Immunization with Chlamydia psittaci plasmid-encoded protein CPSIT_p7 induces partial protective immunity against chlamydia lung infection in mice

The present study evaluated the immune-protective efficacy of the Chlamydia psittaci ( C. psittaci ) plasmid protein CPSIT_p7 and analyzed the potential mechanisms of this protection. The current study used recombinant CPSIT_p7 protein with Freund’s complete adjuvant and Freund’s incomplete adjuvant to vaccinate BALB/c mice. Adjuvants alone or PBS formulated with the same adjuvants was used as negative controls. Mice were intranasally challenged with 10 5 inclusion-forming units (IFU) of C. psittaci . We found that CPSIT_p7 vaccination significantly decreased the mouse lung chlamydial load, interferon-γ (IFN-γ) level, and pathological injury. This protection correlated well with specific humoral and cellular immune responses against C. psittaci . In vitro or in vivo neutralization of C. psittaci with sera harvested from immunized mice did not reduce the number of recoverable C. psittaci in the infected lungs, but CD4 + spleen cells collected from CPSIT_p7-immunized mice significantly decreased the chlamydial load via adoptive transfer to native mice. These results reveal that the protection conferred by CPSIT_p7 is dependent on CD4 + T cells.