Abstract
Heat shock is a routine method used for inducible gene expression in animal models including zebrafish. Environmental temperature plays an important role in the immune system and infection progression of ectotherms. In this study, we analyzed the impact of short-term heat shock on neutrophil function using zebrafish (Danio rerio) as an animal model. Short-term heat shock decreased neutrophil recruitment to localized Streptococcus iniae infection and tail fin wounding. Heat shock also increased random neutrophil motility transiently and increased the number of circulating neutrophils. With the use of the translating ribosome affinity purification (TRAP) method for RNA isolation from specific cell types such as neutrophils, macrophages and epithelial cells, we found that heat shock induced the immediate expression of heat shock protein 70 (hsp70) and a prolonged expression of heat shock protein 27 (hsp27). Heat shock also induced cell stress as detected by the splicing of X-box binding protein 1 (xbp1) mRNA, a marker for endoplasmic reticulum (ER) stress. Exogenous expression of Hsp70, Hsp27 and spliced Xbp1 in neutrophils or epithelial cells did not reproduce the heat shock induced effects on neutrophil recruitment. The effect of heat shock on neutrophils is likely due to a combination of complex changes, including, but not limited to changes in gene expression. Our results indicate that routine heat shock can alter neutrophil function in zebrafish. The findings suggest that caution should be taken when employing a heat shock-dependent inducible system to study the innate immune response.
Highlights
Fever is an evolutionarily conserved response during infection
There was a decrease in neutrophil recruitment to the site of S.i. otic infection in Heat shock (HS) larvae compared to controls (Figure 1C)
Since it has been shown that tilapia are more susceptible to S.i infection at higher temperatures [28], we tested if shortterm HS can affect the survival of zebrafish larvae after S.i infection
Summary
Fever is an evolutionarily conserved response during infection. In ectotherms such as fish, where regulation of body temperature depends on external sources, behavioral fever is often displayed as a result of infection, manifested as an acute change in thermal preference. Our data suggest that short-term heat shock affects innate immune function in vivo including a decrease in neutrophil recruitment to sites of infection and wound, and an increase in the mobilization of neutrophils into the circulation. This short-term heat shock, had no effect on larval survival with infection. Neutrophil specific over-expression of Hsp, Hsp and spliced Xbp did not recapitulate the observed heat shock phenotypes These findings suggest against a cell autonomous role for these specific heat shock-induced genes on neutrophil function. Our findings suggest that caution should be taken when using the heat shock procedure to study innate immune responses since heat shock alone can induce changes in neutrophil function
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