3.2 Cells and the Immune system

Question 1

Define antigens.

Answer 1

Antigens are molecules (usually proteins) that can generate an immune response when detected by the body.
Extra Info: Usually found on surface of cells and used by immune system to identify pathogens.

Question 2

What are the 4 main stages in an immune response?

Answer 2

1) Phagocytes engulf pathogens
2) Phagocytes activate T-cells
3) T cells activate B cells which divide into plasma cells
4) Plasma cells make more antibodies specific to antigen.

Question 3

What are specific and non-specific mechanisms involved in immunity?

Answer 3

Non-specific:
They DO NOT distinguish between one type of pathogen/antigen and another but respond to all in the same way.
Specific: They do distinguish between different pathogens/antigens. These responses are slower but give long lasting immunity.

Question 4

What’s an antigen?

Answer 4

Antigens are large molecules recognised as non-self by the immune system which stimulates an immune response including antibody generation.

Question 5

Give details of how phagocytosis works. There are about 6 main points to cover.

Answer 5

In blood, white blood cells that carry out phagocytosis are called phagocytes - this is a non-specific response.
• Chemical products of pathogens are dead, damaged or abnormal cells act as attractants causing a phagocyte to move towards the pathogen.
• Phagocyte have several receptors on CSM - recognise and attach to chemicals on the surface of the pathogen.
• Engulf pathogen –> Forms vesicles –> Called Phagosome.
• Lysosomes move towards the vesicle and fuse with it.
• Digestive, hydrolytic enzymes called lysozyme in lysosome destroy ingested bacteria - hydrolysis of cell wall. Process same as that for digestion of food into intestine, names hydrolysis of large insoluble molecules into smaller soluble ones.

Question 6

What does phagocyte do after phagocytosis?

Answer 6

Presents the antigens on the plasma membrane

Question 7

What are the specific immune responses?

Answer 7

Specific immune response depends on type of white blood cell called a lymphocyte.

Question 8

What are the 2 types of lymphocytes called? Give some info on them

Answer 8

T lymphocytes and B lymphocytes. They’re formed in the bone marrow and develop and mature in different places. Have millions of different types of B and T lymphs. Each type recognises one.

Question 9

What’s cell mediated immunity?

Answer 9

This is an immune response that doesn’t involve antibodies. But rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

Question 10

How do T - Lymphocytes work?

Answer 10

T lymphocytes can distinguish invades cells from normal cells because:

• Phagocytes that have engulfed and hydrolysed a pathogen present some of pathogens antigens on own CSM.
• Body cells –> invaded by virus–> Present viral antigens on CSM
• Transplanted cells from same species –> different antigens on CSM
• Cancer cells different from normal cells –> present antigens on the CSM.

Question 11

What are APCs (antigen presenting cell) and how are they used?

Answer 11

Present antigens of other cells on it’s own CSM as T-lymphs only respond to antigens on OWN body cells - This is called cell-mediated immunity/ cellular response (because it’s on its own cells). There’s a vast number of T-lymphs - each responds to different antigens.

Question 12

What are the different stages of the response of T-lymphocytes? i.e. describe a cellular response.

Answer 12

1) Pathogens invade body cells/taken in by phagocytes.
2) Phagocyte places antigens from pathogen on its very own CSM
3) Receptors on T-helper cells fit exactly onto the antigen.
4) Attachment activates T cells to divide rapidly –> form clone of genetically identical cells.
5) Cloned T cells:
- Develop into memory cells–> enable rapid response to future infection by the same pathogen.
- Stimulate phagocytes to engulf pathogens by phagocytosis.
- Stimulates B cells to divide and secrete antibody.
- Activate cytotoxic t cells.

Question 13

What happens after T cell activates?

Answer 13

Mitotic division starts to occur to form clones that are genetically identical cells. The cloned cells then:

• Activate T killer cells.
• Form T memory cells
• stimulate to divide to form plasma cells and secrete antibodies
• stimulate phagocytes to engulf pathogens

Question 14

How do T killer cells work?

Answer 14

• T killer cells get activated
• activated when detects something that is non-self, may be infected.
• Release perforin
• makes holes in the CSM
• Freely permeable to substances and eventually dies from water loss

Question 15

What does humoral immunity involve? Why is it called humoral immunity?

Answer 15

Humoral immunity involves antibodies which are soluble in the blood tissue fluid of the body and tissue fluid can also be called humour hence the name humoral immunity.

Question 16

How do B cells/B lymphocytes function? I.e. What happens when a non-self ANTIGEN enters the blood and meets a b cell?

Answer 16

1. There’s only one B cell complementary to the antigen.
2. The B cell binds to foreign antigens & processes them.
3. Helper T cells (activated earlier) bind to these processed antigens and ACTIVATE B cells.
4. The activated B cell divides by mitosis –> Forms clones of B cells that are genetically identical.
5. Cytokines released by Th cause some B cells to form plasma cells –> This is called clonal selection. These produce/secrete antibodies (specific in shape to a foreign antigen), MONOCLONAL antibodies.
6. The antibody binds to the non-self antigens and destroys them (primary immune response)
7. Some B cells develop into memory B cells. These are responsible for primary immune response giving long-lasting immunity.

Question 17

What are monoclonal antibodies?

Answer 17

Many different B cells from clones, each of which produces ONE specific antibody, these antibodies are referred to as MONOCLONAL ANTIBODIES.

Question 18

What are plasma cells and what do they do?

Answer 18

Plasma cells are basically B and T lymphocytes that have differentiated to become plasma cells. The function of plasma cells is to produce antibodies that are complementary to an antigen.

Question 19

What are the 3 main organelles found in plasma cells?

Answer 19

• 80s ribosomes
• mitochondria - release energy for ATP for protein synthesis.
• Golgi apparatus - modify proteins chemically.

