immunology

Question 1

.State two ways that pathogens cause harm/disease?

Answer 1

1- can produce toxins which can directly damage tissues
2- can sometimes replicate inside and destroy host cells

Question 2

What is an antigen?

Answer 2

A molecule (usually a protein) that stimulates an immune response that results in the production of a specific antibody. (Antibody generator)

Common antigens: Glycoproteins & Glycolipids

Question 3

Give the types of cell, other than pathogens, that can stimulate an immune response.

Answer 3

1- (Cells from) other organisms/transplants;
2- Abnormal/cancer/tumour (cells);
3- (Cells) infected by virus;
4- Pathogen (Bacterium / Fungus / Protist)
REJECT VIRUS (Acellular)

Question 4

Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)

Answer 4

This is called PHAGOCYTOSIS

1-Pathogen is engulfed by the phagocyte.
2- Engulfed pathogen enters the cytoplasm of
the phagocyte in a vesicle;
3- Lysosomes fuse with vesicle releasing
digestive enzymes;
4- Lysosome enzymes break down the pathogen.
5- Waste materials are ejected from the cell by exocytosis;

Question 5

Describe how a phagocyte destroys a pathogen present in the blood. [3]

Answer 5

1- Engulfs;
2- Forming vesicle/phagosome and fuses with lysosome;
3- Hydrolytic enzymes digest/hydrolyse;

Question 6

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how [6]

Answer 6

1- Vaccine contains antigen from pathogen;
2- Macrophage presents antigen on its surface;
3- T (helper) cell with complementary receptor protein binds to antigen;
4- T cell stimulates B cell;
5- (With) complementary antibody on its surface;
6- B cell divides to form clone secreting / producing same antibody;
7- B cell / Plasma cell rapidly secretes large numbers of antibody;

Question 7

Describe the role of T-helper cells

Answer 7

1- binds to the antigen presenting cell
2- releases cytokines that attract phagocytes to the area of infection
3- release cytokines that activate Cytotoxic Killer T Cells(Tc)
4- activates a specifically complementary B cell
5- form memory T-H cells

Question 8

What does the word ‘ethical’ mean?

Answer 8

Harm inflicted.

Question 9

Describe the role of Tc Cell ( cytotoxic killer t cells)

Answer 9

1- locate and destroys infected body cells that present the correct antigen
2- binds to antigen-presenting-cells
3- releases Perforin( protein) which creates holes in the cell surface membrane which destroys the APC

Question 10

Give three roles of cytokines

Answer 10

1- stimulate more phagocytic cells
2- stimulate clonal expansion
3- cause B cells to make and secrete antibodies

Question 11

What is clonal selection/ expansion

Answer 11

1- A specific Th cell binds to presented antigen via its complementary receptor
2- T cell is activated and clones to produce many Th cells with complementary receptors to the antigen.

Question 12

Explain how the humoral response leads to immunity. [3]

Answer 12

1- B cells specific to the antigen reproduce by mitosis.
2- B cells produce plasma and memory cells
3- Second infection produces antibodies in larger quantities AND more rapidly.

Question 13

Explain the B cell activation

Answer 13

1- a specific Th cell with the correct receptor binds to the presented antigen and then locates AND ACTIVATES a specifically complementary B cell
2- the specific Th releases cytokine chemicals that signal the specific B cell to clone by mitosis(clonal expansion)

Question 14

Which two types of cell does the B cell differentiate into ?

Answer 14

1- PLASMA CELLS
produce and secrete vast quantities of specific antibodies into the blood plasma
2- MEMORY(B) CELLS
remain in the body to respond to pathogen rapidly and extensively

Question 15

What is an antibody

Answer 15

protein made in response to foreign antigen

Question 16

Describe and explain the role of antibodies in stimulating phagocytosis.

Answer 16

-OPSINISATION: Bind to antigen OR Are markers;
AGGLUTINATION: (Antibodies) cause clumping/ aglutination OR attract phagocytes

Question 17

How do antibodies assist in the destruction of pathogens?

