Immunity

Question 1

What is a pathogen

Answer 1

A bacterium, virus, or other disease-causing organism

Question 2

What is the role of the non-specific defences of the immune system?

Answer 2

To defend the body against any type of invading pathogen

Question 3

Non-specific immune response? (second line)

Answer 3

1) Inflammatory response
2) Action of phagocytes

Question 4

What is involved in the first line of immune defence? (also are non-specific body defences)

Answer 4

1) Closely packed Epithelial Cells form a Physical barriers
(Skin, Inner linings of Respiratory and Digestive systems)

2) Chemical (defences) secretions produced against invaders

Question 5

Name four examples of chemical secretions

Answer 5

1) Tears
2) Saliva
3) Mucus
4) Stomach acid

Question 6

Describe the process of phagocytosis.

Answer 6

1) Phagocytes recognise foreign antigens on pathogens and destroy them by phagocytosis
2) Phagocytosis involves the engulfing of pathogens and their destruction by digestive enzymes contained in lysosomes

Question 7

What is the role of the specific defences of the immune system? (third line)

Answer 7

To defend the body against a particular type of invading pathogen

Question 8

What is the role of phagocytes in the specific immune response??

Answer 8

-Phagocytes release cytokines which attract more phagocytes to the site of infection.
- Cytokines are protein molecules that act as a signal to specific white blood cells causing them to accumulate at the site of infection.

Question 9

Describe the stages involved in an inflammatory response.

Answer 9

1) Mast cells release histamine to trigger the inflammatory response.

2) Histamine causes vasodilation of blood vessels and increased capillary permeability.

3) Increased blood flow leads to the accumulation of phagocytes and clotting elements at the site of infection.

Question 10

How does the action of phagocytes initiate the specific immune response?

Answer 10

Phagocytes releases cytokines which act as signals for specific WBC to accumulate at the site of injury or infection

Question 11

What is involved in the third line of immune defence? (specific cellular defences)

Answer 11

1) Action of T and B lymphocytes
2) Immunological memory

Question 12

What is the role of lymphocytes?

Answer 12

-Lymphocytes are the white blood cells involved in the specific immune response.
-They are the WBCs that respond to specific antigens on invading pathogens.

Question 13

What is an antibody?

Answer 13

• Y-shaped proteins that have 2 receptor binding sites specific to a particular antigen on a pathogen
• Antibodies bind to antigens and inactivating the pathogen
• The resulting antigen-antibody complex can then be destroyed by phagocytosis

Question 14

What is the role of B-Lymphocytes?

Answer 14

Produce specific antibodies against foreign antigens to destroy a pathogen

Question 15

What happens during the clonal selection of lymphocytes?

Answer 15

1) Antigen on a pathogen binds to the lymphocytes specific membrane receptor.

2) Selected lymphocyte undergoes repeated rounds of division to form a clonal population of identical lymphocytes specific to that antigen

Question 16

What are the two types of lymphocyte ?

Answer 16

B lymphocytes and T lymphocytes.

Question 17

What is the role of T-lymphocytes?

Answer 17

Destroy infected cells by recognising foreign antigens and inducing apoptosis
(Programmed cell death)

Question 18

Describe the action of T-Lymphocytes during the process of apoptosis

Answer 18

• Attach onto the pathogen’s antigen on the infected cell membrane and release proteins which diffuse into
  the infected cell
• The Proteins cause the production of self-destructive enzymes inside the infected cell.
• Self-destructive enzymes cause cell death
• The remains of the cell are then removed by phagocytosis.

Question 19

What are antigens ?

Answer 19

Antigens are molecules, often proteins located on the surface of cells that trigger a specific immune response.

Question 20

How do T-lymphocytes cause an autoimmune disease?

Answer 20

• T lymphocytes can normally distinguish between self-antigens on the body’s own cells and foreign antigens on infected cells.
• Failure of the regulation of the immune system leads to T lymphocytes responding to self-antigens.
• This causes autoimmune diseases, where the T lymphocytes attack the body’s own cells.
• This causes autoimmune diseases such as type 1 diabetes and rheumatoid arthritis.

Question 21

How do B-lymphocytes cause an allergic reaction?

Answer 21

B-Lymphocytes respond to antigens on substances that are harmless to the body. This hypersensitive response is called an allergic reaction.

Example: Pollen

B.All.

Question 22

How does immunological memory develop?

Answer 22

-Some of the cloned T and B Lymphocytes survive long-term as memory cells.

-When a secondary exposure to the same antigen occurs, these memory cells rapidly give rise to a new clone of specific lymphocytes,

-These destroy the invading pathogen before the individual shows symptoms.

Question 23

Describe the role of memory cells during a secondary exposure to the same antigen.

Answer 23

1) Rapidly give rise to a new clone of specific lymphocytes.

2) Destroy the invading pathogen before the individual shows symptoms.

