Topic 2.3 - Cell Recognition And The Immune System

Question 1

What is a pathogen?

Answer 1

A pathogen is an organism that causes disease to its host.

Question 2

What is an infection?

Answer 2

The interaction between the pathogen and the body’s various defence mechanisms.

Question 3

What is immunity?

Answer 3

Preparing the body’s defences for a second infection from the same infection, to kill it before it can cause any harm.

Question 4

What is the white blood cell used for defences called?

Answer 4

A lymphocyte.

Question 5

What are the two types of lymphocytes and what kind of responses do they have?

Answer 5

1. T-lymphocytes that are involved in cell-mediated response.
2. B-lymphocytes that are involved in humoral response.

Question 6

Give 4 examples of non-self cells that can trigger an immune response.

Answer 6

1. Pathogens such as HIV.
2. Cells from other organisms of the same species.
3. Toxins, including those from certain pathogens.
4. Abnormal cells, such as cancer cells.

Question 7

What are the 2 types of defence mechanisms?

Answer 7

Specific and non-specific.

Question 8

What is the difference between non-specific and specific defence mechanisms?

Answer 8

Specific is slower and targeted to each pathogen, however non-specific is immediate and me same for all pathogens.

Question 9

Give 2 examples of non-specific response.

Answer 9

1. Physical barriers such as skin.
2. Phagocytosis.

Question 10

Give 2 examples of specific response.

Answer 10

1. Cell-mediated response.
2. Humoral response.

Question 11

What is the difference between a phagocyte and a lymphocyte?

Answer 11

A phagocyte engulfs and digests the pathogen in a process called phagocytosis. This is done before it can cause harm. Lymphocytes are involved in immune responses. Phagocytes are a non-specific defence mechanism as opposed to lymphocytes that apart of the specific defence mechanism.

Question 12

What is the process for phagocytosis?

Answer 12

Chemical products of pathogens or dead, damaged and abnormal cells act as l attractants, causing phagocytes to move towards these cells.
Phagocytes have many receptors on their cell-surface membrane which attach to the chemicals on the pathogens.
The phagocytes then engulf the pathogen and form a vesicle around mean called a phagosome.
The phagocyte contains lysosomes which fuse with the phagosome to form a phagolysosome.
The lysosomes have hydrolyticenzymes which hydrolyse (digests) the pathogens.
The cytoplasm of the pathogen then absorbs the soluble products from the breakdown of the pathogen.
The phagocyte then presents the antigens from the pathogen on its cell- surface membrane.

Question 13

What is an antigen?

Answer 13

A part of an organism that is recognised as non-self by the immune system and stimulates an immune response.

Question 14

Why are T-lymphocytes called T-lymphocytes?

Answer 14

They are T because they mature in the thymus gland.

Question 15

What happens in cell-mediated response?

Answer 15

Phagocytes that have the antigens presented on their cell-surface membrane can have 3 complementary cells bound to them (B-lymphocytes, T-lymphocytes and Helper T cells).
The helper T cells secrete cytokines which activate the B and T cells.
The T cells are then activated and clone by mitosis to form genetically identical cells.
The cloned tells can:
1. Develop into memory cells for a rapid response to future infections.
2. Stimulate phagocytes to undergo phagocytosis.
3. Stimulate B cells to divide and secrete their antibodies.
4. Activate cytotoxic T cells.

Question 16

What do Cytotoxic T cells do?

Answer 16

They kill abnormal and body cells that are infected by pathogens by producing a protein called perform which creates holes in the cell-surface membrane. This allows the membrane to become freely permeable to all substances and the all dies as a result.

Question 17

What happens in humoral response?

Answer 17

The surface antigens of a pathogen are taken up by a B cell.
The B cells process the antigens and present them on their surface. (clonal selection).
Helper T cells then attach themselves onto the antigens and activate the B cell.
The B cells then divide by mitosis to give a clone of plasma cells. (clonal expansion).
The cloned plasma cells then secrete antibodies that exactly fit the antigen of the pathogen and destroys them.
Some B cells can be developed into memory cells for future infections (secondary immune response).

Question 18

What is the difference between plasma cells and memory cells?

Answer 18

Plasma cells secrete antibodies and so are short lived, memory cells can last decades and so are used in the secondary response.

Question 19

If the question asks or mentions anything about antibodies, which response do you use?

Answer 19

Humoral.

Question 20

If the question asks or mentions anything about the destruction of cells, which response do you use?

Answer 20

Cell-mediated.

Question 21

How do antibodies lead to the destruction of antigens?

Answer 21

They cause agglutination of the bacterial cells, in this way clumps of bacterial cells are formed so the pathogens are less spread out.
They then serve as markers that stimulate phagocytes to engulf the cells.

Question 22

What is a Monoclonal antibody?

Answer 22

A single type of antibody that can be cloned.

Question 23

Give 3 uses for monoclonal antibodies.

Answer 23

1. Targeting medication to specific cells.
2. Medical diagnosis.
3. Pregnancy testing.

Question 24

How are Monoclonal antibodies used in targeting medication to specific cell types?

