Protection of turkeys against Chlamydophila psittaci challenge by parenteral and mucosal inoculations and the effect of turkey interferon-gamma on genetic immunization.

Plasmid DNA (pcDNA1::MOMP A) expressing the major outer membrane protein of an avian Chlamydophila psittaci serovar A strain was tested for its ability to induce protective immunity against challenge with the same C. psittaci serovar. A combined parenteral (intramuscular injection) and mucosal route (DNA drops administered to the nares) of DNA inoculation was compared to three other, different routes of administration (intramuscular inoculation, DNA drops administered to the nares and aerosol immunization). In addition, the effect of turkey interferon gamma (tIFN-gamma) on intramuscular immunization was evaluated by co-expressing pCIneo::tIFN-gamma. A significant level of protection was observed in turkeys immunized via the combined parenteral/mucosal route, the intramuscular route or by aerosol. Severe clinical signs and lesions were observed in the non-vaccinated control groups, in 80% of turkeys inoculated with a mixture of pcDNA1::MOMP A and pCIneo::tIFN-gamma, and in 60% of turkeys vaccinated with DNA drops administered to the nares. The use of MOMP-based DNA vaccination as a means of preventing severe clinical signs and lesions in a turkey model of C. psittaci infection was demonstrated, as was down-regulation of the immune response by co-expression of tIFN-gamma.