| Infectious Bronchitis is an economically important viral respiratory tract infection of chickens characterized by signs of respiratory depression, gasping, and 30%-40% mortality. The disease may cause severe production losses and/or decreased egg production. The causative agent of the disease is an Corona virus, infectious bronchitis virus (IBV), classified as Corona .Present vaccines for IB are all modified live viruses derived either by sequential passage embrocated chicken eggs. As Immunogenicity of IBV is usually correlated with its virulence, almost all modified live IB vaccines remained insufficient attenuation and have shown a variety of side effects including spread of vaccine virus to no vaccinates, occurrence of long term "carrier" birds, and increasing virulence during in vivo passage. Therefore, vaccination has generally been used only in areas where the disease is endemic.There has been proved that vaccination with infectious bronchitis virus (IBV) spike1 lipoproteins can induce humoral protective immunity. Therefore,S1 is a major protective immunogen of IBV, and therefore a prime candidate for constructing recombinant vaccines.In the study, a gene coding for glycoprotein S1 (S1) of IBV strain XJ3 (a virulent strain isolated in xinjiang) was amplified using a pair of primers based on the published sequence of IBV strain XJ3. The S1 gene was then cloned into pUC19 at BamHI site. The sequence analysis showed that the S1 gene contains a complete open reading frame of 1659bp. The cloned IBV S1 gene and LacZ gene were inserted individually into a transfer vector with promoters in frame of each gene. FPV infected chicken embryo fibroblast (CEF) cells were transfected with the transfer vector pSY781 taking lipofectin transfection procedure. Recombinant FPV was selected by blue plague purification. A recombinant FPV stably expressing IBV S1 (designated as rFPV-IBVS1) was obtained by six passages of plague purification. Expression of S1 gene in rFPV-IBVS1 infected CEF was determined by Western blotting. Protection study was performed in both SPF chickens. SPF chickens were divided into Four groups: commercial IBV vaccine; rFPV-IBVS1; S-FPV-017 ; unvaccinated (control). The number of chickens in each group is 16 for SPF chicken At 4 weeks of age, chickens were eye-drop immunized with the recommended dose of commercial IBV vaccine, or vaccinated intradermally via wing with 5×106 PFU rFPV-IBVS1 or 5×106 PFU S-FPV-017. Four weeks after vaccination, chickens in all groups were challenged by bronchitis injection with a lethal dose (0.2ml 8.5EID50/0.1ml) of IBV XJ3 strain After challenge, chickens immunized with rFPV-IBVS1 and commercial IBV vaccine were all protected from death; the result indicated that rFPV-IBVS1 can protect chickens from the infection of IBV. After immunization and followed challenge, antibody level to IBV induced by rFPV-IBVS1 is lower than that induced by commercial IBV vaccine. Virus isolation and PCR detection of IBV after challenge indicated that commercial IBV vaccine could better resist replication of challenge virus than rFPV-IBVS1 in SPF chickens。Taking all results together, rFPV-IBVS1 is able to mostly induce humoral immune response against challenge by virulent IBV. As the current commercial IBV vaccines have several disadvantages as mentioned above, the recombinant virus rFPV-IBVS1 can be considered very safe and therefore a promising substitution of live attenuated IBV vaccines for future eradication of avian infectious Bronchitis.
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