All types of human papillomavirus Papovaviridae have the same structure, and HPV 6 type virions also exist in the form of an icosahedral capsid with a diameter of 52-55 nm, built of several dozen units of the structural proteins L1 and L2 - self-organizing pentamer capsomers.
An unprotected lipid envelope capsid contains one circular DNA molecule of the viral genome, consisting of two chains or filaments linked by proteins of cell nuclei - histones. The genome contains approximately eight open reading frames (ORFs) that are all transcribed from a single DNA strand.
HPV 6, like other papillomaviruses, is characterized by high epitheliotropicity, adaptability to the host and protection from the cell-mediated immune response. By expressing viral genes and replicating its DNA, it neutralizes the immunocompetent cells of the epidermis (T cells, macrophages / monocytes, etc.) and penetrates into the keratinocytes of the stratified epithelium of the skin of the anogenital zone and the oral cavity. The life cycle of the virus, first of all, its lytic phase, is associated with the differentiation of basal cells, which ensure the proliferation of skin tissue cells.
For replication, HPV has proteins (E1- E7) - recognizing its onset, regulating gene transcription and stimulating differentiating skin cells to replicate the DNA doubling period, that is, the S-phase of the cell cycle.
A specific feature of the papillomavirus type 6, as a low oncogenic risk virus, is the absence of aggressive inactivation of cellular tumor suppressor proteins p53 and pRb with its potential oncogenic proteins E6 and E7, which do not lead to the launch of the program of malignant differentiation of skin cells and their mutation (occurring in cancerous types HPV).
In addition, this virus has a latent phase of the life cycle, when, after the initial infection, the division of viruses ceases. At this stage, their genes can remain passive for a long time, being in the cytoplasm or the nucleus of the host cells, in the form of separate structures of episomal DNA. However, the virus is able to reactivate the process of DNA replication without re-infection of the person.
How is HPV 6 transmitted? Most often, the virus spreads through the skin contact between an infected and an uninfected person - sexually.
Read also - Human papillomavirus: structure, life cycle, how it is transmitted, prevention
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