Abstract: To enhance the immunocompetence of recombinant plasmid against canine distemper virus, four CpG-oligodeoxynueleotides (CpG-ODN) were designed and used in this research. Following lymphocytes proliferation test determined by 3H-TdR incorporation, one CpG-ODN was selected with optimistic immunostimulatory activity which sequence is 5′TCGTCGTTTTGTCGTTTTGTCGTT-3′. 30 healthy Beagle dogs were assigned into two groups and each group was further divided into 5 subgroups. All the subgroups were tested with different dose of CpG-ODN and recombinant plasmid pcDNA-H (which contain the haemagglutinin gene of CDV) respectively. On the 2nd, 4th and 6th week after immunization, the neutralization antibody specific to CDV and the level of gama-interferon (IFN-γ) were determined, and the data showed that the CpG-ODN could elicit a better antibody response to CDV and increase the level of IFN-γ. Furthermore, the effect of different levels of CpG-ODN were dissimilar on improving immune response, while the optimistic CpG-ODN level is 30 μg with 50 μg pcDNA-H for each animal. Five Beagle dogs were inoculated with optimistic level of CpG-ODN and pcDNAH, while another 10 dogs were only injected with pcDNA-H or normal saline water as control, all the animals were challenged with CDV 4 weeks post immunization, and the data showed that there were no Canine Distemper clinical symptom and no CDV infection in the first group, while 2(40%) and 5(100%) animals were infected with CDV in the pcDNA-H and normal saline water control group respectively.

Key words: CpG-ODNs, canine distemper, nucleic vaccine, immune response, effect