Immunology

Question 1

What are the key components involved in the body’s defense against infection?

Answer 1

Defense against infection involves chemical and physical barriers, followed by the innate and acquired immune systems.

Question 2

Innate immune response is _____ and does not have memory of ______

Answer 2

The innate response is rapid and does not have memory of previous infections.

Question 3

Which cell types are considered part of the innate immune system?

Answer 3

Innate immune cells include neutrophils, macrophages, dendritic cells (DC), natural killer (NK) cells, and others.

Question 4

What is Phagocytosis

Answer 4

Phagocytosis is an important innate cell function

Question 5

What is one of the key roles of the innate immune system in response to infection?

Answer 5

Innate immune system initiates inflammation

Question 6

What are the characteristic signs of inflammation, and what does the process involve?

Answer 6

Inflammation – redness, heat, swelling, pain - involves influx and activation of immune cells

Question 7

What triggers the initiation of inflammation in the body?

Answer 7

Inflammation is initiated by tissue damage and/or specific pathogen molecules – PAMPs

Question 8

How do innate immune cells respond to the presence of pathogens?

Answer 8

Innate immune cells have receptors for Pathogen-associated molecular pattern molecules (PAMPs), leading to release of chemokines, cytokines and inflammation.

Question 9

What role do dendritic cells (DC) play in the immune response?

Answer 9

DC are innate immune cells important for activating T cells in the acquired immune response

Question 10

Where do immune cells develop in the body?

Answer 10

Immune cells develop from stem cells in the bone marrow.

Question 11

Where do T cells mature

Answer 11

T cells mature in the thymus

Question 12

True or False: Due to its lack of specificity, the innate immune system cannot clear any infections, but it is important for keeping them under control until the acquired immune response has developed.

Answer 12

his statement is incorrect because the innate immune system does have the ability to clear many infections, especially those that are less complex. While the acquired (adaptive) immune response provides a highly specific and targeted response, the innate immune system plays a crucial role in the immediate defense against a wide range of pathogens, including bacteria, viruses, and fungi. It can clear many infections on its own and also contributes to the overall control of infections until the acquired immune response fully develops.

Question 13

Allergies are predominantly a result of

Answer 13

Binding of allergen by IgE antibodies leading to histamine release from mast cells.

Question 14

Where does the activation of naive T cells by recognition of foreign antigens happen

Answer 14

Spleen and lymph nodes

Question 15

Antibodies are

Answer 15

Proteins released by B cells that are capable of binding a huge variety of different molecular structures.

Question 16

What are Cytotoxic T lymphocytes important for

Answer 16

Are important for killing tumor cells and virus-infected cells.

Cytotoxic T lymphocytes (CTLs) play a crucial role in the immune response by recognizing and eliminating virus-infected cells and cancer cells. They are specific for foreign antigens and are involved in cell-mediated immunity, where they directly target and kill abnormal or infected cells.

Question 17

What are autoimmune disease triggered by:

Answer 17

Often triggered by environmental factors such as infections.

Question 18

What values of Reff will lead to an infection eventually dying out, and what values of Reff will lead to exponential growth?

Answer 18

Values of Reff that will lead to an infection eventually dying out are less than 1. When Reff is less than 1, each infected person, on average, infects fewer than one other person. As a result, the number of infected individuals decreases over time, and the infection eventually dies out.

Values of Reff that will lead to exponential growth are greater than 1. When Reff is greater than 1, each infected person, on average, infects more than one other person. This leads to a situation where the number of infected individuals increases over time, causing the infection to spread exponentially within the population.

Question 19

A new virus that replicates in the liver was found in intravenous drug users. (i) Describe one acquired immune response that should act directly against virally-infected cells, and discuss
the mechanism involved.

Answer 19

Cytotoxic T lymphocytes (CTL) will directly kill the virally-infected liver cells. The viral antigens are cleaved
into peptides and displayed on MHC molecules on the surface of the infected cell. The T cell receptor of the
CTL recognises the peptide displayed on the infected cell surface and releases granules that induce cell death
in the target cell.

Question 20

Describe one acquired immune response that attacks the extracellular virus, and a mechanism through
which this might reduce viral load.

Answer 20

Antibody is produced by B cells and will bind to molecules on the surface of the viral particles. This may have a neutralising effect, whereby it blocks binding to cell surface receptors or blocks the function of a viral surface protein, stopping entry into the cell. This then stops infection of new cells and production of
more virus.

