Foundations in Immunology

Question 1

List the major cell types involved with the innate immune response

Answer 1

Macrophages
Neutrophils
Basophils
Eosinophils

Question 2

List the major cell types involved in the adaptive immune response

Answer 2

Lymphocytes (T and B cells)

Question 3

Describe the main role of the innate immune system

Answer 3

The innate immune system acts as the body’s first line of defence. It involves the use of:
o	Physical Barriers
•	Tight junctions between epithelia
•	Mucous membranes
o	Phagocytic cells
•	Macrophages
•	Neutrophils
o	Soluble factors

Question 4

Describe the function of natural killer cells

Answer 4

Kills tumour and virally infected cells, through two different methods:
• Degranulation - bore holes in target cells by secreting perforin onto them and forming a MAC
• FasL-dependent cell suicide dependent on the expression of both inhibitory and activating receptors. Inhibitory receptors on the NK cells recognise and bind to MHC1

Question 5

Describe the process of phagocytosis and intracellular killing

Answer 5

Phagocytosis is triggered when the phagocyte recognises a foreign cell. It is the internalization of foreign matter by cells into cytoplasmic vesicles. Once inside, the matter is digested following the fusion of the phagosomes to the lysosomes , which contain degradative enzymes.

Question 6

Define the primary lymphoid organs and their function

Answer 6

These organs are where lymphocytes are generated.
• Thymus
• Bone marrow
• Foetal liver

Question 7

Define the secondary lymphoid organs and their function

Answer 7

Where immune responses are initiated and lymphocytes maintained.
• Lymph Nodes
• Spleen

Question 8

Describe the fundamental properties of the adaptive immune response

Answer 8

o Specificity
o Diversity
o Memory
o Recruitment of other defence mechanisms

Question 9

Describe the role of B lymphocytes in immunity

Answer 9

B cells differentiate further to form plasma cells. These cells synthesise antibodies specifically designed for use against the detected pathogen. The pathogen is recognised first by membrane bound antibody. The antibodies produced by plasma cells are soluble in plasma, and upon recognition of the particular antigen they are against, produce a must faster immune response that upon first encounter.

Question 10

Illustrate the structure and function of an antibody

Answer 10

The section which binds to the antigen is known as the paratope, and it binds to the antigen epitope.

Antibodies are made up by two heavy chains and two light chains, making up constant regions (mediate effector reactions) and variable regions (recognise specific Ags, what gives Ab its specificity). The chains are held together by disulphide bonds.

Question 11

What is an antigen?

Answer 11

Antigens are proteins able to evoke an immune response and react with immune products.

Question 12

Briefly describe the complement system and its function

Answer 12

The complement system is made up of 25 serum proteins whose sequential activation and assembly into functional units can bring about three events.
o Recruitment of inflammatory cells
o Coating/Opsonisation of Bacteria
o Lysis of bacteria

Question 13

Describe how antigen presenting cells and T lymphocytes interact

Answer 13

MHC class II is found only on ‘Professional Antigen Presenting Cells’ (APCs) and it prresents exogenously produced Ag to CD4+ T cells to activate macrophages and B cells and produce a innate immune response to clear any infections.

All cells possess MHC class I, which presents internal antigens or viral peptides to CD8+ Tc cells to initiate cell death of the infected cell.

Question 14

Describe the role of Th1 and Th2 cells in the immune response

Answer 14

Proliferating helper T cells that develop into effector T cells differentiate into two major subtypes of cells known as Th1 and Th2 cells.
o Th1 helper cells are the host immunity effectors against intracellular bacteria and protozoa.
o Th2 helper cells are the host immunity effectors against extracellular parasites including helminths.

Question 15

Describe the role of cytokines

Answer 15

Cytokines are small chemical messengers used by cells to communicate with other cells to coordinate immune reactions. They can act in an autocrine, paracrine and endocrine fashion.

Question 16

Give 5 examples of pathogens

Answer 16

• Virus
• Protozoa
• Bacteria
• Fungi
• Parasite

Question 17

What is tolerance?

Answer 17

One of the most remarkable properties of the immune system is its ability to react to foreign antigen and yet not to react to self antigen. This is vitally important for the health of the host. Immunological unresponsiveness to an antigen is called tolerance. Self-tolerance is maintained by a number of mechanisms including the elimination of lymphocytes which react to self antigens or self markers in their early stages of development and allowing lymphocytes to encounter self antigens in a setting which leads to their destruction if they react to these self antigens

Question 18

Describe the fundamental properties of the innate immune response

Answer 18

Non-specific
First line of defence
No memory

Question 19

Name two professional phagocytes

Answer 19

Macrophages

Neutrophils

Question 20

Describe the functions of eosinophils

Answer 20

Release granules to combat large extracellular pathogens, though alongside mast cells can play a role in allergy and asthma.

