Case 17 questions 1-10

Question 1

Which is NOT a component of the humoral immune response?

1. C1
2. Membrane attach complex (MAC)
3. IgG
4. CD8 molecule
5. IgM

The correct answer is option d, CD8 molecule

The cluster of differentiation 8 (CD8) molecule is a co-receptor of the T cell receptor found on mainly cytotoxic T cells and is considered to be part of the cell mediated immune response

1 and 2 are part of the complement system which is part of the innate humoral response

3 and 5 are types of antibodies which are part of the adaptive humoral response

Question 2

Which statement best describes the function of major histocompatibility complex class 1 (MHC1) molecules?

1. MHC1 molecules are found on all nucleated cells and present processed peptides to regulatory T cells
2. MHC1 molecules are found on all nucleated cells and present full protein antigens to natural killer cells and cytotoxic T lymphocytes
3. MHC1 molecules are found on all nucleated cells and present processed peptides to natural killer cells and cytotoxic T lymphocytes
4. MHC1 molecules are found on antigen presenting cells and present processed peptides to CD4+ T cells
5. MHC1 molecules are found on all antigen presenting cells and present processed glycoproteins to cytotoxic T lymphocytes

The correct answer is option c.

3 is the correct answer (MHC1 molecules are found on all nucleated cells and present processed peptides to natural killer cells and cytotoxic T lymphocytes )

1 is incorrect as MHC1 presents peptides to CD8 T cells (i.e. cytotoxic) rather than CD4 T cells (i.e. regulatory)

2 and 5 is incorrect as MHC molecules present processed peptides only and not proteins or glycoproteins

4 describes the function of MHC2 molecules

Question 3

Which best describes the function of the immunoglobulin, IgA?

1. Provides mucosal immunity against parasites
2. Is secreted into breast mild and can provide immunity to breast feeding babies
3. Activates the complement system
4. Provides immunity within the blood
5. Provides immunity to the gastrointestinal and respiratory system

The correct answer is option e, IgA provides immunity to the gastrointestinal and respiratory system<

IgA mainly provides humoral immunity to mucosal membranes (i.e. eyes, respiratory mucosa, GI mucosa) so 5 is correct

1 describes the function of IgE

2 describes the main function of IgG

3 describes the main function of IgG and IgM

4 describes the main function of IgG and IgM

Question 4

A junior doctor is working on an infectious diseases ward. They take blood from a patient with a new diagnosis of HIV and obtain a needle stick injury. At the scene they wash and clean the wound and inform occupational health.

From the following, what is the most appropriate action?

1. Commence treatment with two nucleoside reverse transcriptase inhibitors and an integrase inhibitor for 28 days.
2. Test for HIV infection now and in 28 days, initiate HIV treatment if positive.
3. Commence treatment with two nucleoside reverse transcriptase inhibitors for 28 days.
4. No further intervention is needed
5. Commence treatment with two nucleoside reverse transcriptase inhibitors and an CCR5 co-receptor antagonist for 28 days.

The correct answer is option a, Commence treatment with two nucleoside reverse transcriptase inhibitors and an integrase inhibitor for 28 days.

The NICE guideline for post exposure prophylaxis indicates the use of 2NRTIs and 1 INI for 28 days post any exposure to HIV therefore 1 is correct (typically emtricitabine and tenofovir disoproxil and raltegravir but specific drugs used is not core knowledge you need at this stage)

3 shows the treatment indicated for pre-exposure prohyalaxis

4 and 2 are incorrect as they do not reduce the risk of primary HIV infection.

Question 5

A patient presents to the GP surgery with a loss of taste and white plaques over the tongue which can be scrapped off.

They are prescribed fluconazole for oral thrush. What is the mechanism of action of fluconazole?

1. Inhibition of glucan synthesis
2. Disruption of ergosterol function
3. Inhibition of dihydrofolate reductase and inhibition of purine synthesis
4. Inhibition of ergosterol synthesis through antagonism of 14 alpha demethylase
5. Inhibition of squalene epoxidase which prevents ergosterol production

The correct answer is option d, Inhibition of ergosterol synthesis through antagonism of 14 alpha demethylase

4- This is the mechanism of azoles (e.g. fluconazole) and is correct

1- This is the simplified mechanism of echocandins

2- This is the simplified mechanism of polyenes

3- This is the simplified mechanism of trimethoprim (which can be used to treat some fungal infections e.g. PCP)

5- This is the mechanism of allylamines

Question 6

Which antiretroviral drug causes immunosuppression as part of its mechanism of action?

