Effect of age on the pathogenesis of DHV-1 in Pekin ducks and on the innate immune responses of ducks to infection.

Duck hepatitis virus (DHV) affects 1-week-old but not 3-week-old ducks, and it causes a more severe disease in the younger ducks. These differences may be partially due to the host response to DHV infection. In order to understand this difference, we characterized the pathobiology of and innate immune response to DHV infection in 1-day-old (1D) and 3-week-old (3 W) ducks. Viral RNA was detected in duck livers at 24, 36 and 72 h after inoculation with DHV at a dose of 10(3) LD50. Virus-induced pathology ranged from no clinical signs to severe disease and death, and it was more severe in the 1D ducks. Infection with DHV induced up-regulation of gene expression of Toll-like receptor (TLR)-7, TLR3, retinoic-acid-inducible gene I (RIG-I), melanoma differentiation-associated gene 5 (MDA-5), interleukin (IL)-6, interferon (IFN)-α, interferon-induced transmembrane protein 1 (IFITM1), interferon-stimulated gene 12 (ISG12), and 2'-5' oligoadenylate synthetase-like gene (OASL) in the livers of 3 W ducks. Of these, IL-6, OASL and ISG12 mRNA levels were more than 100-fold higher in infected 3 W ducks than in mock-infected ducks of the same age. These genes were induced much less in infected 1D ducklings. We present evidence that a lower level of viral replication in the hepatocytes of 3 W ducks, whose basal level of cytokines is higher than that in 1D ducklings, may be related to the strong innate immunity induced. From our data, we conclude that duck age plays an important role in the pathogenicity of and innate immune responses to DHV.

Immunoproteomics analysis of whole cell bacterial proteins of Riemerella anatipestifer.

Riemerella antipestifer is one of the most important duck pathogens. It has worldwide distribution, and the lack of the information on bacteria-host interactions and an effective vaccine are limitations on the control of this infection. In this study, an immunoproteomic assay was used to identify immunogenic proteins among the whole cell bacterial proteins of R. anatipestifer virulent strain Th4. Duck antiserum against R. anatipestifer Th4 recognized 64 protein spots which were transferred from two-dimensional electrophoresis (2-DE) gel of the whole cell bacterial proteins onto polyvinylidene fluoride (PVDF) membrane. Immunogenic proteins on a duplicate gel were excised and identified by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) and peptide mass fingerprinting (PMF), a total of 34 immunogenic proteins were found. With the exception of OmpA and GroEL, the other 32 proteins were newly recognized immunogenic antigens of R. anatipestifer. In addition, TonB-dependent outer membrane receptor was found to be a cross immunogenic antigen among serotypes 1, 2 and 10 of R. anatipestifer. Bioinformatics analysis showed that most of the immunogenic proteins were located in the outer membrane and cytoplasm, and were involved in cellular processes and metabolism. The newly identified immunogenic proteins of R. anatipestifer may help us to uncover the pathogenesis of the bacteria, develop novel vaccine candidates and serological diagnosis marker.