Immune response Flashcards
Read the following passage.
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.
Presence of) antigen of the (pathogenic) bacteria;
Assume bacteria are pathogenic unless otherwise stated
- (Causes) more T cells produced / faster T cell production;
- Against (the pathogen and) normal bacteria;
- (Long lasting as) cells do not die / live for longer;
- (More) cytokines / chemicals causing swelling are produced
Suggest why 5-ASA is only effective in controlling the swelling of the lining of the intestines in some people with Crohn’s disease (lines 11–12).
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Some people might) produce (very) large amounts of cytokine / have large amounts of swelling;
- (That) 5-ASA drugs cannot control / reduce;
OR
- Some people may be allergic to / cannot tolerate 5-ASA
Suggest the meaning of ‘a genetic tendency to Crohn’s disease’ (line 10).
Some people) have a mutation / allele / gene;
- (That) increases the chances / risk / makes it more likely for / causes them to have an unusually large T cell response;
OR
(That) lowers / removes tolerance to (normal) intestinal bacteria;
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
Lack of adenine and guanine) will slow / stop DNA synthesis / replication (in T cells);
- 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.
- (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
- (So) less cytokine is produced (and therefore less swelling
Explain why it is important to wash the well at the start of Step 4 after doing monoclonal antibodies
Removes unbound 2nd antibodies;
Otherwise enzyme may be present / may get colour change
anyway / false positive;
The cancerous B-cells are found mainly in the lymphatic system of patients. Before treating any patient with Zevalin containing yttrium, doctors test the patient with a different form of Zevalin. This form has radioactive indium attached to the antibody instead of yttrium. The radioactivity from indium is strong enough for doctors to detect but not strong enough to kill a patient’s cells.
The diagram shows the lymphatic systems of two patients, P and Q, after being given Zevalin with indium. The crosses (+) show where indium was detected.
(b) The doctors decided they could treat Patient P with Zevalin containing yttrium but not Patient Q.
Suggest why Patient P could be treated with Zevalin containing yttrium and Patient Q could not.
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(Extra space) ________________________________________________________
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(3)
(c) Suggest one reason for the difference in distribution of the radioactivity detected in these patients.
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Patient P treated with Zevalin/yttrium (no mark);
Assume ‘Zevalin’ means ‘with yttrium’ unless they state
otherwise
Where indium/antibody (only) on lymphatic system/groin and armpits;
So only (cancerous) B-cells killed;
In patient P high concentration of radioactivity/antibodies high enough
to kill cancer cells;
Patient Q ‒ radioactivity in places where other body cells could be killed/
organs damaged/named example;
Could harm patient more than cancer;
Patient Q cancer has spread;
So too late to treat;
3 max
(c) Patient Q ‒ (cancerous) B-cells outside of lymphatic system/metastasis;
So antibody bound in other parts of the body (as well);
Patient Q ‒ has different receptors/distribution of receptors compared
to patient P;
Other body cells (than B-cells) have receptors for antibody;
The antibody in Zevalin comes from mice. Patients are tested for antibodies against Zevalin before treatment for their cancer.
Suggest why.
Might be allergic to mouse antibody/protein;
(Mouse) antibody acts as an antigen;
Causes an immune response/antibody production;
Antibody destroys Zevalin;
Releases radioactivity into body/prevents activity against the cancer;
