Cloning of interleukin-15 gene of Tibetan pig and adjuvant effect of its recombinant plasmids packed with PEG and PEI modified chitosan nanoparticles on immunity of mice to FMD vaccination

IL-15 cDNA of Tibetan pig was firstly cloned from its activated lymphocytes, and then was sub-cloned into VR1020 to construct recombinant VRTIL-15 plasmid to study the in vitro and in vivo biological effects on animal. The VRTIL-15 was entrapped with chitosan modified with PEG-PEI (CS-PEG-PEI) to transfect HEK293 cells for the preliminary study of its expression in eukaryotic cells. The total RNA of HEK293 cell was isolated in 48 h, and the successful expression of IL-15 was detected by RT-PCR and the supernatant of HEK293 cells was found to stimulate significant proliferation of lymphoblasts of pig. Subsequently, VRTIL-15 packed with CS-PEG-PEI was utilized to intramuscularly inoculate Kunming female mice at the age of 21 days. Their bloods were collected before and after inoculation on 1, 2, 3, 4 and 5 weeks to detect the changes of innate and adaptive immunity of animals. The results were found that Th and Tc, specific antibody to FMD, IgG, IgG1, IgG2a content markedly increased in the blood of treated mice compared with the control group (P < 0.05). The mRNA expression of TLR1, TLR4 TLR6, TLR9, TGF-β, IL-2, IL-4, IL-6 and IL-23 were significantly higher in the treated group than those of the control (P < 0.05). These results indicate that the VRTIL-15 wrapped with CS-PEG-PEI can significantly improve the innate, humoral and cellular adaptive immunity of animal, which could inspire the development of effective immune adjuvant to improve the comprehensive immune protection of animals against FMD.