Distribution and activation of eosinophils in inflammatory bowel disease using an improved immunohistochemical technique

Eosinophils are a recognized feature of inflammatory bowel disease (IBD), b ut their tissue distribution and functional importance in Crohn's disease ( CD) and ulcerative colitis (UC) remain obscure. This study describes an imp roved immunohistochemical protocol to identify eosinophils in full thicknes s bowel wall specimens of IBD (n=40) and their in situ relationships with t he chemoattractants eotaxin and RANTES. Eosinophils were identified using i mmunohistochemistry with a combination of monoclonal antibodies (EG1 + EG2 + MBP), an ultrasensitive technique superior to other methodologies, and th eir tissue distributions were related to those for eotaxin, RANTES, mast ce lls and neutrophils. Increased numbers of eosinophils (up to 400 cells/mm(2 )) were observed in active, fulminant inflammation in both CD and UC, this being related to the severity of inflammation and not the diagnosis of the two disorders. The chemoattractants eotaxin (CCL11) and RANTES (CCL5) were upregulated in IBD tissues showing eosinophilia. Neutrophils and mast cells were commonly associated with eosinophil accumulations. Eosinophil numbers and their in situ activation are increased in active rather than chronic I BD. The observations strongly suggest a pivotal role for the eosinophil and its potent mediators in many pathophysiological symptoms of CD and UC, whe re it represents the major proportion of all granulocytic cells in active i nflammatory bowel disease. Copyright (C) 2001 John Wiley & Sons, Ltd.