Cells And The Immune System

Question 1

What is an antigen?

Answer 1

A molecule (usually a protein) that can generate an immune response when detected by the body and is found on the surface of cells.

Question 2

What are the 4 things antigens allow the immune system to identify?

Answer 2

1. Pathogens:
   • Microorganisms that cause disease.
2. Abnormal body cells:
   • Contain abnormal antigens on their surface, generating an immune response e.g. cancerous/pathogen-infected cells.
3. Toxins (poisons):
   • Molecules, not cells.
4. Cells from other individuals of same species:
   • e.g. organ transplant, cells contain different antigens from your own, foreign antigens generate immune response. This response leads to the rejection of transplanted organs if drugs are not taken to suppress the recipients immune system.

Question 3

What is a phagocyte?

Answer 3

A macrophage that carries out phagocytosis.

Question 4

What type of immune response is phagocytosis?

Answer 4

Non-specific immune response, meaning the process is the same regardless of the non-self cell detected.

Question 5

Describe the full process of phagocytosis:

Answer 5

1. Phagocyte recognises antigens around pathogen/non-self cell.
2. Cytoplasm of phagocyte moves around pathogen, engulfing it. Pathogen is contained in phagocytic vacuole in the cytoplasm of the phagocyte.
3. Lysosome fuses with phagocytic vacuole, lysozymes break down pathogen.
4. Phagocyte presents pathogens antigens on its surface to activate more immune system cells, phagocyte acts as antigen-presenting cell.

Question 6

What are T-lymphocytes?

Answer 6

A type of white blood cell made in the bone narrow and matured in the thymus, which are responsible for the cell mediated response.

Question 7

What type of immune response is the cell-mediated response?

Answer 7

A specific immune response: responds to an exact antigen/cell-surface molecule.

Question 8

What are antigen-presenting cells (APC’s):

Answer 8

Cells that present a non-self antigen e.g. phagocytes present destroyed pathogens antigens on their surface to activate more immune system cells.

Question 9

Describe the full process of the cell-mediated response:

Answer 9

1. Once phagocyte has destroyed pathogen, it presents the pathogens antigens on its surface, becoming an APC, APC triggers cell-mediated response.
2. Helper T-Cells contain receptors on their surface which attach to antigens on APCs.
3. Once attached, this activates helper T-Cell to divide by mitosis to replicate and make a large no. of clones.
4. The cloned helper T-cells differentiate into different cells:
   - Some remain T-Helper cells to activate B-lymphocytes.
   - Some stimulate macrophages for phagocytosis.
   - Some differentiate into T-memory cells for that shaped antigen.
   - Some differentiate into cytotoxic T-cells which destroy abnormal/infected cells.

Question 10

How to cytotoxic T-Cells destroy abnormal/infected cells?

Answer 10

By releasing a protein called perforin which imbeds in the cell-surface membrane and makes a pore to allow any substances to enter or leave the abnormal/infected cell, causing cell death.

Question 11

What is the most common example of cytotoxic T-cells releasing perforin to destroy abnormal/infected cells.

Answer 11

During viral infection: body cells are sacrificed to prevent viral replication.

Question 12

What are B-lymphocytes?

Answer 12

A type of white blood cell made and matured in bone marrow.

Question 13

What type of immune response is the humoral response?

Answer 13

Specific immune response.

Question 14

Describe the full process B-cell activiation:

Answer 14

1. B-cells have antibodies on their surface, complementary to specific antigens.
2. Antigens in the blood collide with their complementary antibodies on a B-cell: the B-cell takes in the antigen by endocytosis and presents it on its cell-surface membrane.
3. When the B-cell collides with a T-Helper cell receptor, this activates the B-cell to go through clonal expansion and differentiation (clonal selection).
4. B cells undergo mitosis to make a large no of cells: these differentiate into plasma cells and B-memory cells.
   - plasma cells make antibodies
   - B-memory cells divide by mitosis to produce plasma cells rapidly when re-infected with the same pathogen to produce antibodies rapidly.

Question 15

What is the difference between plasma cells and B-memory cells.

Answer 15

B-memory cells are very long lived, whereas plasma cells are short lived.

Question 16

Active immunity:

Answer 16

• Memory B-cells divide by mitosis to produce plasma cells rapidly when re-infected with the same pathogen.
• This means antibodies are produced so rapidly that the pathogen is destroyed before any symptoms occur.

Question 17

Agglutination

Answer 17

• Antibodies are flexible and can bind to multiple antigens to clump them together.
• This makes it easier for phagocytes to locate and destroy pathogens.

Question 18

What are lymphocytes?

Answer 18

Cells that are able to identify self and non-selfs cells.

Question 19

How do lymphocytes recognise cells?

Answer 19

• Lymphocytes are made when you’re a foetus, when you’re a foetus you are unlikely to be exposed to any cells other than self-cells.
• The lymphocytes complementary to the antigens on self-cells will die or production will be suppressed. This is to prevent your lymphocytes from attacking your own cells.
• As a result of this you don’t have many lymphocytes complementary to the antigens on your self-cells, the only remaining lymphocytes are complementary to pathogenic/non-self cells.

