Immunogenicity analysis of a recombinant protein CPSIT_p7 and its expression in HeLa cells during persistent Chlamydophila psittaci infection

Objective To construct a prokaryotic expression plasmid for CPSIT_p7 gene from Chlamydophila psittaci （ Cps） 6BC strain and to evaluate immunogenicity of the recombinant protein His-CPSIT_p7 and detect its dynamic expression at mRNA and protein levels in HeLa cells during persistent Cps infection.Methods The fusion protein His-CPSIT_p7 was expressed in E.coli BL21 and purified by Ni-NTA affinity chromatography .BALB/c mice were immunized with the recombinant protein to prepare polyclonal antibody for evaluation of the immunogenicity of His-CPSIT_p7 by ELISA.Penicillin sodium was used to establish a model of Cps persistence infection .RT-PCR and Western blot assay were performed to de-tect the expression of CPSIT_p7 at mRNA and protein levels during Cps persistent infection .Results The fusion protein His-CPSIT_p7 was successfully expressed with the use of constructed recombinant expression plasmid pET30 a-CPSIT_p7 and purified .ELISA result showed that the specific antibody titer against CPSIT_p7 reached 1 ∶1 000 000 on the 40th days after immunization .The expression of CPSIT_p7 at mRNA and protein levels were increased in a time-dependent manner in Cps-infected HeLa cells .The peak of mRNA level was reached at the time point of 36 hours after infection , followed by a time-dependent decrease during Cps acute infection .However , the expression of CPSIT_p7 at mRNA and protein levels were not decreased until 60 hours after infection during Cps persistent infection .Conclusion His-CPSIT_p7 protein was suc-cessfully expressed in the prokaryotic expression system and purified , showing an advantage of good immuno-genicity.Highly expressed CPSIT_p7 at mRNA and protein levels were detected during Cps persistent infection. Key words: Chlamydophila psittaci; Cloning and expression; Immunogenicity; Per-sistent infection