Antigens

• Antigen - A protein found on the outside of cells, that triggers an immune response
• Antigens enable the immune system to identify:

  • Pathogens (micro-organisms that cause disease)
  • Cells from other organisms of the same species (e.g in transplanted organs)
  • Abnormal body cells (e.g cancerous cells)
  • Toxins (poisonous molecules often released by bacteria)
• On the surface of all cells are chemical markers (eg proteins) called antigens

  • Each antigen has its own unique shape
  • The more closely related 2 individuals are, the more antigens they have in common
• Self vs non-self cells:

  SELF - The body's own cells and molecules

  • Your body recognises the antigens on your cells as your own
• Self vs non-self cells:

  NON-SELF (foreign) - Not your own body's cells and molecules
• Non-self cells: (not your own body cell's and molecules)

  • Anything with different antigens to you stimulates an immune response
  • In an immune response, your body will recognise the antigen as foreign (and therefore bad) and will attack it
• Recognising your own cells: (self vs non-self cells)

  • To defend the body from invasion by foreign material, lymphocytes must be able to distinguish the body's own cells (Self) from those that are foreign (non-self)
• Antigen variability:

  • Pathogens DNA can mutate frequently - if a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change
  • Any previous immunity to this pathogen is no longer effective, as all the memory cells will have a memory of the old antigen shape
• Effect of antigen variability on disease prevention:

  • Reduces the effectiveness of vaccines
  • Antibodies are no longer complementary to antigens (don't bind)