Construction of recombinant BCG bearing S1 glycoprotein of nephropathogenic IBV and study on its immunogenicity on chickens

Abstract:

Glycoprotein S1 was the major protein to determine infection and immunogenicity of Infectious bronchitis virus（IBV）. The S1 glycoprotein gene of IBV isolates were amplified by reverse transcriptase-polymerase chain reaction (RT-PCR) and proved to be S1 gene by sequencing. The E. coli-mycobacterium expression shuttle plasmid pR-α-S1 was constructed by inserting the S1 gene to the pRR3 with human mycobacterium tuberculosis HSP70 promoter and α signal peptide. Then the plasmid pR-α-S1 was introduced into mycobacterium bovis BCG by electroporation to construct a recombinate strain rBCG-S1. The S1 protein could be highly expressed in M. smegmatis mc² 155 when induced by heating and was detected by ELISA and Western blot assays using monoclonal antibody against S1 glycoprotein of IBV. 6 week-old SPF chicken were subcutaneously immunized with 10⁶ cfu rBCG-S1 and each chick was immunized three times at 3 week intervals with the same antigen used for the primary immunization. The protective immunity of rBCG-S1 was identified in vaccinated chickens. Results from the protection test showed the two immunizations with rBCG-S1 could provide protection for chickens from the challenge with virulent nephropathogenic IBV strain X. Haemagglutination inhibition titers were also increased in chickens immunized with the expressed rBCG-S1, and significantly higher titers were detected after challenge. These data indicate that the rBCG-S1 could be used as candidate of a live vector vaccine for NIBV.