Effects Of Canine IL-2and IL-7Genes On Enhancing Immunogenicity Of Canine Parvovirus VP2Gene Vaccine In Mice

Canine parvovirus (CPV) disease is one of the most infectious diseases threateningcanine industry. At present time, there is no effective drug for its treatments. Theprevention for this disease was mainly conducted by vaccination with attenuated vaccine.But the potential subclinical infection and reversion to virulence may be occurred uponvaccination with attenuated vaccine. In recent years, the DNA vaccines are widelyconcerned since it not only induce the humoral immune response but also induce cellularimmune responses. However, the immunogenicity of DNA vaccine is relatively low.Therefore, developing appropriate adjuvant to enhance the immunogenicity of DNAvaccine is necessary. Cytokine expression vectors as adjuvants of DNA vaccines have beenextrensively applied because of its slow release, long duration and strong adjuvant action.Interleukin-2(IL-2) as a biological adjuvant has been widely applied to the researchand application of DNA vaccine and subunit vaccine. Interleukin-7(IL-7) was recentlyconsidered as a potential adjuvant, including our provious work on using canine IL-7(cIL-7) vector as a adjuvant to enhance the immunogenicity of canine parvirus (CPV) VP2DNA vaccine in mice, indicating that the cIL-7has the obvious promoting effects on boththe humoral immune and cellular immunity. In order to explore whether cIL-7and cIL-2have the synergistic effects on enhancing the immunogenicity of DNA vaccine, CPV VP2DNA vaccine was used in this research to investigate the synergistic effects of cIL-2andcIL-7genes.The bicistronic vectors of cIL-2and cIL-7genes was constructed using the eukaryoticexpression vector contain internal ribosome entry site (IRES). The cIL-2/clL-7dicistronicvector plus previously constructed vectors, including CPV VP2DNA vaccine vector, cIL-2vector and cIL-7vector, were used to co-immunize the mice with the differentcombinations, consisting of VP2alone, VP2+cIL-2, VP2+cIL-7and VP2+cIL-2/cIL-7. TheVP2-specific antibody levels in immunized mice were measured by ELISA at differenttime post-immunization. The proliferation indexes and interferon-γ expression weremeasured by lymphocyte proliferation assay and ELISA, respectively.The results showed that the contruct of cIL-2/cIL-7bicistronic vector was correct andcould mediate cIL-2and cIL-7gene expression in eukaryotic cells. Immunization results revealed that the antibody titers and the neutralizing antibody levels of the miceco-immunized with VP2+cIL-7/cIL-2vectors were significantly higher than that witheither VP2+cIL-2vectors or VP2+cIL-7vectors (P <0.05). The lymphocyte proliferationindexes of VP2+cIL-7/cIL-2vector-immunized mice were also higher than that of othertwo groups although not statistically significant. However, the IFN-γ expression levels ofVP2+cIL-7/cIL-2vector-immunized mice were significantly higher than other immunizedmice (P <0.05). Inconclusion, the cIL-2and cIL-7genes showed the significant synergiceffects on enhancing the immunogenecity of CPV VP2DNA vaccine.