HIV, monoclonal and ELISA

Question 1

What are monoclonal antibodies?

Answer 1

Each antigen on the surface of a microorganism will induce a different B cell to multiply and form a clone of itself.
Each of these clones will produce a different antibody.
It is of considerable medical value to be able to produce antibodies outside the body and be isolated and cloned.

Question 2

What are the useful functions of monoclonal antibodies in medicine?

Answer 2

Targeting medication to specific cell types by attaching a therapeutic drug to an antibody.
Medical diagnosis.
Pregnancy testing.

Question 3

How are monoclonal antibodies used to treat cancer?

Answer 3

Direct monoclonal antibody therapy:
Monoclonal antibodies are produced that are specific to antigens on cancer cells.
These antibodies are given to a patient and attach themselves to the receptors on their cancer cells, and block the chemical signals that stimulate their uncontrolled growth.

Question 4

What is Herceptin?

Answer 4

Herceptin is a monoclonal antibody used to treat breast cancer.
The advantage of direct monoclonal antibody therapy is that since the antibodies are not toxic and highly specific, they lead to fewer side effects than other forms of therapy.
They can be used in smaller doses, as they are targeted on specific sites. This is not only cheaper but also reduces any side effects the drug might have.

Question 5

What is indirect monoclonal antibody therapy?

Answer 5

It involves attaching a radioactive or cytotoxic drug to the monoclonal antibody.
When the antibody attaches to the cancer cells, it kills them.

Question 6

How are monoclonal antibodies used in medical diagnosis?

Answer 6

They are used for the diagnosis of influenza, hepatitis and chlamydia infections where they produce a much more rapid result than conventional methods of diagnosis.
They are important in diagnosing certain cancers.

Question 7

How are monoclonal antibodies used to diagnose cancer?

Answer 7

For example, men with prostate cancer often produce more of a protein called prostate specific antigen (PSA) leading to unusually high levels of it in the blood.
By using a monoclonal antibody that interacts with this antigen, it is possible to obtain a measure of the levels of PSA in a sample of blood.
While a higher than normal level of PSA is not itself a diagnosis of the disease, it gives an early warning of its possibility and the need for further tests.

Question 8

How are monoclonal antibodies used in pregnancy testing?

Answer 8

The kits rely on the fact that the placenta produces a hormone called human chorionic gonadotrophin (hCG) found in the mother’s urine.
Monoclonal antibodies present on the test strip of a home pregnancy testing kit are linked to coloured particles.
If hCG is present in the urine it binds to these antibodies.
The hCG-antibody-colour complex moves along the strip until it is trapped by a different type of antibody creating a coloured line.

Question 9

How are mice linked to the ethical use of monoclonal antibodies?

Answer 9

Production of monoclonal antibodies involves the use of mice.
These mice are used to produce both antibodies and tumour cells.
The production of tumour cells involves deliberately inducing cancer in the mice.
Despite the specific guidelines drawn up to minimise suffering, some people still have reservations about using animals in this way.

Question 10

How is death linked to ethical use of monoclonal antibodies?

Answer 10

Monoclonal antibodies have been used successfully to treat a number of diseases, including cancer and diabetes, saving many lives.
There have also been some deaths associated with their use in the treatment of multiple sclerosis.
It is important that patients have full knowledge of the risks and benefits of these drugs before giving permission for them to be used - informed consent.

Question 11

How is testing linked to ethical use of monoclonal antibodies?

Answer 11

Testing for the safety of new drugs presents certain dangers.
In March 2006, 6 healthy volunteers took part in the trial of a new monoclonal antibody (TGN1412) in London.
Within minutes they suffered multiple organ failure, probably as a result of T cells overproducing chemicals that stimulate an immune response or attacking the body tissues.
All the volunteers survived, but it raises issues about the conduct of drug trials.

Question 12

What is HIV?

Answer 12

Human immunodeficiency virus causes the disease acquired immune deficiency syndrome (AIDS).
Among contagious diseases, it is a relative newcomer, having been first diagnosed in 1981.

Question 13

What is the structure of HIV?

Answer 13

On the outside is a lipid envelope, embedded in which are peg-like attachment proteins
Inside the envelope is a protein layer called the capsid that encloses two single strands of RNA and some enzymes.
One of these enzymes is reverse transcriptase, that catalyses the production of DNA from RNA - the reverse of transcriptase.
HIV belongs to a group of viruses called retroviruses.

Question 14

How is HIV replicated?

Answer 14

Being a virus, HIV cannot replicate itself.
Instead it uses its genetic material to instruct the host’s cells biomechanical mechanisms to produce the components required to make new HIV.

Question 15

What is the process of HIV replication?

