Antigenic Variation

• What do antigens on the surface of pathogens activate?

  The primary response
• What happens when a person is infected a second time with the same pathogen (which has the same antigens on its surface)?


  the antigens activate the secondary response and the person does not get ill

  • however some pathogens can CHANGE their SURFACE ANTIGENS
• Describe antigenic variation?

  • Some pathogens can change their surface antigens
  • This antigen variability is called antigenic variation
• What is antigenic variation?

  Different antigens are formed due to changes in the genes of a pathogen
• What is the effect of antigenic variation ?

  When a person is infected for a second time, the memory cells produced from the first infection WON'T RECOGNISE the different antigens.

  • So the immune system has to start from scratch & carry out a primary response against these new antigens
• Why does a person get ill again (if antigenic variation has occurred)?

  the primary response takes TIME to get rid of the infection
• What does antigenic variation make it difficult to do?

  Develop vaccines against some pathogens
• Give 2 examples of pathogens which show antigenic variation?

  HIV and the INFLUENZA VIRUS