Question 21

What is the major class of pathogen associated molecular patterns (PAMPs) in viruses that lead to activation of the innate immune system?

Answer 21

Viral nucleic acids (RNA and DNA) are the principal PAMPs activating the innate immune response.
0.5 mark for saying only RNA OR DNA

Question 22

Outline of an Immune Response to Infection

Answer 22

1.Detection of pathogen molecules or cellular damage by cells at site
2. Release of chemokines and cytokines
3. Inflammation – redness, swelling, pain, heat
4. Influx of neutrophils – phagocytosis
5. Influx of macrophages - phagocytosis
6. Phagocytosis of organism by dendritic cell (DC) and activation of DC by foreign
molecules
7. Migration of DC bearing foreign antigen in the draining lymph to the lymph node if
infection is in tissues (or MALT if in mucosa or spleen if in blood)
8. Presentation of foreign antigen on major histocompatibility molecules (MHC) of DC
to T cells in lymph node/MALT/spleen
9. Activation of naïve T cells which specifically recognise foreign antigen
10. Proliferation of specific T cell into a large clone of cells
11. T cells become cytotoxic T cells (CTL) or T helper cells
12. In lymph node/MALT/spleen, T helper cells promote differentiation and
proliferation of B cells which secrete antibodies binding to pathogen
13. Activated T cells leave lymph node and travel to site of infection
14. T helper cells help macrophages kill ingested organisms
15. CTL directly kill virally infected cells
16. After infection is cleared, B and T cell clones decline, but memory cells remain

Question 23

Explain Primary and secondary lymphoid tissues

Answer 23

Primary lymphoid organs: These organs include the bone marrow and the thymus. They create special immune system cells called lymphocytes. Secondary lymphoid organs: These organs include the lymph nodes, the spleen, the tonsils and certain tissue in various mucous membrane layers in the body (for instance in the bowel)

Question 24

Examples of Ways in Which Antibodies Act:

Answer 24

1. Neutralisation - antibody binding to virus can block entry into cells. Antibody can
   also neutralise bacterial toxins (e.g. tetanus toxin) and prevent effects on cells
2. Opsonisation (coating of organisms) to promote phagocytosis via receptors for
   antibodies on phagocytes.
3. Activation of the complement system (see previous lecture) – leading to bacterial
   lysis and inflammation
4. IgE binds to mast cells. When it recognises antigen (frequently allergens) the mast cells release histamine (inflammatory small molecule).

Question 25

For an infectious organism, the basic reproduction number, R0 ______

Answer 25

is the average number of people in a susceptible population that will be infected by one person, and it depends on population density.

Question 26

Do T cell receptor have a secreted form that enhances phagocytosis of its target antigens.

Answer 26

No, T cell receptors (TCRs) are typically cell surface receptors found on the surface of T cells, and they do not have a secreted form that directly enhances phagocytosis.

It’s the cytokines and signaling molecules released by T helper cells, such as Th1 cells, that play a role in enhancing phagocytosis by recruiting and activating phagocytic cells like macrophages and neutrophils. TCRs are responsible for recognizing specific antigens presented on the surface of antigen-presenting cells but do not have a secreted form to enhance phagocytosis directly.

Question 27

What are some autoimmune diseases

Answer 27

Type 1 diabtes

Multiple sclerosis

Narcolepsy

rheumatoid arthritis

Question 28

Innate Immune defences are

Answer 28

mediated by soluble factors like complement proteins and antibodies as well as a range of phagocytic cells.

Question 29

Explain the role of adjuvant in vaccination, by discussing the two signals that are required for T cell activation.

Answer 29

Adjuvants are a substance that enhances the body’s immune response to an antigen, through their involvement in providing the two essential signals required for T cell activation:
1. T cell receptor (TCR) recognition of antigens presented on MHC molecules.
2. Co-stimulation, typically provided by interactions between APCs and T cells.

Adjuvants are added to vaccines to mimic the role of Pathogen-Associated Molecular Patterns (PAMPs), which are foreign molecules often associated with pathogens.

By mimicking PAMPs, adjuvants provide the necessary “Signal 2” for T cell activation, thus acting as co-stimulators.

Adjuvants enhance the activation and maturation of APCs, particularly dendritic cells (DCs), by simulating an infection-like environment. This activation is a key step in initiating a robust immune response.

