This news item is about: Immune systems have their sinister side, especially when they have not learned how hard to fight. Inflammatory bowel diseases like Crohn’s disease inflict more than a million Americans with debilitating pain and digestive unrest because of uncontrolled immune responses in the gut. How this happens remained a mystery until immunologists at the Cornell University College of Veterinary Medicine caught a key culprit in Crohn’s disease: a cell from our own immune forces. With unconventional help from a common parasite, Dr. Eric Denkers and Research Associate Dr. Charlotte Egan identified a renegade cell responsible for this largely arcane and increasingly prevalent illness.