Whenever a microbe or a substance with a different uniform enters into the body, the immune system is activated. After entering B-cell and T-cell starts to react immediately, this causes the elimination of the substance. Sometimes the agent which enters our body is the kind that remains outside of our body all the time (virus-often remains) in which case B-cells produce antibodies which are circulated all around our body in our bloodstream and eventually bind to the agent. This is the best response for this kind of agent. Our immune system has mechanisms which are very good at killing microbes. Sometimes the agent goes inside the cell. That means the agent lives there most of the time and in which case the best way of killing the agent is through the activation of cytotoxic T-cell ( circulate in the bloodstream and lymph). These cytotoxic T-cells eliminate the agent by killing the cells which contain agents. The response of both B-cell and cytotoxic T-cell happens against agents which provide a two-pronged attack. These actions wonderfully protect us against lots of infections. A gradual elimination of the Th1 and Th2 helper T-cell in immune system results in HIV.
HIV escaping a helper T cell
The virus HIV (Human Immunodeficiency Syndrome)
Retroviruses are a group of viruses which are capable of copying RNA into DNA. HIV is a member of this group. However the structure of HIV is different from other retroviruses. The HIV virus is around 120nm diameter (120 billionths of a meter).
HIV is composed of two exact copy of single stranded RNA protected by the viral protein p24. Each RNA is 9749 nucleotides long and its surrounded by a plasma membrane which comes from the host-cell. The RNA is bound around protein P7 and essential enzymes such as reverse transcription and integrase. The nucleocapsid associates with the genomic RNA and protects the RNA from digestion inside the cell. A structure of protein P17 surrounds the capsid protecting the nucleocapsid. Viral protein and enzymes are in the particle such as Vif, Vpr, Nef, P7 and viral protease. An envelope consisting of the host cell is budding of the capsid from host cell. The envelope contains gp120 and gp41.
A graphic of HIV
How HIV especially affects the immune system
One of the proteins that are a part of a HIV virus is called gp120 .Gp120 is a sugar containing protein called glycoprotein. There is a kind of protein on helper T cells named CD4 (cluster of differentiation antigen NO.4) which is recognised by gp120. The CD4 protein is a part of a helper T cell (Th1 and Th2). Thus HIV targets especially T-cell with special CD4 which is a specific receptor for HIV. However other cells can become infected by the HIV virus. During the first stages of infection a number of T-cells will be killed by the virus. Here the symptoms of an infection which is infecting the immune system such as fever, headache, and tender lymph nodes and generally feeling unwell will display. However the speed of infection stabilises once the antibodies have formed by B-cells. The HIV virus has not been destroyed but all the symptoms will disappear for months to even several years. Here the virus has been stabilised and it will continue to grow even at a much slower rate. The person who is infected by HIV becomes very weak. When a microbe enters the bloodstream the immune system sends T-cells to fight the microbe but as the T-cells are infected, they are weaker than normal T-cells so they can be killed very easily from a microbe attack or they start to divide to make more T-cells. So more infected T- cell will be produced. As time passes the amount of virus in the body will increase until it reaches a certain level. The number of T-cells will decrease. This makes the immune system totally useless. Table 1 shows the diseases that usually define the beginning of AIDS.
Figure1 some common features of AIDS
Now a days the amount of CD4 T-cells and the amount of virus in the body can be measured. Understanding the immune system helps people infected with HIV to live longer and healthier. Perhaps one day our understanding will grow to the point that we know how to rebuild a defective immune system completely.
HIV infection
What is the difference between HIV and AIDS?
HIV stands for Human Immunodefiency Virus. The virus destroys the cells of the immune system and stops them from working. Someone who is infected by HIV is more vulnerable to cancers and infections.
AIDS stands for Acquired Immune Deficiency Syndrome. Someone whose immune system has been infected by HIV does not have AIDS until a level that, the immune system has been severely weakened. By this point the person has the illness and most of the immune system cells have been destroyed.
Treatments
What treatments are available for HIV and AIDS?
When AIDS first surfaced in United States, there were no medicines available. However over the past ten years we have developed to fight HIV infections and its associated infections and cancers. Although AIDS drug do not cure the condition but they help infected people with HIV and AIDS to stay healthier and live longer.
Drugs for treating HIV at early stages of infections when the virus is making copy of itself include:
These drugs may slow the rate of infection in the body. Drugs for treating HIV at its later life cycle include:
- Ritonavir (Norvir)
- Saquinivir (Invirase)
- Indinavir (crixivan)
- Amprenivir (agenerase)
- Nelfinavir (viracept)
- Lopinavir (kaletra)
RT inhibitors and protease inhibitors are major factors in significantly reducing the number of deaths from AIDS. When RT inhibitors and protease inhibitors are used together, it is called highly active antiretroviral therapy or HAART. HAART is not a cure but it does reduce the amount of virus in the blood to nearly undetectable levels. It can not treat the virus as it hides in lymph nodes, brain, testes and eyes. HAART has beneficial effects however there are side effects such as lipodystrophy, diarrhea, nausea, and vomiting.
There are problems with AIDS drugs:
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Side effects of drugs which include Lipodystrophy, Rash, Lactic Acidosis,
How is HIV transmitted?
HIV can be transmitted in three main ways:
- sexual contact
- direct blood contact
- mother to child during pregnancy, breastfeeding
Sexual transmission is the most common means of transmission. HIV is transmitted through sexual activities both vaginal and anal with an infected person. However oral sex is less risky than unprotected anal and vaginal sex. Using condoms during sex reduces the risk of getting HIV.
Mother-to-child transmission
Mothers can transmit HIV to their babies during pregnancy, birth and later thorough breastfeeding. One third of all babies who have been given birth by an untreated pregnant woman infected with HIV will infected. However if an infected pregnant woman takes drug AZT during her pregnancy she can significantly reduce the chances that her baby becomes infected. The pregnant woman also needs to deliver her baby by caesarean section (an operation to deliver a baby through its mothers abdominal wall) to reduce the chances of baby being infected to a rate of 1 percent. NIAID (National Institute of Allergy and Infections Diseases) in Uganda found a very effective and safe drug which is more affordable. The drug is called antiretroviral drug nevirapine/ NVP. A HIV infected woman needs to take a single oral dose of NVP and her baby within 3 days of birth needs to take one to reduce the transmission rate of HIV to half percent compared with AZT.
Transmission through blood
HIV is also transmitted by sharing equipment during intravenous drug abuse and by blood products. Sharing needles, syringes, drugs and other drug equipments can put drug users at a high risk of becoming infected with HIV even if syringes and needles are sterile. HIV can also be transmitted by blood products. Blood screening is now carried out in all developed countries before any blood has been used in surgeries. Blood screening reduces the risk of HIV being transmitted through blood to less than 1 in 500000 pin.
HIV can be transmitted by tattooing, skin piercing and cutting. Health care workers (lab technicians, cleaners) are also at risk for becoming infected with HIV during clinical or surgical procedures.
References
1-www.avert.org
2-Denning – D (1995) HIV and AIDS. Biological Science Review 7(4) 30-35
3-www.stanford.edu
4-www.javon.com
5-www.aps.org
6-www.biology.kenyon.edu
7-www.critpatt.org
8-www.mcld.co.uk
9-Denning-D (2001) HIV and AIDS update- Biological Science Review 14 (1) 37-40
10-
http://aids.about.com/od/hivmedicationfactsheets/a/drugcost.htm
