人類乳突瘤病毒感染與宿主細胞特性

HPV and cervical cancer related articles Part II- HPV basic virology

當HPV 進入宿主細胞後，病毒DNA 相當於細胞內的質體。所謂質體（plasmid） 是指細胞核內染色體以外（extrachromosomal） 的遺傳物質，可以自行複製。它通常是由一小段環狀閉鎖雙股DNA 所構成，僅含有少數幾個基因，並且可以進行轉錄（transcription） 與轉譯（translation） 反應，製造出有意義的蛋白質產物。依照定義，病毒質體必須與細胞染色體分開，呈游離態。但HPV 的DNA 具備有插入宿主細胞染色體的能力，一旦穿插嵌入（integrate），病毒質體將融入宿主細胞染色體並且合而為一，所以這種對宿主細胞染色體具有穿插能力的游離態質體又被稱為游離基因（episome）。被HPV 感染的病變組織與轉形細胞中，可以發現一些特殊病毒蛋白質，除了參與HPV 本身DNA 的複製工作外，又與宿主細胞的轉形與癌化有相當密切的關係。

Human papillomaviruses (HPVs) infect either cutaneous or mucosal epithelialcells, as well as depend on epithelial differentiation in order to complete theirlife cycle. The expression of viral genes is intimately regulated as the infectedbasal cell migrates towards the epithelial surface. Latent infections illustrate along-term maintenance of the HPV genome in the form of plasmids. Such infectionscan be reactivated after several years, particularly as a result of immunosuppression.Productive infections represent the active proliferation of theHPV genome and production of whole infectious virions. Productive infectionsare limited to epithelia that will undergo maturation and differentiation. Abortiveinfections show that the productive life cycle of HPVs is not completed. Abortiveinfection of HPVs is a staged series of induced proliferation and transformationof host epithelial cells. Additionally, such abortive infections can predispose tocancer.