing ability (Billing et al, 2020). In contrast, long‐term exogenous corticosterone exposure decreased the antibody response (lower IgM and IgY) against the bacteria Aeromonas hydrophila (Billing et al, 2020). Moreover, they described that the lower IgY is a product of weaker and delayed isotype switching in the corticosterone‐treated group than controls (Billing et al, 2020).…”

Introduction to the special issue Amphibian immunity: stress, disease and ecoimmunology

“…Stress-driven immunomodulation has gained more attention in ectothermic vertebrates in the last decades [25,27,39,[56][57][58][59][60][61][62], with implications on the stress-induced protective and harmful effects on several immune functions. As observed in other vertebrates, the amphibian immune system is subjected to stressors and its endocrine mediators, including glucocorticoid-induced immunomodulation [27,28,31,32,63,64]. Stress-induced immunomodulation has been described when animals are facing environmental changes (e.g.…”

Lipopolysaccharide Regulates Pro- and Anti-Inflammatory Cytokines, Corticosterone, and Melatonin in Toads

“…2021b ). In addition, Billig et al. (2020) reported that southern leopard frog ( Lithobates sphenocephalus ) tadpoles treated with glucocorticoid had greater plasma bacterial killing ability than controls after a short-term and long-term exposure to exogenous glucocorticoid.…”

“…(2020) reported that southern leopard frog ( Lithobates sphenocephalus ) tadpoles treated with glucocorticoid had greater plasma bacterial killing ability than controls after a short-term and long-term exposure to exogenous glucocorticoid. On the other hand, tadpoles treated with the hormone had lower IgM and IgY after 12 weeks ( Billig et al. 2020 ).…”