Increased Response of Blood Eosinophils to Various Chemotactic Agents in Quiescent Crohn Disease

BACKGROUND: The number of eosinophils is increased in the mucosae of the digestive and the respiratory tracts in Crohn disease, even clinically quiescent. The mechanisms underlying this panmucosal eosinophilia are unknown. METHODS: The response of blood eosinophils to various chemotactic agents was assessed in 15 patients with clinically quiescent Crohn disease. The results were compared with 15 healthy controls. After purification, eosinophils were placed in Boyden microchambers and the chemotactic effect of PAF (10(-7) M), RANTES (50 ng/ml), IL-5 (0-20 ng/ml), IL-8 (0-50 ng/ml), Eotaxin (0-50 ng/ml) was evaluated. The number of eosinophils in induced sputum of these Crohn disease patients and controls was also assessed and the correlation between chemotaxis and eosinophil count in induced sputum was studied. RESULTS: PAF and RANTES induced a chemotactic effect both in Crohn disease patients and controls. The chemotactic index was significantly higher in Crohn than controls for PAF (2.09+/-0.24 versus 1.37+/-0.14; P < 0.05) but not RANTES. With IL-5, IL-8 and Eotaxin, there was no detectable chemotactic effect in controls while in Crohn, we observed a significant dose-dependent chemotactic effect. Furthermore, with Eotaxin 50 ng/ml, the chemotactic index was significantly higher in Crohn disease patients than controls (2.42+/-0.18 versus 1.56+/-0.28; P < 0.05). A significant increase in sputum eosinophil count and a significant decrease in sputum macrophage count in Crohn disease were observed. However, there was no correlation between eosinophil chemotaxis and sputum eosinophil count in individual patients. CONCLUSION: There is an increased response of blood eosinophils to various chemotactic agents, mainly PAF and Eotaxin, in clinically quiescent Crohn disease. This may participate in the mucosal infiltration by eosinophils in this disease.