Enhancement of shrimp antiviral immune response through caspase-dependent apoptosis by small molecules.

Epidemic diseases cost large amount of economic loss in the shrimp aquaculture. To control the epidemic diseases, it is a very efficient approach to enhance the shrimp immunity by immunostimulants. In aquaculture, however, the applications of the available immunostimulants are very limited due to the lack of information about the roles of these immunostimulants in animal immunity. In the present study, a caspase protein (PjCaspase), required in shrimp antiviral apoptosis, was used as the target protein to screen for small molecules which would enhance the shrimp immunity. Based on screening using the EGFP-PjCaspase fusion protein in insect cells, four small molecules could enhance the activity of PjCaspase protein. Among them, IL-2 and evodiamine were further evidenced to enhance the apoptotic activity of shrimp hemocytes in vivo, suggesting that the small molecules improved the activity of apoptosis through the activation of the PjCaspase protein. The results indicated that the enhancement of apoptotic activity effectively inhibited the white spot syndrome virus (WSSV) infection in shrimp, which further led to the decrease of mortalities of WSSV-infected shrimp. Therefore, our study, for the first time, presented that the strategy using the key proteins in immune responses of aquatic organisms as the target proteins was a very efficient approach for the screening of immunostimulants to prevent the aquatic organisms from pathogen infections.