Why does stress make my Crohn's worse?

I found a good, readable summary of how stress, depression, genetics and the immune system are linked. Click the link below to read
This article is surprisingly consistent with the principles behind the BUDI (TM) system.
Esther Sternberg is an MD who has researched the operation of the immune system following the onset of arthritis after a period of extreme and prolonged stress.
 http://being.publicradio.org/programs/stress/mindbodyessay.shtml