Elsevier

Vaccine

Volume 29, Issue 22, 17 May 2011, Pages 3888-3894
Vaccine

Improvement of the immunity of pig to Hog cholera vaccine by recombinant plasmid with porcine interleukin-6 gene and CpG motifs

https://doi.org/10.1016/j.vaccine.2011.03.036Get rights and content

Abstract

In order to observe the dosage-effect of recombinant pig interleukin-6 gene and CpG motifs on the immune responses of swine to vaccine, a novel recombinant eukaryotic VPIL6C plasmid was packed with chitosan nanoparticles (CNP) prepared by ionic cross linkage, which contains pig interleukin-6 gene and immunostimulatory sequence consisted of 11 CpG motifs. CNP-VRIL6C was then utilized to inoculate 30-day-old piglets intramuscularly at the dosage of 0.5, 1.0 and 1.5 mg/per capita, respectively. Meanwhile, the piglets were injected with attenuated classical Hog cholera vaccine and designated as A1, A2 and A3 group. The blood was weekly collected from the piglets after vaccination to detect the changes of immunoglobulins, specific antibody, interleukins, IFN-γ and immune cells. The results were found that compared to those of the control piglets injected with VR1020-CNP, the content of IgG, IgA and IgM, specific antibodies, IL-2, IL-6 and IFN-γ significantly increased in the sera from the treated three groups from 14 to 70 days after vaccination (P < 0.05); the number of TH, TC and CD3+ positive T cells raised obviously in the blood of VPIL6C treated piglets (P < 0.05). Also the above immune indexes of A1 group were significantly lower to different extent in comparison with those of A2 and A3 group from 14 to 56 days post inoculation (P > 0.05). Moreover, the lymphocytes also remarkably elevated in the treated groups (P < 0.05). These indicate that VPIL6C entrapped with CNP is a novel effective adjuvant to boost the humoral and cellular immunity of pig to Hog cholera, implying it's potentiality to enhance the resistance of pig against infectious diseases.

Introduction

Classical swine fever (CSF) or hog cholera is one of the most devastating porcine haemorrhagic viral diseases. Outbreaks of CSF usually lead to significant losses in many countries worldwide [1]. CSF virus (CSFV) mainly infects endothelial cells and macrophages and at the same time promotes bystander apoptosis of the surrounding T cells, causing strong immune suppression and high mortality rates [2], [3], [4], [5]. Presently, novel vaccine and adjuvant is critical for enhancing immunity and resistance of pig against various infections. Vaccinations are frequently compromised due to rapid mutation of virus and bacteria.

Nowadays adjuvant is still important for boosting immunity and improving resistance in animals. Traditional adjuvants are mainly consisting of chemical molecule and microbial components, such as Al (OH)3, BCG and incomplete Freund's adjuvant, derived bacteria and plant components [6]. Recently cytokines had been utilized as new effective adjuvants [7], [8]. Moreover, pig Interleukin (IL-6) gene was ever proved to be able to enhance the immune responses of animal [9], which was one of key cytokines balancing between inflammation and the immune responses during the infection or injury process [10]. CpG motifs were also reported to represent another emerging adjuvant to strengthen the innate immunity of animal. The unique unmethylated CpG motifs could activate B cells, dendritic cells (DCs), NK T cells and monocytes and play an important role in infection and vaccination [11], [12]. Clinical studies demonstrate that CpG could be applied in therapy against infectious diseases, cancer, asthma and allergy [13]. The adjuvant activity of CpG ODN was demonstrated in humans and numerous animal species [14], [15], [16]. But they are usually not safe or effective enough to provoke strong and persistent immunoprotection in animals against most infectious diseases, especially immune defective diseases. There is pressing need to develop novel strong adjuvant to improve immunity and enhance protection against infectious diseases.

Until now, there are few reports about synergetic effects between IL-6 and CpG motifs, which were once employed to enhance immune responses of mice in vivo in our lab [17], [18]. Therefore, the present experiment was firstly carried out to detect the modulation of pig IL-6 and CpG motifs on the immune responses of pig to swine fever vaccine for the sake of developing a safer and more effective adjuvant to enhance immunity to conventional vaccines and facilitating the control of infectious diseases of animals.

Section snippets

Hog cholera vaccine

The vaccine is rabbit-attenuated Swine fever virus (provided by Chengdu Medicine and Appliances Factory, China), and employed in this experiment as conventional vaccine, which are extensively utilized to intramuscularly immunize swine in China to prevent Hog cholera.

VPIL6C (VR1020-PIL6-CpG)

Plasmid VR1020, provided by Vical Company of America, is used as the eukaryotic expression vector. Pig interleukin-6 gene (PIL-6) and CpG motifs were cloned and inserted into the VR1020; the recombined plasmid was named as VPIL6C in

Identification of VPIL6C-CNP

Observation by transmission electron microscopy elucidates that most of VPIL6C-CNP is spherical. Analysis by Zetasizer 3000 HS/IHPL shows that the average diameter of granule is 155 nm. Ranged from 132 to 230 nm, the dispersion rate is 0.22; zeta potential +17.6 mV, suggesting that the CNPs are positively charged, and the package rate of plasmids by CNP is over 98%.

Amount of specific antibody

14 days post inoculation, the amount of antibody to rabbit-attenuated swine fever virus significantly increased in the sera of the

Discussion

Classical swine fever (CSF) is a highly contagious disease of swine caused by CSFV, an enveloped positive sense, single-strand RNA Pestivirus in the flaviviridae family [22]. Most piglets suffer acute infection to die or survive by producing specific antibody to CSFV. In order to avoid or reduce the economic loss, effective vaccination and strict sanitation measures are critical for the control of outbreak of classical swine fever. There is a clear demand to construct safe and efficient novel

Acknowledgements

This research was supported by the grants from National Natural Science Foundation of China (grant no. 30170703 and 30571359), Outstanding Scholar and Key project of Science and Technology of Sichuan Province. We thank Dr. Guang-De Feng and Kai-YuanWu for their technical assistance.

References (33)

Cited by (11)

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1

These authors contribute equally to the research.

2

Biology group of North Sichuan Medical College, Nan Chong 637007, Sichuan, China.

3

Bioengineering Department of Sichuan University of Science & Engineering, Zigong 643000, China.

4

Animal Academy of Sichuan province, Chengdu 610035, China.

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