Construction and immunogenicity of recombinant adenovirus expressing the major outer membrane protein (MOMP) of Chlamydophila psittaci in chicks.

Avian chlamydiosis is caused by Chlamydophila psittaci. The major outer membrane protein (MOMP) encoded by the outer membrane protein 1 (omp1) gene is an excellent candidate for genetic engineering of a vaccine against avian chlamydiosis. In this study, the MOMP gene was amplified by PCR and cloned into the transfer vector pShuttle-CMV. The recombinant plasmid was obtained by recombination between the plasmid pShuttle-CMV-MOMP and skeleton vector pAdEasy-1 in Escherichia coli strain BJ5183. The titer of recombinant adenovirus containing the MOMP gene (rAd-MOMP) of C. psittaci was 3.4x10(10)TCID(50)/ml in human embryonic kidney 293 (HEK293) monolayer cells. The expression of the MOMP in HEK293 cells infected with rAd-MOMP was confirmed by an indirect immunofluorescence assay. Specific pathogen free (SPF) chicks were inoculated with 10(6), 10(8), and 10(10)TCID(50) of rAd-MOMP/chick. Inoculated chicks generated antibodies against MOMP of C. psittaci, which were detected by an indirect hemagglutination test (IHA). The vaccinated chicks were challenged with a virulent Chinese field isolate. Nine out of 10 chicks in the vaccinated group were protected, while birds in the wild-type adenovirus control group and the PBS control group all showed clinical signs after challenge. The results indicate that the recombinant adenovirus containing the MOMP gene of C. psittaci might be a candidate vaccine against avian chlamydiosis.