What do you find most interesting to learn about the immune system??

Question: What do you find most interesting to learn about the immune system??

Asked by gemma to Mark on 17 Jun 2010 in Categories: General.
- Mark Travis answered on 17 Jun 2010:
  
  How all the different cells of the immune system can work together in such an intricate way to get rid of things that can potentially harm the body, but normally not bother with things that are harmless.

Question: What do you find most interesting to learn about the immune system??