Immunity

• Antigen


  a protein that stimulates an immune response
• What kind of cells can the immune system identify?

  - Pathogens

  - Cells from other organisms of the same species

  - Abnormal body cells

  - Toxins
• Pathogen

  a microorganism that causes disease
• What do pathogens do to cause disease?

  - Release toxins

  - Kill/damage cells
• What is the process of phagocytosis?

  1. Phagocyte receptors bind to antigens on the pathogens cell-surface membrane, recognising it as foreign

  
  

  2. Engulfs pathogen, containing it in a phagosome

  
  

  3. Lysosome containing lysozyme enzymes fuses with phagosome, releasing enzymes into the phagosome

  
  

  4. Lysozymes digest and hydrolyse the pathogen

  
  

  5. Antigens are presented on outside of the phagocyte - antigen presenting cell

  
• How does phagocytosis trigger the immune system?

  Phagocyte presents the antigen on its cell-surface membrane so other immune cells can bind and be activated
• What is the process of the cellular response? (Specific)

  1. T helper cell with specific complementary shaped receptor binds to antigen on antigen-presenting cell (eg phagocyte)

  
  

  2. Activates Th cell to divide and multiply by mitosis producing genetically identical clones

  
  

  3. Clones:

  - become memory cells

  - stimulate phagocytes

  - stimulate B cells

  - activate cytotoxic T cells

  
• What do cytotoxic T cells do?

  Produce perforin which hydrolyses cell-surface membrane

  
  

  Makes holes in membrane (PERFORates it) so freely permeable
• What is the process of the humoral response?

  1. B cell with specific complementary antibody binds to complementary antigen on pathogen - forms antibody-antigen complex

  
  

  2. Antigen enters by endocytosis and antigen presented on surface

  
  

  3. tH cell binds activating B cell so divides by mitosis producing clone plasma cells - CLONAL SELECTION

  
  

  4. Plasma cells secrete specific complementary antibodies - MONOCLONAL ANTIBODIES

  
  

  5. Some produce memory cells
• Antibody

  a protein specific to an antigen produced by plasma cells
• What is the structure of an antibody?

  3 regions:

  - Variable

  - Constant

  - Hinge

  
  

  Consists of 4 polypeptide chains connected by disulfide bridges

  
• Why are antibodies specific?

  The variable region is different on each antibody

  - specific unique tertiary structure

  - hence different amino acid sequence

  - complementary to one specific antigen

  - binds to form Ab-Ag complex
• How do antibodies aid the immune response?

  1. Specific antibody bind to complementary specific antigen, forming antigen-antibody complex

  
  

  2. Antibody has two binding sites hence clumps pathogens together - AGGLUTINATION

  
  

  3. More easily engulfed and digested by phagocytes

  
• Describe the primary response?

  Initially few/no B cells producing complementary Ab (no memory cells)

  
  

  Antigen on pathogen stimulates immune response and complementary antibody production

  
  

  SLOW because full immune response must be conducted

  
  

  Produces memory cells

  
• What is the role of memory cells in the secondary response?

  Memory cells recognise pathogen and become activated

  
  

  Rapidly produce MORE antibodies

  
  

  FASTER because memory cells already present

  
  

  Pathogen killed before harm caused - IMMUNITY

  
• How do vaccines work?

  1. Vaccines contain dead or weakened pathogens

  
  

  2. Produce memory cells

  
  

  3. On second exposure memory cells produce antibodies

  
  

  4. RAPIDLY produce MORE antibodies

  
  

  5. Antibodies cause pathogen destruction

  
• What is herd immunity?

  - large proportion of population vaccinated

  - most people immune

  - less chance unvaccinated person coming into contact with infected individual
• What is active immunity?

  Immune system makes own antibodies (by plasma cells) resulting in the production of memory cells and long term immunity
• What is an example of natural active immunity?

  Immunity after primary infection
• What is an example of artificial active immunity?

  After vaccination containing antigen
• Why is active immunity long term?