Answer 17

1- agglutination
2- opsonisation
3- lysis : bind to antigens and destruct pathogen’s membrane
4- antitoxin and anti venom
5- prevent pathogen replication

Question 18

Describe the difference between active and passive immunity. [5]

Answer 18

1- Active involves memory cells, passive does not;
2- Active involves production of antibody by plasma cells/memory cells;
3- Passive involves antibody introduced into body from outside/named source;
4- Active long term, because antibody produced in response to antigen;
5- Passive short term, because antibody (given) is broken down;
6- Active (can) take time to develop/work, passive fast acting;

Question 19

State why some antibodies are referred to as monoclonal

Answer 19

(Antibodies) produced from a single clone of B cells / plasma cells;
OR

(Antibodies) produced from the same B cell / plasma cell;

Question 20

Give some uses of monoclonal antibodies

Answer 20

1- research
2- immuno assays eg. pregnancy kits and ELISA
3- diagnosis ( showing presence of a particular antigen )
4- targeting drugs
5- killing specific cells
6- isolating specific chemicals

Question 21

Different antibodies from the same organism bind to different antigens. Explain why

Answer 21

1- Variable region of each polypeptide has a different tertiary structure.
2- Variable region provides (highly) specific antigen binding site with specific shape.
3- Antigen binding site is only complementary to a specific antigen to form antigen antibody complex

Question 22

What is the role of the disulfide bridge in forming the quaternary structure of an antibody?

Answer 22

Joins two (different) polypeptides

Question 23

What are the ethical considerations associated with vaccines and monoclonal antibodies?

Answer 23

Animal & Human testing for production, efficacy and safety.
Animal rights.
Risk : Benefit ratio (if few people have severe side effects but the majority of the population have mild or no symptoms, is this justifiable?)
Vaccine availability: Free for all or who pays for those who can’t afford the preventative treatment.

Question 24

Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why. [3]

Answer 24

1- Specific) primary structure / order of amino acids;
2- (Specific) tertiary / 3D structure / shape;
3- (So) Only binds to / fits / complementary to one antigen;

Question 25

Describe the structure of the human immunodeficiency virus (HIV). [5]

Answer 25

1- RNA (as genetic material);
2- Reverse transcriptase;
3- (Protein) capsomeres/capsid;
4- (Phospho)lipid (viral) envelope OR Envelope made of membrane;
5- Attachment proteins;

Question 26

Explain how HIV affects the production of antibodies when AIDS develops in a person. [3]

Answer 26

1- Less/no antibody produced;
2- (Because HIV) destroys helper T cells; Accept ‘reduces number’ for ‘destroys’
3- (So) few/no B cells activated / stimulated OR (So) few/no B cells undergo mitosis/differentiate/form plasma cells;

Question 27

Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). [4]

Answer 27

1- RNA converted into DNA using reverse transcriptase;
2- DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
3- DNA transcribed into (HIV m)RNA;
4- (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);

Question 28

Name two features of HIV particles that are not found in bacteria. Do not include attachment protein in your answer. [2]

Answer 28

1- Capsid;
2- Reverse transcriptase;
3- RNA genome;
4- (viral lipid) Envelope;

Question 29

Describe how a person infected with HIV will develop AIDS (if untreated) and die of secondary infections. [4]

Answer 29

1- High viral load leads to increased destruction of helper T/CD4 cells;
2- Less activation of B cells/cytotoxic T cells/phagocytes;
3- Less production of plasma cells/antibodies OR (With cytotoxic T cells) less able to kill virus infected cells;
4- (Less able to) destroy other microbes/pathogens OR (Less able to) destroy mutated/cancer cells;

Question 30

What are ELISA tests used to determine

Answer 30

the presence of the antibody (indirect ELISA) or the antigen ( sandwich ELISA)

Question 31

Describe the role of antibodies in producing a positive result in an ELISA test. [4]

Answer 31

1- (First) antibody binds/attaches /complementary (in shape) to antigen;
2- (Second) antibody with enzyme attached is added;
3- (Second) antibody attaches to antigen;
4- (Substrate/solution added) and colour changes;

Question 32

Which immune cell destroys (self) cells infected with a virus?

Answer 32

Tc Cell
(Cytotoxic Killer T cell)

Question 33

Which immune cell destroys bacteria?

Answer 33

Phagocyte
(e.g., Macrophage)

Question 34

Name a virus that infects bacteria

Answer 34

Bacteriophage

Question 35

When is a person / cell / organism infected by a virus such as HIV?

Answer 35

The moment the viral DNA is inserted into the host cells genome.

Question 36

What is Herd immunity?

Only applicable to contagious pathogens.

Answer 36

When the majority of a population is vaccinated / immune to a contagious pathogen;
Those not yet vaccinated (Infants / eldery / immuno-suprressed/deficient) will have protection as the pathogen will spread less rapidly.

Herd Immunity Threshold is (usually) between 85-95% depending on the named pathogen.

Herd immunity applies a selection pressure to the named pathogen.

Question 37

What threatens Herd immunity?

Answer 37

• Low vaccine uptake
• Vaccine hesitancy / choice not to vaccinate
• Mutation of pathogen
• Vaccine does not produce long term immunity
• Vaccinated population does not mix randomly