Question 24

How do levels of antibody production during a secondary exposure compare to the primary exposure of a pathogen ?

Answer 24

1) Antibody production is greater
2) Antibody production is more rapid

Question 25

How does HIV compromise the immune system?

Answer 25

Virus attacks and destroys T-lymphocytes, causing a depletion of T Lymphocytes and the development of AIDS

Question 26

How does AIDS effect the health of an individual?

Answer 26

Individuals have a weakened immune system and are more vulnerable to opportunistic infections

Question 27

What is immunisation ?

Answer 27

The process by which a person develops immunity to a disease causing organism.

Question 28

What is vaccination ?

Answer 28

Immunity can be developed by vaccination using antigens from infectious pathogens, so creating memory cells.

Question 29

What can the antigens used in a vaccine be?

Answer 29

1) Inactivated pathogen toxins 2) Dead pathogens 3) Parts of pathogens 4) Weakened (attenuated) pathogens

Question 30

What does a vaccine normally consist of ?

Answer 30

Antigens from infectious pathogens are usually mixed with an adjuvant when producing the vaccine.

Question 31

What is an adjuvant ?

Answer 31

An adjuvant is a substance which makes the vaccine more effective, so enhancing the immune response.

Question 32

What is herd immunity ?

Answer 32

-Herd immunity occurs when a large percentage of a population is immunised. -Establishing herd immunity is important in reducing the spread of diseases -Non-immune individuals are protected as there is a much lower probability they will come into contact with infected individuals.

Question 33

What is the herd immunity threshold and what does it depend on ?

Answer 33

The herd immunity threshold is the percentage of immune people needed for effective herd immunity to occur. The herd immunity threshold depends on the: - type of disease -effectiveness of the vaccine - density of the population

Question 34

How is herd immunity established ?

Answer 34

Mass vaccination programmes are designed to establish herd immunity to a disease.

Question 35

Difficulties can arise when wide spread vaccination is not possible due to:

Answer 35

1) Poverty in the developing world (can't access vaccine) 2) When vaccinations are rejected by a percentage of the population in the developed world.

Question 36

What is antigenic variation ?

Answer 36

-Some pathogens can change their antigens, meaning that memory cells are not effective against them. -This makes it possible for new versions of a pathogen to appear, for which we have no immunity.

Question 37

Explain the role and impact of antigenic variation in influenza.

Answer 37

Antigenic variation occurs in the influenza virus explaining why it remains a major public health problem and why individuals who are at risk require to be vaccinated every year.

Question 38

Why are vaccines and drugs are subjected to clinical trials before being licensed for use?

Answer 38

to establish their: -Safety ( no/minimum side effects/toxic effects) -effectiveness (do what their intended for - produce an acceptable level of immunity)

Question 39

How are clinical trials designed to test vaccines and drugs ?

Answer 39

Involves double-blind, randomised and placebo-controlled protocols.

Question 40

What is a placebo controlled protocol ?

Answer 40

-One group of subjects receives the vaccine or drug while the second group receives a placebo-control (like a control in an experiment) -Ensures a valid comparisons of results

Question 41

What is a double blind trial ?

Answer 41

-Neither the subjects nor the researchers know which group subjects are in. -Prevents biased interpretation of the results.

Question 42

What is a randomised trial ?

Answer 42

-Subjects in clinical trials are divided into groups in a randomised way, all individuals have equal chances of being placed in either group, e.g. by using a computer programme to allocates or names out a hat. -Reduces bias in the distribution of characteristics such as age and gender.

Question 43

Explain the importance of group size in reducing experimental error and establishing statistical significance

Answer 43

-Groups must be of a suitable size to reduce the magnitude of experimental error. -At the end of the trial, results from these two groups are compared to determine whether there are any statistically significant differences between them.

Question 44

What is an error bar

Answer 44

-Used to indicate the variability of data around the mean -Used to determine statistically significant differences between mean results -If the error bars in the treatment experiment overlap with the error bars in the control experiment, it is not usually possible to state with confidence that the treatment has had an effect. ## Footnote Usually, a valid conclusion can be drawn where the average value in the control experiment is significantly different from the average when a treatment has been applied.

Question 45

Describe the action of B Lymphocytes

Answer 45

-B lymphocyte produces a specific antibody against antigens and this leads to the destruction of the pathogen. -Antibodies are Y-shaped proteins that have receptor binding sites specific to a particular antigen on a pathogen. -Antibodies become bound to antigens, inactivating the pathogen. -The resulting antigen-antibody complex can then be destroyed by phagocytosis.

Question 46

What receptors do lymphocytes have ?

Answer 46

-Lymphocytes have a single type of membrane receptor which is specific for one antigen. -The membrane receptors allow the lymphocytes to distinguish between the surface molecules of the body's own cells (self-antigens) and the cells with foreign molecules on their surface (foreign antigens)

Question 47

How is herd immunity established ?

Answer 47

Mass vaccination programmes