Topic 11 - Animal Physiology

• Antigen


  Unique molecules on the cell surface membrane that act as markers to identify an organism
• Antigens


  • Found on cell surface membranes of cancer cells, bacterial cell walls, the envelopes of viruses and even pollen grains
  • Some glycolipids and glycoproteins on the outer surface of cell surface membranes act as antigens
• Allergies


  Result of an immune response triggered by antigens on the surface of an allergen, such as pollen

  
• Blood group antigens


  Specific markers on the surface of red blood cells that determine the blood group of an individual

  
• Blood group antigens


  • ABO marker
  • Rhesus (Rh) marker

  
• Blood type A


  Has a type A antigen consisting of an initial 'H' marker which is modified with another molecule called N-acetylgalactosamine

  
• Blood type B


  Has a type B antigen consisting of an initial 'H' marker which is modified with another molecule called galactose

  
• Blood type AB


  Has type A and B antigens consisting of two 'H' markers one of which is modified with N-acetylgalactosamine and the other with galactose

  
• Blood type O


  The 'H' marker is not modified and so there are no A or B antigens

  
• Agglutination


  Red blood cells clump together due to the binding of antigens and antibodies

  
• Antigen presenting cell


  A cell with non-self antigens on its surface membrane

  
• Specific immune response


  1. Phagocytes engulf pathogens and present the pathogen antigens

  2. T-helper cells with complementary receptors bind to the antigen and become activated

  3. Activated T-helper cells bind with complementary receptors on B-lymphocytes and activate them

  
• Plasma cells


  Produce large volumes of antibodies specific to the single type of antigen that triggered the immune response

  
• Clonal selection and expansion

  1. Identify and activate a B-cell with the complementary receptor to the target antigen

  2. Activated B-cell divides by mitosis to create many clones

  3. Some clones differentiate into plasma cells, others become memory cells

  
• Primary immune response


  • Relatively slow as the immune system takes time identifying the complementary antibody for each new antigen
  • Infection may result in symptoms

  
• Secondary immune response


  • More rapid, producing more antibodies than the primary response, in a much shorter time frame
  • Symptoms do not develop as the pathogen can be destroyed before significant cell damage occurs

  
• Functions of antibodies


  • Agglutination
  • Opsonisation
  • Neutralisation of viruses and bacteria
  • Activity reduction
  • Neutralisation of toxins
  • Complement activation

  
• Immunity


  Initiated when exposure to a specific antigen results in the production of complementary antibodies and memory cells

  
• Vaccines


  A source of antigens that are intentionally put into the body to induce immunity
• Types of vaccines


  • Live attenuated
  • Inactivated
• Vaccinations produce long-term immunity as they cause memory cells to be created</b>

  
• Vaccines


  Substances that are deliberately put into the body to induce immunity
• Vaccines


  • Cause a specific immune response where antibodies are released by plasma cells

  
• Types of vaccines


  • Live attenuated - weakened versions of the pathogen
  • Inactivated - killed, non-living components of pathogens or even just the antigens alone

  
• Vaccine administration


  Given by injection or orally (by mouth)
• Vaccinations by injection


  Can be into a vein or muscle
• Vaccinations


  • Produce long-term immunity as they cause memory cells to be created
  • Memory cells recognise the antigen when re-encountered and produce antibodies, in a faster, stronger, secondary response

  
• Vaccines trigger the primary immune response (T helper cells trigger B plasma cells to secrete specific antibodies) which leads to the production of memory cells which will give a faster and larger (higher concentration of antibodies) secondary response

  
• Smallpox was a highly infectious disease caused by the variola virus which first emerged thousands of years ago
• Smallpox


  • Notable symptoms included fever and an extensive rash with pus filled pustules
  • Long term effects included scarring and blindness
  • There was a 30% death rate in those who contracted the disease
• Variolation


  A method used to try and protect people from the most serious symptoms of smallpox, involving scratching material from smallpox pustules into the arms of patients
• Symptoms resulting from variolation tended to be less serious than those of naturally infected patients
• Sometimes the pus used in variolation contained functional pathogens so variolation could still cause disease and death
• Edward Jenner's observation


  Milkmaids who had been exposed to cowpox were showing a level of immunity to smallpox
• Jenner's hypothesis


  Milkmaids were protected due to their exposure to the cowpox virus which was similar but less serious
• Jenner's development of a cowpox inoculation

  1. Took pus from the skin lesions caused by cowpox and scratched it into the skin of a patient

  2. The inoculation proved successful; when Jenner later attempted to infect the boy with the variola virus no illness developed
• Jenner tested his vaccine for smallpox on a child
• Herd immunity


  Arises when a sufficiently large proportion of the population has been vaccinated (and are therefore immune) which makes it difficult for a pathogen to spread within that population

  
• Smallpox emerged thousands of years ago but outbreaks occurred periodically for many years afterwards and was still widespread as late as 1966 in South Africa, Africa and Asia
• WHO's smallpox eradication programme

  1. Began in 1967, with the intention to eradicate the virus within ten years

  2. Focused on vaccination (aim to vaccinate more than 80% of populations at risk, and ring vaccination around reported cases)

  3. Focused on surveillance