Abstract

Vaccines against Porcine circovirus type 2 (PCV2) have been studied intensely and found to be effective in decreasing mortality and improving growth in swine populations. In this study, interleukin-23 (IL-23) gene was cloned from peripheral blood mononuclear cells (PBMCs) of Tibetan pigs and inserted into a eukaryotic VR1020 expression vector-VRIL23. Coated with chitosan (CS), the VRIL23-CS was intramuscularly injected into 3-week-old piglets with PCV2 vaccine. The blood was collected after vaccination at 0, 1, 2, 4, 8, and 12 weeks, respectively, to detect the immunological changes. The IgG2a and specific PCV2 antibodies were detected using ELISA, and blood CD4+ and CD8+ T cells were quantified by flow cytometry. Quantitative fluorescence PCR was used to evaluate the expression of immune genes. The results indicate that leukocytes, erythrocytes, and CD4+ and CD8+ T cells increased significantly in the blood of VRIL23-CS inoculated piglets in comparison with the control (p < 0.05) and so did the IgG2a and PCV2 antibodies. In addition, the expressions of Toll-like receptor (TLR) 2, TLR7, cluster of differentiation (CD) 45, IL-15, IL-12, signal transducer and activator of transcription (STAT)1, STAT2, STAT3, STAT4, and B-cell lymphoma (Bcl)-2 genes were also obviously higher in the VRIL23-CS inoculated pigs at different time points (p < 0.05). Overall, the results demonstrated that VRIL23-CS can enhance the comprehensive immune responses to PCV2 vaccine in vivo and has the promising potential to be developed into a safe and effective adjuvant to promote the immunity of pig against PCV disease.

Highlights

  • Porcine circovirus type 2 (PCV2) causes post-weaning multisystemic wasting syndrome (PMWS), which results in a major economic loss for the pork industry worldwide [1]

  • The recombinant plasmid was packed with chitosan nanoparticles and used as adjuvant for PCV2 vaccine

  • The IL-23 gene was first cloned from Tibetan pig, and its eukaryotic recombinant plasmid was constructed and expressed in vitro

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Summary

Introduction

Porcine circovirus type 2 (PCV2) causes post-weaning multisystemic wasting syndrome (PMWS), which results in a major economic loss for the pork industry worldwide [1]. PCV2 infections are frequently reported in many pig farms in China [2]. Due to intensive pig production, mixed infections with other pathogens, such as porcine reproductive and respiratory syndrome virus (PRRSV), classical swine. Vaccines 2020, 8, 250 fever virus (CSF), porcine parvovirus, and mycoplasma, further worsen the situation for animal disease control [3,4]. The most effective measure to control PCV2 infection has depended mainly on vaccination; the immunologic potency of available vaccines is still inadequate, and development of effective adjuvant remains a priority. A few reagents, including IFN-α [5], IL-2, IL-4, IL-6 [6], IL-12 [7], α-galactosylceramide (α-GalCer) [8], CpG motifs [9], and chitosan oligosaccharides (COS) [10], have been reported to serve as vaccine adjuvants of porcine diseases.

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