Normally, the HIV (Human Immunodeficiency Virus) damages the body’s immune system in the following way: When the HIV virus enters the body it approaches and attaches to the lymphocytes or T cells. T cells are small white blood cells that are essential components of our immune system and they are HIV’s principal target. In order to replicate (i.e. reproduce) HIV needs to transfer its genetic material (RNA) into the host cell. This viral RNA contains a protein called “reverse transcriptase” which is required for the replication of virus in the host cell.
For the virus to enter the host cell it needs two main receptors on the host cell (CD4 and CCR5 receptors). If any one of these receptors is absent the viral core containing the RNA will not be able to enter the cell. A combination of two molecules (gp120 and the gp41) present on the surface of the virus help the virus to get attached to the receptors on host cell and infect it.
Once the virus attaches, it transfers its core with the viral RNA and reverse transcriptase into the cell. Now to infect the host cell the viral RNA has to enter the cells nucleus so that it can change the information laid down by the DNA and change the host cell into a virus-producing unit. But for this to occur viral RNA has to be converted into DNA first.
Normally, in our body the nucleus in the cell communicates with the rest of the cell by converting DNA into RNA (i.e. DNA makes the RNA and sends it out of the nucleus to convey messages). But the reverse happens in case of HIV. Because of the presence of the substance called reverse transcriptase the viral RNA gets converted into Viral DNA. The viral DNA enters the cells nucleus and prevents the cell from performing its normal functions and instead commands it to produce new virus.
Due to its unique way of reproduction the HIV virus destroys the immune system and damages increasing number of T cells, thereby putting the individual at an increased risk of opportunistic infections.
Now the question is, how does the HIV virus outsmart the human cell and cause AIDS? It seems that scientists finally have an answer to this question. According to scientists in the U.S. the HIV dodges one of the body’s major defenses against infection- an antiviral system that we were not aware of – a single protein called APOBEC3G.
Scientists say that this protein is a powerful viruse inhibitor, especially HIV. However, it seems that the HIV has managed to outsmart even this protein. During the long battle between the host cell and the virus, the HIV has developed a special gene, which counteracts the effect of the APOBEC3G. This gene is called virion infectivity factor (Vif).
In a HIV infected cell this gene called Vif binds to the protein, APOBEC3G and prevents it from entering the new viruses. Hence, the viruses continue to replicate and spread throughout the body.
Recently scientists have found that mice too have APOBEC3G (the antiviral protein). Surprisingly HIV cannot identify this protein in the mouse. Hence, APOBEC3G in mouse acts as a powerful blocker and thereby prevents HIV replication.
What happens is that when the virus is produced in the infected cell the antiviral protein (APOBEC3G) enters the virus. Initially the protein does nothing, but when virus infects a new cell it gets activated. As soon as HIV starts to copy its genes into DNA the antiviral protein attacks the virus, causing substantial mutations in the viral genetic material. The viral DNA is so badly mutated that it cannot function as before (i.e. cannot replicate).
Scientists say that this discovery may prove to be a breakthrough for treating AIDS. New drugs can be developed that attach to APOBEC3G, thereby preventing the Vif from binding to the antiviral protein. If this happens the HIV Replication can be stopped and thereby disease can be controlled.