HIV - The Key Facts

Sep 1, 2011
Jessica King

hiv virus - the biologian

A recently released report found increased rates of those undergoing treatment for HIV. But how exactly does the virus work?

A report released recently by a House of Lords Select Committee has found that the number of people in the UK being treated for AIDS has trebled in the past ten years, and predicts that almost 100,000 people will have HIV by 2012. The emphasis has been placed now on prevention, through raising awareness about the dangers of the disease – and possibly encouraging wider use of home testing kits, previously restricted due to concerns over misdiagnosis.

Committee chairman Lord Fowler, who ran the 1980s awareness campaign, said: "In the last 25 years the development of new drugs has dramatically reduced the death toll but that should not encourage a false sense of security.” (It also serves to put an incredible financial burden on the NHS.) “Acquiring HIV is not remotely consequence-free. Prevention must be the key policy. One essential message remains the same as in the 1980s: the more the partners, the greater the risk.”

How AIDS functions

Acquired Immunodeficiency Syndrome is a condition where the body’s immune system becomes weakened, leading to increased vulnerability to opportunistic infections. It is caused by a small virus, the HIV virus or human immunodeficiency virus.

HIV is formed of RNA genes encased by a lipid coat. The RNA codes for its own unique proteins, one of which is an enzyme called ‘reverse transcriptase.’ It is able to then reverse the normal process of gene transcription so that a DNA copy of the viral genes can be created from its RNA. This DNA copy is then spliced into the DNA of the infected human cell, thus incorporating the virus’s genes into the human genome.

The viral genes then assume command of the infected cell, instructing it to make thousands of new viruses which then spread and repeat the process ad infinitum. So far, then, it acts in a similar manner to other viruses. Where HIV differs is that one of the virus proteins is a glycoprotein in the viral coat (gp120). This is instrumental in specifically targeting the immune system cells, which thus become infected and injured.

Helper T lymphocytes, which are central to the communication between cells of the immune system, contain a molecule on their surface membrane (CD4) which the viral gp120 molecule is perfectly fitted to bind with. When the virus then binds to a second molecule on the host cell’s surface, the virus membrane and that of the lymphocyte fuse, allowing the virus to enter. Other cells of the immune system – notably macrophages and related cells – also carry CD4 and can become infected in the same way.

The infected cells have been shown to die prematurely, both because of the virus itself and by killer T cells attempting to eliminate the virus-infected cells. The body’s immune system thus attacks itself; this has knock-on effects on the rest of the system: macrophages cannot be activated to destroy certain organisms, B lymphocytes are unable to develop new antibody responses, and killer T cells demonstrate impaired functions. Much of this is due to reduced signals from the helper T lymphocytes that act to coordinate the disparate elements of the immune system.

Treatment?

Drug therapy for HIV is complex and involves a diverse number of treatments targeted to specific symptoms. Nucleoside and non-nucleoside reverse transcriptase inhibitors, protease inhibitors,

entry or fusion Inhibitors and integrase inhibitors of different kinds are all offered to try and prevent the damage the virus can do. Obviously their effectiveness is greatly increased if the condition is diagnosed early, and reportedly it is possible to live a relatively ‘normal’ life while subsisting on this regular cocktail.

But is it really worth the risk and the trauma? Among the opportunistic infections often experienced are one that induces blindness (cytomegalovirus, a herpes virus), a specific virus-induced tumour (Kaposi’s sarcoma), and influenza and pneumonia. Enlargement of the lymph nodes, or lymphoma, is a product of the virus itself and can become very painful and inflamed and even lead to lumps in the gut or brain. This in turn leads to dementia, paralysis, loss of sensation or fits. The virus has also been known to cause damage to the nervous system, via infected macrophages.

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