Antigens (WJEC GCSE Biology: Combined Science)

• All cells have proteins and other substances projecting from their cell membrane
• These are known as antigens and are specific to that type of cell
• Lymphocytes can ‘read’ the antigens on the surfaces of cells and recognise any that are foreign
• They then make antibodies which are a complementary shape to the antigens on the surface of the pathogenic cell and so they are specific to the foreign antigen that is present

Antibody production diagram

Antigens and antibodies

• The antibodies attach to the antigens and cause clumping together of the pathogens
• This means the pathogenic cells cannot move very easily (so can more easily be destroyed)
• At the same time, chemicals are released that signal to phagocytes that there are cells present that need to be destroyed

Antibody action diagram

Clumped together pathogens cannot move easily

Activation of a lymphocyte

• Once a lymphocyte encounters a pathogen, it can take a few days to identify the specific antibody that is complementary to the antigen on the pathogen
  • During this time an individual may get sick
• Once the antibody has been identified, the lymphocyte clones itself many times
• It can then produce antibodies in large quantities
• Lymphocytes make ‘memory cells’ that retain the instructions for making those specific antibodies for that type of pathogen
  • This means that in the case of reinfection by the same type of pathogen, antibodies can be made
    • more quickly
    • in greater quantities
  • Pathogens can therefore be destroyed before they can multiply and cause illness
• This is how people can become immune to certain diseases after only having them once
  • However, if a pathogen mutates and the antigens change, a new immune response would be required to fight the disease
    • This happens commonly with cold and influenza viruses