The protective effect of specific yolk antibody against nervous necrosis virus infection in Mandarin fish(Siniperca chuatsi)

Nervous necrosis virus (NNV), a member of the Nodavirus genus, is a highly contagious disease that is found all over the world. As of right now, there aren't many reliable commercial vaccines available to combat this infection. In a previous study, we isolated a Mandarin fish (Siniperca chuatsi)-derived NNV strain, tentatively named MFNNV. By immunizing hens with MFNNV recombinant capsid protein (CP), this study produced high-purity anti-MFNNV yolk antibodies. According to the ELISA results, the purified anti-MFNNV IgY titer peaked at week 8 after the first vaccination; western blotting and indirect immunofluorescence results showed that IgY could act as a primary antibody to specifically recognize recombinant CP and virus particles. At the cellular level, specific IgY significantly reduced the appearance of vacuolated cytopathic effect in GS cells after incubation with an equal volume of virus compared with non-specific IgY. Mandarin fish was fed diets supplemented with anti-MFNNV IgY or non-specific IgY at 33 % (w/w) for 7 days prior to artificial infection with MFNNV. On the 14th day of artificial infection with MFNNV, the mortality rate was 53.3 % in the specific group and 83.3 % in the nonspecific group, and the relative protection rate of the specific IgY group was about 36 % compared with that of the nonspecific IgY group. In histopathological analysis, vacuolizing lesions were observed in the brain tissues of Mandarin fish in the non-specific group, whereas only slight vacuolization was observed in the brain tissues of the specific group. Further analysis revealed that compared with the non-specific group, the MFNNV-CP gene expression in the eyes as well as the brain of Mandarin fish in the specific group showed a significant decrease, and the mRNA expression levels of immune-related factors, such as TNF-α, IFN-h, IL-1, IL-8, Mx proteins, and IgM in the spleen, liver, kidney, and hindgut tissues of the specific group also showed a decrease of varying degrees, suggesting that oral administration of specific IgY could neutralize virus and reduce the immune responses as well as tissue pathological damage induced by the Nervous necrosis virus. Consequently, we suggested that IgY could protect Mandarin fish from MFNNV infection by acting as a passive immunological measure.