Cloning and expression of the L1 major capsid protein of the human papillomavirus 18 in murine cells

Human papillomavirus (HPV) type 18 is strongly associated with the development of cervical cancer. Studies of a model system with animal papillomaviruses have demonstrated the importance of neutralizing antibodies in preventing papillomavirus-associated disease. The immune response to HPV is poorly understood, and there are non- standardized serological assays to identify HPV infections. In our study, the assessment of antibody responses against HPVs (previously hampered by the lack of viral source) was enabled by the expression of the L1 major capsid viral protein type 18 (HPV18) into L929 murine cells using the pTARGET mammalian expression vector system (MEVS). The cloning was validated by PCR with specific primers for the L1 gene, as well as by enzyme restriction and in situ hybridization. The evidence for the viral cloned gene expression was acquired by RT-PCR. Presence and antigenic properties of the recombinant L1 protein were shown using it as antigen in an indirect enzyme linked immunosorbent assay (ELISA) system. Significantly higher reactivity was noted when the sera samples were from persons infected with HPV18 as compared with the non-infected individuals but a moderately different reactivity was observed when the sera from patients infected with other HPV genotypes were tested. The results showed that the murine transfected cells could be used as antigen in order to detect the presence of the specific antibodies in HPV infected persons.