Enhancement of the Humoral Immune Response against the Attenuated Salmonella typhimurium Harbouring Newcastle Disease Virus DNA Vaccine by C3d Molecule
Abstract：The fusion protein (F) gene of Newcastle disease virus was amplified by polymerase chain reaction (PCR) from the recombinant eukaryotic expression plasmid pVAX1-F, and subcloned into the plasmid pTR-C3d3 containing three copies of C3d. The F-C3d3 gene was identified by sequencing and cloned into eukaryotic expression vector pVAX1. The recombinant plasmid pVAX1-F-C3d3 was transformed into attenuated Salmonella typhimurium SL7207, and the recombinant was designated as SL7207(pVAX1-F-C3d3). One-day-old SPF chickens were immunized orally with SL7207(pVAX1-F-C3d3) at the dosage of 1×109 CFU and boosted two weeks later with the same dose. The serum antibodies responses specific to NDV were observed in chickens immunized with SL7207(pVAX1-F-C3d3) on day 14 and 28, and their levels were significantly higher than that of SL7207(pVAX1-F) (P < 0.05). Intestinal mucosal immune response were observed in chickens immunized with recombinant bacteria on day 28, and their levels were significantly higher than that of negative and positive control (P < 0.05), but there was not significance between the groups SL7207(pVAX1-F-C3d3) and SL7207(pVAX1-F). These results indicated that three copies C3d could enhance humoral immune response against NDV induced by attenuated Salmonella typhimurium harbouring DNA vaccine. A novel mucosal DNA vaccine was developed and could be useful for controlling the infection and epidemic of Newcastle disease in the poultry.
