Immunostimulatory effects and delivery of oligodeoxynucleotides containing CpG motifs (CpG-ODN) in neonatal broiler chickens

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) have been shown to stimulate the innate immune system against a variety of bacterial, viral, and protozoan infections in a variety of vertebrate species. The objectives of this study were to investigate the immunostimulatory effect of CpG-ODN against Salmonella Typhimurium infection and the formulation and delivery of CpG-ODN by the in ovo route. Day-old broiler chicks or embryonated eggs (day 18th of incubation) received either 50 µg of CpG-ODN, 50 µg of non-CpG-ODN, or saline. At day four-post hatch, all birds were subcutaneously inoculated by Salmonella Typhimurium. Clinical signs, pathology, bacterial isolations from the air sacs, and mortality were observed for ten days following challenge. The survival rate of the birds that received CpG-ODN via in ovo or in vivo treatments was significantly higher than the control group. Salmonella Typhimurium level in the peripheral blood and pathology were significantly lower (p < 0.001) in CpG-ODN group compared to the control group. In order to investigate the effect of formulation of CpG-ODN, embryonated eggs (day 18th of incubation) were inoculated with either 50µg of CpG-ODN alone or CpG-ODN formulated with polyphosphazene, liposome, or Emulsigen®. Four days after administration of CpG-ODN formulations, the birds were challenged with E. coli by subcutaneous injection. Clinical signs, pathology, bacterial isolations from the air sacs, and mortality were observed for seven days following challenge. The birds that received either CpG-ODN or CpG-ODN formulated with polyphosphazene had significantly higher survival rates (30 and 60%) compared to the birds in groups receiving either non-CpG-ODN or saline. Bacterial loads in the air sacs were lower in groups treated with formulated CpG-ODN compared to the CpG-ODN alone or control groups. However, formulation of CpG-ODN with liposomes or Emulsigen® did not increase the immunoprotective effect against E. coli infection. We showed that treatment with CpG-ODN protects neonatal chickens against an intracellular bacterial infection and that co-treatment of CpG-ODN with polyphosphazene enhances the immunoprotective effect of CpG-ODN