Vaccine potential of recombinant Ornithobacterium rhinotracheale antigens.

Ornithobacterium rhinotracheale is a pathogen involved in respiratory infection and systemic disease in poultry. Previously, eight potential vaccine candidates were identified that induced cross-protective immunity when administered to chickens as a multi-component vaccine. In this study, we analyzed the immunogenicity of these eight recombinant proteins by subunit vaccination, and characterized the different proteins and corresponding genes more thoroughly by sequencing, in vitro expression analysis, and cellular localization experiments. We found, that all genes encoding the eight antigens were highly conserved among different O. rhinotracheale serotypes, but the different antigens were not expressed by all serotypes. Cellular fractionation experiments indicated that the majority of the antigens are predominantly located in the outer membrane fraction. Vaccination of chickens with single-antigen vaccines demonstrated that the Or77 antigen was protective against serotypes that expressed Or77 in vitro, suggesting that the protein has strong potential as a vaccine antigen. Furthermore, immunization with four-component subunit vaccines indicated the existence of immunogenic synergism between the candidate vaccine antigens.