Bioinformatic analysis and characteristics of glycoprotein C encoded by the newly identified UL44 gene of duck plague virus

Glycoprotein C is one of the duck plague virus (DPV) glycoproteins and is encoded by the DPV UL44 gene. DPV glycoprotein C (DPV-gC) comprises 431 amino acids with a putative molecular mass of 47.35 kDa. Sequence analysis indicated that the protein possesses typical characteristics of type-I membrane glycoproteins, containing an N-terminal signal sequence, an external domain, a C-terminal membrane anchor region, and a short cytoplasmic domain. Comparisons of 22 alphaherpesvirus-gC protein sequences revealed eight conservative Cys-residue sites, which may play a crucial role in the biological functions and structural stabilization of the DPV-gC protein. Estimates of potential antigenic epitopes and secondary structure identified four B cell dominant epitopes, which are located at amino acids 68-71, 87-91, 369-352, and 372-374. A model for the structure of DPV-gC was derived by associating its predicted secondary and three-dimensional structures. In conclusion, these results will provide a basis for further functional studies of DPV-gC, establishing novel clinical diagnoses of DPV, and in the development of a new DPV vaccine.

Development and application of an indirect immunohistochemical method for the detection of duck plague virus vaccine antigens in paraffin sections and localization in the vaccinated duckling tissues

The objective of the present study was to develop and apply a streptavidin-alkaline phosphatase labeling system of indirect immunohistochemistry (SP-IHC) to detect antigenic distribution and localization regularity of duck plague virus (DPV) vaccine antigens in paraformaldehyde-fixed paraffin-embedded tissues of experimentally vaccinated ducklings. Male New Zealand rabbits were immunized with purified DPV antigens, which were engaged by a combination of differential centrifugation and sucrose-density gradient ultracentrifugation. The rabbit anti-DPV polyclonal antibodies were purified and used as the primary antibodies. Forty-eight 28-d-old DPV-free Pekin ducklings were subcutaneously inoculated with attenuated DPV vaccine in the immunization group and sterile PBS in the control group. The tissues were collected at sequential time points between 4 h and 18 wk postvaccination (PV) and were prepared for SP-IHC observation. The presence of DPV-specific antigens was first observed in the liver and spleen at 12 h PV; in the bursa of Fabricius, thymus, Harderian gland, esophagus, and intestinal tract at 1 d PV; and in the heart, lung, kidney, pancreas, and brain at 3 d PV. The positive staining reaction could be detected in the vaccinated duckling tissues until 18 wk PV, and no positive staining cells could be observed in the controls. The highest levels of positive staining reaction were found in the liver, spleen, bursa of Fabricius, thymus, and intestinal tract, whereas a few DPV vaccine antigens were distributed in the heart, pancreas, and esophagus. The target cells had a ubiquitous distribution, especially in the mucosal epithelial cells, lamina propria cells, macrophages, hepatocytes, and lymphocytes, which served as the principal sites for antigen localization. These findings demonstrated that SP-IHC was a reliable method for detecting antigenic distribution and localization regularity of DPV vaccine antigens in routine paraffin sections. The present study may be useful for describing proliferation and distribution regularity of DPV vaccine in the vaccinated duckling tissues and enhance further studies and clinical application of attenuated DPV vaccine.