Levamisole enhances immunity in ducklings vaccinated againstRiemerella anatipestifer

A novel bivalent inactivated vaccine for ducks against Riemerella anatipestifer based on serotype distribution in southern China

Riemerella anatipestifer (RA) causes epizootic infectious polyserositis in ducks with high mortality and leads to huge economic losses worldwide. Bacterial resistance poses a challenge for the control of the disease, vaccines failed to provide ideal cross-protection. Thus, the preparation of vaccines based on popular serotypes is important. In this study, we collected 700 brain and liver tissues of dead ducks from 8 provinces in southern China from 2016 to 2022 and obtained 195 RA isolates with serotypes 1, 2, 7, and 10. Serotypes 1 and 2 were the most prevalent (82%). A novel bivalent inactivated vaccine WZX-XT5 containing propolis adjuvant was prepared, we chose XT5 (serotype 1) and WZX (serotype 2) as vaccine strains and evaluated WZX-XT5-induced immune response and protective efficacy in ducks. Results showed that the XT5 (LD50, 3.5 × 103 CFU) exhibited high virulence and provided better protection against RA compared with ZXP, DCR and LCF1 (LD50, 108 CFU). Notably, the dose of 109 CFU provided ideal protection compared with 108 CFU, propolis and oil emulsion adjuvants induced stronger protective efficacy compared with aluminum hydroxide adjuvant. Importantly, WZX-XT5 immunization induced high levels of RA-specific IgY, IFN-γ, IL-2, and IL-4 in serum and offered over 90% protection against RA with ultra-high lethal dose in ducks. Additionally, no clinical signs of RA infection or obvious pathological damage in tissues were observed in protected ducks. Overall, this study first reports the identification, serotyping and virulence of RA in ducks of southern China and the preparation of a novel bivalent inactivated vaccine, providing useful scientific information to prevent and control RA infection.

Vitamin D3 Protects Mice from Diquat-Induced Oxidative Stress through the NF-κB/Nrf2/HO-1 Signaling Pathway

Vitamin D3, as an indispensable and fat-soluble micronutrient, plays an important role in the health of humans and animals. At present, studies are focusing on the calcium absorption and immunoregulation function of vitamin D3; this study was aimed at exploring the antioxidative stress ability of vitamin D3 on diquat-induced intestinal dysfunction of ICR mice and the underlying mechanism. The results showed that oral gavage of vitamin D3 daily significantly improved the body weight gain and immune organ index and significantly reverted the abnormal changes of ALT, AST, SOD, GSH-Px, T-AOC, and MDA in the serum and jejunum induced by diquat. The addition of vitamin D3 also significantly reduced the concentration of DAO, D-LA, and certain proinflammatory cytokines in serum. Moreover, vitamin D3 improved the pathological morphology of the duodenum, jejunum, colon, liver, and kidney tissues, and it also largely attenuated the degree of inflammatory infiltration of macrophages and cell apoptotic index of jejunal epithelial tissue induced by diquat. The results demonstrated that vitamin D3 significantly recovered the intestinal barrier injury by enhancing the expression of mucins and tight junction proteins in the jejunum. In addition, the results indicated that vitamin D3 could significantly reduce the phosphorylation level of NF-κB (p65) and enhance the expression of Nrf2 and HO-1 in the jejunum compared with the diquat-induced group. This study suggested that oral administration of vitamin D3 can protect mice against oxidative damage by inhibiting the phosphorylation level of NF-κB (p65) and activating Nrf2-related signaling pathways.

Anti-inflammatory activity of diindolylmethane alleviates Riemerella anatipestifer infection in ducks

3,3’-Diindolylmethane (DIM) is found in cruciferous vegetables and is used to treat various inflammatory diseases because of its potential anti-inflammatory effects. To investigate effects of DIM in Riemerella anatipestifer-infected ducks which induce upregulation of inflammatory cytokines, ducks were treated orally with DIM at dose of 200 mg/kg/day and infected the following day with R. anatipestifer. Infected and DIM-treated ducks exhibited 14% increased survival rate and significantly decreased bacterial burden compared to infected untreated ducks. Next, the effect on the expression level of inflammatory cytokines (interleukin [IL]-17A, IL-17F, IL-6, IL-1β) of both in vitro and in vivo DIM-treated groups was monitored by quantitative reverse-transcription PCR (qRT-PCR). Generally, the expression levels of the cytokines were significantly reduced in DIM-treated splenic lymphocytes stimulated with killed R. anatipestifer compared to stimulated untreated splenic lymphocytes. Similarly, the expression levels of the cytokines were significantly reduced in the spleens and livers of DIM-treated R. anatipestifer–infected ducks compared to infected untreated ducks. This study demonstrated the ameliorative effects of DIM in ducks infected with R. anatipestifer. Thus, DIM can potentially be used to prevent and/or treat R. anatipestifer infection via inhibition of inflammatory cytokine expression.

Riemerella anatipestifer infection in ducks induces IL-17A production, but not IL-23p19

R. anatipestifer (RA) is one of the most harmful bacterial pathogens affecting the duck industry, and infection is associated with the production of proinflammatory cytokines, including IL-17A. Another proinflammatory cytokine, IL-23, is critical for the development of Th17 cells, which produce IL-17. However, IL-23 roles have not been studied in this infection. Here, we describe the identification and mRNA expression analysis of duck IL-23p19 (duIL-23p19) in splenic lymphocytes and macrophages stimulated with killed RA and in spleens of RA-infected ducks. Expression of duIL-23p19 transcript identified in this study was relatively high in livers of healthy ducks and was upregulated in mitogen-activated splenic lymphocytes as well as in splenic lymphocytes and macrophages stimulated with killed RA. In spleens of RA-infected ducks, expression levels of duIL-23p19 transcript were unchanged at all time points except on days 4 and 7 post-infection; however, duIL-17A and IL-17F expression levels were upregulated in both spleens of RA-infected ducks and splenic lymphocytes and macrophages stimulated with killed RA. In sera collected at 24 h after this infection, duIL-23p19 expression levels were unchanged, whereas IL-17A significantly upregulated. These results suggest that IL-23p19 does not play a critical role in the IL-17A response in early stages of RA-infected ducks.

Immunogenicity and safety of a live Riemerella anatipestifer vaccine and the contribution of IgA to protective efficacy in Pekin ducks

Riemerella anatipestifer (RA) infections cause major economic losses in the duck industry. In this study, we developed an RA vaccine to control virulent serotype 1 and 2 RA, which predominate in worldwide prevalence. We established a strategy for vaccine candidate screening, and selected strains D15-RDA-92 (serotype 1) and D14-RDA-8 (serotype 2). These strains were characterized by ≤50% embryo mortality and <3.0 serum resistance assay values in in vitro screening. We evaluated the protective efficacy of live bivalent RA vaccines against virulent homologous serotype RA. Ducklings received two oral immunizations with the bivalent vaccine and showed significant protection against two virulent strains (serotypes 1 and 2) at 21 days post-immunization. No death or clinical signs of diarrhea, tremors, or limb swelling were observed in the immunized ducks. In a safety evaluation, ducks immunized with 100 times higher doses showed no clinical signs, mortality, gross lesions, or histological lesions, and body weight of the ducks showed no significant difference compared to that of negative controls. In addition, IgA analysis showed a significant increase in secretory IgA antibodies generated in the trachea and duodenum of orally immunized ducks at 28 days of age. The IgA might be involved in one of the major immune responses to RA and contributes to protecting against virulent RA. In this study, we developed monovalent and bivalent RA vaccines that were safe in ducks and provided significant protective efficacy against virulent homologous RA strains.