immunology

Question 1

Scientists have developed a new technique that can identify whether people smoke tobacco. Tobacco contains nicotine, which is broken down to cotinine. Cotinine is found in fingerprints. The new technique uses antibodies against cotinine.

(a) These scientists injected laboratory mice with cotinine. D

Answer 1

Cotinine is an antigen;
Antigen/cotinine binds to (specific) T-cell/activates T-cell;
T-cell activates B-cells;
Specific B cell becomes activated;
(Specific) B cell divides/ clonal expansion;
Forms (clone of) plasma cells;
(Plasma) cell produces antibodies;

Question 2

The antibodies bind only to cotinine, and not to any other substance in the fingerprint.
Explain why.

Answer 2

Antibodies are proteins with tertiary structure/specific shape/binding sites;
Antibodies specific shape for cotinine;
Only cotinine fits;

Question 3

Azidothymidine (AZT) is a drug used to treat people infected with human

immunodeficiency virus (HIV). It inhibits the enzyme that synthesises

DNA from HIV RNA. This does not destroy HIV in the body but stops or

slows the development of AIDS.

5 In the past, some people who took AZT on its own eventually developed

AIDS. Some of the HIV in their bodies had become resistant to AZT.

To prevent this from happening, people infected with HIV are now treated

with highly active antiretroviral therapy (HAART). This involves taking AZT

with other anti-HIV drugs at the same time.

10 AZT is taken in low doses. This is because people who took high doses

over long periods of time suffered muscle wastage. It was found that high

doses of AZT inhibit replication of mitochondria.

Use information from the passage and your own knowledge to answer the questions.

(a) Suggest and explain why AZT does not destroy HIV in the body but stops or slows the development of AIDS (lines 3–4).

Suggest and explain two advantages of using HAART (lines 7–9).

Advantage 1 ________________________________________________________

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Advantage 2 ________________________________________________________

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Suggest why high doses of AZT lead to muscle wastage (lines 10–11).

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Answer 3

(a) 1. Person (infected with HIV) has HIV DNA (in their DNA);

2. New HIV (particles) still made;
3. (AZT) inhibits reverse transcriptase;
4. (AZT) stops these (new HIV particles) from forming new HIV DNA;

OR

Slows / stops replication of HIV;

5. Stops destruction of more / newly infected T cells;
6. So immune system continues to work (and AIDS does not develop);
7. Context is important
8. Allow slows / stops (re)production of HIV
9. Reject (AZT) prevents DNA replication

4 max

(b) 1. Slows / stops the development of AIDS;

2. Because HIV resistant to AZT is damaged / destroyed / prevented from replicating (by other drugs);

OR

3. AZT continues to work as a drug;
4. Because HAART prevents the spread of AZT-resistant HIV to rest of the human population;

OR

5. No new HIV particles made;
6. Because HAART might interfere with viral protein synthesis;

Mark in pairs.

Do not mix and match.

2. Neutral HIV killed
3. Accept other drugs prevent HIV resistant to AZT from infecting new / more cells
4. Accept blocks transcription / translation / synthesis of lipid envelope / aspect of viral structure

4 max

(c) 1. (Fewer mitochondria so) less (aerobic) respiration;

2. (Muscles receive) less ATP (so waste);

Question 4

NMO is a disease that leads to damage to nerve cells in the spinal cord.

A person with NMO produces anti-AQP4 antibody that attacks only these nerve cells.

Explain why the anti-AQP4 antibody only damages these cells.

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(4)

(b) Scientists measured the concentration of anti-AQP4 antibody in the blood of people with NMO.

The spinal cord is surrounded by small bones called vertebrae. For each person, the scientists also determined the number of vertebrae surrounding damaged nerve cells.

Their results are shown in the graph.

A scientist suggested that the concentration of anti-AQP4 antibody in a person’s blood could be used to predict the number of vertebrae surrounding damaged nerve cells they are likely to have.

Use the graph above to suggest reasons why this suggestion might not be valid.

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(3)

(c) A new treatment for NMO involves using a monoclonal antibody. The structure of the variable region of this monoclonal antibody is identical to the variable region of an anti-AQP4 antibody, but the rest of its structure is different.

