2. Immune System - phagocytes, B cells and T cells

Question 1

Antigen Presentation

Answer 1

Question 2

Macrophage to Death`

Answer 2

Question 3

Explain the increase in specific plasma cells and antibody in people infected with the Ebola virus

Answer 3

1.Antigen/glycoprotein on Ebola binds to/stimulates (a specific) B cell;
Accept correct reference to stimulation of B cells by T cells

2.(Binding causes) replication/cloning of B cell
;Accept replication/cloning of plasma cell

;3.Plasma cells/B cells release/produce antibodies;

Question 4

Explain how a blood transfusion from a patient recently recovered from Ebola may be an effective trea

Answer 4

1.Lots of antibodies (against Ebola) in recovered patient

;2.Transfusion/plasma contains antibodies;Ignore reference to cells

3.Antibodies (specific so) will bind with (Ebola) antigen;

4.(In recipient) virus destroyed/cannot

Question 5

A high mutation rate makes it difficult to develop a vaccine (line 11).Explain why

Answer 5

1.(High mutation rate leads to) antigens change/antigenic variability;Accept (high mutation rate leads to) changes in base sequence coding for antigen;

2.Vaccine contains specific antigen;

3.Antibodies not complementary to (changed) antigen / won’t bind to (changed) antig

Question 6

Using your knowledge of the structure of the cell-surface membrane, suggest how LDL enters the cell

Answer 6

1. Lipid soluble / hydrophobic2. Enters through (phospholipid) b

Question 7

Explain how the monoclonal antibody would prevent the regulator protein from working

Answer 7

Any two from:

1. (Monoclonal antibody) has a specific tertiary structure / variable region / is complementary to regulator protein
   Do not award MP1 if reference to active site.
2. Binds to / forms complex with (regulator protein)
   “It” refers to monoclonal antibody in MP1 and MP2
3. (So regulator protein) would not fit / bind to the receptor / is not complementary to receptor

Question 8

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

Answer 8

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

Question 9

Differences between B cells and T cells

Answer 9

Question 10

B Cells and the Humoral Immune System

Answer 10

The body contains millions of different B-lymphocytes (another type of white blood cell)
Each one is covered in antibodies
When antigens enter the body there will be a B- cell with complementary antibodies.
This B cell will combine with the antigen.
This binding, together with substances from T cells activates the B cells
They divide rapidly by mitosis to form daughter cells- clonal selection
Some will form plasma cells which release antibodies
A small number will remain as memory cells

Question 11

Primary Response

Answer 11

Occurs when antigen enters body for the first time
It is slow as there aren’t many B cells initially that can make the antibody
Person will show symptoms until there are sufficient antibodies to overcome the infection
After exposure to an antigen both T and B cells produce memory cells
Memory cells are retained in the body for a long time
The person is now immune and has the ability to respond quickly to a second infection

Question 12

Secondary Response

Answer 12

If the same pathogen enters the immune system will produce a quicker, stronger immune response
Clonal selection happens faster
Memory B cells divide to form plasma cells which produce the right antibody
Memory T cells are activated to kill the cell carrying the antigen
Secondary response often gets rid of pathogen before the person shows any symptoms

Question 13

Phagocytosis

Answer 13

Carried out by neutrophils and macrophages
Shortly after engulfing bacteria neutrophils die as they have used up a lot of energy
Macrophages are longer lasting. After they have engulfed a bacteria they present some of the foreign antigens on their own membrane. They become antigen presenting cells (=APC)
Cells infected by viruses can also be APCs- this sends a signal to other cells that it should be destroyed.
Phagocytes are able to attack and destroy almost any foreign cell or material that enters the body
The response is non- specific

Question 14

Clonal Selection

Answer 14

Question 15

Active immunity vs Passive

Answer 15

Active -Your immune system makes antibodies in response to an antigen
It can be natural- you become immune after catching a disease
Or artificial- you become immune after being vaccinated

Passive - You are given antibodies from a different organism
It can be natural- via placenta/breast milk
Or artificial- you are injected with antibodies directly e.g. rabies/ tetanus

Question 16

How does a vaccine work?

Answer 16

1. Disease causing antigens are introduced into the body- by injection or orally
2. Antigens stimulate immune response
3. Response is slight as only a small amount of antigen has been introduced. If the pathogen is used it has been attenuated to prevent it multiplying
4. Memory cells are produced
5. These remain in blood and allow a greater, more immediate response to future infections of that antigen

Question 17

Why does vaccination not eliminate a disease?

Answer 17

Vaccination fails to induce immunity in certain individuals
Someone might develop the disease immediately after the vaccination before immunity has developed
The pathogen may mutate. The vaccine would then become ineffective. (antigenic variability)
There may be too many varieties of a particular pathogen
Some pathogens “hide” from the immune system e.g. inside cells
People may refuse vaccination for a number of reasons

Question 18

Ethical issues…

Answer 18

Vaccines are tested on animals prior to human use
Sometimes animal based substances may be used to produce a vaccine
Testing vaccines can be risky
May be side effects- scientists have to gather evidence in order to validate (confirm) theories. Other scientists may try to reproduce the results

Question 19

Monoclonal antibodies

Answer 19

Antibodies produced from a single group of genetically identical B- cells (plasma cells)
They are all identical in structure.
Monoclonal antibodies are useful in treating illnesses and in medical diagnosis

Question 20

Pregnancy tests

Answer 20

The urine of pregnant women contains the hormone-human chorionic gonadotropin (hCG)
The application area on the pregnancy testing kit contains antibodies bound to a coloured bead
The hCG if present in the urine will bind to the antibody forming an antigen-antibody complex
The strip will turn blue due to the hCG binding to the antibody attached to the result area

Question 21

Cancer treatment

Answer 21

Cancer cells have antigens called tumour markers that are antigens not found on body cells
Monoclonal antibodies are made which bind to these tumour markers
Anti cancer drugs are attached to the antibodies
The monoclonal antibodies will attach to the tumour markers on the cancer cells
The drug accumulates where there are cancer cells

Question 22

direct ELISA

Answer 22

1. The antigen from the patient is attached to the inside of a well in a well plate
2. A detection antibody (with attached Enzyme) that is complementary to the antigen is added
3. The antibody will bind to the antigen and becomes immobilised
4. The well is washed. To remove unbound antibody/enzyme complex; which would give a false positive
5. A substrate is added
6. If the enzyme is present then the substrate will react to give a colour change
7. This is a positive result for the antigen

Question 23

Indirect ELISA

Answer 23

HIV antigen attached to well in well plate
Patient’s plasma is added. If HIV antibodies are present they will bind to antigen due to complementary nature
Wash To remove unbound antibodies
Second antibody is added. It is specific for first antibody. It has an enzyme attached
Wash To remove unbound antibodies
Substrate is added. It will only be converted to coloured product if enzyme is present