HIV/AIDS Program
How does HIV work in the body?
> The HIV Virus Lifecycle
| 1. |
After a person is exposed to HIV, HIV attaches to the body's infection fighting cells (called CD4 or T cells) in the immune system. The envelope proteins of the virus bind to two receptors on the surface of the CD4 cells. The interaction of the envelope proteins on the surface of HIV with the two receptors triggers fusion of the virus with the host cell, allowing the virus to enter the host cell. |
| 2. |
HIV stores its genetic material as a single strand of genetic code. Most other organisms have DNA, a double strand of genetic code, instead. When HIV infects a human cell, its RNA has to be converted to DNA through a process called using an enzyme called "reverse transcriptase". |
| 3. |
The resulting double-stranded viral DNA then enters the host cell nucleus through pores in the nuclear membrane. A viral enzyme, integrase, then inserts the double-stranded viral DNA at random into the DNA of the host. The viral DNA then becomes integrated into the human DNA, turning the host cell into a "factory" for manufacturing more virus. |
| 4. |
The viral enzyme "protease" the cuts and structures the new viral proteins, which are produced like a long ribbon and need to be separated into individual viral particles. |
| 5. |
The new viral components gather at the cell membrane. The cell membrane then begins to form mini-bubbles, which eventually bud out of the cell releasing new viruses that can then move to and infect other cells. |
| 6. |
CD4 cells do not usually survive invasion by HIV. Either they disintegrate because of the large number of viruses budding off, or the body's immune system will recognize the viral envelope proteins in the cell membrane and destroy the infected and damaged cells. |
> HIV and the Immune System
The body is protected by the skin and linings of the gut, and by an immune system, is a collection of cells and proteins that works to protect the body from potentially harmful, infectious microorganisms (microscopic life-forms), such as bacteria, viruses, protozoa and fungi. For example, when a cold virus invades your body, your immune system sends special cells to fight it. You may sneeze, sniffle, and feel lousy for a few days. But finally your immune system works to kill or control the virus, and you feel fine again.
HIV is different from a cold virus because it directly attacks the infection fighting cells (called CD4 or T4 cells) and other cells in the immune system. Over time, HIV can destroy virtually all of an infected person's T cells. Often (as shown on the graph below) there is a big drop in cellular immunity in the early weeks of infection, then some recovery, then a more gradual decline.
Viral load is the amount of virus in the bloodstream. As seen in the graph at the right, viral load is highest during the acute phase of primary infection (before antibodies are developed) and at end stage AIDS. Viral load tests indicate the effectiveness (or lack of effects) of treatment and the expected rate of disease progression--the higher the viral load, the faster the progression.
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