Expression Improvement of Recombinant Plasmids of the Interleukin-7 Gene in Chitosan-Derived Nanoparticles and Their Elevation of Mice Immunity

SIMPLE SUMMARY: To explore a safe and effective way to potentiate the systemic immunity of animals against infectious diseases in an economical way, the interleukin-7 (IL-7) gene of Tibetan pig was utilized to construct a recombinant eukaryotic plasmid. We first detected the bioactivity of expressed IL-7 on porcine lymphocytes in vitro and then encapsulated the IL-7 gene with different chitosan (CS) and its two modified derivatives, CS-PEG-PEI and CS-PEG-GAL nanoparticles. Then, we injected mice intramuscularly or intraperitoneally with various nanoparticles containing the IL-7 gene to evaluate their immune effects in vivo. We observed a significant increase in neutralizing antibodies and specific IgG levels in response to the rabies vaccine in the treated mice compared to the controls. Treated mice also manifested elevated leukocytes, CD4+ and CD8+ T cells, and mRNA levels of toll-like receptors (TLR1/4/6/9), IL-1, IL-2, IL-4, IL-6, IL-7, IL-23, and transforming growth factor-beta (TGF-β). Notably, the recombinant IL-7 gene encapsulated in CS-PEG-PEI provoked the best increases of immunoglobulins, CD4+ and CD8+ T cells, TLRs, and cytokines in the blood of the mice, implying that chitosan-PEG-PEI can become a promising carrier for in vivo IL-7 gene expression to enhance the innate and adaptive immunity for the prevention of animal diseases. ABSTRACT: To investigate a safe and effective approach for enhancing the in vivo expression of recombinant genes and improving the systemic immunity of animals against infectious diseases, we employed the interleukin-7 (IL-7) gene from Tibetan pigs to construct a recombinant eukaryotic plasmid (VRTPIL-7). We first examined VRTPIL-7’s bioactivity on porcine lymphocytes in vitro and then encapsulated it with polyethylenimine (PEI), chitosan copolymer (CS), PEG-modified galactosylated chitosan (CS-PEG-GAL) and methoxy poly (ethylene glycol) (PEG) and PEI-modified CS (CS-PEG-PEI) nanoparticles using the ionotropic gelation technique. Next, we intramuscularly or intraperitoneally injected mice with various nanoparticles containing VRTPIL-7 to evaluate their immunoregulatory effects in vivo. We observed a significant increase in neutralizing antibodies and specific IgG levels in response to the rabies vaccine in the treated mice compared to the controls. Treated mice also exhibited increased leukocytes, CD8+ and CD4+ T lymphocytes, and elevated mRNA levels of toll-like receptors (TLR1/4/6/9), IL-1, IL-2, IL-4, IL-6, IL-7, IL-23, and transforming growth factor-beta (TGF-β). Notably, the recombinant IL-7 gene encapsulated in CS-PEG-PEI induced the highest levels of immunoglobulins, CD4+ and CD8+ T cells, TLRs, and cytokines in the mice’s blood, suggesting that chitosan-PEG-PEI may be a promising carrier for in vivo IL-7 gene expression and enhanced innate and adaptive immunity for the prevention of animal diseases.