Section 2: Immunology

Question 1

What is an antigen?

Answer 1

• Recognised as non-self/ foreign which can stimulate an immune response and lead to the production of antibodies
• Proteins on the surface of cells

Question 2

What do antigens allow the immune system to identify?

Answer 2

• Pathogens
• Cells from other organisms of the same species
• Abnormal body cells
• Toxins released from bacteria

Question 3

What is phagocytosis?

Answer 3

• Phagocyte recognises foreign antigen on pathogen and binds to the antigen
• Phagocyte engulfs pathogen by surrounding it with its cell-sirface membrane
• Pathogen contained in vacuole/vesicle/phagosome in cytoplasm of phagocyte
• Lysosome fuses with phagosome and releases lysozymes into the phagosome
• These hydrolyse/digest the pathogen
• Phagocyte becomes antigen presenting and stimulates specific immune response

Question 4

How do T-lymphocytes respond to foreign antigen?

Answer 4

• T-lymphocytes recognise antigen presenting cells in phagocytosis
• Specific T helper cell with receptor complementary to specific antigen binds to it, becoming activated and dividing rapidly

Question 5

What are the types of cells that T helper cells activate?

Answer 5

• Stimulate B-cells for the humoral response
• Stimulate cytotoxic T cells to kill infected cells by producing perforin
• Stimulate phagocytes to engulf pathogens by phagocytosis

Question 6

What is the response of B-lymphocytes in humoral response?

Answer 6

• Clonal selection
  
  • Specific B-cell binds to APC and releases cytokines. Divides rapidly by mitosis to form clones
• Some become B plasma cells for primary response
• Some become B memory cells - secondary immune response

Question 7

What is the primary response?

Answer 7

• Produces antibodies slower and at lower concentration because
  
  • Not many B-cells available to make antibody
  • T helpers need to activate B plasma cells to make antibodies - take time

Question 8

What is the secondary response?

Answer 8

• Produces antibodies faster and at higher concentration because
  
  • B and T memory cells present
  • B memory cells undergo mitosis quicker

Question 9

What are antibodies?

Answer 9

• Quaternary structured protein
• Secreted by B - lymphocytes
• Binds specifically to antigens forming an antigen-antibody complex

Question 10

Describe and explain how the structure of an antibody relates to its function.

Answer 10

• Primary structure of protein
  
  • Determines folds in secondary structure determines specific tertiary structure and position of bonds
• Quaternary structure comprised of 4 polypeptide chains
  
  • Enables specific shaped variable region which is complementary to the antigen
  • Enables antigen-antibody complex to form

Question 11

How do antibodies work to destroy pathogens?

Answer 11

• Binds to 2 pathogens at a time forming an antigen-antibody complex
• Enables antibodies to clump the pathogens together - agglutination
• Phagocytes bind to antibodies and phagocytose many pathogens at once

Question 12

What is a vaccination?

Answer 12

• Injection of antigens
• From dead and weakened pathogens
• Stimulates memory cells
• Can lead to symptoms because pathogen can be active and reproduce to produce toxins

Question 13

How are vaccines used to protect people?

Answer 13

• Memory cells produced
• On reinfection to the same antigen, secondary response therefore antibodies produced faster
• Leads to destruction

Question 14

How do vaccines lead to herd immunity?

Answer 14

• Large proportion of population vaccinated
• Makes it more difficult for pathogen to spread
  
  • More immune so fewer to spread
  • Fewer susceptible

Question 15

What are the differences between active and passive immunity?

Answer 15

• Active: Initial exposure to antigen. Passive: No exposure to antigen
• Active: Antibody is produced and secreted by plasma cells. Passive: Antibody introduced into body from another organism (breast milk/ placenta)
• Active: Slow. Passive: Fast
• Active: Long term immunity. Passive: Short term immunity

Question 16

What are the ethical issues surrounding vaccines?

Answer 16

• Tested on animals before humans - can feel pain
• Tested on humans - volunteers put themselves in risk. Vaccine may not work
• Can have side effects
• Expensive

Question 17

What is the effect of antigen variability on disease?

Answer 17

• Change in antigen shape
• Not recognised by B memory cell - no plasma cells/ antibodies
• Not immune
• Must undergo primary immune response

Question 18

What is the effect of antigen variability on disease prevention?

Answer 18

• Change in antigen shape
• Existing antibodies can’t bind to changed antigens - no antigen-antibody complex

Question 19

What are the use of monoclonal antibodies?

Answer 19

• Antibody produced from a single group of genetically identical B-cells
• Bind to specific antigen - has a variable region with a specific tertiary structure

Question 20

How are monoclonal antibodies used in treating cancer cells?

Answer 20

• Monoclonal antibodies made to be complementary to antigens specific to cancer cells
• Anti-cancer drug attached to antibody
• Antibody binds to cancer cells
• Delivers attached anti-cancer drug directly to specific cells so fewer side effects

Question 21

How are Monoclonal antibodies used in pregnancy tests?

Answer 21

• Pregnant women have hormone hCG in their urine
• There are 3 different antibodies parts
• If pregnant: hCG binds to antibodies in application area (complex). Then binds to antibodies at position 2 = blue line
• Not pregnant: No hCG so doesnt bind to antibodies in application area so not binding at position 2. Binds to position 3 = control