How the immune system controls infections

Epidemiology Assignment Questions –

1. Make a table with two columns to compare and contrast the ways in which T cells and B cells recognise antigen, the antigens that are recognised by the two types of cell, and the ways in which the cells become activated. Aim to make at least five distinct comparisons.

2. BCG (Bacillus Calmette-Guerin) is a live attenuated strain of tuberculosis that is used in many countries to immunise against infection with M. tuberculosis. In very rare instances, the vaccine produces a disseminated infection that affects many organs; this generally occurs because the recipient of the vaccine is immunodeficient or immunosuppressed.

In a family from a MiIDle Eastern country, it is found that a girl and a boy, from a family of five children, have developed a disseminated infection with BCG following vaccination; it is suspected that these children are immunodeficient.

Comment on what kind of immunodeficiency these children might have, and how it prevents the immune system from controlling infection with BCG. Your explanation should be based on understanding how the immune system controls infections caused by mycobacteria.

3. (a) Briefly explain why IgG and IgA antibodies are generally of higher affinity than IgM antibodies.

(b) Despite this, IgM antibodies can be very effective in activating complement and promoting phagocytosis of bacteria. Provide an explanation for this observation.

4. A patient in hospital develops a fever and an acute infection of the upper respiratory tract. It is suspected that they may be suffering from infection with influenza A (H IN I), so a nasopharyngeal swab and a serum sample are taken. The hospital laboratory can do ELISA, RT-PCR, viral culture, haemagglutination and haemagglutination-inhibition (HAI) tests, and has suitable reagents available to carry out all/any of these assays to identify and type the influenza virus.

Briefly discuss which of these tests are most suitable for detecting a current infection with influenza A, and which tests could distinguish the strain of virus. Be sure to state which clinical sample would be used in which type of test.

5. Read the research paper by Santin et al., ‘In vitro activity of the essential oil of Cymbopogon citrants and its major component (citral) on Leishmania amazonensis’ (published in 2009 in the journal Parasitology Research, volume 105 (November), pages 1489-96).

Write about 800 words in total

(a) (i) In one sentence, state what the authors set out to determine.

(ii) Why did they consider that this research was necessary?

(iii) Summarise each of their three main findings and, for each one, briefly explain why the authors consider these findings to be important.

(b) (i) Describe the data presented in Fig. 1 of the paper and explain its relevance for developing drugs against Leishmania.

(ii) How do the authors account for the differences in the effectiveness of the essential oil (‘FA’) versus citral on parasite viability?

(c) The authors suggest several cellular targets and mechanisms by which the essential oil and citral damage and kill Leishmania parasites. List these cellular targets and summarise the evidence the authors present to support each mechanism of action.

(d) Give a brief evolutionary explanation for why plants such as Cymbopogon citratus contain compounds with anti-protozoan activity.

(e) (i) Draw the life cycle of Leishmania amazonensis, with numbers for each step, and then use short sentences to describe the most important stages.

A simple block diagram, or something that is hand-drawn and then scanned, is fine. (Hint: one way to adapt a figure is to combine several pieces of information into a single new depiction). If you adapt an existing figure, then you must cite where the original image(s) came from, and include a screenshot of the original(s) at the end of your answer.

(ii) Describe the various ways in which Leishmania amazonensis is adapted to life inside a human host.

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