Self vs. Non-Self

• Self

  Body cells
• Non-self

  Foreign materials
• Immune system

  • Capacity to distinguish between self and non-self
  • Reacts to presence of non-self with immune response to eliminate it
• Major histocompatibility complex (MHC class I)


  Self markers that identify cells as belonging to the organism
• The immune system will not normally react to cells bearing these genetically determined self markers (self-tolerance)
• Antigen


  Any substance recognised as foreign and capable of triggering an immune response (non-self)
• Epitope


  Characteristic shape of an exposed portion of an antigen that is recognised by lymphocytes
• Paratope


  Complementary binding site on lymphocytes that binds to the epitope
• Antigenic determinants


  • Surface markers on foreign bodies (bacterial, fungal, viral, parasitic)
  • Self markers of cells from a different organism (transplant rejection)
  • Proteins from food (unless broken down by digestion)
• Antigens on red blood cell surface


  Stimulate antibody production in a person with a different blood group
• Red blood cells are not nucleated and do not possess the same distinctive and unique self markers as all other body cells
• Red blood cells do possess basic antigenic markers which limit the capacity for transfusion (the ABO blood system)
• ABO blood groups


  Red blood cells may possess surface glycoproteins A, B, both (AB), or neither (O)
• Compatibility of ABO blood groups

  • AB can receive from any type
  • A cannot receive B or AB
  • B cannot receive A or AB
  • O can only receive from O
• An additional glycoprotein (Rhesus factor) is either present or absent, resulting in positive and negative blood groups