3.2.4 (immune response)

Question 1

What is an antigen?

Answer 1

A protein that can generate an immune response when detected by the body

Question 2

Which cells have antigens?

Answer 2

All cells have antigens
Body cells have ‘self’ antigens
Allows body cells to recognise other cells as foreign- can then be attacked by immune system

Question 3

What do antigens enable the immune system to identify?

Answer 3

Pathogens
Cells from other organisms of same species
Abnormal body cells
Toxins

Question 4

What are phagocytes?

Answer 4

Also known as macrophages
A type of white blood cell
Found in blood and tissues
First immune cells to respond to foreign invaders
Engulfs pathogens

Question 5

Describe phagocytosis

Answer 5

Phagocyte recognises pathogen’s antigens as foreign
Phagocyte binds to receptors on pathogen
Cytoplasm of phagocyte engulfs pathogen by moving around it
Pathogen is contained in phagocytic vacuole in cytoplasm of phagocyte
Lysosome fuses with phagocytic vacuole forming a phagosome
Lysosomes break down pathogen using hydrolytic enzymes
Phagocyte presents pathogen’s antigens on its cell membrane to active other immune cells- is now an antigen presenting cell

Question 6

Describe lymphocytes

Answer 6

White blood cells involved in specific responses
Each lymphocyte only attacks one type of antigen present on a cell
Do not have lysosomes in cytoplasm

Question 7

Describe B-lymphocytes

Answer 7

Mature in bone marrow
Cause humoral response (bodily fluids)
Secrete antibodies
Huge variety of B-lymphocytes, each producing a different antibody to counteract a specific antigen

Question 8

Describe T-lymphocytes

Answer 8

Mature in thymus gland
Involved in cell mediated immunity (the cellular response)
Responds to cells infected with pathogens
Many different T cells, each with a different receptor on surface

Question 9

Summarise the cellular response

Answer 9

T lymphocytes respond to organisms invaded by non self material
Only responds to antigens on surface of cells rather than bodily fluids

Question 10

How are T cells sensitised?

Answer 10

When phagocytes present foreign antigens from ingested pathogens, T cells with receptors complementary to the non self antigens attach to it
Called t helper cells

Question 11

What do sensitised T cells do?

Answer 11

Divide rapidly by mitosis to form clones
Develop into memory cells that respond rapidly should the same pathogen invade again in the future
Stimulate phagocytes to ingest pathogens by phagocytosis
Activate cytotoxic T cells

Question 12

What do cytotoxic t cells do?

Answer 12

Kill infected cells by producing a protein called perforin which makes holes in the cell membrane
Means cell becomes permeable to all substances so cell dies

Question 13

Describe the function of B cells

Answer 13

Stimulated to produce specific antibodies by presence of antigens and chemicals from helper cells

Question 14

Describe clonal selection

Answer 14

A B cell has one shaped binding site on its surface
If it is complementary to the shape of the antigen they will bind

Question 15

Describe clonal expansion

Answer 15

Selected B cells from clonal selection divide by mitosis

Question 16

What can B cells differentiate to become?

Answer 16

In primary immune response, become plasma cells which produce antibodies that bind to antigens to form antibody-antigen complexes which results in destruction of pathogen (however antibodies can only survive for a short time)
In secondary immune response, memory cells will recognise the same antigen again should it reenter the blood, produces new plasma cells by cloning rapidly (so lasts longer)

Question 17

Draw an antibody molecule

Answer 17

https://cdn.savemyexams.com/uploads/2021/02/Antigen-antibody-complex.png

Question 18

How do antibodies work?

Answer 18

Some types of antibodies bind to antigens on surface of foreign organism causing them to stick together in clumps- agglutination
Acts as a marker to phagocytes which engulf the pathogen cells attached
Other antibodies function as antitoxins which bind to toxins (as they are seen as foreign antigens) and neutralise them

Question 19

Agglutination

Answer 19

When antibodies bind to antigens on surface of foreign organism causing them to stick together in clumps

Question 20

What is the purpose of agglutination?

Answer 20

Acts as a marker to phagocytes which the engulf the pathogen cells attached

Question 21

Describe what antitoxins do

Answer 21

Antibodies which act as antitoxins bind to toxins which are seen as antigens
Neutralise the toxins so they become harmless

Question 22

How is each antibody different?

