Immunogenicity study of HPV 6b virus-like particles

OBJECTIVE: To confirm human papillomavirus (HPV) 6b virus-like particles (VLP) have strong immunogenicity and the protective antibody induced by HPV 6b VLP have cross-reactive immunity against HPV11 VLP and bovine papillomavirus (BPV) 1 VLP. METHOD: The late gene L1 for HPV6b, HPV 11 and L1/L2 for BPV 1 were molecularly cloned into recombinant baculovirus, respectively. The recombinant viruses were expressed in insect cells (Sf-9 cells). The expressed L1 proteins self-assembled into virus-like particles (VLP) for HPV6b, HPV 11 and BPV 1. VLP were purified from insect cell nuclei by CsCl centrifugation. The Balb/c mice were immunized on days 0 and 21 with 50 microgramHPV6b VLP intramuscularly. Sera were collected after a further 7 days and 3 months. The titers of IgG against HPV 6b VLP, HPV 11 VLP and BPV1 VLP were detected. Hemagglutination inhibition assay was conducted to detected that whether antisera produced by HPV 6b VLP immunization could inhibit HPV11 VLP and BPV 1 VLP agglutinate mouse red blood cells. RESULT: After 7 days of two immunizations, the titers of IgG against HPV6b VLP, HPV11 VLP and BPV1 VLP were 1:6 400, 1:1 600 and 1:1 600 by ELISA, respectively. Three months later, the titers of IgG against HPV6b VLP, HPV11VLP and BPV1 VLP were 1:800, 1:400 and 1:100, respectively. Hemagglutination inhibition assay results showed that the antisera produced by HPV6b VLP inhibit HPV6b VLP and HPV11 VLP to mouse red blood cells binding. CONCLUSION: HPV 6b VLP have potent immunogenicity. Antisera produced by HPV6b VLP could inhibit the binding of HPV6b VLP and HPV11 VLP and cells. Both HPV6b and HPV11 share neutralizing epitopes which are cross-reactive and HPV6b VLP may be used in prophylactic and therapeutic vaccine for HPV6b and/or HPV 11 infections