Vaccines, disease and monoclonal antibodies

• Vaccine:

  • contains dead/attenuated pathogens that causes the body to produce memory cells against it, without causing disease
  • produces long-term immunity
  • can be injected or taken orally
• Herd immunity:

  • when a large proportion of a population is vaccinated and therefore immune to a disease
  • protects those not vaccinated, as it is difficult for the disease to spread within the population
• Problems with vaccines:

  • people can have a poor response (eg due to malnutrition - little protein to make antibodies)
  • antigentic variation: antigens of a disease changes frequently due to genetic mutations
  • antigenic concealment: pathogen hides from immune system
• Antigenic variation:

  • antigens of some pathogens change frequently due to genetic mutations
  • this is a problem as surface receptors on lymphocytes/memory cells are complementary to only one antigen
  • memory cells would not recognise the new antigens so primary immune response takes place instead
  • makes it difficult to develop vaccines
• Active immunity:

  • immune system makes its own antibodies
  • natural: through exposure to pathogens
  • artificial: through vaccinations
• Passive immunity:

  • antibodies given is made by a different organism
  • natural: from mother to baby through the placenta and in breast milk
  • artificial: antibodies manufactured and injected/transfused into body (eg via blood transfusion)
• Active vs passive immunity:

  • Active requires exposure to antigens, passive does not
  • Active takes a while for protection to develop, passive has immdiate protection
  • Active produces memory cells, passive does not
  • Active is long-lasting (as antibodies produced will remain present in the body), passive is short-term (as antibodies are not replaced when they’ve broken down)
• Monoclonal antibodies:

  • antibodies produced from a single group of genetically identical B-cells
  • highly specific, as their antigen-binding sites have a unique tertiary structure that is complementary to one antigen only
• Medical diagnosis eg pregnancy test:

  1. Application area contains antibodies for hCG, bounded to a blue coloured bead
  2. Urine is applied, any hCG present binds to the antibodies
  3. Urine moves up the stick, carrying any beads towards the test strip which contains immobilised hCG antibodies
  4. If hCG is present, test strip turns blue as immobilised antibodies bind to hCG. If not, no colour change as beads pass through the test area
• HIV

  • a retrovirus that affects the immune system
  • spread by direct exchange of body fluids eg blood, semen
• Structure of HIV:

  • 2 RNA strands
  • proteins (inc. reverse transcriptase)
  • attachment proteins
  • capsid
  • viral envelope (made from membrane of the host helper T-cells)
• Symptoms:

  • immediately after infection: flu-like symptoms
  • latency period: no symptoms, HIV replication drops to lower levels
  • AIDS: viral DNA becomes active, number of helper T-cells decreases, leads to opportunistic infections eg tuberculosis
• Antiviral drugs: slow down the progression from HIV to AIDS
• HIV stands for Human Immunodeficiency Virus

  AIDS stands for Acquired Immunodeficiency Syndrome
• ELISA stands for Enzyme-linked Immunosorbent Assay
• ELISA

  • used to see if a patient has any antibodies to a certain antigen (or vice versa)
  • can be tested for pathogenetic infections, allergies, etc
  • a colour change means a positive result, the colour intensity reflects the quantity of antibody/antigen
• Direct ELISA: uses a single antibody that is complementary to the antigen being tested for

  Indirect ELISA: uses 2 different antibodies (primary + secondary)
• ELISA test:

  1. Antigen is bound to the bottom of a well in a well plate
  2. Add antibodies specific to the antigen and let it bind to antigens + wash the well to remove unbound antibodies
  3. Add a secondary antibody that has a specific enzyme attached to it, let it bind to the primary antibodies + wash to remove unbound antibodies
  4. Add a substrate that can react with the enzyme and produce a coloured product