Question 20

Antigen variability:

Answer 20

• Pathogens DNA mutates frequently; if a mutation occurs in a gene which codes for that antigen then the shape of the antigen will change.
• Any previous immunity is no longer effective as all the memory cells in the blood have a memory of the old antigen shape.

Question 21

Describe and explain the function of the different parts of the HIV virus:

Answer 21

• Core - contains genetic material (RNA) and the enzyme reverse transcriptase, which is needed for viral replication.
• Capsid - Outer protein coat
• Envelope - Extra outer layer made out of membrane from the host’s cell membrane.
• Protein attachments - on the exterior of the envelope to enable the virus to attach to host helper T-cells.

Question 22

Describe the process of HIV replication in helper T-cells:

Answer 22

• HIV virus is transported around the blood until it attaches to a CD4 protein on the helper T-cells surface.
• The HIV protein capsule fuses with the helper T-cell membrane, allowing RNA and enzymes from HIV to enter the helper T-cell.
• The HIV enzyme reverse transcriptase copies the viral RNA into a DNA copy and moves to the nucleus of the helper T-cell (this is why its called a retrovirus)
- Here mRNA is transcribed and the helper T-cell creates viral proteins to make new viral particles.

Question 23

What does HIV positive mean?

Answer 23

When someone has been infected with HIV.

Question 24

How does aids occur?

Answer 24

• When the replicating HIV viruses in the helper T-cells interfere with their normal functioning of the immune system.
• Its the destruction of the immune system that leads to death, not the HIV directly.

Question 25

What is a monoclonal antibody?

Answer 25

A single type of antibody that can be isolated and cloned.

Question 26

Give three uses of monoclonal antibodies:

Answer 26

1. Medical treatment e.g. cancer 2. Medical diagnosis e.g. hepatitis 3. Pregnancy tests

Question 27

Targeted medication: Direct monoclonal antibody therapy:

Answer 27

• Some types of cancer can be treated using monoclonal antibodies with binding sites complementary to antigens on the outside of the cancer cells. • While the antibodies are bound to the cancer antigens, this prevents any chemicals binding to the cancer cells that enable uncontrolled cell division. • Therefore, monoclonal antibodies prevent cancer cells from growing, and as they are only complementary to the cancer cells, they don’t harm any other cells.

Question 28

Targeted medication: Indirect monoclonal antibodies therapy:

Answer 28

•Some types can be treated using monoclonal antibodies with binding sites complementary to the antigens on the surface of cancer cells with drugs attached to them e.g. cytotoxic drugs. • The cancer drug is delivered directly into the body and kills the cancer cell, and reduces the harmful side effects that traditional chemotherapy and radiotherapy produce.

Question 29

How do pregnancy tests (an ELISA test) use the presence of a hCG protein in urine to detect pregnancy?

Answer 29

1. The pregnancy test contains mobile antibodies complementary to the hCG protein in urine, which contain coloured dyes attached to them. 2. A second antibody complementary to the antigen is immobilised, the antibody containing the hCG protein attaches to it. 3. A third antibody complementary in shape to the first antibody is immobilised (regardless if the test is positive or negative).

Question 30

How do you make an ELISA test for medical diagnosis?

Answer 30

1. Add the patient’s test sample to the base of a beaker. 2. Wash to remove any unbound test sample. 3. Add an antibody complementary in shape to the antigen that’s presence is being tested for to the test sample. 4. Wash to remove any unbound antibody. 5. Add a second antibody complementary in shape to the first antibody and binds to the first, with an enzyme attached to it. 6. Add the substrate for the enzyme (which is colourless), the substrate will produce coloured products in the presence of the enzyme. 7. The presence of the colour indicates the presence of the antigen, and the intensity of the colour indicates the quantity of antigen present.

Question 31

What are the ethical issues behind monoclonal antibodies?

Answer 31

Monoclonal antibodies require mice to make the antibodies and tumour cells, which leads to ethical debates whether this use of animals is justified to enable better cancer treatments for humans and to detect/diagnose diseases.

Question 32

What is passive immunity?

Answer 32

When the antibodies are introduced to your body e.g. through an injection.

Question 33

What is the disadvantage of passive immunity?

Answer 33

No long term immunity.

Question 34

Name one importance of passive immunity?

Answer 34

Breastfeeding

Question 35

What is active immunity?

Answer 35

When the immune system makes the antibodies in response to exposure from the pathogen or its antigens.

Question 36

State and describe the sub divisions of active immunity:

Answer 36

• Natural active immunity - Following up from an infection, the body creates its own antibodies and memory cells. • Artificial active immunity - Following the introduction of a weakened version of the pathogen or its antigens via a vaccine.

Question 37

How does a vaccine work?

Answer 37

• Small amounts of dead/weakened pathogen; or introduction of its antigens in the mouth or by injection. • Exposure to the antigens activates the B-cell to go through clonal expansion and differentiation (clonal selection). • B-cell undergoes mitosis to produce a large no. of cells: these differentiate into plasma cells and B-memory cells. - plasma cells produce antibodies - B-memory cells divide by mitosis rapidly and differentiate into plasma cells when re-infected by the same pathogen, resulting in rapid antibody production.

Question 38

What is herd immunity?

Answer 38

• If enough of the population are vaccinated this means the pathogen can’t spread easily between the population. • This provides protection for those who aren’t already vaccinated e.g. those too ill for vaccination, or those too young.