Abstract: Objective To obtain human papillomavirus type 18 virus-like particles using an optimized HPV 18 L1 gene and prepare antiserum from guinea pig. Methods HPV 18 L1 gene was optimized by combined strategy including codon replacement, truncation of 32 amino acids at C terminal and reduction of secondary structure of mRNA. The optimized HPV 18 L1 gene was synthesized and cloned into pFastBac1 vector. The recombinant baculovirus was obtained and then used to infect sf9 cells. 72h later, the cell lysate was analyzed by western blot. HPV 18 L1 VLP was purified by gradient centrifugation and analyzed by SDS-PAGE and transmission electron microscopy. The guinea pig was immunized with purified HPV 18 L1 VLPs, and the Freund's adjuvant was used. Then antiserum against HPV 18 L1 VLP was produced. Results Optimized HPV 18 L1 gene was expressed efficiently in sf9 cells. The HPV 18 L1 VLP could be purified by gradient centrifugation and the purity was over 90%. Electron microscopy showed the VLP was about 50nm in diameter. The serum antibody titer of guinea pig was 5.12×105. Conclusions HPV 18 L1 VLP could be expressed efficiently in sf9 cells using optimized HPV 18 L1 gene. And guinea pig antisera could be used for further research of HPV 18 L1 VLP based vaccine.

Key words: Human papillomavirus type 18, virus like particles, baculovirus expression system, antisera