The adjuvant’s role in providing Signal 2 helps ensure that T cell activation occurs in response to the vaccine’s antigens and results in a powerful and sustained immune reaction.

Question 30

‘Subunit’ vaccines that contain purified protein antigens are reliant on adjuvants. Discuss TWO (2) OTHER types of vaccines and how they deliver antigens to the immune system. Are all types
of vaccines equally reliant on added adjuvants and, if not, why not?

Answer 30

Live attenuated organism vaccine - mimic a natural infection, provides weakened or attenuated pathogens of the virus to host, stimulating immune response leading to development of immune memory. Pathogens replicate inside of host, providing a continuous source of antigens. Not reliant on adjuvants.

mRNA vaccines deliver genetic instructions encoding a part of the pathogen, the host cell can then produce the pathogen antigen themselves. The immune system recognizes this antigen as foreign and forms an immune response, indirectly serving as an adjuvant. Not reliant on adjuvants.

Different vaccine types deliver antigens to the immune system through several mechanisms, so not all are reliant on adjuvants.

Question 31

The following equation relates the critical immunisation threshold (qc) to the basic reproduction number (R0), qc = 1 - 1/R0.

Using this equation, what percentage of people need to be vaccinated to generate herd immunity, if each person on average passes the infection to 10 other people?

Answer 31

qc = 1 - 1/R0

qc = 1 - 1/10

qc = 1 - 0.1

qc = 0.9

Percentage needed to be vaccinated = qc * 100

Percentage needed to be vaccinated = 0.9 * 100

Percentage needed to be vaccinated = 90%

So, if each person, on average, passes the infection to 10 other people (R0 = 10), approximately 90% of the population needs to be vaccinated to achieve herd immunity.

Question 32

The activation of naive T cells by recognition of foreign antigens happens in which sites?

Answer 32

spleen, lymph nodes

Question 33

Antibodies are

Answer 33

Proteins released by B cells that are capable of binding a huge variety of different molecular structures.

Question 34

Cytotoxic T lymphocytes are _____

Answer 34

Are important for killing tumor cells and virus-infected cells.

They recognize antigens presented on the surfaces of these abnormal cells and initiate their elimination, contributing to the immune response against infections and cancer.

Question 35

Are protein antigens needed for mRNA vaccines

Answer 35

The mRNA’s purpose is to instruct the host cells to produce the viral spike protein. The immune system recognizes this spike protein as foreign, and an immune response is initiated. It’s the spike protein itself that serves as the antigen for T and B cell recognition. The mRNA in these vaccines acts as an instruction manual for antigen production and is not recognized as foreign by the immune system. The mRNA vaccines do require a protein antigen for immune recognition.

Question 36

Autoimmune diseases are more common in men or women

Answer 36

Autoimmune diseases are generally more common in women than in men.

Question 37

What are autoimmune diseases triggered by

Answer 37

They are often triggered or influenced by various environmental factors, including infections, that can lead to the onset or exacerbation of these conditions. The other statements are not accurate descriptions of autoimmune diseases:

Question 38

What values of Reff will lead to an infection eventually dying out, and what values of Reff will lead to exponential growth?

Answer 38

If Reff is less than 1 (Reff < 1) indicates a decline in the number of cases over time, and the infection will eventually die out.

If Reff is greater than 1 (Reff > 1) indicates that the disease is spreading and lead to expotential growth

Question 39

Over the course of the COVID-19 pandemic, what factors do you think have changed the Reff, and
how have they acted?

Answer 39

Interventions and Public Health Measures:

Implementation of non-pharmaceutical interventions (NPIs) such as lockdowns, social distancing, mask mandates, and travel restrictions has effectively reduced Reff by limiting person-to-person transmission.
Vaccination Campaigns:

The development and deployment of COVID-19 vaccines have had a significant impact on reducing Reff. Vaccination reduces the number of susceptible individuals, making it more challenging for the virus to spread.
Emergence of Variants:

The appearance of new variants of the virus, some of which may be more transmissible or partially resistant to immunity, has the potential to increase Reff by facilitating the virus’s ability to infect and transmit.
Behavioral Changes:

People’s behavior and compliance with public health guidelines can influence Reff. For example, people gathering in crowded settings without precautions can lead to an increase in Reff, while adherence to guidelines can reduce it.
Herd Immunity Threshold:

