How Does HIV Infect Cells?
Have you ever wondered how HIV manages to infect the cells in the human’s body? In order to understand the disease and find a way to cure it, we must get informed on how the infection process starts and develops.
Viruses are parasitic, at least in a way. All viruses have tiny genomes that encode a limited number of proteins. Knowing this and the fact that viruses are not alive, this means that viruses need the proteins by a living host in order to reproduce.
So, what is HIV exactly?
HIV is not a living organism, but genetic information. Every virus is RNA or DNA packaged with a specific protein code. In this case, HIV infects the T Helper Cell and turns it into a replicating cell of the virus.
Generally speaking, there are approximately 1 million T Helper Cells per single milliliter of blood. This is why it takes a lot of time for HIV to reduce the number of the cells and develop AIDS in the patient.
This is good news for people infected with HIV. With the latest treatments and medicines, they can reduce the reproduction of HIV before it is too late.
Viruses are extremely small, which means that all the understanding we have on their working is based on what can be observed by using electron microscopes. For this reason, HIV was identified decades after it first occurred in the human’s live cells.
The human immunodeficiency virus or the HIV has a lipid membrane. This membrane is similar to other organisms’ cell membranes. Attached to it are several proteins, used to attach to the living cell of the host.
Within the membrane exists yet another layer of proteins that comprises the HIV capsule.
How HIV Infects the Cells – Step by Step
Step 1: Entering the Host
Firstly, HIV enters the host. This is done by attaching to host receptors, but not any host receptors. In the case of HIV, these receptors are the CD4 cell surface antigen, which is located on the T Helper cells’ surface.
The CD4 antigens can be found on the cell membranes of the T Helper cell. Once the HIV enters the host receptors, the virus and the cell membranes fuse. Then, the virion core enters the cell.
What’s a virion core?
The virion core contains proteins and the RNA, all essential to the replication of the HIV.
Step 2: Unpacking
Once the virus has managed to fuse with the cell, it starts the second phase – unpacking its contents.
The HIV virus leaves the envelope proteins behind, more specifically on the cell’s surface. In addition, it unpacks the protease, a protein that assembles the virus during the last infection step.
Aside from these proteins, there is a third protein in the HIV virus called integrase. This particular enzyme helps the viral material to integrate into the DNA of the host.
Since the genome of the virus comes in the form of RNA, it first converts to DNA by using the transcriptase enzyme. This makes HIV a retrovirus.
What’s a retrovirus?
A retrovirus is a virus that uses the reverse RNA and transcriptase method. For exactly this reason, it is highly difficult to develop HIV vaccines. Single-stranded genetic materials develop more frequent mutations than the DNA viruses.
This is basically why we get a flu shot yearly, but get one polio vaccine during our lives.
At the end of this stage, the DNA is a double-stranded molecule. This means it is now ready to move into the nucleas of the living cell.
Step 3: Entering the Nucleus
The viral DNA gets transported into the nuclear membrane and the nucleus. Here, the integrase enzyme fuses with the normal DNA of the host and may persist there for many years.
This step makes it very hard to treat and cure the disease since the virus is in a latent state and remains in the cell’s DNA despite all efforts.
Using the cellular enzyme of the host, RNA polumerase, the virus gets transcribed back into two RNA splices.
Imagine a copy machine, where the cell uses DNA to make thousands of copies of the virus. This is exactly what happens in the host’s cell.
The two splices made in this step are the following:
- Short splice that contains the viral protein instructions for making
- Long splice or the copy of the original viral RNA
Step 4: Viral Proteins Constructed
The first type of splices, the short spliced RNAs are now transported to the cell’s cytoplasm. In this phase, the golgi apparatus and the ribosomes use the code we mentioned to construct the viral proteins. On the other hand, the long splices become the core of every new virus and are the fill length viral RNA in the cell.
The virus uses protease to assemble all proteins into the final form. This is the last stage of the HIV infection.
Step 5 : Budding Off the Host Cell
Now that the proteins are assembled from the apparatus and the long strands have completed the viral RNA, the virus buds off the living host cell. In the majority of cases, the budding process completely destroys the host cell, which means that more and more cells are destroyed as the virus multiplies.
Once the infection creates millions of new virus cells by hijacking the healthy DNA in the host’s body, it comes closer to the person developing AIDS. With most viruses, the immune system fails to identify the virus inside the cells, which is why it starts destroying the infected cells before the virus manages to make new copies.
Drugs that can stop and slow down this process are called protease inhibitors. Nowadays, the most popular treatment is the antiretroviral treatment, where people infected with HIV use medicines to treat this infection. By combining several medicines that target the life cycle of HIV, such medicines prevent the reproduction of HIV. This helps people live longer and healthier lives.
Unfortunately, a cure for HIV is yet to be discovered.