Answer 15

Following infection HIV enters the bloodstream and circulates around the body.
A protein on the HIV readily binds to a protein called CD4. While this protein occurs on a number of different cells, HIV most frequently attaches to helper T cells.
The protein capsid fuses with the cell surface membrane. The RNA and enzymes of HIV enter the helper T cell.
The HIV reverse transcriptase converts the virus’ RNA into DNA.

Question 16

What is the process of HIV replication - DNA?

Answer 16

The newly made DNA is moved into the T cell’s nucleus where it is inserted into the cell’s DNA.
The HIV DNA in the nucleus creates messenger RNA using the cell’s enzymes. This mRNA contains the instructions for making new viral proteins and the RNA to go into the new HIV.
The mRNA passes out of the nucleus through a nuclear pore and uses the cell’s protein synthesis mechanisms to make HIV particles.
The HIV particles break away from the helper T cell with a piece of its cell-surface membrane surrounding them which forms their lipid envelope.

Question 17

What is HIV positive?

Answer 17

Once infected with HIV a person is said to be HIV positive.
However, the replication of HIV often goes into dormancy and only recommences, leading to AIDS, many years later.

Question 18

How does HIV cause the symptoms of AIDS?

Answer 18

HIV causes AIDS by killing or interfering with the normal functioning of helper T cells.
An uninfected person normally has between 800-1200 helper T cells in each mm^3 of blood vs a sufferer of AIDS can be as low as 200mm^-3.

Question 19

What does a lack of helper T cells cause?

Answer 19

Without a sufficient number of helper T cells, the immune system cannot stimulate B cells to produce antibodies or the cytotoxic T cells that kill cells infected by pathogens.
Memory cells may also become infected and destroyed.
As a result, the body is unable to produce an adequate immune response and becomes susceptible to other infections and cancers.

Question 20

How does HIV cause death?

Answer 20

Many AIDS sufferers develop infections of the lung, intestines, brain and eyes, as well as experiencing weight loss and diarrhoea. It is these secondary diseases that often cause death.
HIV does not kill individuals directly.
By infecting the immune system, HIV prevents it from functioning normally.
As a result those infected by HIV are unable to respond effectively to other pathogens.
It is these infections, rather than HIV, that ultimately cause ill health and eventual death.

Question 21

What is the ELISA test?

Answer 21

Enzyme linked immunosorbent assay.
It uses antibodies to detect the presence and quantity of a protein in a sample.
It is extremely sensitive and so can detect very small amounts of a molecule.

Question 22

What is the procedure of the ELISA test?

Answer 22

Apply the sample to a surface, e.g. slide, to which all the antigens in the sample will attach.
Wash the surface several times to remove any unattached antigens.
Add the antibody that is specific to the antigen and leave to bind together.
Wash the surface to remove excess antibody.
Add a secondary antibody which binds with the first, the secondary has an enzyme attached to it.
Add the colourless substrate of the enzyme. The enzyme acts on the substrate to change it into a coloured product.
The amount of the antigen present is relative to the intensity of colour that develops.

Question 23

How is ELISA used?

Answer 23

It can be used to detect HIV and the pathogens of disease including tuberculosis and hepatitis.
It is especially useful where the quantity of an antigen needs to be measured, for example in testing for particular drugs in the body.
The mere presence of a drug is often less important than its quantity as many drugs are found naturally in low concentrations.
ELISA is very useful in both drugs and allergen tests.

Question 24

Why are antibiotics ineffective against viral diseases like AIDS?

Answer 24

Viruses rely on host cells to carry out their metabolic activities and therefore lack their own metabolic pathways and cell structures.
As a result antibiotics are ineffective because there are no metabolic mechanisms or cell structures for them to disrupt.
Viruses also have a protein coat rather than a murein cell wall and so do not have sites where antibiotics can work.
In any case, when viruses are within an organism’s own cells, antibiotics cannot reach them.

Question 25

How do antibiotics work in bacterial cells?

Answer 25

Antibiotics like penicillin inhibit certain enzymes required for the synthesis and assembly of the peptide cross-linkages in bacterial cell walls.
This weakens the walls, making them unable to withstand pressure.
As water enters naturally by osmosis, the cell bursts and the bacterium dies.

Question 26

How do bacterial cells usually resist destruction?

Answer 26

In bacterial cells, as in plant cells, water constantly enters by osmosis.
This entry of water would normally cause the cell to burst.
That is doesn’t burst is due to the wall that surrounds all bacterial cells, made of murein (peptidoglycan) a tough material that is not easily stretched.
As water enters by osmosis, the cell expands and pushes against the cell wall.
Being relatively inelastic, the cell wall resists expansion and so halts further entry of water.
It can not do this against antibiotics.