How Does HIV Work?
There are five basic steps to the life cycle of HIV. These are the steps scientists use to develop drugs — fighting HIV every step of the way, as it were.
1. Attachment, Fusion and Entry
HIV attaches itself to the body’s CD4 cells (also called T-cells). The virus does this by using receptors on the surface of the cell. Next, HIV fuses (or melts) into the surface of the cell. When all the separate steps of fusion take place, like arms reaching out and completing a handshake, HIV is pulled inside the cell. (By the way, the virus also infects other cells of the body, such as the lymph nodes or the brain. Sometimes it just sits there instead of going through the steps below. But the CD4s, which are immune system cells, are its favorite target.) There are several key receptors that affect cell attachment and fusion. Science knows of two types of receptors, the CD4 receptor and the chemokine co-receptor.
2. Reverse Transcription
Once inside the cell, HIV uses its transcriptase enzyme to change itself in preparation for becoming part of the body’s genetic code. When that happens, the body will be forced to produce HIV like it does anything else — tears, new liver cells, etc. Because HIV works backwards compared to most viruses (making it a “retrovirus”), this is called a “reverse transcriptase” enzyme. (Enzymes are proteins that cause substances to change.) The RT enzyme changes HIV’s genetic material from RNA to DNA. (To put it simply, RNA and DNA are part of our genetic structure, which form the blueprints for all of the body’s functions. HIV has its own genetics.)
3. Integration
The HIV DNA then enters the nucleus, the command center of the cell. Once inside the nucleus, HIV uses another enzyme, integrase, to re-program the cell, integrating the virus with the cell’s DNA.
4. Cutting and Assembly
Every time the T-cells become activated due to an immune response — for example, you catch a flu virus and T-cells come to fight the flu out of your system — spare parts of the HIV DNA separate and form what is called a messenger RNA. The messenger RNA leaves the center of the cell and forms a long chain of instructions to make new HIV particles, like a parent would leave a list of instructions for a babysitter. Then an enzyme called protease comes to play. This is why we have protease inhibitors, which inhibit this part of the HIV life cycle. The protease enzyme cuts the long list of instructions into separate parts that assemble and come together to form a new HIV particle.
5. Budding
The new HIV particle moves out of the cell through a process called budding, because its action is like a blooming flower. The HIV particle pushes through the cell wall, taking parts of the cell’s covering to form the new coat of HIV. The HIV particles are constantly maturing and growing, or blooming, from the time it becomes the messenger piece of information to the time it buds from the cell.
