PCV cap proteins fused with calreticulin expressed into polymers in Escherichia coli with high immunogenicity in mice
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RESEARCH ARTICLE
Open Access
PCV cap proteins fused with calreticulin expressed into polymers in Escherichia coli with high immunogenicity in mice Chang Liu1†, Yunchao Liu1†, Hua Feng1, Baolei Zhao2, Yumei Chen3, Huimin Huang2, Pan Wang1, Ruiguang Deng1 and Gaiping Zhang1,2,3*
Abstract Background: Porcine circovirus type 2 (PCV2) is the main causative agent of porcine circovirus diseases (PCVDs) which causes huge yearly economic losses in the swine industry. Capsid protein (Cap) is the major structural protein of PCV2 that can induce a protective immune response. Therefore, developing a novel and safe subunit vaccine against PCV2 infection is needed. Results: In this study, the Cap gene was bound to the truncated calreticulin (CRT) (120–250 aa/120–308 aa) at the N/C terminal, and then the CRT-Cap fusion genes were expressed in Escherichia coli (E.coli). The size-exclusion chromatography and dynamic light scattering (DLS) data showed that the purified recombinant CRT-Cap fusion protein (rP5F) existed in the form of polymers. Immunization with rP5F stimulated high levels of PCV2 specific antibody and neutralization antibody in mice, which were almost identical to those induced by the commercial subunit and inactivated vaccines. The lymphocyte proliferation and cytokine secretion were also detected in rP5F immunized mice. According to the results of PCV2-challenge experiment, the virus loads significantly decreased in mice immunized with rP5F. The data obtained in the current study revealed that rP5F had the potential to be a subunit vaccine candidate against PCV2 in the future. Conclusions: We have successfully expressed Cap-CRT fusion proteins in E.coli and optimized rP5F could form into immunogenic polymers. Mice immunized with rP5F efficiently induced humoral and part of cellular immune responses and decreased the virus content against PCV2-challenge, which suggested that rF5P could be a potential subunit vaccine candidate. Keywords: Porcine circovirus type 2, CRT-cap fusion protein, Escherichia coli, Polymers, Immunogenicity
* Correspondence: [email protected] † Chang Liu and Yunchao Liu contributed equally to this work. 1 Key Laboratory of Animal Immunology of the Ministry of Agriculture, Henan Provincial Key Laboratory of Animal Immunology, Henan Academy of Agricultural Sciences, Zhengzhou 450002, Henan, China 2 College of Animal Science and Veterinary Medicine, Henan Agricultural University, Zhengzhou 450002, Henan, China Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in
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