Meeting Abstract
The physiological reactions in amphibians to stressors and the consequences of glucocorticoid elevation on their immune responses are still poorly understood. To assess the effects of acute stress on immune reactions in amphibians, invasive cane toads from Florida received either a transdermal application of corticosterone (CORT), the primary glucocorticoid in amphibians, or peanut oil followed by an immune challenge (lipopolysaccharide (LPS) or saline injection; N=6/group). Two hours after the exogenous CORT administration and LPS challenge, we measured the expression of proinflammatory genes (i.e., interleukin (IL) 1β, IL6, IL8, IL12 and tumor necrosis factor alfa (TNFα)), as well as plasma CORT and plasma bacterial killing ability (BKA). CORT levels were significantly higher in animals in the CORT+LPS treatment when compared to the Oil+Saline (Control) group as well as the Oil+LPS treatment (F2,12=33.466; p≤0.001). BKA was higher in Control animals (F2,12=6.741; p=0.008) when compared to Oil+LPS and CORT+LPS. There was upregulation in 3 of the 5 pro-inflammatory genes investigated on the LPS+CORT animals compared with Controls: IL1β was upregulated by log2fold factor of 4 (p=0.018); IL6 upregulated by log2fold factor 4.8 (p=0.005); and IL8 upregulated by log2fold factor 4.7 (p=0.018). Thus, LPS alone didn’t trigger a significant change in gene expression, but the combination of LPS and acute increase in circulating CORT caused by the exogenous CORT administration stimulated the immune response. The multiple immune genes being upregulated have different roles, including phagocytic stimulation. These results may warrant investigation to whether CORT alone triggers differentially expressed immune genes in cane toads.
