High expression of the classical swine fever virus (CSFV) envelope protein E2 by a single amino acid mutation and its embedded in the pseudorabies virus (PRV) vector for immunization.

Pseudorabies (PR) and classical swine fever (CSF) are economically important infectious diseases in pigs. Most pig farms in China are vaccinated against these two diseases. Gene-deleted pseudorabies virus (PRV) can be used to develop promising and economical multivalent live attenuated viral vector vaccines. It has been reported that recombinant PRV can express a truncated E2 protein (1-338 aa), but it has not been reported that recombinant PRV can express a full-length E2 protein. We constructed nine groups of E2 proteins with different expression forms and found that the E2 protein could be expressed in vitro only when the transmembrane region of E2 was removed and the signal peptide was added. Analysis of the transmembrane region of E2 revealed that the high hydrophobicity of the E2 transmembrane region was the main reason for its inability to express. By mutating an amino acid to reduce the hydrophobicity of the transmembrane region, it was found that the full-length mutant of E2 (E2FL-muta3 or E2FL-muta4) could be expressed. The expressed full-length mutant E2 could also localize to the cell membrane. Mice immunized with a PRV vector vaccine expressing E2FL-muta3 or E2FL-muta4 developed specific cellular immunity to the E2 protein and stimulated higher levels of E2 antibody than mice immunized with a PRV vector expressing truncated E2. After immunizing the rabbits, the lethal challenge by PRV-ZJ2013 and the febrile response elicited by CSFV were simultaneously prevented. These results suggest that rPRV-dTK/gE-E2FL-muta4 is a promising bivalent vaccine against CSFV and PRV infections.

Recombinant pseudorabies virus (PRV) expressing stabilized E2 of classical swine fever virus (CSFV) protects against both PRV and CSFV.

Pseudorabies (PR) and classical swine fever (CSF) are economically important infectious diseases of pigs. Most pig farms in China are immunized against these two diseases. Here, we describe a stabilized E2 protein as an immunogen inserted into the PRV genome as a bivalent live virus-vectored vaccine. The E2 protein has 48 variant sites, there are 2-5 candidate amino acids per variant site, and the relative energy contribution of each amino acid to E2 energy was calculated. Combined substitutions of amino acids at the neighbor variant site (neighbor substitution) were performed to obtain the E2 protein sequence with the lowest energy (stabilized E2). Multiple amino acid substitutions at 48 variant sites were performed, and the results were consistent with neighbor substitutions. The stabilized E2 sequence was obtained, and its energy decreased by 22 Rosetta Energy Units (REUs) compared with the original sequence. After the recombinant PRV expressing stabilized E2 of CSFV was constructed, the secretion efficiency of stabilized E2 was increased by 2.97 times, and the thermal stability was increased by 10.5 times. Immunization of mice resulted in a 2-fold increase in antibody production, and a balanced antibody level against subtype 1.1 and subtype 2.1d E2 was achieved. In rabbits immunized, the lethal challenge of PRV-ZJ and the fever response induced by CSFV could be prevented simultaneously. These findings suggest that rPRV-muta/287aaE2 is a promising bivalent vaccine against CSFV and PRV infections.

[Studies on the apoptosis of RK13 cells induced by rabbit hemorrhagic disease virus].

The apoptosis of RK13 cells induced by RHDV was investigated with DAPI staining, DNA ladder, Caspase 3 activity and flow cytometry, etc. The results showed that nuclear staining of infected cells with DAPI showed gradually morphological changes of the nuclei. As shown in the paper, a canonic oligonucleosome-sized DNA ladder was observed in cells harvested at 24h, 48h and 72h post-infection, confirming that DNA fragmentation was induced by RHDV infection. The results of flow cytometry showed that about 63% of cells were in apoptosis at 48h post-infection. Besides, we also demonstrated that the activation of Caspase 3 occurred during the infection process. In conclusion, our results showed that apoptosis in RHD might be determinant in the development of the pathogenesis of RHD.

[Construction of rabbit hemorrhagic disease virus replicons and its replication in RK-13 cells].

To provide an efficient and safe technology platform for studying the replication and pathogenesis mechanisms of RHDV, the interaction between the RHDV and its host cells, a replicon system of RHDV, was constructed based on the infectious cDNA clone of RHDV, in which VP60 gene encoding the capsid protein was deleted, but all the necessary protease coding regions and non-coding regions were retained. Results from RT-PCR, IFA and qRT-PCR confirmed that the replicon RNA could efficiently replicate in RK-13 cells. Besides, the results also suggested that the capsid protein which is the structural protein of RHDV is necessary for maintaining the viral infectivity.