Answer 24

One way is to produce a monoclonal antibody that is specific to the antigens of a cell (e.g. a cancer cell). Then the antibodies are given to a patient and attach themselves to the receptor on their cancer cells. This then blocks the chemical signals that stimulate their uncontrolled growth preventing the cancer to spread further.
Another way is to attach radioactive or cytotoxic drugs to the antibody so that when it is attached onto the cell it kills them. This is known as indirect monoclonal antibody therapy.

Question 25

What is the advantage of direct monoclonal antibody therapy as opposed to indirect?

Answer 25

Direct provides fewer side effects as it is not toxic and the antibodies are highly specific.

Question 26

How are Monoclonal antibodies used in medical diagnosis?

Answer 26

Usually used in a form of testing called the ELISA test.

Question 27

What does ELISA stand for?

Answer 27

Enzyme Linked Immunosorbant Assay.

Question 28

How does an ELISA test work?

Answer 28

1. Apply the sample to the surface, such as a slide, to which all the antigens in the sample will attach.
2. Wash the surface several time to removed any unattached antigens.
3. Add the antibody that is specific to the antigen and ensure it is immobilised. The antibodies will form an antibody-antigen complex with the antigens.
4. Wash the surface again to remove an excess antibodies.
5. Add a second antibody that will bind to the first antibody and has the enzyme attached to it.
6. Again wash the surface to remove excess antibodies.
7. Add the colourless substrate to the sample and if a colour change occurs the test result is positive.

This test can be used in medical diagnosis to diagnose for different conditions such as HIV etc.

Question 29

How are Monoclonal antibodies used in pregnancy testing?

Answer 29

Monoclonal antibodies found on the test are linked to coloured particles. If the hCG hormone (found in the placenta of a woman who is pregnant) is present in the urine it will bind to these antibodies to form a hCG-antibody-colour complex. This forms a line and a positive result is shown.

Question 30

What are some ethical issues around monoclonal antibodies?

Answer 30

1. Mice are used to produce both antibodies and tumour cells, so deliberately inducing cancer in mice is seen as an ethical issue and is against animal rights.
2. Drug trials raise an issue as it is unclear how a person may react and if it kills someone, that would be an issue.

Question 31

What are the 2 types of immunity?

Answer 31

Active and Passive immunity.

Question 32

What is the difference between active and passive immunity?

Answer 32

Active immunity is the immunity gained from direct contact with a pathogen or its antigens, whereas passive immunity is where the body receives antibodies initially from an outside source and requires no direct contact with the pathogen or its antigens.

Question 33

What are the different types of active immunity and explain the difference between them?

Answer 33

1. Natural active
2. Artificial active.

Natural active is where the antibodies are created naturally but the body, e.g. a body comes into contact with a disease and the body makes its own antibodies to fight it.
Artificial active is where an immune response can be made without someone suffering the symptoms of the disease e.g. by vaccinations.

Question 34

What are the different types of Passive immunity and explain the difference between them?

Answer 34

1. Natural Passive.
2. Artificial Passive.

Natural passive os where another sources passes on antibodies e.g a mother passes her antibodies to a child through breast milk.
Artificial passive is where antibodies are already made and can be used right away e.g. anti-venom contains antibodies that can be injected.

Question 35

What makes a successful vaccine?

Answer 35

1. Must be economically available.
2. Must have few, if any, side effects.
3. Must be easy to produce, store, transport.
4. Must produce some form of herd immunity.

Question 36

What is herd immunity?

Answer 36

Where a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population.

Question 37

Why can’t vaccines eliminate disease?

Answer 37

Numerous reasons however main 3:

1. Pathogen may mutate frequently, so the antigens change frequently and the vaccine becomes ineffective.
2. People may have objections e.g. due to religious reasons or false reports in the media.
3. Vaccines fail to induce immunity in certain individuals.

Question 38

How does HIV replicate?

Answer 38

1. HIV enters the bloodstream after infection and circulates the body.
2. A protein on the HIV readily binds to a protein called CD4. This protein is on a number of different cells, but HIV most commonly attaches to the helper T cells.
3. The protein capsid fuses with the cell-surface membrane. The RNA and enzymes of HIV enter the helper T cell.
4. The HIV reverse transcriptase converts the virus’s RNA into DNA.
5. This new DNA is moved into the helper T cell’s nucleus where it is inserted into the cell’s DNA.
6. The HIV DNA creates mRNA which then passes out the nucleus and undergoes translation to make more HIV particles.
7. These particles break away from the helper T cell, taking some of it’s cell-surface membrane to create the lipid envelope again.

Question 39

What does AIDS stand for?

Answer 39

Acquired Immune Deficiency Syndrome.

Question 40

How does HIV lead to AIDS?

Answer 40

HIV attacks the helper T cells and kills them. These are important to stimulate B cells and T cells, so without them the body cannot provide an immune response and a person can be susceptible to various infections.