Effects of oral recombinant VP28 expressed in silkworm (Bombyx mori) pupa on immune response and disease resistance of Procambarus clarkii

Immunostimulation of shrimp through oral administration of silkworm pupae expressing VP15 against WSSV

White spot syndrome virus (WSSV) is one of the most concerning pathogens in penaeid shrimp and can cause severe loss in shrimp aquaculture worldwide. Among the WSSV structural proteins, VP15, a DNA-binding protein located in the WSSV nucleocapsid, is an antiviral protein candidate to protect kuruma shrimp (Marsupenaeus japonicus) from WSSV infection. We identified that the truncated VP15, VP15_(26-57), is responsible for the protective effect against the WSSV. This study attempts to develop an immunizing agent against WSSV using silkworm pupa as a delivery vector through oral administration. The VP15, VP15_(26-57), and SR11 peptide derived from VP15_(26-57) were expressed in silkworm pupae. Oral administration of feed mixed with the powdered pupae that expressed VP15-derived constructs enhanced the survivability of kuruma shrimp with an overall relative percent survival (RPS) higher than 70%. There is no death for the group receiving pupa/VP15_(26-57), and the RPS is 100%. In addition, we also investigated the relative mRNA expression levels of immune-related genes by qPCR at different time points. Our results indicate that the oral administration of pupa/VP15-derived products could provide a high protective effect against WSSV and be a practical approach for controlling WSSV in aquaculture.

Oral administration of porcine epidemic diarrhea virus spike protein expressing in silkworm pupae failed to elicit immune responses in pigs

The silkworm (Bombyx mori) and its pupae have been used for decades as nutritional additives and applied on the production of high-quality recombinant proteins via the baculovirus expression vector (BEV) system. The bio-capsule, the fat-rich body, and some body components of the silkworm pupae, which deliver antigens passing through the harsh environment of digestive tract and reaching the intestine, have been used as a vehicle for oral vaccines. In the present study, to develop a novel oral vaccine against porcine epidemic diarrhea virus (PEDV), the PEDV spike (S) protein was expressed in silkworm pupae and BmN cells using the BEV system. After three doses of oral administrations with 2-week intervals in pigs, neither PEDV S protein-specific humoral nor mucosal immune responses can be detected. The failure of eliciting the PEDV-specific immune response suggested that the BEV system using BmN cells or silkworm pupae as oral immunogen-expression vehicles was not able to overcome the immunological unresponsiveness, which was possibly due to gastrointestinal specific barriers and oral tolerance. Better strategies to enhance the delivery and immunogenicity of oral vaccines should be further investigated. Nevertheless, the PEDV S protein generated in the BmN cells and silkworm pupae herein provides an efficient tool to produce the recombinant antigen for future applications.

Host and virus protein interaction studies in understanding shrimp virus gene function

Protein-protein interaction studies have been widely used in several fields to characterize an unknown protein. This in turn helps to find out several pathways to understand a complex mechanism or discover a drug for treatment. Among the methods, yeast two-hybrid has widely been used in human, animal and plant research studies. This aspect of research has also been found useful in understanding the shrimp virus gene function. With respect to White spot syndrome virus, interaction studies have been applied to elucidate virus structure, understand the mode of entry of the virus, mechanism of virus replication and also to discover some of the host anti-viral proteins. Interaction studies on other shrimp viruses are scanty and only few reports available on Yellow head virus and Taura syndrome virus. All these findings are still in preliminary stage and lot more studies are necessary to have the clear picture. Protein interaction research on other shrimp viruses are still lacking. Considering all these, it appears that this field of research has a wide scope to understand the virulence mechanism of shrimp viruses where very little information is available till date.

Histological alterations and immune response in the crayfish Procambarus clarkii given rVP28-incorporated diets

There is growing evidence that recombinant VP28 protein (rVP28) can significantly enhance immune response and disease resistance against white spot syndrome virus (WSSV) in shrimp, although the underlying mechanisms have not been entirely clarified yet. The aim of this study was to determine the effect of rVP28 on histological alterations and WSSV-induced apoptosis in crayfish Procambarus clarkii. Crayfish were fed commercial diets supplemented with different doses of HyNPV-VP28 infected pupae (rVP28-hp) for 4 weeks. Results showed that rVP28-hp may be used as a safe and effective source of medicinal proteins in aquaculture when supplemented in diet at low dose (10 g kg(-1) and 50 g kg(-1)), which could obviously reduce the percentage of apoptotic cells in stomach, gut and hepatopancreas tissues induced by the WSSV challenge and showed the relative percent survival (RPS) of 82.2% and 94.4%, respectively. But rVP28-hp would be detrimental to crayfish survival and decrease resistance to WSSV infection at the high dose (100 g kg(-1) and 200 g kg(-1)), with the cumulative mortality of up to 48.2% and 56.6% after WSSV challenge, respectively. During a 28-d feeding period, the survival rate of crayfish was only 54.5%-75.6%, and histopathological observation showed that one of the principal lesions was serious cell swelling, vacuolar degeneration and necrosis in hepatopancreatic epithelia and myocardial cells. These results suggested that rVP28-hp can influence the immune functions of crayfish in a dose-dependent manner, and the rVP28-hp at the dose of 50 g kg(-1) was recommended to prevent WSSV in crayfish culture.