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

Glycoprotein Si 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-alpha-S1 was constructed by inserting the S1 gene to the pRR3 with human mycobacterium tuberculosis HSP70 promoter and a signal peptide. Then the plasmid pR-alpha-S1 was introduced into mycobacterium bovis BCG by electroporation to construct a recombinate strain rBCG-Sl. 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 10(6) 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.