Cell Recognition + The Immune System

Question 1

What are the two types of defence systems? What do they mean?

Answer 1

Non-specific: generic defences that are immediate and respond in the same way to each pathogen.
Specific: slower defences that are specific to each pathogen.

Question 2

What are examples of non-specific defence systems?

Answer 2

• Physical and chemical barriers (e.g. skin)
• Phagocytosis

Question 3

What are examples of specific defence systems?

Answer 3

• Cell-mediated response
• Humoral response

Question 4

Swelling/inflammation is known as the non-specific inflammatory response. How does this work and help the body?

Answer 4

Histamine is secreted and vasodilation increases the blood supply. This increases the supply of phagocytic cells to the area.

Question 5

What term describes a body’s own cells?

Answer 5

‘Self’

Question 6

What term describes foreign cells?

Answer 6

‘Non-self’

Question 7

What are examples of physical barriers?

Answer 7

• Skin
• Scabs
• Tears
• Eyelashes
• Stomach acid
• Nasal hair
• Cilia
• Goblet cells (secrete mucus)

Question 8

What are the two types of phagocytes?

Answer 8

Neutrophils and macrophages.

Question 9

Describe the features of a neutrophil.

Answer 9

It is made in the bone marrow, travels via the blood and squeezed out into tissue fluid. It is short lived and has a multi-lobed nucleus.

Question 10

Describe the features of a macrophage.

Answer 10

It is made in the bone marrow, travels via the blood as a monocyte. They are longer lasting and can become antigen presenting cells (APC).

Question 11

Describe phagocytosis.

Answer 11

Phagocyte engulfs pathogen, and places it into a vesicle called a phagosome. The phagosome fuses with lysosomes to form a phagolysosome. The lysosome releases lysozymes which hydrolyse the pathogen.
If the phagocyte is a neutrophil, it will collect as pus. If it is a macrophage, it will present the antigen from the pathogen on its cell surface membrane once the pathogen has been hydrolysed (becomes an APC).

Question 12

What types of cells do T lymphocytes respond to?

Answer 12

• Cells transplanted from a donor
• Cancer cells
• Antigen presenting phagocytes/cells (weaker answer, only sometimes accepted)

Question 13

What triggers the cell mediated response?

Answer 13

Antigen presenting cells (e.g. macrophages)

Question 14

Where are T cells produced and where do they mature?

Answer 14

They are produced in the bone marrow.
They mature in the thymus.

Question 15

Where are B cells produced and where do they mature?

Answer 15

They are produced in the bone marrow.
They mature in the bone marrow.

Question 16

Describe the cell mediated response.

Answer 16

T helper cells have receptors on their surface which bind to antigen on APC. This activates T helper cells to divide by mitosis and make a large number of clones (clonal expansion). The cloned helper T cells are then able to differentiate.

Question 17

What do the cloned T helper cells differentiate into?

Answer 17

• Memory cells for long term immunity
• Stimulate phagocytes to engulf pathogen
• Remain T helper cells and stimulate specific B cells to divide and secrete antibodies
• Activate cytotoxic T cells (killer T cells)

Question 18

How are cytotoxic T cells activated?

Answer 18

By T helper cells, which release chemicals called cytokines.

Question 19

How do cytotoxic T cells work?

Answer 19

They release a protein called perforin, which makes holes in the membrane of the target cell and makes it freely permeable and causes the cell to be destroyed.

Question 20

Describe the humoral response.

Answer 20

The pathogen’s antigen enters the B cell via endocytosis, this antigen is then presented on the surface membrane. A T helper binds to this antigen/receptor complex. The T helper cell stimulates the B cells to divide via mitosis. These B cells then differentiate into plasma cells, which produce monoclonal antibodies or B memory cells.

Question 21

What is an antigen?

Answer 21

A protein which stimulates a specific immune response.

Question 22

What is an antibody?

Answer 22

An immunoglobulin, which is complementary to a specific antigen.

Question 23

Describe the structure of an antibody.

Answer 23

A Y shaped protein (called an immunoglobulin) made up of 4 polypeptide chains (quaternary structure) ~ 2 heavy chains, 2 light chains. It has a variable region and a constant region. The antigen binding sites are in the variable region, which is specific to a particular antigen due to it being different sequences of amino acids for different antibodies. It is held together by disulfide bridges. It has a hinge region, which gives the molecule flexibility.

Question 24

What is agglutination and why does it occur?

