Increased metabolic rate associated with immune stimulation of heat-killed Vibrio anguillarum at different temperatures in zebrafish (Danio rerio).

Abstract

The action of the immune response in zebrafish (Danio rerio) has been a target of many studies. However, the energetic demands involved in the immune response are poorly understood in ectothermic poikilotherms, such as fish. This research aims to characterize the energetic response of zebrafish to an immune challenge of heat-killed Vibrio anguillarum at 22°C and 27.5°C. Zebrafish were either not injected, injected intraperitoneally with 10μl of saline and Freund's incomplete adjuvant (sham), or heat-killed Vibrio anguillarum & Freund's incomplete adjuvant (1.21×1010 cfu/ml). Respirometry was then performed on these zebrafish for a period of 27h. Following this, spleen was collected for quantitative PCR analysis of the catalytic subunit of AMPK (ampka1 & ampka2), the nuclear factor kappa-light-chain-enhancer of activated B cells (nf-kb), and several cytokines (tnfa, il-1b, il-8, il-10). While there was no increase in oxygen consumption with any treatment at 22°C, there was a marked 30% increase in oxygen consumption in zebrafish injected with heat-killed Vibrio at 27.5°C. Furthermore, temperature had a strong effect on the timing of the immune response. At 22°C, there was a 2-3-fold increase in the cytokines measured associated with heat-killed Vibrio injection, whereas there were no differences found at 27.5°C. Furthermore, while there was an increase in ampka2 at 22°C, there was a sharp decrease in ampka2 at 27.5°C, although the changes in ampka2 transcript abundance could not be solely attributed to heat-killed Vibrio, as there were similar changes associated with the sham group. The results of this study demonstrate some of the first evidence that zebrafish increase routine metabolic rate associated with immune stimulation.