Porcine Circovirus Type 3 Cap Protein Expression And The Preliminary Evaluation Of The Immune Efficacy

Porcine circovirus type 3(pcv3)a new virus firstly reported in 2016 and spread wildly in the world,has been considered to be associated with a variety of clinical diseases in pigs.China has the largest pig industry and pork consumption,accounting for more than half of the world.With the continuous development of China’s pig industry,the breeding scale is becoming larger and larger,but the accompanying diseases are becoming more complicated.In China,PCV3 infection is common in pigs,but research on its pathogenicity,epidemiology and molecular biology is still at a preliminary stage.In particular,there is a gap in preventive PCV3 vaccines and no commercially available vaccines to date.Therefore,in this study,the recombinant protein of pcv3 a cap was expressed based on the domestic epidemic characteristics of pcv3,and then several pcv3 a subunit vaccines were prepared by combining with different adjuvants.Subsequently,the immune effect assessment of the pcv3 a subunit vaccines was performed.This study establishes the preliminary basis for the diagnosis and development of a vaccine against pcv3.In this study,we firstly conducted an epidemiological survey of PCV3 in a large-scale pig farm in China,and then analyzed the epidemic characteristics and major genotypes of PCV3.Secondly,we designed and expressed recombinant Cap protein of porcine circovirus type 3 on the basis of dominant genotypes,and then the highly pure PCV3 a Cap protein was purified by chromatography.Lastly,piglets were immunized with the pcv3 a cap protein combined with various adjuvants.Serum antibody levels were detected to evaluate the immune efficacy of pcv3 Cap subunit vaccines.The epidemiological investigation and analysis indicated that the positive rate of PCV3 on a large-scale pig farm in China was 14%,and the genotypes were PCV3 a.The results of SDS-PAGE and Western-Blot showed that the E.coli expression system expressed the PCV3 a Cap protein successfully,and the PCV3 a Cap recombinant protein with a purity of 92% was obtained after purified by chromatography.PCV3 a subunit vaccines were prepared in combination with ISA15 VG,ISA251CVG,Gel02 and IMS1313 VG adjuvant,respectively.The results of safety experiments in mice and piglets showed that physical and chemical testing of all four groups of PCV3 a subunit vaccines met the requirements of the Vaccine Production Regulations,and the vaccines were safe for mice without vaccine-related side effects,but the safety of piglets was different.The IMS1313 VG adjuvant group vaccine had the highest safety for piglets,followed by the ISA251 CVG group.Evaluation of the vaccine’s effectiveness revealed that the PCV3 a Cap protein had good immunogenicity and could stimulate piglets to produce antibodies.The ELISA antibody titre of the adjuvant group ISA251 CVG and the adjuvant group IMS1313 VG were significantly higher than that of the adjuvant group ISA15 VG and the adjuvant group Gel02.The clinical trial evaluation results of the adjuvant group IMS1313 VG showed that in comparison with the control group,the incidence of respiratory symptoms in piglets in the immunized group decreased from 7.5% to5%,the pathogen detection rate in lymph nodes declined from 22.3% to 13.8%,and the abortion rate in pregnant sows decreased from 5.38% to 2.35%,which indicated that the adjuvant group IMS1313 VG could provide better protection effect.In conclusion,we expressed and prepared high purity of recombinant protein of PCV3 a Cap based on the results of epidemiological investigation of PCV3 in a large-scale pig farm in China,and prepared PCV3 a Cap subunit vaccines with different adjuvants.The PCV3 a Cap subunit vaccine containing IMS13 VG adjuvant had good immunogenicity,which provided important data for the study of the commercialized PCV3 subunit vaccine and laid the foundation for the comprehensive prevention and control of PCV3.