The cellular immune response produced in BALB/c mice immunized with HPV6b L1/Ct MOMP multi-epitope chimeric DNA

Objective To study on the specific cellular immune response produced in BALB/c mice immunized with human papillomavirus (HPV) type 6b capsid protein L1 and Chlamydia trachomatis (Ct) major outer membrane protein(MOMP) multi-epitope chimeric DNA (HPV6b L1/Ct MOMP multiepitope) , and the enhancement of the specific cellular immune response to Ct MOMP multi-epitope by HPV6b L1. Methods The Ct MOMP multi-epitope gene was connected to the C terminal of HPV6b L1,the gene of HPV6b L1 had been optimized according to the codon usage of eukaryotic system, and then the HPV6b L1/Ct MOMP multi-epitope chimeric gene was cloned to pcDNA3.1 ( + ) vector. After identification by restriction enzyme digestion and DNA sequencing, the recombinant plasmid was transfected into COS-7 cells, Indirect Immunofluorescence (IIF) was used to confirm the expression of proteins. Then, BALB/c mice were randomly assigned to receive (intramuscular injection) either pcDNA3.1 ( + )/HPV6b L1/Ct MOMP or pcDNA3.1 ( + )/Ct MOMP or pcDNA3.1 ( + ) or PBS ( n = 12, 150 μg/time), and the same immunization schedule was repeated third times at 2 week intervals. The level of cytokine( IFN-γ, IL-4, IL-10) -producing CD3+ T cells in spleen, the cytotoxicity of Ct MOMP-specific and HPV6b L1-specific cytotoxic T lymphocyte (CTL) in spleen were detected by intracellular cytokine staining-fluorescence activated cell sorter (ICS-FACS) and LDH release assays, respectively. Results After immunization, when the efCTL (44.56%±4.02%, 35.35% ±2.89% ) and HPV6b L1 specific cytotoxicity of CTL (27.08% ±2.04%, 21.68% ±4.06% ) in pcDNA3.1 ( + )/HPV6b L1/Ct MOMP multi-epitope chimeric DNA immunized mice, were significantly higher than that in pcDNA3.1 ( + )/Ct MOMP multi-epitope DNA (35.50%±2.68%, 30.24% ±1.75%; 12.27% ±3.36%, 9.32% ±3.07%) and other control groups(F=72.87, F=114.55, P＜0.05; F=30.04, F=10.47, P＜0.05), and Ct MOMP multi-epitope specific cytotoxicity of CTL in pcDNA3.1 ( + )/Ct MOMP multi-epitope DNA immunized mice were significantly higher than that in control groups( F = 58.85, F = 120.21; P<0.05). The level of intracellular cytokine IFN-γ in pcDNA3.1 ( + )/HPV6b L1/Ct MOMP multi-epitope DNA immunized mice(4.34% ±0.06%)was higher significantly than that in pcDNA3.1 ( + )/Ct MOMP multi-epitope DNA immunized mice(3.14% ± 0.18%, P<0.05 ) and other control groups ( F = 473.83, P<0.05 ), while, the levels of IL-4 ( F =0.97, P ＞ 0.05 ) and IL-10 ( F = 2.25, P ＞ 0.05 ) had no significant difference between groups. Conclusion Both Ct MOMP and HPV6b L1 protein specific cellular immune response could be induced in BALB/c mice immunized with HPV6b L1/Ct MOMP multi-epitope chimeric plasmid, and the HPV6b L1 gene optimized by eukaryotic codon could significantly enhance the cellular immune response induced by Ct MOMP multi-epitope gene in BALB/c mice. Key words: Human papillomavirus;  Chlamydia trachomatis;  Major outer membrane protein; CTL;  Epitope