Activation of eosinophils in the pathophysiology of ulcerative colitis.

We studied the role of eosinophils as effector cells in the pathophysiology of ulcerative colitis. In the active stage of this disease, the colonic mucosa exhibited infiltration of numerous eosinophils positive to the EG2 antibody, which reacts specifically with the secretory form of eosinophil cationic protein. Electron microscopic studies demonstrated that the eosinophils had specific granules in various stages of degranulation. Hence, it is strongly suggested that the eosinophils infiltrating the inflamed mucosa are activated and may induce tissue damage during the degranulation and release of this cationic protein. Changes in the levels of serum eosinophil cationic protein in 14 patients who remained for in long-term remission were studied. Four of these patients showed persistently high concentrations of eosinophil cationic protein (equal to or greater than 30 micrograms/l) and persistently high percentage (mean, 30.2%) of hypodense eosinophils (specific gravity < 1.082) in the peripheral blood. Such findings were associated with mild active disease at colonoscopy. These features suggest that the activation of eosinophils is one of the factors that contribute to the chronic inflammation in ulcerative colitis.