Antigens & Antibodies

• All cells have molecules, such as proteins, projecting from their cell membranes

  • These are known as antigens
• Different individuals have different antigens on their cell surface membranes
• Lymphocytes can recognise foreign antigens, e.g. the antigens of a pathogen inside the body

  • In response to foreign antigens lymphocytes make antibodies which are complementary in shape to the antigens on the surface of the pathogenic cell
• Lymphocytes producing antibodies diagram

  A) antibodies

  B) complementary

  C) antigens

  D) pathogen

  E) enhance

  F) immune response

  G) antigen

  H) antibody

  I) specific

  J) antigen

  K) lymphocyte

  L) produces

  M) type

  N) antibody

  
• Phagocytes and agglutination diagram

  A) antibodies

  B) enhance

  C) phagocytes

  D) antibodies

  E) agglutination

  F) clumping

  G) pathogens

  H) specific

  I) antibodies

  J) pathogen

  
• The initial response of a lymphocyte encountering a pathogen for the first time can take a few days, during which time an individual may get sick
• After an initial encounter with a pathogen, lymphocytes can give rise to memory cells that retain the instructions for making specific antibodies

  • This means that in the case of reinfection by the same type of pathogen, antibodies can be made very quickly and in greater quantities; the pathogens are destroyed before they multiply and cause illness
  • This is how people become immune to certain diseases after only having them once
• Note that immunity does not work with all disease-causing microorganisms as some of them mutate quickly and change the antigens on their cell surface

  • Therefore, if they invade the body for a second time the memory cells made in the first infection will not produce antibodies that match the new antigens
• Make sure you know the difference between antigen, antibody and antitoxin:

  • An antigen is a molecule found on the surface of a cell
  • An antibody is a protein made by lymphocytes that is complementary to an antigen and, when attached, clumps them together and signals the cells they are on for destruction
  • An antitoxin is a protein that neutralises the toxins produced by bacteria
• All pathogens have antigens

  • antigens - unique shapes
• Phagocytes engulf pathogens
• Antibodies

  • white blood cell finds a microbe and makes antibodies
  • antibody type depends on type of antigen
  • need to be right shape to match the pathogen, complementary
  • act as markers so phagocytes know what to destroy
• Lymphocytes make antibodies