HIV causes a weakness of the immune system. When it infects the body, it prefers to attack certain cells of our defense system. The virus almost fully specializes on these white blood cells since these cells have CD4 molecules on the surface to which the virus binds. HIV replicates in these CD4 positive cells and impairs their function. In the initial stage, the destruction of CD4 cells matches their replacement. The infected person becomes immuno deficient when there is a gap in the destruction & replacement of cells and the CD 4 count starts to fall.The
The virus, to put it simply, consists of genetic information on the inside and a protective outer shell of proteins and glycoproteins. Since viruses use the host cell’s resources for reproduction, they don’t need to contribute much themselves. That’s why they are much smaller than the host cells, e.g. helper T cells. In the host cell’s nucleus, displayed in blue here, there are more than 100,000 times as much genetic information stored than under the protein shell of the virus. However, there is no way for the host cell to stop the virus once the cell has been infected.
The infection proceeds in this manner: The virus anchors itself to a special protein (CD4) on the surface of the helper T cell. This causes the viral membrane to fuse with the host cell’s membrane. This way the genetic information gets inside the cell.
HIV belongs to a special group of viruses. Its genetic information is not encoded as DNA, but instead as RNA (ribonucleic acid) and therefore has to be reverse transcripted into DNA. The tools for this are delivered by the host cell itself, except for a little helper protein (reverse transcriptase) which the virus has brought with itself. The DNA is now legible for the cell and is transferred to the nucleus. This process is already finished by a half of a day after infection. The foreign piece of DNA is then inserted randomly into the host DNA and it is now ready to be transcribed. At the beginning of AIDS, the viral DNA is being transcribed to form many RNA molecules–the signal which causes this is yet unknown. The accruing RNA is carried to the cytoplasm of the cell, where it can start making proteins.
The RNA, with the help of the host’s resources, begins to make many copies of the different parts of the virus (the protective shell and the helper and anchor proteins). After everything has been copied, thousands of bubbles like these are produced and migrate to the cell membrane surface and fuse with it.
Finally, a copy of the RNA genetic information is added to the bubble. Then this section of the cell membrane turns inside out and new viruses leave the cell. Naturally, the release of the new viruses significantly weakens the host cell which soon dies. That is how the immune system weakens and AIDS starts. In early 1996 there were 28m people infected worldwide. This number includes people who already died of AIDS.
Friday, Sep 30th
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