HIV 101: The Stages of HIV Infection
By Michelle Betton and Chelsea Bailey | August 29, 2013
In the last installment of HIV 101, we introduced you to the basics behind HIV and AIDS. Today, we’ll take you through the process by which HIV infects a cell.
There are six phases in the HIV life cycle: budding and entry; reverse transcription; integration; replication; budding; and maturation.
Budding and Entry: During this phase, HIV attaches to the outside of a CD4 white blood cell—the cells that defend the body against illness. Once attached, HIV can inject its core into the cell.
Reverse transcription: Once inside the cell, the virus’ core breaks open and releases its ribonucleic acid (RNA) and an enzyme called reverse transcriptase. The reverse transcriptase enzyme turns the virus’ RNA into viral deoxyribonucleic acid (DNA). The process of translating HIV RNA to HIV DNA is highly error prone – the likelihood that the genetic information may be incorrectly copied is high. This results in a high mutation rate for HIV. The high mutation rate means that some HIV medications may no longer work against mutated HIV.
Integration: The viral DNA is then integrated into the cell's normal DNA. Once the HIV DNA gets inserted into the cellular DNA, the CD4 cell is turned into a “factory” to produce more and more HIV.
Replication: Once integrated into the cell’s DNA, the HIV DNA now effectively "hijacks" the cell to make the various HIV viral proteins.
Budding: The HIV components gather inside the perimeter of the infected CD4 cell and are assembled into new HIV viruses. When assembled, these viruses “bud” off from the host CD4 cell. Effectively, they rip themselves from the cell, taking a piece of the cell membrane with them to form their own viral membranes.
Maturation: After the new virus buds from the infected CD4 cell, it has all of the necessary parts to infect other CD4 cells, but it first has to mature. During the maturation process, the protease enzyme cuts the HIV proteins into smaller units that reassemble into a mature virus that can infect other cells. Without the enzyme protease, this maturation cannot occur, and HIV cannot go on to infect other cells.
The Elizabeth Glaser Pediatric AIDS Foundation (EGPAF)’s Michelle Betton, Jeffrey Safrit, and Chelsea Bailey contributed to this blog.