As the population develops immunity through vaccination and natural infection, the herd immunity threshold is approached, leading to a decrease in Reff as fewer individuals are susceptible to the virus.
Seasonal Factors:

Some respiratory viruses, including the SARS-CoV-2 virus responsible for COVID-19, may exhibit seasonal variation. Changes in weather and indoor activities can influence Reff by affecting the virus’s ability to spread.
Testing, Contact Tracing, and Isolation:

Effective testing, contact tracing, and isolation strategies can help reduce Reff by identifying and isolating infected individuals, thereby breaking transmission chains.
Global Travel and Mobility:

International and domestic travel can facilitate the spread of the virus to new regions, potentially increasing Reff. Travel restrictions and quarantine measures can help mitigate this impact.
Healthcare Capacity:

The capacity of the healthcare system to manage cases and provide care can influence Reff. Overwhelmed healthcare systems can lead to increased transmission, while well-functioning healthcare systems can help reduce Reff by effectively managing cases.

Question 40

The activation of naive T cells occurs in

Answer 40

the spleen and lymph nodes

Question 41

The role of adjuvants in vaccines is

Answer 41

to provide an innate immune stimulus

Question 42

What happens when the innate immunity fails to clear an infection

Answer 42

The adaptive immune system takes over if the innate immune system is not able to destroy the germs. It specifically targets the type of germ that is causing the infection.

Question 43

Comparison between B cell receptors (BCR) and T cell receptors (TCR)

Answer 43

T-cell receptors act as both receptors and soluble effector molecules, whereas B-cell receptors only act as receptors. Both T-cell and B-cell receptors are diverse, detecting a wide range of antigens. T-cell receptors are transmembrane proteins, whereas B-cell receptors are intracellular proteins.

• The B cell antigen receptor (BCR) is a membrane bound antibody (Ig) molecule.
• T cells recognise antigen through the T cell receptor (TCR) which is evolutionarily related to the BCR,
  but has no secreted form. It has two chains (a and b), with variable and constant regions like BCR.
  The two chains together form one variable antigen-binding site.
• Each B cell makes one specific BCR/antibody and each T cell makes one specific TCR.
• Antibodies/BCR and TCR recognise a small region of a whole protein antigen
• BCR/antibody can recognise an intact protein antigen, whereas the TCR requires the antigen to be processed by proteases into short peptides (8-13 amino acids) that are bound on the surface of an antigen presenting cell (APC) on MHC molecules.

Question 44

Allergies are predominantly a result of

Answer 44

binding of allergen by IgE antibodies leading to histamine release from mast cells

Question 45

What are neutrophils

Answer 45

They are cells of the innate immune systems and are a phagocyte.

• 60-70% of all white blood cells in humans
• Multi-lobed nucleus and cytoplasmic “granules”. Granules are membrane-bound vesicles containing
  antimicrobial peptides, lysozyme enzyme that attacks bacterial cell wall, degradative enzymes.
• The first cell type to migrate to sites of infection or tissue damage
• Phagocytose and kill invaders.
• Short-lived, and many die at the site of infection, contributing to the formation of pus. In the process of dying
  they can release DNA and anti-bacterial proteins which together trap and kill organisms.

Question 46

A new virus that replicates in the liver was found in intravenous drug users.
Answer parts a) - c) based on this information.

a) Describe ONE (1) acquired immune response that should act directly against virally-infected cells, and discuss the mechanism involved.

Answer 46

Cytotoxic T lymphocytes

It kills virally infected cells, and in this case would recognise the antigens in the liver causing secretion of granules containing proteins which induce cell death in the cells.

Question 47

A new virus that replicates in the liver was found in intravenous drug users.
Answer parts a) - c) based on this information.

Describe ONE (1) acquired immune response that attacks the extracellular virus, and a mechanism through which this might reduce viral load.

Answer 47

Neutralisation - antibody binding to virus can block entry into cells.

Through neutralization, the immune response effectively prevents extracellular viruses from infecting host cells, limiting their ability to replicate and spread. This reduces the viral load and aids in the control of the infection.

Question 48

What is the major class of pathogen associated molecular patterns (PAMPs) in viruses that lead to activation of the innate immune system?

Answer 48

The major class of pathogen-associated molecular patterns (PAMPs) in viruses that leads to the activation of the innate immune system is viral nucleic acids. These viral PAMPs are recognized by specific pattern recognition receptors (PRRs) in the host’s cells, which are a key part of the innate immune response.