HIV causes AIDS (Acquired Immune Deficiency Syndrome). Those who have contracted HIV can have it for years before it develops into AIDS.
HIV is minuscule, it enters the blood. In HIV positive individuals, the virus can be found in the blood, breast milk and sex fluids (such as vaginal fluids and sperm).
Definition – What is HIV?
HIV (Human Immunodeficiency Virus) is a virus which targets the immune system of a person. With time, this HIV weakens and eventually damages the immune system of the individual. The body starts to lose the ability to defend itself against germs, bacteria and infections. Hence it is difficult to fight this disease.
Structure of HIV
Approximately, HIV has a diametre of 100 nm. It has an envelope of lipids, which embeds the gp41 trimeric transmembrane glycoprotein. To this, the gp120 surface glycoprotein is attached. Both proteins are involved in attaching to the host cell. It is encoded by the env gene of the RNA genome of the virus. Core proteins p6 and p24, p17 – matrix protein, and p7 – nucleocapsid protein, all of which are encoded by the viral gag gene, are seen underneath the envelope.
There are two copies of the ~10 kilobase (kb) positive-sense viral RNA genome together with the integrase, protease and enzymes reverse transcriptase in the viral core. The viral pol gene encodes for all these enzymes.
There are numerous other proteins that are coded by HIV-1 and HIV-2, with different immuno-modulatory or regulatory functions such as vpr (viral protein R), vif (viral infectivity protein), nef (negative regulatory factor), rev (regulator of viral protein expression) and tat (transactivator of transcription).
HIV-1 comprises two copies of non-covalently associated, positive-sense single-stranded RNA encased by a capsid comprising p24 viral protein. Both copies of RNA strands significantly contribute to the HIV-1 recombination occurring at the time of reverse transcription of the viral replication. Psuedodiploidy is when two copies of single-stranded RNA are contained inside a virion; however, only a single DNA provirus is produced. The long Open Reading Frames (ORFs) encode the viral structural proteins, while the smaller ORFs encode the regulators of the viral life cycle.
Transmission of HIV
Up till now, there are four main methods of transmission of HIV that are known, they are –
- Sexual intercourse
- Use of contaminated syringes, needles and other piercing instruments
- Use of contaminated blood and its products, organs and tissues
- Mother to child transmission (MTCT)
Attack of HIV on a person’s Immune system
Upon its entrance, HIV targets and attacks the immune system of an individual. The immune system comprises different types of white blood cells to fight pathogens. HIV detects the white blood cells – CD4 cells and enters these cells, making copies of themselves. Thus, the HIV kills the CD4 cells, the new HIV copies locate other CD4 cells to enter and repeat the cycle.
In response, the immune system tries to control HIV by synthesizing more CD4 cells. However, when the immune system cannot rapidly make the CD4 cells, the count of HIV in the body increases while the count of CD4 cells reduces. Since the immune system can no longer control HIV at this stage, the person becomes sick.
HIV infection cycle of CD4 cells
Entry and binding
HIV locates the CD4 cells and attaches to the receptors on the outer membranes of the cell. Then, it unites with the cell, releasing the viral RNA and enzymes in it.
Reverse transcription
Conversion of single-stranded viral RNA to double-stranded DNA with the aid of the reverse transcriptase enzyme.
Integration
The virus fuses the newly created viral DNA into the nucleus of the CD4 cells using the integrase enzyme. It takes possession of the CD4 cell by integrating its genetic information.
Replication
CD4 cells start making new copies of the virus. The process may cause variations and mutations in the new virions.
Budding and maturation
The new virions of HIV approach the outer membrane of the CD4 cells. The protease enzyme helps convert the immature virions to mature infectious virions. Budding is when it pushes itself out of the cell and finds other CD4 cells to repeat the process all over again.
This was a brief on HIV, its structure, and how HIV invades the immune system of a person. For related information, visit BYJU’S.
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Frequently Asked Questions on HIV
Where in the body is HIV found?
HIV is seen in the body fluids such as blood, breast milk and sex fluids (such as vaginal fluids and sperm).
Is HIV a retrovirus?
Yes, HIV is a retrovirus, it carries single-stranded RNA as its genetic matter as opposed to the double-stranded DNA that human cells carry. Also, the retroviruses have the reverse transcriptase enzyme which enables copying RNA to DNA and uses it to infect the host cells.
Which cells does the HIV target when it enters the host?
HIV targets the human immune system, its cells such as the helper T cells (particularly CD4+ T cells), dendritic cells and macrophages.
When CD4 + T cells count eventually declines below a critical point due to the action of HIV, the cell-mediated immunity is lost. The body progressively becomes more susceptible to opportunistic infections, resulting in AIDS developing.
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