| MadSci Network: Virology |
First question:
Q. How, exactly does the HIV virus recognize a helper T-cell?The HIV virus has a protein that binds to a host protein in your body called CD4. CD4 is expressed only on a subset of the body's T-cells, called T-helper cells. These cells have a significant regulatory function within the immune system. Infection with the virus kills them and subsequently weakens the immune system.
Second question:
Q. Does the HIV virus have a specific cell in which it inserts its DNA into, and is it a lysogenic or lytic virus?As to the specific cell - it's the T-helper cells that are infected.
HIV belongs to an intresting class of viruses called retroviruses. Retroviruses use RNA as their packaged genetic material instead of DNA, so it is RNA that is inserted into the infected cell, vs. DNA. An enzyme called reverse transcriptase travels along with the viral RNA. This enzyme has the unique ability to 'reverse' the flow of biological information. In most living systems, things proceed with DNA -- RNA -- Protein. Once HIV hits the cytoplasm reverse transcriptase converts the RNA strand into a DNA strand (RNA -- DNA !!!). Some of these DNA copies make it into the nucleus and are inserted into the genomic DNA. In this manner HIV behaves like a lysogenic virus. When induced into the lytic phase, the flow of biolgical information proceeds more to the norm: DNA -- RNA -- protein.
A good HIV/AIDS resource can be found at The Body.
-P.R.