  Antibodies produced in response to antigen and hence memory cells
• What is passive immunity?


  Antibody introduced to body from outside hence no memory cells and only short term immunity
• What is an example of natural passive immunity?


  Mother to baby via breast-feeding or placenta
• What is an example of artificial passive immunity?


  Antivenom
• Why is passive immunity short term?


  Antibody broken down
• How does antigen variation cause multiple infections?


  Antigen changes - diff tertiary structure

  
  

  Memory B and T cells no longer recognise

  
  

  Antibodies used previously are no longer complementary to the new antigen
• Compare active and passive immunity

  Active

  - Ag exposure

  - Takes a while to develop immunity

  - Memory cells

  - Long term

  
  

  Passive

  - No Ag exposure

  - Immediate

  - No memory cells

  - Short term (Ab broken down)
• What is the structure of HIV?


  Core - contains genetic material and reverse transcriptase

  
  

  Core surrounded by capsid

  
  

  Lipid envelope - made of membrane from previous host

  
  

  Attachment proteins

  
• How is HIV replicated?

  1. Attachment protein attaches to receptor on host T helper cell

  
  

  2. Capsid released into cytoplasm, uncoats, releasing RNA

  
  

  3. Reverse transcriptase makes complementary DNA strand from viral RNA template

  
  

  4. Double stranded DNA made and inserted into host DNA

  
  

  5. Host enzymes make viral protein from viral DNA

  
  

  6. Makes new virus which buds off

  
• How does HIV cause AIDS?

  Replication of HIV destroys T helper cells causing them to decrease in number

  
  

  Decreased Th cells mean the individual cannot produce an immune response - hence at risk of opportunistic infections
• When does HIV become AIDS?

  - T helper cell count drops below set number

  - Failing immune system symptoms
• Why are antibiotic ineffective against viruses?

  Work by targeting bacterial enzymes/ribosomes

  - different from human enzymes and ribosomes hence no effect

  
  

  Viruses don't have own enzymes/ribosomes - use host cells

  
  

  Hence can't inhibit as no effect on human processes
• What are monoclonal antibodies?

  Antibodies produced by a single clone of B cells
• What are the uses of monoclonal antibodies?

  - Target medication to specific cell types

  - Medical diagnosis
• How are monoclonal antibodies used in targeting medication?

  CANCER THERAPY

  1. Diff cells = diff antigens

  2. Cancer cells have specific tumour markers

  3. Monoclonal Abs complementary to tumour markers made

  4. Anti-cancer drugs attached to Abs

  5. Abs bind to tumour markers hence drug accumulates only at cancer cell - less side effects

  
• How are monoclonal antibodies used for medical diagnosis?

  PREGNANCY TESTS

  1. hCG antibodies bound to blue bead in application area

  2. Urine applied - any hCG binds to beaded antibody forming Ab-Ag complex

  3. Urine moves carrying bead, to test strip, containing immobilised hCG antibodies

  4. If hCG present, test strip goes blue

  - immobilised Ab binds to hCG

  - increase [hCG-Ab complex + blue bead] conc

  
• Describe the ELISA test?


  1. HIV antigen bound to bottom of well

  2. Blood plasma added - any HIV specific antibodies bind to HIV antigen on well

  3. Wash - remove unbound antibodies

  4. Secondary Ab with enzyme added - binds to HIV Ab

  5. Wash - remove unbound secondary Ab

  6. Solution containing substrate added

  7. Substrate reacts with enzyme producing a coloured product

  8. Colour change = HIV Ab in blood = HIV +ve

  
• What can be problems with vaccination programmes?


  - Vaccine doesn't work (eg pathogen 'hides')

  - Vaccine not safe (major side effects)

  - Many pathogen strains

  - Cannot achieve herd immunity (large pop, religion etc)

  - Antigen variability
• Self Cells


  The body's own cells and molecules
• Non-Self Cells


  Foreign cells and molecules invading someone