Question 20

What’s an antibody?

Answer 20

An antibody is a protein that B cell secretes in response to a non-self antigen.

Question 21

Describe the structure of an antibody.

Answer 21

• An antibody is a y shaped molecule
• Made up of 4 polypeptide chains, two long or two heavy chains and two short or light chains held together by disulfide bridges/bands.
• Variable regions are different on different antibodies and bind to non-self antigens.
• The variable region is a sequence of amino acids that form a specific 3D shape - bind to a single type of antigen with a complementary molecular shape.
• Y shape has linked a hinge, allows arms to flex so variable region can change mold to fit more precisely around antigen.

Question 22

What is the purpose of an antibody and how does it work to kill foreign pathogens?

Answer 22

Antibody’s variable region should be complementary in shape to a foreign antigen. Due to the complementary shape, able to form an antigen-antibody complex. The antibody is flexible and can bind to another antigen on another a pathogen - can, therefore, cause agglutination. Agglutination makes it easier for phagocyte to consume pathogen.

Question 23

Other than causing agglutination, what else can antibodies do?

Answer 23

Antibodies are able to neutralise toxins.

Neutralising toxins can prevent symptoms.

Question 24

Define antigen, antibody agglutination and neutralisation.

Answer 24

Antigen - A large molecule that is recognised as non-self by the immune system and stimulates an immune response including the production of antibody.

Antibody - (immunoglobulin) is a protein that a B lymphocyte cell secretes in response to a non-self antigen. Every antibody is a y-shaped molecule, made of 4 polypeptide chains.

Agglutination - stick the pathogens by binding antigens and clumping them together.

Neutralisation - neutralise toxins/stop pathogens from entering cells.

Question 25

Define active immunity and passive immunity and give examples of both.

Answer 25

Active: Stimulation of antibody production by the individual’s own immune system - e.g. when a pathogen enters the body, vaccination

Passive immunity: The introduction of antibodies from an outside source e.g. antivenom, antibodies from breastmilk.

Question 26

How are plasma cells involved in a primary and secondary immune response? What’s the difference between primary and secondary immune response?

Answer 26

Plasma cells produce monoclonal antibodies specific to the antigen. Memory cells remember the shape of the antibodies complementary to the foreign antigen - this occurs in the primary immune response. In the secondary immune response, there are more memory cells that are complementary to the antigen - they can differentiate to plasma cells and produce more antibodies faster. The secondary immune response is a stronger and faster immune response.

Question 27

What’s the structure of HIV

Answer 27

• attachment protein
• two strands of DNA/RNA
• protein coat
• the envelope of a lipid bilayer with glycoproteins
  (- Reverse transcriptase)

Question 28

How does HIV enter and Replicate in Th cells? (6 main points)

Answer 28

HIV’s attachment protein attaches on to the CSM of the cell and membrane fuses.

1. HIV viruses membrane fuses with the cell’s membrane of the T helper cell by attaching to CD4 Receptor
2. Reverse transcriptase reverses the RNA into DNA.
3. The single-stranded DNA becomes double-stranded by DNA replication. It uses the enzyme DNA polymerase in the cell.
4. Then, viral DNA is integrated into the DNA of the cell. This can remain in the cell DNA for many years - it can undergo replication.
5. Then the cell undergoes DNA translation and DNA transcription. DNA is made into RNA for replication. RNA is translated by tRNA and amino acids assembled.
6. Viral RNA can assemble the proteins to make the virus protein and the virus is reconstructed. It can then leave the cell and be released into the bloodstream which from here it can infect other cells.

Question 29

How is HIV spread?

Answer 29

• sexual intercourse
• blood transfusion from an infected person given to an uninfected person.
• intravenous drug abuser shares a needle with an infected person.
• From an infected mother to an unborn baby.

Question 30

How does HIV cause disease?

Answer 30

Infects and destroys a type of T helper cells. WIthout T helper cells being activated B cells and T cells left alone.

Question 31

HIV can only infect T helper cells. Explain why.

Answer 31

T helper cells have specific receptors in their CSM that the protein on the surface of HIV can attach to.

Question 32

Why are T helper cells important in the immune system?

Answer 32

T helper cells are needed to stimulate T and B cells to divide and B cells to secrete antibodies. Without T helper cells, B cells will not be activated and no antibodies are produced. Hence a person’s ability to produce antibodies to kill a pathogen is reduced. Also, cytotoxic T cells are not stimulated.

Question 33

How does HIV cause symptoms of AIDS?

Answer 33

HIV can cause symptom of aids (acquired immune deficiency syndrome) is set of symptoms in final stage of HIV infection.

-occurs when virus destroyed the immune system, by destroying helper T cells causing B cells to not function properly - leave person immunocompromised

suffer from disease not normally cause problem called opportunistic diseases.

Question 34

Learn The use of monoclonal antibodies in:
• targeting medication to specific cell types by attaching a
therapeutic drug to an antibody
• medical diagnosis.

Answer 34

I cba

Read over in revision guide/textbook

Question 35

Ethical issues associated with the use of vaccines and monoclonal
antibodies

Answer 35

Read over in revision guide/textbook

Question 36

Describe how antibodies are Used in elisa test (for this example take test for prostate cancer - Prostate cancer is a cancer of the prostate gland so occurs in men. One way is to test for antigen PSA. Men with this have high conc. of PSA in blood)

Answer 36

Antibodies to PSA bound to well in test plate. Blood from patient added. PSA binds to antibody - other antigens don’t bind. Antibody with enzyme attached is added. Only bind to first AB if PSA present
Second AB binds to AB with PSA attached. Well is wased to remove unbound ABs. Colourless substrate is added. Enzymes convert colourless substrate to coloured product.