Development and immunogenicity of recombinant Mycoplasma gallisepticum vaccine strain ts-11 expressing chicken IFN-γ

Mycoplasma gallisepticum (MG) is a poultry pathogen that causes respiratory disease and loss of egg production worldwide. A live attenuated vaccine, ts-11, has been used for the control of MG in several countries. To improve the functionality of the vaccine and investigate its potential as a delivery vector for host immune molecules and foreign antigens, we have developed ts-11 as a vector to express and secrete chicken IFN-γ (ts-11 C3) using a transposon-based delivery vector. Following administration of ts-11 C3 in chickens by eye drop, up to 2 weeks post-vaccination, neither significant systemic IFN-γ expression nor an antibody response as determined by the rapid serum agglutination (RSA) could be detected, while moderate RSA scores were detected in birds vaccinated with ts-11. However, the MG-specific IFN-γ response in spleen cultures was significantly enhanced in ts-11 C3 vaccinated chickens and, more interestingly, significant heterophil infiltration was detected in the tracheal epithelium in ts-11 C3 vaccinated birds, but not in ts-11 vaccinated birds. These results indicate that the IFN-γ expressed by ts-11 C3 enhanced host cellular immunity rather than humoral immunity and may also have stimulated mucosal heterophil infiltration. These results also suggest that ts-11 is a promising vector for protective antigens of other chicken respiratory pathogens.