1. NRTIs (nucleoside reverse transcriptase inhibitors)
2. CCR5 coreceptor inhibitors
3. Integrase inhibitors
4. Protease inhibitors
5. Fusion inhibitors

The correct answer is option b, CCR5 coreceptor inhibitors

CCR5 inhibitors function through preventing the function of the CCR5 coreceptor. This means the less effective CXCR4 coreceptor becomes dominant in CD4 cells and therefore the use of CCR5 inhibitors leads to a mild immunosuppression.

Question 7

What describes the process of forming antibodies with a higher affinity for a given antigen?

1. Somatic hypermutation
2. Class switching
3. V(D)J recombination
4. Bone marrow positive selection
5. Negative selection

The correct answer is option a, Somatic hypermutation

Somatic hypermutation leads to the rapid clonal division of B cells (due to cytokine release from helper T cells). This leads to further additional VDJ recombination and positive selection to form higher affinity variable regions of the antibody.

Question 8

If a cell presents an abnormal peptide on an MHC class 1 molecule to a T cell, which process is most likely to happen?

1. Apoptosis of the peptide presenting cell
2. Opsonisation of the presenting cell
3. Cytokine release leading to clonal B cell replication
4. Class switching
5. TCR-beta selection

The correct answer is option a, Apoptosis of the peptide presenting cell

MHC class 1 molecules are found on all nucleated cells and present peptides to cytotoxic T cells and natural killer cells. If this peptide is recognised as abnormal (i.e. due to proliferation of viral particles, tumours or intracellular bacteria such as pseudomonas aeruginosa), this causes the activation of cytotoxic T cells to trigger apoptosis and destroy the infected cell (as well as lead to clonal replication to find any other affected cells).

Question 9

A patient presents with a confirmed latent pulmonary TB infection. What treatment should be considered in this patient?

1. 2 months isoniazid (with pyridoxine) and rifampicin, pyrazinamide and ethambutol then then 4 months isoniazid (with pyridoxine) and rifampacin
2. 6 months isoniazid (with pyridoxine) and rifampacin
3. 3 months of isoniazid (with pyridoxine) and rifampacin
4. 3 months of isoniazid (with pyridoxine) and ethambutol
5. 3 months of rifampacin and ethambutol

The correct answer is option c, 3 months of isoniazid (with pyridoxine) and rifampacin

NICE suggests the management for latent TB should be:

• 3 months of isoniazid (with pyridoxine) and rifampicin

OR

• 6 months isoniazid (with pyridoxine)

This is management for active pulmonary TB

Incorrect duration of treatment

Ethambutol is not typically used for latent TB

This combination alone is not typically used for latent TB

Question 10

A 6 month old baby presents to the GP with their mother complaining of a rash. On further questioning, it is found the patient had a fever and was irritable with a cough a few days ago but this has now resolved and a rash appeared this morning.

On examination, the patient is well and is babbling and sit unassisted. A rash on the face, neck and trunk with 3mm blanching macules visible.

What is the most likely causative organism for this presentation?

1. Kaposi’s Sarcoma Associated Virus (HHV8)
2. Human Immunodeficiency Virus
3. Neisseria Meningitides
4. B19 Parvovirus
5. Roseola (HHV 6)

The correct answer is option e, Roseola (HHV 6)

This is a classical presentation of roseola (caused by HHV 6/7) where there is an illness (i.e. fever, cough, irritability ) followed by a blanching, macular rash over the face and trunk. Roseola is common cause of rash in infants but is usually self-limiting and benign.

1-Typically asymptomatic and unlikely to cause skin lesions at this age and absence of immunodeficiency

2-Although HIV can cause a rash as part of a primary infection alongside fever, this is rarely seen in infants and it is unlikely this is an initial presentation of HIV infection. The usually rash presents as a maculo-papular rash in HIV primary infection.

3-Sepsis and meningitis should be considered IN ALL who present with fever and rash and Neisseria Meningitides is a leading cause of paediatric sepcis and meningitis. However, this is unlikely as patients presenting with a rash would likely be far more unwell and likely require rapid hospitalisation. Rash in this case would also be non-blanching.

4- B-19 parvovirus (fiths disease/ slapped cheek syndrome) is a common cause of illness in infants and does cause a rash. However, this rash is usually occurs at the same time as fever and is normally confined to the cheeks.