The Cross Immune Protection Of Porcine Circovirus-like Virus P1 Vaccine To Porcine Circovirus Type 2

Porcine circovirus-like virus P1,a circular,single strand,negative strand DNA virus,was isolated from the serum of pigs with suspecteable cases of clinical postweaning multisystemic wasting syndrome(PMWS).It is the smallest animal virus,a total length of 648 nucleotides.The genome of P1 are highly homology with the sequence of the open reading frame 2 of the porcine circovirus 2.Previous studies have shown that similar to PCV2,similar clinical symptoms of PMWS was found in P1 virus-infected pigs.In this study,we investigated whether the PI vaccine has the protection against PCV2.1.Preparation of PI subunit vaccine and P1 DNA vaccineP1 virus mainly consists of 3 open reading frames,ORF1 encoded the structural protein of P1,So we use P1-ORF1 as the target gene to construct recombinant eukaryotic expression plasmid pcDNA3.1(+)-ORF1.We extracted a large number of recombinant plasmids as P1 DNA vaccine.At the same time,we regard the ORF1 protein expressed by the recombinant baculovirus pFastbacTM-ORF1(preserved in the laboratory)as PI subunit vaccine.The results show that the recombinant plasmid pcDNA3.1(+)-ORF1 could be expressed in PK-15 cells by immunohistochemistry and reverse transcription experiments.The expression products of pFastbacTM-ORF1 could react with P1 polyclonal antibody specificly by Western Blot.2.animal experiment24,6 weeks Balb/c nices were divided into 4 groups,P1 subunit vaccine group,P1 DNA vaccine group,the PCV2 challenged control group and the negative control group.Booster immunization after 2 weeks of the first immunization and PCV2 challenge after two weeks of booster immunization.After 4 weeks of challenge,all of mices were killed.The lung,spleen and kidney were collected for histopathological lesions and immunohistochemistry.Blood samples were collected once every two weeks after immunization.The average daily weight gain of each group was analyzed after the challenge.3.vaccine protection testAfter infection,the mice had no obvious clinical symptoms.The average daily weight gain was not significantly different between all the groups.The histopathological results showed that there was no pathological changes in the negative control group.Microscopic lesions of PI DNA vaccine group was minor,while the PCV2 challenged control group and subunit vaccine group had more severe lesions.Iununohistochemical results also showed that the PCV2 virus positive cells of the subunit vaccine group and the PCV2 challenged control group were more than the PI DNA vaccine group.The results of serological antibody test showed that the antibody levels of the DNA vaccine group was higher significantly than the rest group from the first 2 weeks after first immunization.And the rest group did not appear P1-ORF1 antibody level.The PCV2 viral load of DNA vaccine group was significantly lower than the challenged control group,and the difference was not significant between the subunit vaccine group and the challenged control group.The results showed that the PI nucleic acid vaccine had a certain cross protection effect against PCV2 virus.However,PI subunit vaccine did not produce antibodies,which may be due to the protein in SF9 cells can not be self-assembled into virus like particles.The PCV2 virus load in the subunit vaccine group was higher than that in other groups,the possible reason is that the stimulus of the Gel 01 adjuvant or the recombinant protein itself.In mice,we verified that the P1 nucleic acid vaccine had a certain protective effect to PCV2,which laid the foundation for the study of the pig in the future.