VARIABILITY

• WHY DOES ANTIGENIC VARIABILITY OCCUR?

  pathogen DNA changes shape frequently causing antigen shape changes
• PROCESS OF ANTIGEN VARIABILITY?

  • pathogen DNA mutates frequently
  • antigen shape changes
  • any previous immunity is now ineffective
• WHY IS ANY PREVIOUS IMMUNITY INEFFECTIVE AFTER AN ANTIGEN SHAPE CHANGE?

  memory cells are based on old shape
• EXAMPLES OF VARIABLE ANTIGENS?

  influenza virus