Attenuated Salmonella typhimurium delivering DNA vaccine encoding duck enteritis virus UL24 induced systemic and mucosal immune responses and conferred good protection against challenge

Abstract

Orally delivered DNA vaccines against duck enteritis virus (DEV) were developed using live attenuated Salmonella typhimurium (SL7207) as a carrier and Escherichia coli heat labile enterotoxin B subunit (LTB) as a mucosal adjuvant. DNA vaccine plasmids pVAX-UL24 and pVAX-LTB-UL24 were constructed and transformed into attenuated Salmonella typhimurium SL7207 resulting SL7207 (pVAX-UL24) and SL7207 (pVAX-LTB-UL24) respectively. After ducklings were orally inoculated with SL7207 (pVAX-UL24) or SL7207 (pVAX-LTB-UL24), the anti-DEV mucosal and systemic immune responses were recorded. To identify the optimum dose that confers maximum protection, we used different doses of the candidate vaccine SL7207 (pVAX-LTB-UL24) during oral immunization. The strongest mucosal and systemic immune responses developed in the SL7207 (pVAX-LTB-UL24) (1011 CFU) immunized group. Accordingly, oral immunization of ducklings with SL7207 (pVAX-LTB-UL24) showed superior efficacy of protection (60-80%) against a lethal DEV challenge (1000 LD50), compared with the limited survival rate (40%) of ducklings immunized with SL7207 (pVAX-UL24). Our study suggests that the SL7207 (pVAX-LTB-UL24) can be a candidate DEV vaccine.

An Attenuated Duck Plague Virus (DPV) Vaccine Induces both Systemic and Mucosal Immune Responses To Protect Ducks against Virulent DPV Infection

“…In addition, the levels of serum IgG were significantly higher than those of serum IgA. This suggested that IgG is the main antibody against DPV, which coincided with previous studies (8,21).…”

“…Serum IgG and IgA play critical roles in humoral immunity against specific antigens (21,33). In this study, the DPV attenuated vaccine enhanced production of both IgA and IgG antibodies.…”

“…JQ647509) was obtained by A. Cheng in Sichuan Province, China (22). Currently, the virus is stored in the Avian Disease Research Center of the Sichuan Agricultural University of China (21). The DPV attenuated vaccine strain CHa is a modified live commercial vaccine (China Animal Husbandry Industry Co. Ltd.) that was the product of a DPV CHv isolate cultured in chicken embryo fibroblasts (CEF) for 80 serial passages (17).…”

“…After the mesentery was removed, 1-cm sections of intestinal tract and trachea were cut and processed as tissue homogenates in 1 ml T-PBS (100 g/ml of trypsin inhibitor [Sigma-Aldrich, St. Louis, MO] in PBS). Each of the supernatants was collected after centrifugation at 10,000 ϫ g for 20 min at 4°C (21). Meanwhile, 0.5-g portions of the spleen, bursa of Fabricius, thymus, harderian gland, lung, and liver were cut and processed as tissue homogenates in 0.5 ml T-PBS, and the supernatants were collected as described above.…”

“…Systemic and mucosal immune responses are important in resisting and clearing viral infections (20,21). Prior to this study, the immune responses after subcutaneous immunization with the DPV attenuated vaccine strain CHa had not been elucidated, and no conclusions about its protective effect could be established, since no challenge studies had been performed.…”