Answer 24

Antibodies have at least 2 binding sites, which leads to agglutination. It causes the pathogens carrying antigen-antibody complexes to clump together, preventing pathogens spreading and making it easier for phagocytes to engulf a number of pathogens at the same time.

Question 25

Other than binding to antigens, what else can antibodies do?

Answer 25

Bind to toxins produced by pathogens, making them harmless.

Question 26

Describe the primary immune response.

Answer 26

There is a slight delay due to antigen presentation, selection of complimentary T and B cells and mitosis. The cloned plasma cells produce antibodies and eventually die off, which is when the antibody concentration declines. Memory cells remain in circulation and stored in lymph nodes.

Question 27

Describe the secondary immune response.

Answer 27

There is a rapid increase in antibody concentration due to immediate activation of memory T and B cells. Many cloned plasma cells produce very large quantities of antibodies in a short period of time. As plasma cells die off, antibody concentration declines. Memory cells remain in circulation and stored in lymph nodes.

Question 28

Why may we suffer from the same disease twice?

Answer 28

Antigen variability - where gene mutation changes the antigen on the surface of the pathogen (e.g. cold virus or influenza). Antigens are no longer complimentary to the surface receptors of memory cells so no longer secondary response.

Question 29

What are the two different categories of immunity?

Answer 29

- Passive or active - Natural or artificial

Question 30

What is active natural immunity?

Answer 30

- An individual becoming infected with a disease - Body / plasma cells produce own antibodies - B memory cells formed

Question 31

What is passive natural immunity?

Answer 31

- Baby becomes immune due to the antibodies received from mother through placenta or breast milk - Short lived - No memory cells

Question 32

What is active artificial immunity?

Answer 32

- Vaccination - Memory cells formed

Question 33

What is passive artificial immunity?

Answer 33

- Become immune after being injected with antibodies from someone else - E.g. antivenom (antibody, venom = antigen) - Short lived - No memory cells

Question 34

What are the features of active immunity?

Answer 34

- Requires exposure to antigen - Takes a while for production of antibodies to develop - Memory cells are produced - Long term protection

Question 35

What are the features of passive immunity?

Answer 35

- Does not require exposure to antigen - Protection is immediate - Memory cells are not produced - Short term production ~ antibodies are broken down

Question 36

What is a vaccination?

Answer 36

When a small amount of an inactive form of a pathogen (disease causing microorganism) into the body.

Question 37

How does the body respond to the vaccine?

Answer 37

The same as the humoral response, where B lymphocytes are activated and divide via mitosis. They differentiate into memory cells or plasma cells. Plasma cells produce monoclonal antibodies. B memory cells provide long term immunity from the live pathogen.

Question 38

What is antibiotic resistance?

Answer 38

Where a certain strain of bacteria can no longer be killed by antibiotics.

Question 39

What causes antibiotic resistance?

Answer 39

- Doctors overprescribing antibiotics - Patients not finishing their courses of antibiotics

Question 40

What are the features of a successful vaccination program?

Answer 40

- Economically available in sufficient quantities - Few side effects - Vaccinating vast majority of the vulnerable population (herd immunity) - Being able to produce, store and transport the vaccine

Question 41

What is herd immunity?

Answer 41

When a significant proportion of the population are vaccinated, which makes it difficult for a pathogen to spread.

Question 42

What are monoclonal antibodies?

Answer 42

One type of antibody produced from a clone of plasma cells.

Question 43

What are the uses of monoclonal antibodies?

Answer 43

- For diagnosis - In labs, to measure levels of hormones/chemicals in the blood, or to detect pathogens - To treat certain diseases by binding them to radioactive substances or toxic drugs - In research to locate or identify specific molecules in a cell or tissue by binding them to a fluorescent dye

Question 44

What is direct MAB therapy?

Answer 44

When the MAB attaches to a specific antigen and blocks chemical signals that stimulate uncontrolled cell division.

Question 45

What is indirect MAB therapy?

Answer 45

When a therapeutic drug is attached to the MAB to target a specific cell type, e.g. the magic bullet.

Question 46

What are the advantages of direct MAB therapy?

Answer 46

- Antibodies are non toxic - Antibodies are highly specific - Fewer side effects than other forms of therapy

Question 47

What are the advantages of indirect MAB therapy?

Answer 47

- Small doses required - cheaper + reduces side effects - Target specific sites - Doesn't damage healthy cells