Eukaryotic expression and DNA immunization of hemolysin HlyX gene from Leptospira serovar Lai

Objective To study on the expression of the eukaryotic recombinant vector carrying HlyX gene of Leptospira serovar Lai in mammalian cell and explore the humoral immune response in BALB/c mice immunized with the recombinant plasmid. Methods The HlyX gene was amplified from Leptospira serovar Lai genomic DNA by PCR and inserted into pcDNA3.1 vector. After transformed into E. coli DH5α,the recombinant plasmid was assayed for identification by PCR analysis,restriction nuclease enzyme digestion and sequencing. The recombinant plasmid was transfected into COS-7 cells,then RT-PCR and Western blot were performed to test the expression of the target gene. The recombinant plasmid was injected intramuscularly into BALB/c mice for three times at intervals of two weeks,and the antibody titer was measured by ELISA. Results PCR showed the full length HlyX gene was about 1100 bp. PCR analysis,restriction nuclease enzyme digestion and sequencing indicated the recombinant vector was constructed successfully. After the plasmid Was transfected into COS-7 cells,a fragment about 1100 bp was found by RT-PCR and a specific band relative molecular mass(Mr)about 40×103,which was consistent with the expected size of the target proteins was showed by Western blot. ELISA showed the antibody titer in BALB/c mice immunized by the HlyX gene of Leptospira serovar Lai can elicit high-titer antibody in BALB/c mice,which has laid the foundation for the application of the DNA vaccine. Key words: Leptospira; Hemolysin gene HlyX; Eukaryotic expression; DNA immunization