AIDS or Acquired Immunodeficiency Syndrome is caused by HIV, which attacks and destroys cells of the immune system. The outcome is a gradual and systematic loss of the body's ability to fight off infection. As a result, the HIV-infected person begins to suffer from diseases that the body can normally deal with such as certain types of pneumonia. If untreated, AIDS will destroy the immune system.
HIV
The human immunodeficiency virus belongs to a group called retroviruses, because their genome is made up of RNA, not DNA. To reproduce itself, the virus must convert RNA into DNA by using a special enzyme called reverse transcriptase. Once the DNA has been made inside the virus, it is able to produce copies of itself. Like all viruses, HIV can only reproduce after infecting a cell. Its reproduction eventually destroys the cell.
Cell Entry
When HIV encounters a cell with a certain type of surface molecule that it recognizes, it can bind to it. Cells carrying these particular molecules are immune cells called CD4 positive cells. These are also called helper T-cells because they are able to activate other types of immune cells when a foreign invader such as a bacterium appears. Because of this, CD4+ cells are crucial to the immune system. When the virus encounters one of these cells, it binds to the cell's surface. Eventually, the viral surface and the cell membrane fuse, which allows the virus to enter the cell.
HIV Hides
Once the human immunodeficiency virus has gained entry into a CD4+ cell, it transforms the cell's RNA into DNA, which becomes incorporated into the cell's own DNA. This happens because the virus contains an enzyme that hides the viral DNA among the cell's own DNA. This hybrid virus-cell DNA may remain inactive for years.
Taking Over the Cell's Machinery
When the CD4+ cell receives a signal to activate, the viral DNA is replicated along with the cell's genome. The result is production of new viral DNA and also of a number of viral proteins, which are all incorporated into many new virus particles. This occurs at the expense of the cell's energy stores and limits its ability to survive.
Leaving the Host Cell
The new HIV particles make their way to the surface of the host cell, where they begin to push their way out, or bud. When this happens, the virus particles becomes covered with some of the cell's outer covering or surface membrane. These new virus particles can move on to infect additional CD4+ cells, amplifying the number of viruses and destroying more host cells. The result is loss of an important population of immune cells and a breakdown of crucial infection-fighting cells.
