ABSTRACT
This study investigated the effects of Cinnamomum osmophloeum leaf hot-water extract (CLWE) on nonspecific immune responses and resistance to Vibrio parahaemolyticus in white shrimp (Penaeus vannamei). Firstly, a cell viability assay demonstrated that the CLWE is safe to white shrimp heamocytes in the concentration of 0-500 mg L-1. Haemocytes incubated in vitro with 10 and 50 mg L-1 of CLWE showed significantly higher response in superoxide anion production, PO activity, and phagocytic activity. In the in vivo trials, white shrimp were fed with 0, 0.5, 1, 5, and 10 g kg-1 CLWE supplemented feeds (designated as CLWE 0, CLWE 0.5, CLWE 1, CLWE 5, and CLWE 10, respectively) over a period of 28 days. In vivo experiments demonstrated that CLWE 0.5 feeding group resulted in the highest total haemocyte count, superoxide anion production, phenoloxidase activity, and phagocytic activity. Moreover, CLWE 0.5 supplemented feed significantly upregulated the clotting system, antimicrobial peptides, pattern recognition receptors, pattern recognition proteins, and antioxidant defences in white shrimp. Furthermore, the shrimp were infected with V. parahaemolyticus injections after 14 days of feeding as challenge test. Based on the challenge test result, both CLWE 0.5 and CLWE 5 demonstrated a strong resistance to V. parahaemolyticus. These two dosages effectively reduced the number of nonviable cells and activated different haemocyte subpopulations. These findings indicated that treatment with CLWE 0.5 could promote nonspecific immune responses, immune-related gene expression, and resistance to V. parahaemolyticus in white shrimp.
