5.5 antibodies

Question 1

What are antibodies?

Answer 1

Proteins with specific binding sites synthesised by B cells

• produced when body is infected with non-self material
• reacts with antigens by binding to them
• each has 2 identical binding sites complimentary to a specific antigen

Question 2

Describe the structure of an antibody.

Answer 2

• made up of four polypeptide chains, two of which are longer heavy chains, and two of which are shorter light chains
• two specific binding sites which fits with a specific antigen to form an antigen-antibody complex
• The binding site is different on different antibodies, so is known as the ‘variable region’
• the rest of the antibody is known as the ‘constant region’ and binds to receptors on cells (EG B cells)

Question 3

What is the function of an antibody?

Answer 3

Antibodies prepare antigen for destruction in a range of ways.
EG: bacterial cells are prepared in two ways;
- agglutination is where clumps of bacterial cells are formed making them easier for phagocytes to locate them. This is where each antibody attaches to two bacterial cells with their two binding sites.
- they act as markers to stimulate phagocytosis of the cells they are attached to.

Question 4

What is a monoclonal antibody?

Answer 4

a single unique antibody which in isolated and cloned.

Question 5

Describe how direct monoclonal antibody therapy is used to treat cancer.

Answer 5

• monoclonal antibodies specific to cancer cells are produced
• these are given to a patient and attach to receptors on cancer cells
• they block chemical signals which stimulate uncontrolled growth
  EG: Hereceptin used to treat breast cancer

Question 6

What is the advantage of direct monoclonal antibody therapy?

Answer 6

It is non-toxic and highly specific so give much fewer side effects than other therapies.

Question 7

Describe how indirect monoclonal antibody therapy is used to treat cancer.

Answer 7

A radioactive or cytotoxic drug is attached to the antibody so that when it attaches, it kills the cell.

Question 8

What is the overall advantage of antibody therapy?

Answer 8

It can be used in small doses due to its specificity. This makes it cheaper and reduces any side effects.

Question 9

What are the advantages of using monoclonal antibodies for medical diagnosis?

Answer 9

They produce a much more rapid result than other methods of diagnosis, and over a hundred diagnostic products are based on them.
they diagnose diseases such as:
influenza, hepatitis, chlamydia, cancers and HIV

Question 10

How are monoclonal antibodies used in diagnosing prostate cancer?

Answer 10

• Men with prostate cancer produce more of the prostate specific antigen (PSA)
• The monoclonal antibody complimentary to PSA can obtain a measure of PSA levels in the blood.
• This acts as an early warning of the possibility of prostate cancer and the need for further testing.

Question 11

How are monoclonal antibodies used in pregnancy tests?

Answer 11

• The placenta produces the HCG hormone which is found in the mothers urine
• monoclonal antibodies on the test strip are linked to coloured particles
• If HCG is present it binds to these particles
• The HCG-antibody-colour complex moves along the test strip until it is trapped by a different type of antibody creating a coloured line

Question 12

What are the three main ethical concerns about using monoclonal antibodies?

Answer 12

1) Mice are used to produce antibodies and tumour cells. this means they are given cancer and some people object to this use of animals.
2) They have treated many diseases successful though there have been some deaths (MS treatment), patients must give informed consent
3) Clinical trials pose certain dangers. in 2006 six volunteers suffered organ failure due to monoclonal antibody testing.