Abstract
Non-lethal heat shock boosts bacterial and viral disease tolerance in shrimp, possibly due to increases in endogenous heat shock protein 70 (Hsp70) and/or immune proteins. To further understand the mechanisms protecting shrimp against infection, Hsp70 and the mRNAs encoding the immune-related proteins prophenoloxidase (proPO), peroxinectin, penaeidin, crustin and hemocyanin were studied in post-larvae of the white-leg shrimp Litopenaeus vannamei, following a non-lethal heat shock. As indicated by RT-qPCR, a 30 min abrupt heat shock increased Hsp70 mRNA in comparison to non-heated animals. Immunoprobing of western blots and quantification by ELISA revealed that Hsp70 production after heat shock was correlated with enhanced Hsp70 mRNA. proPO and hemocyanin mRNA levels were augmented, whereas peroxinectin and crustin mRNA levels were unchanged following non-lethal heat shock. Penaeidin mRNA was decreased by all heat shock treatments. Thirty min abrupt heat shock failed to improve survival of post-larvae in a standardized challenge test with Vibrio harveyi, indicating that under the conditions of this study, L. vannamei tolerance to Vibrio infection was influenced neither by Hsp70 accumulation nor the changes in the immune-related proteins, observations dissimilar to other shrimp species examined.
Highlights
Exposure to long-term hyperthermic stress disrupts the normal physiological processes of shrimp and under severe conditions may decrease feeding, retard growth and molting, and weaken the immune response, resulting in mortality [1]
heat shock protein 70 (Hsp70) mRNA and Protein Increased after nonlethal heat shock (NLHS) Thirty min NLHS from 28uC to 36uC and 38uC followed by recovery for 8 h increased Hsp70 mRNA approximately 1.4 and 2.1-fold, respectively (Fig. 2)
A 30 min NLHS significantly increased the amount of proPO and hemocyanin mRNA in L. vannamei post-larvae, in line with the observation that the shrimp immune response is influenced by temperature [5]
Summary
Exposure to long-term hyperthermic stress disrupts the normal physiological processes of shrimp and under severe conditions may decrease feeding, retard growth and molting, and weaken the immune response, resulting in mortality [1]. Several mechanisms have been proposed to explain how heat shock defends against bacterial and viral diseases in aquatic animals. A NLHS may enhance heat shock protein (Hsp) production, Hsp, which is required to stabilize cells against injury due to pathogen proliferation, properly fold cell proteins synthesized in response to bacterial pathogens, store and re-fold partially denatured proteins and stimulate the innate immune response [4]. NLHS may increase the expression of selected immune-related genes resulting in enhanced immunity. In this context, heating from 24uC to 27uC and 30uC stimulates the prophenoloxidase (proPO) cascade system of L. vannamei, a mechanism important for pathogen melanisation by the innate immune system [5]. In this context, heating from 24uC to 27uC and 30uC stimulates the prophenoloxidase (proPO) cascade system of L. vannamei, a mechanism important for pathogen melanisation by the innate immune system [5]. proPO occurs naturally as an inactive pro-form of phenoloxidase (PO), activated by an endogenous trypsin-like serine protease referred to as prophenoloxidase activating enzyme (ppA) [6]. proPO activates melanin production and increases cell adhesion, encapsulation and phagocytosis [7,8], important mechanisms by which the crustacean innate immune system combats microbial invasion
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