BASIC CONCEPTS AND PRACTICAL APPLICATIONS OF RECOMBINANT DNA TECHNIQUES IN DETECTION OF HUMAN PAPILLOMAVIRUS (HPV) INFECTIONS

Recent studies on the role of infectious agents in the pathogenesis of malignancy have demonstrated a strong association between HPV and several human benign and malignant epithelial neoplasms. There are 60 distinct types of HPV, of which HPV 16, 18, 31, 33, 35 and 39 have been associated with squamous cell neoplasia of the genital tract. Rapid progress in the field of recombinant DNA technology with the availability of specific probes has enabled the detection of HPV genomic sequences in characteristic HPV lesions. In addition, HPV sequences have been found in malignant squamous cell lesions, and even in normal tissues lacking the morphologic signs of HPV infection. Currently, hybridization analysis of the nucleic acid is the most reliable method for diagnosis of HPV infections, also permitting the genotyping of these viruses. A variety of hybridization procedures have been developed with different sensitivities and specificities. Despite the divergent technical modifications, however, all hybridization tests working according to the same basic principles. The double helix of DNA composed of two complementary polynucleotide chains can be opened by heating or by increasing pH. Cooling of the two strands allows reassociation. Labeled HPV DNA or RNA probe hybridizes with the complementary sequences allowing the detection of HPV sequences in the samples. Hybridization assays can be conducted under conditions in which virtually all HPVs will be detected, but not specifically typed (low stringency) or under conditions in which the type can be identified (high stringency). Widely divergent results have been reported both in prevalence of HPV infection and distribution of different HPV types in the genital tract. These discordant results have been explained on the basis of sampling effects, differences in histopathological diagnosis, geographical variations in HPV types and interlaboratory variation in HPV detection and typing techniques. In this review the various procedures for detecting HPV sequences by hybridization and related techniques are shortly described.