Chlamydophila psittaci DNA vaccination in turkeys in the presence of maternal antibodies.

Plasmid DNA (pcDNA1::MOMP D) expressing the major outer membrane protein of an avian Chlamydophila psittaci serovar D strain was tested for its ability to induce protective immunity against Chlamydophila psittaci challenge in the presence of maternal antibodies. A combined parenteral (intramuscular injection) and mucosal route (DNA drops administered to the nares) of DNA inoculation was used. Only placebo-vaccinated turkeys showed a primary response following challenge, although DNA vaccination didn't generate high antibody titres. Following pcDNA::MOMP vaccination, both T-helper and B-cell memory were primed. However, high maternal antibodies titres affected the induction of vaccine-specific antibody responses as assessed by MOMP-specific antibody levels in ELISA. Cell-mediated immunity was unaltered as demonstrated by the significantly heightened proliferative responses of peripheral blood lymphocytes following vaccination. DNA vaccination could significantly reduce clinical symptoms, pharyngeal and cloacal excretion as well as chlamydophila replication, even in the presence of maternal antibodies.