Immunomodulatory effect of recombinant Macrobrachium rosenbergii nodavirus capsid protein (r-MCP) against white tail disease of giant freshwater prawn, Macrobrachium rosenbergii (de Man, 1879)

• Potential to stimulate M. rosenbergii prawn against white tail disease (WTD) with r-MCP capsid protein.
• Quantitative real-time PCR was carried out to determine the immune gene expressions.
• High percentage survival of purified r-MCP protein treated post-larvae challenged with MrNV and XSV.

Giant freshwater prawn (Macrobrachium rosenbergii, de Man, 1879) is an important commercial species due to its importance as food supply as well as a valuable export product. Since invertebrates lack a true adaptive immune response, stimulating M. rosenbergii for protection against white tail disease (WTD) with r-MCP capsid protein is a possible approach. The effectiveness of intramuscular injection of adult freshwater prawn with r-MCP protein and immersion of post-larvae (PL) of M. rosenbergii in r-MCP protein were investigated for their ability to protect against white tail disease. In experiment 1, the r-MCP protein injected adult prawn showed good immune response compared to PBS injected adult M. rosenbergii (mean body weight: 14.3 g). Samples were collected at different day intervals (24, 72, 120 and 168 h) to analyze the hematological and immunological parameters and to study the immune-related and HSP gene expressions with β actin as internal control in hemocytes, gill tissue and hepatopancreas by RT-PCR and quantification of immune and HSP gene expression by quantitative real-time PCR. In experiment II, the PL (10–12) of M. rosenbergii were exposed to r-MCP protein by immersion for 24 h and challenged with MrNV and XSV inoculum at a volume equal to 0.1% of the total rearing medium. The samples were collected at different day intervals, i.e. 1st day, 2nd day and 5th day from treated group and 1st day, 5th day and moribund samples from MrNV and XSV infected PL group to analyze the expression of immune-related gene of M. rosenbergii by RT-PCR. Quantitative real-time PCR was employed to determine the cycle threshold (CT) value of immune gene expression with β actin as host gene. The obtained percentage survival of post-larvae treated with purified r-MCP protein and challenged with MrNV and XSV was 76.03% on 15th day p.i., 99.78% survival was recorded in normal group on 15th day p.i. and 0% survival was recorded in MrNV and XSV infected group on 10th day p.i. This suggests that the prawn immune system is able to specifically recognize and react with protein. This study shows that stimulation of the immune system of prawn with r-MCP helps to control WTD in giant freshwater prawn, M. rosenbergii.