Vaccination With CPSIT₀846 Elicits Protection In Mice Against A Chlamydophila Psittaci Challenge

[Objective] To investigate the anti-infection effects of C. psittaci inclusion protein CPSIT₀846, and lay basis on the development of a new type, efficient and specific C. psittaci subunit vaccine. [Methods] BALB/c mice were intranasally infected with three different dose（5×104、5×105、5×106 IFU） of C. psittaci 6BC to construct an animal infection model. The fusion protein CPSIT₀846 was prokaryotic expressed and purified. And then the protein was used to immunize experimental mice by the intraperitoneal route three times, two weeks after the last immunization, antigen-specific antibody in mice serum were detected and IFN-γ, IL-6 in spleen cell culture supernatant were detected by ELISA. After immunized, some mice were challenged by C. psittaci by intranasal route, then the incidence, survival rate and the lung tissue pathological lesions were compared between immunized group and unimmunized group to evaluate the immune protection of CPSIT₀846. [Results] 1. The BALB/c mice were infected with C. psittaci 5×104, 5×105, 5×106 IFU by intranasal route, and the mice were caused different degrees of clinical symptoms and pathological changes of the viscera organs, these changes showed obviously dose-dependent. 2. The mice were immunized with the recombinant protein by intraperitoneal injection three times, and their serum was collected to test the specific antibody with ELISA method. The serum specific Ig A, Ig G and Ig G subtypes were detected, the titer of total Ig G was 1:48000, Ig G1 was 1:10400, Ig G2 a was 1:3000, Ig G2 b was 1:16000, Ig A was 1:400. 3. The spleen cell supernant was collected, then the cytokine was tested with ELISA. And the mice vaccinated with CPSIT-0846 developed high levels of IFN-γ, 544.97±80.93pg/m L, while PBS group was 25.86±12.54pg/m L and ovalbumin group was 32.29±12.77pg/m L, the IFN-γ level of CPSIT-0846 group had significant difference compared with the control group（P <0.01）. IL-6 of the immunized group was 334.25±34.47pg/m L, PBS group was 27.07±7.55pg/m L, ovalbumin group was 30.20±7.17pg/m L, the CPSIT-0846 group IL-6 level was ignificantly higher than control group（P < 0.01）. The spleen lymphocytes stimulation index（SI） of mice immunized with CPSIT-0846 was 2.27 and significantly higher than the SI of PBS group and ovalbumin group（P <0.01）. 4. At day 10 post-challenge with C. psittaci by intranasal route, the lung tissue pathology lesions of mice immunized with CPSIT-0846 is lighter, and the control group mice’s protect effection is not obviously.[Conclusions]1. C.psittaci 6BC respiratory tract infection mouse model was successfully constructed. 2. The CPSIT₀846 protein can induce specific humoral immune response and cellular immune response, and play roles in anti-C. psittaci infection.