Defence mechanisms & antigens

• What is an antigen?

  A protein on the surface of cells that triggers an immune response
• What usually triggers an immune response?

  A foreign antigen
• How are antigens used to measure the degree of relatedness between individuals?

  More closely related individuals share more similar antigens
• What is a pathogen?

  A microorgansim that has the potential to cause disease
• What are the four types of pathogen?

  Virus, bacteria, protist, fungi
• What is a non-specific immune response?

  The immune response is the same regardless of the pathogen
• Which blood cells are responsible for the non-specific and specific immune responses?

  Specific -> lymphocytes

  Non-specific -> phagocytes
• What sort of molecules do lymphocytes identify?

  • Pathogens
  • cells from other organisms of same species
  • abnormal body cells
  • toxins
• Why is antigen variability a problem?

  • When pathogenic DNA mutates causing a change in shape of antigen
  • previous immunity is no longer effective as memory cells don't recognise new shape of antigen
  • specific antibody no longer binds to new antigen
• State the physical barriers to pathogens in the human body.

  Anatomical barriers to pathogens

  • skin
  • stomach acid
  • lysozymes in tears