Passive Protective Effect Of Chicken Egg Yolk Immunoglobulins Against Experimental Listonella Anguillarum Infection In Sweetfish (Plecoglossus Altivelis)

Yolk antibody (egg yolk immunoglobulin Y, IgY) was extracted from the eggs laid byhens initially immunized with specific antigen, which is a protein with strong immunefunction, and can be used to the prevention and therapy of some diseases. Oraladministration of chicken egg yolk immunoglobulins (IgY) has attracted much attention asa means for controlling infectious diseases caused by microorganisms. IgY isolationprocedures were carried out by salt precipitation (ammonium sulphate in solid form)followed by centrifugation and dialysis, and evaluated the protective effect of IgY againstListonella anguillarum infection in sweetfish. Health sweetfishes divided into three groupsafter the intraperitoneal injection of Listonella anguillarum, fed with anti-L.anguillarumIgY (aLIgY), non-specific IgY (nspIgY), and equal saline. The fish treated with100mg/kgor200mg/kg aLIgY could achieve survival rates of approximately50%and80%at day8,respectively. However, the survival rates of fish treated with100mg/kg or200mg/kgnspIgY were only10%and15%at day8, respectively. All fish in saline-treated groupsdied within seven days after bacterial inoculation. In addition, when the infection and oraladministration were carried out at the same time, the effect of aLIgY was especiallynotable, the survival rate was80%, the fish treated with200mg/kg aLIgY7d before and1dafter bacterial infection achieved survival rates of64%and55%respectively. It revealsthat aLIgY has a positive protective effect for sweetfish infected with Listonellaanguillarum, and the delivery time of IgY is a critical factor in the effect of aLIgY. Abacterial burden assay was performed by the plate count method, the bacterial load inblood, liver, spleen and head kidney was significantly lower in fish treated with aLIgYthan that treated with nspIgY. It suggests that aLIgY may inhibit bacteria growth to protectsweetfish. RT-qPCR was performed to analyze tumor necrosis factor-α (TNF-α),interleukin-1β (IL-1β), transforming growth factor-β (TGF-β), and leukocyte cell-derivedchemotaxin-2(LECT2) transcripts in head kidney, spleen, and liver from nspIgY-treatedor aLIgY-treated sweetfish that were injected ip simultaneously with L. anguillarum.aLIgY treatment significantly reduced TNF-α, IL-1β, TGF-β, and LECT2transcript levels in the head kidney, spleen, and liver of sweetfish challenged by L. anguillarum, comparedwith nspIgY treatment. The results indicated that aLIgY may inhibit the expression ofinflammatory cytokines thereby inhibiting the inflammatory response. The phagocyticactivity of macrophages for L. anguillarum in the presence of aLIgY was significantlyhigher than that seen for nspIgY. It implies that aLIgY may be able to enhance phagocyticactivity of macrophages for L. anguillarum to improve disease resistance of sweetfish.These results suggest that passive immunization by oral intubation with pathogen-specificIgY may provide valuable treatment and prevention for L. anguillarum infection insweetfish, and the protective mechanism may be related to the bactericidal andbacteriostatic effect of specific egg yolk antibody, enhanced phagocytic activity and theregulation of the expression of inflammatory cytokines.