Heat shock protein 70 from Litopenaeus vannamei (LvHSP70) is involved in the innate immune response against white spot syndrome virus (WSSV) infection

Abstract

White spot syndrome (WSS) caused by white spot syndrome virus (WSSV) is a severe infectious disease in shrimp aquaculture. To find effective therapeutics to control WSSV, it is indispensable to understand the innate immune responses of shrimp to WSSV infection. Previous report demonstrated that the Litopenaeus vannamei heat shock protein 70 (LvHSP70) could induce shrimp innate immunity against bacterial infection. Herein, we further investigate the role of LvHSP70 in anti-WSSV infection. The temporal expression of LvHSP70 was significantly upregulated 2.5- and 1.5-fold at 6 and 24 h post systemic WSSV infection suggesting that the LvHSP70 was a WSSV responsive gene. The recombinant protein of LvHSP70 (rLvHSP70) was produced in an Escherichia coli system and its effect in protection against WSSV infection was investigated. Intramuscularly injection of juvenile shrimp with 1 nmol of rLvHSP70 could significantly prolong 50% mortality of WSSV-infected shrimp from 3 days to 5 days as compared to the control group injected with bovine serum albumin (BSA). Consistently, the injection of rLvHSP70 resulted in 24-fold, 20-fold and 100-fold decrease in the viral copy number after 6, 12 and 24 h post injection, respectively, compared to the control shrimp injected with BSA. Interestingly, it was found that the rLvHSP70 enhanced the expression of the key gene in the prophenoloxidase (proPO) activating system, LvproPO, but reduced the expression of Lvcaspase2 and LvIAP in WSSV-infected shrimp. These results suggested that the LvHSP70 is an important molecule involved in antiviral defense in shrimp presumably via modulating the proPO system and apoptosis.