Answer 22

Different antibodies have differently shaped antigen binding sites enabling them to bind with a variety of different antigens

Question 23

Describe the secondary immune response

Answer 23

Memory cells remain in the blood and tissue fluid
Should the same pathogen enter again the antigens are recognised
The memory cells divide rapidly and develop into plasma cells
Antibodies are quickly produced
The pathogen is destroyed before they reproduce or cause symptoms

Question 24

Describe active immunity

Answer 24

Immune system makes antibodies though antigen stimulation
Natural- become immune after catching disease
Artificial- become immune after vaccination

Question 25

Describe passive immunity

Answer 25

Administration of antibodies made by a different organism Natural- receive antibodies from breast milk Artificial- injected with antibodies or received through blood donation

Question 26

Describe the differences between active and passive immunity

Answer 26

Active involves memory cells, passive doesn't Active involves production of antibodies by plasma or memory cells, passive involves introduction of antibodies produced by another source Active is long term because antibody is produced in response to antigen, passive is short term because the antibody given is quickly broken down Active can take a long time to develop/ work, passive is fast acting Active immunity gives exposure to antigen, passive doesn't

Question 27

Describe herd immunity

Answer 27

Vaccinations contain antigens which cause your body to produce memory cells in response to pathogen Means you can be immune without experiencing that disease Reduces the number of people that get the disease Also reduces the number of non vaccinated people that get the disease

Question 28

Describe what a vaccination is

Answer 28

Contains antigens- free or attached to a dead or weakened pathogen Injected or administered orally

Question 29

Why is oral administration of a vaccine not as good?

Answer 29

May need a booster to ensure memory cells are produced

Question 30

Explain how administering a vaccine prevents infection by a pathogen

Answer 30

Antigens injected into blood T helper cells produce memory cells If blood is reinfected by that pathogen more memory antibodies are produced faster Antibodies destroy pathogen

Question 31

Describe the ethical issues surrounding vaccination

Answer 31

Tested on animals prior to humans May contain animal based substances Risk associated with testing human volunteers- may contract disease Unfair that some people don't get vaccinated yet are still protected by herd immunity When in a pandemic, decision about who recieves vaccine first

Question 32

Describe antigenetic variability

Answer 32

Some pathogens are able to change their surface antigens due to making changes in genes

Question 33

Describe consequences of antigenetic variability

Answer 33

Memory cells redundant on reinfection Primary response takes time- will still experience symptoms Harder to develop a vaccine

Question 34

Describe how HIV replicates

Answer 34

HIV attachment proteins bind to CD4 receptors on cell surface membrane of T lymphocytes HIV capsid containing reverse transcriptase enzyme and viral RNA injected into T lymphocyte Reverse transcriptase enzyme converts viral RNA to DNA t-lymphocyte incorporates this DNA with its own Viral DNA transcribed and translated Host cell synthesises HIV viral particles eg proteins HIV cells assembled in host cella nd released, killing the T lymphocyte and releasing more viruses

Question 35

How does HIV develop into AIDS?

Answer 35

HIV attachment proteins bind to CD4 receptor on T lymphocytes HIV replicates, results in destruction of T lymphocytes, reducing their numbers Leads to fewer T helper cells and cytotoxic T cells forming Fewer T helper cells leads to less b lymphocytes activating and dividing by mitosis to form plasma cells so less antibodies are released Fewer cytotoxic t cells lead to less cell mediated response

Question 36

What are monoclonal antibodies?

Answer 36

Antibodies cloned from a single group of plasma cells Have the same tertiary structure Made to bind to a specific target antigen

Question 37

Describe how monoclonal antibodies are produced

Answer 37

Mouse injected with antigen to stimulate immune response B lymphocytes produce specific antibodies Tumour cells are combined with b cells forming a hybridoma (which can make specific antibodies and divide rapidly by mitosis) Screened and purified Antibodies produced called monoclonal antibodies as all come from a single cloned cell

Question 38

Describe 2 uses of monoclonal antibodies

Answer 38

Targeted medication- cancer cells have antigens which signal as abnormal, monoclonal antibodies can bind specifically to antigens on cancer cells, other cancer treatments often harm healthy cells, binding specifically to cancer cells reduces damage to other cells Medical diagnosis- can be used to show presence of a specific antigen, antibodies are attached to a dye, fluorescent or radioactive marker, when complementary antigen is present marker becomes visible

Question 39

How are monoclonal antibodies used in pregnancy tests?

Answer 39

Urine applied to test strip HCG hormone binds to mobile HCG antibodies in reaction zone HCG hormone binds to immobilised HCG antibodies in results zone Antibodies which do not attach to HCG bind to antibodies in control zone Dye appears in control and results zone for a positive result

Question 40

Describe the ethical issues associated with the use of monoclonal antibodies

Answer 40

Production of monoclonal antibodies involves mice- cant consent to being exposed to a disease and given cancer Contreversial outcomes- treatment doesnt always work and sometimes results in death Unsuccessful trials- testing new drugs can be harmful and unsafe

Question 41

Describe how antibodies work in the ELISA test

Answer 41

Antigen of infection being tested for is immobilised in bottom of beaker Blood sample added to beaker If antibodies complementary to immobilised antigen they will bind to form many antigen-antibody complexes Beaker washed to remove any unattached antibodies Secondary antibodies which are attached to an enzyme are added If primary antibodies are present the secondary antibodies attach to them and the enzyme will change the colour of the solution If colour changes indicates the blood sample is infected by the pathogen

Question 42

Why is the control strip important in monoclonal antibody testing?

Answer 42

Prevents false negatives by showing that antibodies have moved up strip