11. Immunity
A section of Biology, 9700
Listing 10 of 303 questions
is a photomicrograph of a transverse section through a region of the wall of the bronchus in the gas exchange system. J K Identify the tissues J and K shown in , and suggest how the wall of a bronchiole differs from the wall of the bronchus for these two tissues. J K difference Tuberculosis (TB) is an infectious disease that affects the human gas exchange system. The pathogen that causes TB secretes a protein that can be detected in saliva. Early diagnosis of TB is important in reducing the transmission of the pathogen. Scientists have developed a test strip for TB that uses monoclonal antibodies. Monoclonal antibodies are specific in their action. This test strip contains: • mobile monoclonal antibodies that bind to one part of the protein secreted by the pathogen • immobilised monoclonal antibodies. shows a simplified diagram of the test strip. 1 a sample pad where saliva is added to the test strip 2 area containing mobile monoclonal antibodies attached to tiny gold particles 3 test area containing immobilised monoclonal antibodies that bind to protein secreted by the pathogen that causes TB 4 control area 5 area where test strip can be held direction of flow of saliva through the test strip A sample of saliva is collected and put onto the sample pad in the test strip. The saliva moves up the test strip through area 2. The mobile monoclonal antibodies are attached to tiny gold particles. If these antibodies collect in test area 3, a gold line becomes visible on the test strip. A gold line that becomes visible in area 4 confirms that the test strip is working and that the results are valid. State the name of the pathogen that causes TB. Name the part of the monoclonal antibody that binds to the protein from the pathogen. Saliva is added to a test strip to test for the presence of the protein secreted by the TB pathogen. is a diagram showing some of the molecules in area 3 of the test strip when a positive result for TB is obtained. monoclonal antibody attached to a tiny gold particle protein secreted by the TB pathogen attached to two different monoclonal antibodies immobilised monoclonal antibody in area 3 attached to test line Use the information in to suggest and explain why this test is specific for TB. Area 4 contains different immobilised antibodies to those in area 3. The mobile monoclonal antibodies bound to tiny gold particles will bind to these immobilised monoclonal antibodies in area 4. If the test has functioned correctly, a gold line will be visible in area 4. Suggest how the structure of immobilised monoclonal antibodies in area 3 differs from the structure of the immobilised monoclonal antibodies in area 4. Vaccination is another way of reducing the transmission of infectious diseases such as TB. The BCG vaccine is used to help control the spread of TB. This vaccine contains a weakened strain of the pathogen that causes TB. The BCG vaccine stimulates the development of antigen-specific memory T-lymphocytes. Explain how memory T-lymphocytes provide protection from TB in a person who has been given a BCG vaccination. The bladder is the organ in the body used to store urine. When cells divide uncontrollably in the bladder, a tumour develops. This can lead to bladder cancer. The BCG vaccine has been used to treat bladder cancer. The BCG vaccine is introduced into the bladder. The tumour cells take up the weakened pathogens in the vaccine and act as antigen-presenting cells. Name the process used by the tumour cells to take up the weakened pathogens. Suggest how antigen presentation by tumour cells stimulates an immune response that leads to the destruction of the tumour cells.
9700_w24_qp_21
THEORY
2024
Paper 2, Variant 1
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The glycoproteins CD28 and CD40 are found on the surface of T-lymphocytes (T-cells). They are binding sites for cell-signalling molecules and are essential for triggering the cloning of T-cells in an immune response. A monoclonal antibody (mAb), which could block the CD40 signalling pathway, was produced from hamsters using the hybridoma method. Outline the procedure, starting with a hamster, for producing mAbs suitable for use in another mammal, such as a mouse. The ability of the mAb produced in to prevent rejection of transplanted hearts in mice was compared with that of a protein, P, which blocks the CD28 signalling pathway. Four groups of mice were treated as follows: • group A – no treatment • group B – treated with protein P only • group C – treated with mAb only • group D – treated with both mAb and protein P. shows the percentage survival of the transplanted hearts in the four groups of mice over a period of 80 days. time / days percentage survival of transplanted hearts D B C A With reference to describe the effectiveness of the four different treatments suggest an explanation for the differences in survival of the transplanted hearts in groups B and D. Examination of the transplanted hearts showed that the hearts in group A had significant damage to their coronary arteries, whereas in group D these blood vessels appeared normal. Explain the importance of the coronary arteries of the heart. State two uses of mAbs in humans, other than preventing rejection of transplanted tissue. 1. 2.