Question 21

What causes anaphylactic shock?

Answer 21

• Anaphylactic shock caused by mast cell degranulation
• Mast cells protect against parasites and contain many granules containing pharmacologically active chemicals, including histamine.
• On first exposure to an allergen (e.g. some people make lots of IgE antibodies against the allergen. Mast cells have receptors on their surfaces which can bind to the Fc region (the constant end) of the IgE antibodies.
• On second exposure to the allergen the IgE antibodies which are bound to the mast cell can now also bind the allergen. This drags the mast cell receptors together and results in a signal being sent to release the chemicals inside the cell into the tissues. This increases capillary permeability allowing fluid to escape from the blood vessels – runny nose and watery eyes. This is usually a local effect but if the toxin spreads throughout your body and triggers massive mast cell degranulation the effects can be serious – blood volume can reduce so much that blood pressure drops massively and the heart can no longer pump efficiently resulting in heart attack. Also, histamine can cause your airway to constrict making it difficult to breathe and can cause suffocation.

Question 22

What make up non-specific humeral factors?

Answer 22

Within body fluids (and mucus) is a variety of soluble substances with protective functions:
o	Growth Inhibitors
o	Enzyme Inhibitors
o	Lysins
o	Complement Proteins

Question 23

Describe acute and chronic inflammation

Answer 23

• Acute inflammation is initial response of the body to harmful stimuli
• Chronic inflammation leads to a progressive shift in the type of cells which are present at the site of inflammation and is characterised by simultaneous destruction and healing of the tissue from the inflammatory process.

Question 24

Describe the lymphatic system and its function

Answer 24

The lymphatic system is a network of conduits that carry a clear fluid called lymph and includes the lymphoid tissue through which the lymph travels.
The functions of the lymphatic system include:
o Drainage of interstitial fluids from tissue
o Absorption and transport of fatty acids as chyle to the circulatory system
o Immunity

Question 25

Describe the structure of lymphatic vessels

Answer 25

Only carry fluid from tissues in one direction.
Smallest are the lymphatic capillaries (blind-ended sacs, highly permeable).
Walls are composed of endothelium in which simple squamous cells overlap to form one-way valves.

Question 26

What occurs in positive selection?

Answer 26

Positive selection “selects for” T cells with TCRs capable of interacting with MHC with weak affinity . Positive selection involves the production of a signal by double-positive precursors that express either MHC Class I or II restricted receptors

Question 27

What occurs in negative selection?

Answer 27

Negative selection removes thymocytes that are capable of strongly binding with “self” MHC peptides.

Question 28

Define active immunity

Answer 28

Active immunity is conferred by a host response to a microbe or microbial antigen. Can have immunological memory

Question 29

Define passive immunity

Answer 29

Passive immunity is conferred by adoptive transfer of antibodies or T lymphocytes specific for the microbe e.g. transfer of maternal Abs. No memory.

Question 30

Describe the development of B cell tolerance

Answer 30

• Central tolerance development in B cells - Immature B cells that recognize self antigens in the bone marrow with high avidity (e.g., multivalent arrays of antigens on cells) die by apoptosis or change the specificity of their antigen receptors (receptor editing). Weak recognition of self antigens in the bone marrow may lead to anergy (functional inactivation) of the B cells.
• Peripheral T cell tolerance in B cells - B cells that encounter self antigens in peripheral tissues become anergic or die by apoptosis. In some situations, recognition of self antigens may trigger inhibitory receptors that prevent B cell activation.

Question 31

Define a pathogen

Answer 31

A pathogen is any microorganism that causes disease – bacteria, virus, parasite.

Question 32

Define a antigen

Answer 32

Any substance capable of triggering an immune response is called an antigen. An antigen can be a virus, a bacterium, a fungus, or a parasite, or even a portion or product of one of these organisms

Question 33

Define an epitope

Answer 33

An antigen announces its foreignness by means of intricate and characteristic shapes called epitopes, which protrude from its surface. Most antigens, even the simplest microbes, carry several different kinds of epitopes on their surface; some may carry several hundred. However, some epitopes will be more effective than others at stimulating an immune response.

Question 34

Describe the two types of B cell activation

Answer 34

• T cell dependent activation requires a signal from the clustered BCR along with a signal form a T cell in which a protein on the surface of a T cell which recognises the same antigen as the B cell binds to a receptor on the B cell.
• T cell independent activation can happen when huge numbers of BCR are clustered together by an antigen with a very large number of repeated epitopes – a mitogen.