PCV cap proteins fused with calreticulin expressed into polymers in Escherichia coli with high immunogenicity in mice

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.

Surface Display of porcine circovirus type 2 antigen protein cap on the spores of bacillus subtilis 168: An effective mucosal vaccine candidate

“…The coat protein of spores is considered an ideal platform for antigen delivery because of its excellent mucosal immune adjuvant properties and strong resistance to harsh physical and chemical environments. Cap protein-based PCV2 subunit vaccines have been reported in many studies ( 39 – 41 ). In addition, the 47 amino acids at the N-terminal of Cap protein were NLS (nuclear localization signal) peptides, which did not contain major antigenic epitopes ( 42 ).…”

Construction of recombinant pseudorabies virus expressing PCV2 Cap, PCV3 Cap, and IL-4: investigation of their biological characteristics and immunogenicity

“…The circovirus Cap protein exhibits high immunogenicity and is one of the key factors in inducing host immunogenicity. Additionally, it can induce apoptosis and inflammatory responses in host cells, further exacerbating the severity of viral infections ( 26 ). Furthermore, the Cap protein possesses distinct immunological active regions, including epitopes that can induce T-cell and B-cell immune responses ( 27 , 28 ).…”

Live-Attenuated Salmonella-Based Oral Vaccine Candidates Expressing PCV2d Cap and Rep by Novel Expression Plasmids as a Vaccination Strategy for Mucosal and Systemic Immune Responses against PCV2d

“…Although PCV2 infection in mice does not similarly resemble that of pigs, several studies have shown that PCV2 can replicate in some mouse strains, including BALB/c mouse [ 48 ], which is one of the extensively used animal models for the PCV2 vaccine studies [ 32 , 34 , 49 , 50 , 51 ]. Secretory IgA (sIgA) in the BALB/c mouse model has been well recognized as an important first line of defense for protection against pathogens in the mucosal surfaces and thus, plays an important role in mucosal immunity [ 52 ].…”