Use this information and your knowledge of antigen-antibody complexes to suggest how this monoclonal antibody prevents anti-AQP4 damaging nerve cells.

Answer 4

(Anti-AQP4) antibody has a (specific) tertiary structure;

2. Has binding site / variable region that only binds to / complementary to one antigen;
3. Antigen to this antibody (only) found on these nerve cells;
4. So, antibody (only) binds to / forms antigen-antibody complex with these nerve cells (causing damage);

Reject “active site” (only penalise once if it occurs throughout)

3. / 4. Accept ‘receptor’ for antigen

4

(b) 1. Only 20 in the study;

OR

Only one study;

2. For some concentrations of antibody there is a range in the number of vertebrae surrounding damaged nerve cells;
3. No statistical test used;
4. Correlation is weak;
5. Accept small sample
6. Accept suitable use of data
7. Accept converse

3 max

(c) 1. The monoclonal antibody binds to nerve cell antigen so less / no anti-AQP4 can bind;

OR

The monoclonal antibody forms antigen-antibody complex with nerve cell antigen so less / no anti-AQP4 can bind;

2. When monoclonal antibody binds it doesn’t cause damage to nerve cell

Question 5

Herpes simplex virus (HSV) infects nerve cells in the face, including some near the lips. Like many other viruses, HSV can remain inactive inside the body for years. When HSV becomes active, it causes cold sores around the mouth.

Human cells infected with a virus may undergo programmed cell death. While HSV is inactive inside the body, only one of its genes is transcribed. This gene is the latency-associated transcript (LAT) gene that prevents programmed cell death of an infected nerve cell.

5

Scientists have found that transcription of the LAT gene produces a microRNA.
This microRNA binds to some of the nerve cell’s own mRNA molecules. These mRNA molecules are involved in programmed cell death of nerve cells. The scientists concluded that production of this microRNA allows HSV to remain in the body for years.

10

Use information from the passage and your own knowledge to answer the following questions.

(a) HSV infects nerve cells in the face (line 1). Explain why it infects only nerve cells.

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(3)

(b) HSV can remain inactive inside the body for years (lines 2–3). Explain why this virus can be described as inactive.

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(2)

(c) Suggest one advantage of programmed cell death (line 4).

The scientists concluded that production of this microRNA allows HSV to remain in the body for years (lines 10–12).

Explain how this microRNA allows HSV to remain in the body for years.

Answer 5

Outside of virus has antigens / proteins;

2. With complementary shape to receptor / protein in membrane of cells;
3. (Receptor / protein) found only on membrane of nerve cells.

Accept converse argument

3

(b) 1. No more (nerve) cells infected / no more cold sores form;

2. (Because) virus is not replicating.

2

(c) Prevents replication of virus.

1

(d) MicroRNA binds to cell’s mRNA (no mark)

1. (Binds) by specific base pairing;
2. (So) prevents mRNA being read by ribosomes;
3. (So) prevents translation / production of proteins;
4. (Proteins) that cause cell death.

Question 6

What is a monoclonal antibody?

Answer 6

reference to hybrid cell from tumour / cancer and
B-lymphocyte / hybridoma;
antibodies all the same / from one type of plasma cell;
specific to / complementary to / fits only one antigen;

Question 7

Explain why this test detects prostate cancer, but not any other disease.

Explain why there will not be a colour change if the blood sample does not contain PSA.

Answer 7

antibodies specific / only binds to PSA;
PSA only associated with prostate cancer / not with other
diseases;

antibody with enzyme only attaches if PSA present / washed
away if no PSA;
no colour change without enzyme;

Question 8

Suggest one reason why it was necessary to give two injections of the vaccine
(line 6).

Answer 8

because one dose does not give a high enough level of
antibody to be effective / because the antibody falls after a while;

Question 9

Although this vaccine is made from antigens from malarial parasites, it does not cause malaria. Explain why this vaccine does not cause malaria.

Answer 9

antigens are only single molecules / part of parasite;
do not actually cause disease;

Question 10

The blood from those taking part in the trial was also examined under the microscope at the beginning of the trial. Explain how this would enable those who had malaria to be identified.

Answer 10

malaria sufferers would have parasites in red blood cells;