Abstract
In many fish species, the immune system is significantly constrained by water temperature. In spite of its critical importance in protecting the host against pathogens, little is known about the influence of embryonic incubation temperature on the innate immunity of fish larvae. Zebrafish (Danio rerio) embryos were incubated at 24, 28 or 32 °C until first feeding. Larvae originating from each of these three temperature regimes were further distributed into three challenge temperatures and exposed to lipopolysaccharide (LPS) in a full factorial design (3 incubation × 3 challenge temperatures). At 24 h post LPS challenge, mortality of larvae incubated at 24 °C was 1.2 to 2.6-fold higher than those kept at 28 or 32 °C, regardless of the challenge temperature. LPS challenge at 24 °C stimulated similar immune-related processes but at different levels in larvae incubated at 24 or 32 °C, concomitantly with the down-regulation of some chemokine and lysozyme transcripts in the former group. Larvae incubated at 24 °C and LPS-challenged at 32 °C exhibited a limited immune response with up-regulation of hypoxia and oxidative stress processes. Annexin A2a, S100 calcium binding protein A10b and lymphocyte antigen-6, epidermis were identified as promising candidates for LPS recognition and signal transduction.
Highlights
In teleosts, the innate immune system is extremely important for host defence
Pathogen-associated molecular patterns (PAMPs) are recognized by pattern recognition receptors (PRRs) on the surface of leukocytes and other cells involved in the innate immune response
No significant difference in mortality was observed between 32 °C and 28 °C incubation groups regardless of subsequent challenge temperatures
Summary
The innate immune system is extremely important for host defence. The above surface barriers and associated factors are sufficient to defend the host against pathogens. If this first line of defence is breached, pathogens will encounter additional humoral immune mediators. Pathogen-associated molecular patterns (PAMPs) are recognized by pattern recognition receptors (PRRs) on the surface of leukocytes and other cells involved in the innate immune response. Teleosts lack some immune organs that are important in mammalian host defence. As most fish are ectotherms, their body temperature changes following ambient thermal fluctuations This is extremely challenging for the innate immune system during early stages of ontogeny in spite of their high developmental plasticity[14]. We used LPS to mimic a bacterial challenge and the mRNA transcriptome was analysed to evaluate the global innate immune response at early larval stages
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