Litopenaeus vannamei heat shock protein 70 (LvHSP70) enhances resistance to a strain of Vibrio parahaemolyticus, which can cause acute hepatopancreatic necrosis disease (AHPND), by activating shrimp immunity

Heat shock protein 70 (HSP70) acts as a molecular chaperone and a stress protein, but also plays important roles in innate and adaptive immune responses. Previous studies have reported that non-lethal heat shock (NLHS) could enhance the resistance of Pacific white shrimp Litopenaeus vannamei to a specific strain of Vibrio parahaemolyticus, which carried a toxin-producing plasmid (VPAHPND), via the induction of LvHSP70 transcription. Here, we further investigated the specific function of LvHSP70 in shrimp immunity. The upregulation of LvHSP70 at the protein level was detected during recovery time after NLHS treatment, using both western blot analysis and immunofluorescence microscopy. We found that NLHS immediately activated the production of LvHSP70 in shrimp hemocytes and that such induction was observed in all three types of hemocytes: hyaline; granular and semi-granular cells. Furthermore, the role of LvHSP70 in bacterial defense was investigated using the heterologous expression of recombinant LvHSP70 (rLvHSP70) in Escherichia coli. Shrimp receiving rLvHSP70 by injection showed an increased survival rate (75%) to VPAHPND infection compared to just 20% survival in the control group injected with bovine serum albumin (BSA). We also demonstrated that the injected rLvHSP70 accumulated in shrimp hemocytes and was detected in the intracellular space of hemocyte cells leading to the induced expression (P<0.05) of several immune-related genes (LvMyD88, LvIKKβ, LvIKKε, LvCrustin I, LvPEN2, LvPEN3, LvproPO1, LvproPO2 and LvTG1). Collectively, these results suggest that LvHSP70 plays a crucial role in bacterial defense by activating the shrimp immune system.