Cell recognition & the immune system

• How do lymphocytes distinguish between the body's own cells and foreign cells?


  Every cell has specific molecules on it's surface that identify it.
• What kind of molecule is the most important in relation to cell recognition? Explain why.

  Proteins. This is because proteins have enormous variety and a highly specific tertiary structure.
• Why may the cell recognition system be problematic for humans?

  It has implications for humans who have had tissue or organ transplants. The immune system recognises these as non-self even though they have come from individuals of the same species. Therefore it may attempt to destroy the transplant.
• How may doctors try and overcome transplant rejection?

  Transplants are matched as closely as possible to those of the recipient (best matches come from relatives who are genetically similar) or immunosuppressant drugs to reduce the level of the immune response that occurs.
• Are specific lymphocytes produced in response to an infection?

  No- they already exists all 10 million different types.
• How do lymphocytes recognise cells belonging to the body?

  In the foetus the 10 million different lymphocytes are constantly colliding with other cells, any lymphocytes that have receptors that exactly fit those of the own body will die or be suppressed.

  In adults any lymphocytes produced in the bone marrow that respond to self antigens will undergo programmed cell death (apoptosis).
• What kind of molecules are antigens?

  Macromolecules
• What do non-self antigens stimulate?

  An immune response.
• What is antigen variability?

  Where the antigens change frequently due to genetic mutations.
• What issue does antigen variability pose for the immune system?

  Surface receptors on lymphocytes and memory cells are complementary to one antigen.

  So when antigen on pathogen changes lymphocytes and memory cells can no longer bind.

  Therefore there is no secondary response.

  When host gets infected it suffers from the disease again.
• What virus are known to mutate frequently?

  Cold, flu and HIV virus.