Oncogenic viruses

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And still for a long time would probably remained doubts about the viral nature of neoplasms, if in the middle of 70-ies it was not revealed the family of retroviruses, selectively infect T cells of a person and cause he's got cancer. The first such virus was discovered in the laboratory R. Gallo at the National cancer Institute of the USA in 1976, the Virus was isolated from leukocytes adult patients with T-cell leukemia, and subsequently of lymphomas. He was a member of the family of retroviruses, which are called HTLV from the initial letters of English words "human T-lymphotropic virus". As it turned out, these viruses have an affinity for T-helper cells, the virus is included in the genome near normal gene encoding the synthesis of IL-2. The result is increasing production growth factor T-cells. They start hard to reproduce. Since it concerns only the T-lymphocytes, the infection can lead to T-cell leukemia, and oppression humoral immunity (B-cells) is already the second time. Normal antigenic stimulation is the cause for the expression of the virus and reproduction infected lymphocytes.
For the functioning of retroviruses important structure of its genome, on both ends of which there are regulatory areas, the so-called long terminal repeats (DCT)that affect interaction of the virus with the cell genes. According to Gallo, DCT viruses series HTLV contain the amino acid sequence similar to the gene of T-helpers, head of synthesis or perception of IL-2. This gene was named tat (trans activation of reduced), it is a virus and turns it into an oncogene. Distortion virus normal tat gene leads not only to a violation of the synthesis of lymphocytes IL-2 and V-interferon, but also to their death.
Open the family of retroviruses is the cause of development of various diseases - from leukaemia and lymphomas to acute immune deficiency, in turn, accompanied by a wave of tumors. These viruses resemble a number of previously known pathogens in animals. It is essential that between proteins of the cell membranes of all HTLV of human viruses and virus feline leukemia found significant similarities. Viral protein, fragmented from particles of these viruses and called peptide 15Z, with the introduction of its healthy animals informs them of complete helplessness to the development of cancer and sarcoma. Even artificially synthesized peptide with the same set of 17 amino acids has a definite immunosuppressive action.
Thus, the nature in the person of oncogenic viruses like "picked up" a United and powerful key to "lock" the immune system. This key is used immunosuppressive protein viruses, in particular, is well pronounced in the human viruses. It has similarities with the normal gene lymphocytes (tat-genome), mounted in its place and "translates the immune regulation, leading immunity to another path leading to breakage.
So, all viral oncogenes have a proto-oncogene that they cause a change in the quality of the encoded physiological product or its amount. According to a series of hypotheses (and now and experimental data) viruses can cause not only the rapid transformation of infected cells, but permanently be stored in countless cell generations in a latent state. They repressed or blocked an unknown protein. What will happen if their depression, when will the genetic switch, depends on many factors, first of all immunologic.
Describes numerous cases of hereditary susceptibility of people to cancer. Family tumors, leukemia, cancer of the breast and uterus, ovaries, and rectum ago already have reason to suspect the involvement of the virus in the development of tumors. However, the cause is not in the vertical transmission of oncogenic viruses, otherwise cancer proclaimed strictly hereditary disease. It is obvious that in many cases inherited oncogenes repressed. Activation of them happens when other hereditary defects, immunological, including inherited immunosuppression.