antigens and T cells

Question 1

Suggest which labelled component of the virus is most likely to act as an antigen. Give a reason for your answer.

Component ____________________________________________________

Reason

Answer 1

glycoprotein AND
different shape to body proteins / RNA and reverse transcriptase
inside virus / phospholipids same as body’s / on the surface
of the virus;

Question 2

Sizes of populations of normal intestinal bacteria are usually controlled by

T cells that are produced slowly and in small numbers by the immune system.

These T cells do not normally survive for very long. As a result, they do not

release large amounts of cytokines. Cytokines are chemicals that can cause

swelling of the lining of the intestines. 5

Crohn’s disease is a long-lasting disease that causes swelling of the lining of

the intestines. It is believed that Crohn’s disease can be caused by a loss of

tolerance to normal intestinal bacteria, as shown by an unusually large

response by T cells. This response can be triggered by pathogenic bacteria in

the intestines of people with a genetic tendency to Crohn’s disease. 10

Some people’s Crohn’s disease can be controlled by a drug called

5-aminosalicylic acid (5-ASA) that reduces swelling. Another drug called

6-mercaptopurine (6-MP) may also be used. 6-MP inhibits an enzyme required

to make adenine and guanine. This is effective because most cells can recycle

nucleotides, but T cells are not able to do so. 15

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

(a) The Crohn’s disease symptom of swelling of the lining of the intestines could be triggered by pathogenic bacteria in the intestines (lines 6–10).

Suggest how.

Answer 2

(Presence of) antigen of the (pathogenic) bacteria;

Assume bacteria are pathogenic unless otherwise stated

2. (Causes) more T cells produced / faster T cell production;
3. Against (the pathogen and) normal bacteria;
4. (Long lasting as) cells do not die / live for longer;
5. (More) cytokines / chemicals causing swelling are produced;

Question 3

Sizes of populations of normal intestinal bacteria are usually controlled by

T cells that are produced slowly and in small numbers by the immune system.

These T cells do not normally survive for very long. As a result, they do not

release large amounts of cytokines. Cytokines are chemicals that can cause

swelling of the lining of the intestines. 5

Crohn’s disease is a long-lasting disease that causes swelling of the lining of

the intestines. It is believed that Crohn’s disease can be caused by a loss of

tolerance to normal intestinal bacteria, as shown by an unusually large

response by T cells. This response can be triggered by pathogenic bacteria in

the intestines of people with a genetic tendency to Crohn’s disease. 10

Some people’s Crohn’s disease can be controlled by a drug called

5-aminosalicylic acid (5-ASA) that reduces swelling. Another drug called

6-mercaptopurine (6-MP) may also be used. 6-MP inhibits an enzyme required

to make adenine and guanine. This is effective because most cells can recycle

nucleotides, but T cells are not able to do so. 15

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

Suggest why 5-ASA is only effective in controlling the swelling of the lining of the intestines in some people with Crohn’s disease

Suggest why 6-MP can be used to control the symptoms of Crohn’s disease (lines 13–15).

Do not include details of enzyme inhibition or protein synthesis in your answer.

Answer 3

(Some people might) produce (very) large amounts of cytokine / have large amounts of swelling;

2. (That) 5-ASA drugs cannot control / reduce;

OR

3. Some people may be allergic to / cannot tolerate 5-ASA;
4. So cannot take it;

QUESTION 6 (Lack of adenine and guanine) will slow / stop DNA synthesis / replication (in T cells);

2. Affects T cells more as they cannot recycle nucleotides;

Needs idea of more / greater effect.

Accept converse idea that ‘other’ cells not as affected as they can recycle nucleotides.

3. (6-MP therefore) suppresses / slows the (unusually large) T cell / immune response

OR

(6-MP causes) fewer / no T cells (to be) produced;

Accept (6-MP) acts as an immunosuppressant drug

4. (So) less cytokine is produced (and therefore less swelling);