AQA A Level Biology复习笔记2.5.2 Antigens



  • Every cell in the human body has markers that identify it
  • Microorganisms (both pathogenic and non-pathogenic), such as bacteria and viruses, also have their own unique markers
  • These markers are called antigens (which are macromolecules) and they allow cell-to-cell recognition
  • Antigens are found on cell surface membranes, bacterial cell walls, or the surfaces of viruses
    • Some glycolipids and glycoproteins on the outer surface of cell surface membranes act as antigens


  • Antigens can be either self antigens or non-self antigens:
    • Antigens produced by the organism's own body cells (those that the immune system does not recognise as foreign antigens) are known as self antigens
    • Self antigens do not stimulate an immune response
    • Antigens not produced by the organism’s own body cells (those that the immune system recognises as being foreign eg. the antigens found on pathogenic bacteria and viruses or if a person receives a different blood type during a transfusion) are known as non-self antigens
    • Non-self antigens stimulate an immune response


Antigen Variability

  • Some pathogens exhibit antigen variability
    • The antigens present on their surface change frequently due to genetic mutations


  • This poses a problem for the immune system of many mammal hosts as lymphocytes and memory cells produce a specific immune response
    • The surface receptors on lymphocytes and memory cells are complementary in shape to only one antigen
    • When the antigen on a pathogen changes the lymphocytes and memory cells can no longer bind
    • As a result, there is no secondary immune response
    • The host gets infected and suffers from the disease again


  • The cold virus and flu virus are common pathogens that exhibit antigen variability
    • Individuals can catch the cold and flu year after year as the antigens on the viruses change and are not recognised by their immune system


Exam Tip

The different types of pathogen include viruses, bacteria, fungi and protozoans!