Topic 5 - Cell Recognition and The Immune System

Question 1

What is the difference between a non-specific and specific defence mechanism?

Answer 1

Non-specific = response is immediate and the same for all pathogens.
Specific = response is slower and specific to each pathogen.

Question 2

What are some non-specific defence mechanisms?

Answer 2

• Skin = microorganisms cannot penetrate this barrier.
  Nose and gas exchange system = lined with cilia, bathed in mucus, = pathogens get stuck and waft up throat and swallowed.
• Stomach = produces hydrochloric acid = kills many pathogens.

Question 3

How does phagocytosis occur?

Answer 3

1) Cytokines of pathogen attract phagocyte towards pathogen.
2) Phagocytes attach themselves to surface of pathogen.
3) Phagocyte engulfs pathogen to form a phagosome.
4) Lysosomes move towards the phagosome and fuse with it.
5) Lysosome releases lysozymes into phagosome.
6) Enzymes hydrolyse the molecules making up the pathogen into smaller soluble products (pathogen is digested).
7) Antigens of pathogen are presented on the cell membrane of the phagocyte.

Question 4

What is an antibody?

Answer 4

A protein, specific to an antigen.

Question 5

How does the body recognise its own cells?

Answer 5

• Each type of cell has specific molecules on its surface that identify it.
• Specific 3D tertiary structure.

Question 6

What is humoral immunity?

Answer 6

1) Pathogens enters blood stream, phagocytosis occurs.
2) Specific B lymphocytes engulf foreign antigens.
3) Foreign antigen displayed on surface of B lymphocytes.
4) Activated T helper cells bind to presented foreign antigens.
5) Activated T helper cells activate B lymphocyte to divide by mitosis.
6) Clones differentiate to form plasma B and memory B lymphocytes.
7) Plasma B cells produce thousands of specific antibodies.
8) Antibodies released into blood stream and bind with antigens, forming antigen-antibody complexes. PRIMARY RESPONSE.
9) Memory B cells remain are are used for repeated invasions by same pathogen. SECONDARY RESPONSE.

Question 7

Why can influenza be caught multiple times, but it is unlikely for you to suffer chicken pox/measles more than once?

Answer 7

• Viruses evolve rapidly = antigens change
• Chicken pox has same antigens so secondary immune response works.

Question 8

What monomers form the heavy and light chains on an antibody?

Answer 8

Amino acids.

Question 9

What is the chemical bonds that join amino acids that form the heavy and light chains in an antibody?

Answer 9

Peptide bonds.

Question 10

How does bacteria produce symptoms of a disease?

Answer 10

• Release toxins which makes an individual ill.
• Damages cells and tissues.

Question 11

In pregnant woman, some antibodies cross the placenta from mother to foetus. These antibodies only provide short-term immunity for new born babies. Explain why these antibodies only provide short-term immunity.

Answer 11

Maternal antibodies are antigens that get destroyed by the foetal antibodies.

Question 12

What is a monoclonal antibody?

Answer 12

Single clone of B or plasma cells.

Question 13

How can monoclonal antibodies be used to make diagnosis?

Answer 13

• Bind to antigen of a disease so it can be detected in the blood.
• Only attaches to a specific antigen.

Question 14

What is a vaccine?

Answer 14

• Made from dead/inactive pathogens.
• Stimulates formation of memory cells and can provide ‘herd immunity’ carried out on large scale.

Question 15

Why don’t the vaccines made from pathogen antigens cause disease?

Answer 15

• Dead/inactive.
• Can’t reproduce inside body.

Question 16

How do vaccines stimulate formation of memory cells?

Answer 16

• Pathogen from vaccine engulfed via phagocytosis.
• T helper cells that present antigens stimulate the B lymphocyte which divides by mitosis.
• Differentiate into plasma B cell and a memory B cell.

Question 17

What are the differences between passive and active immunity?

Answer 17

Passive = introduction of antibodies from an outside source, antibodies not replaced by individual, short lived immunity.

Active = antibodies produced by individuals own immune system, antibodies replaced by individual, long lasting immunity.

Question 18

Why don’t vaccines fully elimate a disease?

Answer 18

• Fails to induce immunity in some.
• Some get disease immediately after vaccine.
• Pathogen may mutate frequently and antigens will change.

Question 19

What are some ethical issues associated with vaccines?

Answer 19

• Often uses animals in development.
• Some have side effects that cause long-term harm.
• On whom should vaccines be tested on?

Question 20

What are antigens?

Answer 20

Molecule that triggers an immune response.

Question 21

How does HIV infect and replicate inside body?

Answer 21

1) HIV enters bloodstream, circulates around body.
2) Attachment protein on HIV has complementary shape to, and binds with, the cell-surface membrane.
3) Protein capsid fuses with cell surface membrane, RNA and reverse transcriptase enter T helper cells.
4) RT catalyse the synthesis of DNA from viral RNA.
5) Viral DNA diffuses through nuclear pore into cell nucleus where it is inserted into cell’s own DNA, can remain here for years.
6) When DNA in cell nucleus becomes active, used to produce messenger RNA. mRNA contains genetic instructions for making new viral proteins.
7) mRNA diffuses out cell nucleus through nuclear pore. mRNA code provides instructions for cell’s protein synthesis mechanisms. Manufactures HIV particles.
8) HIV break away from T helper cells.

Question 22

Why would it be incorrect to say ‘an indivudla died from HIV or AIDS’?

Answer 22

A person dies from all their T helper cells being eradicated and then not being able to trigger an immune response when next infected by a pathogen.

Question 23

How is HIV treated?

Answer 23

• Currently no cure.
• Antiretroviral can help slow spread of virus in body = life expectancy is now the same as a non-infected person.

Question 24

How is HIV transmitted?

Answer 24

• Unprotected sexual intercourse.
• Blood transfusion.
• HIV infected mother to baby.
• Sharing needles.

Question 25

Why could a vaccine of HIV be very unsafe?

Answer 25

• Inactive HIV in vaccine may become active, could cause patient to become HIV positive.
• Attenuated virus may become harmful.