Promotion of the immunity of piglets to Hog cholera vaccine induced by shuffled pig interleukin-2 gene and CpG immunostimulatory sequences encapsulated in chitosan nanoparticles

A novel shuffled pig IL-2 gene and immunostimulatory sequences containing 11 CpG motifs were subcloned into the eukaryotic expression plasmid VR1020 and VR1012, respectively designated as the recombinant VRIL2S and VR1C, then they were encapsulated in chitosan nanoparticles (CNP) prepared by ionotropic gelation method. Forty 21-day-old piglets were divided into four groups and intramuscularly injected respectively with 0.5mg VRIL2S-CNP, VR1C-CNP, VR1020-CNP and CNP along with the rabbit-attenuated swine fever virus vaccines. The bloods were weekly collected from the piglets after vaccination to detect the changes of immunoglobulins, specific antibodies, interleukins, IFN-γ and immune cells. The results were found that in comparison with the control VR1020-CNP and CNP group, the content of immunoglobulins, specific antibodies, IL-2, IL-6, IL-4 and IFN-γ significantly increased in the sera from the treated VRIL2S-CNP and VR1C-CNP group (P<0.05); the numbers of lymphocytes and monocytes also remarkably elevated in the treated groups (P<0.05). Meanwhile, the levels of specific antibody, IgM, IgA and IgG in the VRIL2S-CNP group were significantly higher than those of VR1C-CNP group respectively from 7 or 28 to 56 days after vaccination (P<0.05); so did the amount of IL-2 and IFN-γ in the VRIL2S-CNP group (P<0.05). Moreover, the number of lymphocytes and monocytes rose to different degrees in the VRIL2S-CNP treated pilglets compared to those of VR1C-CNP group (P<0.05). The average weight gain of in VRIL2S-CNP treated pigs was also obviously higher than that of the controls during the experimental period. These indicated that the humoral and cellular immunities of piglets were significantly promoted by VRIL2S-CNP and VR1C-CNP, and VRIL2S could provoked better immunities of piglets to Hog Cholera than VR1C-CNP, implying that the shuffled pig IL-2 gene entrapped with CNP is a safe and powerful adjuvant to boost the specific immunity of piglets against Hog cholera, facilitating the development of a novel effective adjuvant to improve the immunity of pig against Hog cholera.