Y12 MS - Immunity

Question 1

What is an antigen?

Answer 1

A molecule which triggers an immune response

Question 2

What is an antibody?

Answer 2

A protein produced by lymphocytes in response to the presence of specific antigens

Question 3

What is a pathogen?

Answer 3

A microorganism which causes disease

Question 4

What is immunity?

Answer 4

When the body is resistant to a disease

Question 5

What is an immune response?

Answer 5

The production of antibodies against specific antigens of a pathogen

Question 6

What are self cells?

Answer 6

The body’s own cells

Question 7

What are non-self cells?

Answer 7

Cells not from the body (may be from a pathogen, cancer or transport)

Question 8

What are toxins?

Answer 8

The waste products released by pathogens

Question 9

What kind of response is phagocytosis?

Answer 9

Non specific

Question 10

What is the process of phagocytosis?

Answer 10

Phagocytes are white blood cells found in the blood and tissues
Chemical products released by abnormal cells attract them
The receptor binding points on the cell surface attach to the antigen. The phagocyte then changes shape to engulf the pathogen
Once the pathogen is engulfed it is held within a phagosome vesicle which will then fuse with a lysosome
The lysosome releases its contents and the lysozymes hydrolyse the pathogen, destroying it
Soluble products are absorbed and used by the phagocyte

Question 11

Where are phagocytes produced?

Answer 11

The bone marrow

Question 12

What types of molecules can be antigenic?

Answer 12

Proteins
Polysaccharides
Glycoproteins

Question 13

Why does antigenic variability occur?

Answer 13

The shape of antigens frequently alter due to mutations which change the tertiary structure

Question 14

Does the cellular response involve T lymphocytes or B lymphocytes?

Answer 14

T lymphocytes

Question 15

Does the humoral response involve T lymphocytes or B lymphocytes?

Answer 15

B lymphocytes

Question 16

What is exocytosis?

Answer 16

The release of contents from a cell

Question 17

What is the process of the cell mediated response?

Answer 17

Pathogens which invade body cells are destroyed through phagocytosis. The phagocyte presents the antigens from the pathogen on its cell surface
T lymphocytes are activated when they bind to the specific antigen presented on the cell surface and produce cytokines to stimulate rapid cell division by mitosis
Cloned T cells can differentiate into cytotoxic cells which produce perforin, a protein which makes holes in infected cell membranes so they become permeable and die
Cloned T cells can also stimulate B cells to divide by mitosis and secrete antibodies, stimulate phagocytosis and differentiate into memory cells for a more rapid future response

Question 18

What is the process of the humoral response?

Answer 18

A pathogen invades the body with a specific antigen. B cells recognise the antigen and small numbers with complementary antibodies bind to them
When T lymphocytes bind to the antigen of a pathogen presented on the cell surface of a phagocyte, rapid division of B cells by mitosis to form clones which produce the correct antibody
These clones of B cells can differentiate into either plasma cells which can secrete complementary antibodies to destroy the pathogen or memory cells which circulate in the blood and tissue fluid. If the pathogen invades the body again, a rapid response is made as memory cells can divide and develop into plasma cells and more memory cells

Question 19

What does 1 show?

Answer 19

Question 20

What do 2 and 3 show?

Answer 20

Question 21

What does 5 show?

Answer 21

Question 22

What does 4 show?

Answer 22

Question 23

What is a vaccination?

Answer 23

When a dead or weakened pathogen is introduce to induce an immune response where memory cells are produced so that future infection by the same pathogen produces a more immediate immune response

Question 24

What is the structure of an antibody?

Answer 24

An antibody has a quaternary structure with two heavy polypeptide chains bonded to two light chains by disulphide bonds

Question 25

How do antibodies help destroy pathogens in the body?

Answer 25

When an antibody collides with a cell with non-self complementary antigens, an antigen-antibody complex is formed As antibodies have two antigen-binding sites they can bind to more than one pathogen at a time, causing agglutination where groups of pathogens become clumped together This attracts phagocytes to engulf and destroy the pathogens

Question 26

What type of cells does the cell mediated response involve?

Answer 26

T cells

Question 27

What type of cells does the humoral response involve?

Answer 27

B cells

Question 28

Following cloning by mitosis, what can B cells differentiate into?

Answer 28

Memory cells or plasma cells

Question 29

Following cloning by mitosis, what can T cells differentiate into?

