Cell Recognition and the Immune System

• Each type of cell has specific molecules on its surface that identify it, these molecules include proteins and enable the immune system to identify:

  • Pathogens
  • Cells from other organisms of the same species
  • Abnormal body cells
  • Toxins
• What are some of the defence mechanisms the body has against pathogens?

  • Preventing the entry of pathogens by a variety of physical and chemical defences
  • Inflammation of the region invaded by the pathogen
  • Recognising ‘foreign‘ cells and targeting any pathogenic cells
• What are some of the chemical and physical defences used by the body to prevent pathogen entry?


  Skin, mucus membranes, tears and saliva
• How do tears prevent pathogen entry into the body?

  They contain the bacteria destroying enzyme lysozyme
• The process of recognising ‘foreign cells’ and targeting any pathogenic cells is known as a specific immune response
• What is inflammation?


  Swelling and heating of an area
• The inflammation of a region invaded by a pathogen is a process known as a non-specific inflammatory response
• The immune system responds to pathogens and other foreign bodies by detecting the presence of antigens, which are molecules that are present on the cell surface membrane of all cells
• What are antigens?

  Molecules, such as proteins and glycoproteins, that are present on the cell surface membrane of all cells
• Antigens signal to the immune system if cells are ‘foreign’
• The immune system can respond to foreign antigens in a number of ways:

  • Lysozymes break down the foreign cells
  • Phagocytosis of the foreign cells
  • Production of antibodies that bind to the antigens and inhibit the functioning of the foreign cells
• Every cell in the human body has markers that identify it known as antigens.
• Microorganisms, both pathogenic and non-pathogenic, such as bacteria and viruses have their own unique marker to identify them known as antigens
• Antigens are macromolecules on the cell surface membrane of cells that allow cell-to-cell recognition.
• Every cell has a specific antigen
• Antigens bind to complementary receptors on the cell surface membrane of the immune cells.
• If antigens are ‘foreign‘, an immune response will be induced
• What happens when antigens are identified as ‘foreign’?

  An immune response will be induced
• Antigens are molecules, usually proteins, that are often part of the phospholipid bilayer, such as glycoproteins, however, glycolipids can also act as similar markers
• Antigens can be either self or non-self antigens
• What are the two types of antigens?

  Self and non-self
• Antigens produced by the organisms own body (those that the immune system does not recognise as foreign antigens) are known as self antigens, which do not stimulate an immune response.
• Antigens that the immune system does not recognise as foreign antigens are known as self antigens
• Self antigens don't stimulate an immune response
• What type of antigen doesnt produce an immune response?

  Self
• Antigens not produced by the organisms own body cells (those that the immune system recognises as being foreign) are known as non-self antigens, which stimulate an immune response
• Antigens that the immune system identify as foreign are called non-self antigens
• Non-self antigens stimulate an immune response
• What type of antigen stimulates an immune response?

  Non-self
• What is antigen variability?


  Where the antigens present on a pathogen cell surface change frequently due to genetic mutations
• Antigenic variability poses a problem for the immune system of many mammal hosts as lymphocytes and memory cells produce a specific immune response.
• Why does antigenic variability pose a problem for the immune system of hosts?

  • The surface receptors on lymphocytes and memory cells are complementary in shape to only one antigen
  • When the antigen 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
• What are some examples of viruses that exhibit antigen variability?

  Cold and flu virus
• The cold and flu virus are the most common types of pathogens that exhibit antigen variability. Individuals can catch the cold and flu annually as the antigens on the viruses change and are not recognised by the immune system of the individual anymore.
• The surface molecules used by the body to identify cells, viral particles and toxins are known as antigens
• The antigen-binding site, and therefore the antibody, is specific to one antigen
• White blood cells, also called leukocytes, are primarily involved in the immune system, recognising and neutralising invaders such as bacteria and viruses.
• What is another name for white blood cells?

  Leukocytes
• What is the role of white blood cells?

  They are primarily involved in the immune system, recognising and neutralising invaders such as bacteria and viruses
• There are two main types of white blood cells, both of which controlling different types of immune response:

  • Phagocytes, controlling the non-specific immune response
  • Lymphocytes, controlling the specific immune response