3.6

• Antibody


  1. shaped proteins that have receptor binding sites specific to a particular antigen on a pathogen. Antibodies become bound to antigens, inactivating the pathogen. The resulting antigen-antibody complex can then be destroyed by phagocytosis.
• Antigen


  Molecules, often proteins located on the surface of cells that trigger a specific immune response.
• Antitoxin


  An antibody produced by a white blood cell. It can neutralise toxins.
• Apoptosis


  Programmed cell death.
• Lymphocytes


  White blood cells involved in the specific immune response.
• Pathogen


  A bacterium, virus or other organism that can cause disease.
• Phagocytes


  Cells, such as white blood cells, which engulf and destroy harmful micro-organisms (pathogens), or other foreign bodies in the bloodstream and tissues by phagocytosis.
• Phagocytosis


  Involves the engulfing of pathogens and their destruction by digestive enzymes contained in lysosomes.
• Toxin


  A type of natural poison produced by an organism, often as a form of protection.
• Lymphocytes


  • Respond to specific antigens on invading pathogens
  • Have a single type of membrane receptor which is specific for one antigen
  • Antigen binding leads to repeated lymphocyte division creating large numbers of identical lymphocytes bearing that particular receptor
  • Can produce antitoxins to neutralise toxins produced by pathogens
• Types of lymphocytes


  • B lymphocytes
  • T lymphocytes
• B lymphocytes


  • Produce antibodies against antigens, leading to the destruction of the pathogen
  • Can respond to antigens on substances that are harmless to the body, leading to allergic reactions
• T lymphocytes


  • Destroy infected body cells by recognising antigens of the pathogen on the cell membrane and inducing apoptosis
  • Can identify the difference between antigens found on the body's own cells (self-antigens) and antigens belonging to the pathogen (non-self-antigens)
• Failure of the regulation of the immune system can result in lymphocytes attacking the body's own cells, leading to autoimmune diseases
• Autoimmune diseases


  • Type 1 diabetes
  • Rheumatoid arthritis
• Memory cells


  Lymphocytes that continue to remain in the immune system after the pathogen is removed, allowing for a rapid response to secondary exposure
• Secondary exposure to the same antigen

  Memory cells rapidly give rise to a new clone of specific lymphocytes, which destroy the invading pathogens before the individual shows symptoms
• Secondary response


  Antibody production is greater and more rapid than during the primary response
• The human immunodeficiency virus (HIV) attacks and destroys T lymphocytes, leading to the development of AIDS (acquired immune deficiency syndrome)
• Individuals with AIDS have a weakened immune system and are more vulnerable to opportunistic infections, such as those that cause tuberculosis and pneumonia