9700_s10_qp_41
THEORY
2010
Paper 4, Variant 1
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The bacterium, Treponema pallidum, causes the sexually-transmitted infectious disease, syphilis. If left untreated, the disease can be fatal, but early diagnosis can lead to successful treatment. One of the difficulties of diagnosing this disease in its early stages is the problem of recognising T. pallidum among the other species belonging to the genus Treponema that live in humans. These other treponemes are harmless. A mouse was injected with some cells of T. pallidum. Outline the steps that would then be necessary to produce a clone of hybridoma cells secreting an antibody against this bacterium. A monoclonal antibody, H9-1, has been developed that is specific to a surface protein on T. pallidum, but which is not present on four other species of treponemes found in humans. Each molecule of H9-1 carries a fluorescent yellow marker. One of the first visible signs of syphilis is a painless sore. Suggest how H9-1 is used in the diagnosis of syphilis, using a sample taken from a sore and placed on a microscope slide. Before the development of H9-1, two tests for the presence of T. pallidum were commonly used: • dark-field microscopy (in which treponemes could be seen moving against a dark background) • testing for the presence of anti-treponemal antibodies in the blood plasma. Suggest why, in the early stages of an infection, the presence of T. pallidum might not be detected by either of these tests. The accuracy of the diagnosis of infection by T. pallidum using H9-1 was compared with that using dark-field microscopy and with blood testing. The results are shown in Table 2.1. A positive test result indicated that T. pallidum is present and a negative test result that it is absent. Table 2.1 test test results of 30 people later confirmed to have the infection test results of 31 people later confirmed not to have the infection H9-1 all positive all negative dark-field microscopy one negative two positive blood test three negative two positive With reference to Table 2.1: compare the accuracy of diagnosis of the presence of T. pallidum using the different tests suggest why blood testing for anti-treponemal antibodies gave two positive results in patients later found not to have the infection. Describe briefly one use of a monoclonal antibody in the treatment of disease.
9700_s12_qp_42
THEORY
2012
Paper 4, Variant 2
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When preparing infertile women for in-vitro fertilisation (IVF), it is necessary to stimulate the growth and maturation of several ovarian follicles. This is done by giving daily injections of the glycoprotein hormone, follicle stimulating hormone (FSH). Each molecule of FSH has quaternary structure and consists of two different polypeptide chains, α and β. Explain what is meant by quaternary structure. Human FSH can be extracted from women’s urine (u-hFSH). A procedure involving the use of monoclonal antibodies is used to produce purified u-hFSH. Suggest how monoclonal antibodies can be used to obtain purified u-hFSH from urine. Recombinant human FSH (r-hFSH) can be produced by adding the genes coding for the α and β polypeptide chains of FSH to mammalian ovary cells. Suggest why mammalian cells are needed to produce r-hFSH, rather than bacterial cells. In IVF treatment, a second hormone, human chorionic gonadotrophin (hCG) is injected when mature ovarian follicles (Graafian follicles) have developed. Draw a labelled diagram to show the structure of a mature ovarian follicle. The effectiveness of r-hFSH was compared with that of u-hFSH. Women starting IVF treatment were randomly divided into two groups and given either r-hFSH or u-hFSH. The differences between the two groups of women after FSH treatment are shown in Table 2.1. Table 2.1 women receiving r-hFSH women receiving u-hFSH number of women mean number of mature follicles per woman concentration of oestrogen in the blood / nmol dm−3 6.55 3.95 With reference to Table 2.1, compare the effects of treatment with r-hFSH and u-hFSH and suggest explanations for the differences. The probability of the results for the mean number of mature follicles per woman occurring by chance is  0.002. Explain what is meant by this probability.
9700_s15_qp_41
THEORY
2015
Paper 4, Variant 1
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Questions Discovered
303