Answer 29

Cytotoxic cells

Question 30

Describe a secondary immune response

Answer 30

When the antigen enters the body a second time, the memory cells produced from the initial immune response quickly divide to produce more plasma cells. These plasma cells secrete antibodies complementary to the antigen

Question 31

What is antigenic variation?

Answer 31

Where a pathogen may mutate mutate frequently so its antigens change suddenly and vaccines become ineffective against it because the antigen are no longer recognised by the immune system

Question 32

What is herd immunity?

Answer 32

When a sufficiently large proportion of the population has been vaccinated and are therefore immune so it is more difficult for the pathogen to spread

Question 33

Why may vaccinations be ineffective?

Answer 33

Antigenic variation Symptoms may be hard to diagnose or trace

Question 34

What is active immunity?

Answer 34

When an antigen enters the body and triggers a specific immune response, producing antibodies as a result Can be naturally acquired through exposure to microbes or artificial through a vaccination

Question 35

What is passive immunity?

Answer 35

Immunity without an immune response so no antibodies produced by the body Can be acquired naturally by antibodies received from another organism such as via the placenta or artificially with antibodies manufactured and injected into an organism e.g monoclonal antibodies

Question 36

What is the structure of HIV?

Answer 36

HIV is made up of two RNA strands, proteins (e.g reverse transcriptase), a capsid, attachment proteins and viral envelope consisting of a lipid bilayer and glycoproteins

Question 37

HIV is a ------

Answer 37

Retrovirus

Question 38

What is HIV transmitted by?

Answer 38

The direct exchange of bodily fluids such as from mother to child by breastmilk, blood donation or sharing needles

Question 39

How does HIV replicate?

Answer 39

When HIV enters the bloodstream, it attaches its receptors onto a T cell and injects its genetic material into the cell The HIV uses the cellular machinery to replicate itself as the viral reverse transcriptase produces DNA from the RNA of HIV so each time the cell divides, the viral genetic information is copied After many copies are made, the host cell is destroyed by the HIV

Question 40

How does HIV lead to the inability of the immune system to respond to infection

Answer 40

By HIV replication, T cells are destroyed meaning there is a decreased lymphocyte number. Therefore, there is reduced ability to produce antibodies against pathogens

Question 41

How are monoclonal antibodies produced?

Answer 41

A mouse is immunised with a specific antigen and an immune response is triggered the spleen cells are extracted from the mouse where some B cells will be producing antibodies against the antigen B cells from the mouse and cancerous B cells which divide rapidly and indefinitely are fused with the addition of detergent to disrupt the phospholipid bilayer. This produces hybridoma cells The cells are then placed in a culture medium where only fused cells can grow The hybridoma cells are separated and tested for required antibody production. They are then allowed to multiply and the antibodies are collected and purified for use e.g cancer treatments, pregnancy tests

Question 42

What are the uses of monoclonal antibodies?

Answer 42

Diagnostically Pregnancy tests Detecting cancer cells Therapeutically Targeted breast cancer treatment Preventing blood clotting

Question 43

What is an ELISA test and what are the two types?

Answer 43

The ELISA test is used to see whether a patient has any antibodies to a specific antigen or any antigens to a specific antibody These can be direct (using a single antibody) or indirect (using two antibodies)

Question 44

Describe an indirect ELISA test

Answer 44

Indirect tests for specific antibodies e.g for HIV First the HIV antigens are bound to the bottom of a reaction vessel A blood plasma sample is taken from the patient and added to the sample Any HIV specific antibodies present in the sample bind to the antigens Any other antibodies which are unbound are washed away A second type of antibody with an enzyme attached to it is added to the reaction vessel These secondary antibodies bind to the primary antibodies and the reaction vessel is washed again to remove any unbound antibodies A solution containing a substrate which reacts with the enzyme attached to the secondary antibodies is added. If the secondary antibodies are present, there is a colour change indicating the patient has the HIV antibodies in their blood

Question 45

Describe a direct ELISA test

Answer 45

A direct ELISA test can be used to test whether a patient has specific antigens in their blood plasma e.g for prostate cancer The antibodies specific to the prostate cancer antigens are bound to the bottom of the reaction vessel The patient blood plasma sample is added and if present, the prostate cancer antigens bind to the primary antibody. The vessel is then washed A secondary antibody with an enzyme attached is added and will only bind if the prostate cancer antigens are present A solution containing the substrate complementary to the enzyme attached to the secondary antibody is added and if a colour change is present, the prostate cancer antigens are present