Immunomodulatory Effects of Recombinant Capsid and B2 Proteins of <i>Macrobrachium rosenbergii</i> Nodavirus in Freshwater Prawn <i>M. rosenbergii</i> (de Man)

Abstract

The present study evaluated the role of recombinant capsid and B2 proteins of Macrobrachium rosenbergii nodavirus (MrNV) in modulating the immune response and MrNV load in infected prawns. In the first experiment, the sub-adult prawns were injected with recombinant capsid and B2 proteins at a concentration of 0, 1.0 and 10 μg (per prawn), and immune parameters and expression of some immune-related genes measured up to 14 days post-injection (dpi). In another experiment, early juvenile prawns were immunized with similar dose of both proteins and the animals were then challenged by immersion with MrNV. Following the challenge, the infection status in these prawns was detected in muscle by nested RT-PCR up to 14 dpi. In the sub-adult prawns, exposure to capsid and B2 proteins modulated the immune response as observed in total and differential haemocyte counts, total protein, lysozyme and prophenol oxidase activities, and expression changes in cytochrome oxidase, superoxide dismutase and β-glucan binding protein genes in hepatopancreas at different time post-exposure. In early juvenile prawns, only the exposure to capsid protein remarkably reduced the viral load 14 days after challenge as observed in screening through nested RT-PCR based assay. On the other hand, there was no significant reduction in viral load upon injection of only B2 protein at both the dose levels of exposure. The present study opens up scope for using capsid protein as immunomodulator in reducing viral load and enhancing immune status of prawn M. rosenbergii.