Immunization with Chlamydia psittaci plasmid-encoded protein CPSIT_p7 induces partial protective immunity against chlamydia lung infection in mice
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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 105 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.
KeywordsC. psittaci Plasmid protein CPSIT_p7 Protective immunity CD4+ T cells
This study was funded by the Natural Science Foundation of China (Grant No. 31270218, Grant No. 81171588, Grant No. 81671986) and the Special Foundation of Hunan Provincial Science and Technology Department (2013TT1003), the construct program of Hunan Provincial Key Laboratory for Special Pathogens Prevention and Control Foundation (Grant No. 2014-5), Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study (Grant No. 2015-351), and the Foundation of the First Hospital of Changsha City (Grant No. Y2018-18).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The Animal Welfare and Ethics Committee of the University of South China approved all animal procedures and treatments, which were performed in accordance with the regulations of the institution.
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