of a Lecture at the Workshop sinophils. Real-time PCR analysis showed that eosinophils expressed mRNA for ST2, a putative receptor for IL-33. We found that IL-33 at 1–100 ng/ml potentially enhanced the adhesiveness of human eosinophils. In addition, CD11b expression of eosinophils measured by flow cytometry was upregulated by IL-33. Apoptosis was determined by flow cytometry; IL-33 maintained the viability of eosinophils. Neutralization of ST2 with blocking antibodies eliminated the effects of IL-33 on eosinophil CD11b expression and cell survival. On the other hand, IL-33 failed to elicit degranulation or leukotriene C 4 synthesis in eosinophils. From these results, we revealed that IL-33 potently induces eosinophil adhesion and CD11b expression, and enhances survival of eosinophils in vitro. The IL-33-ST2 pathway may be critically involved in the pathogenesis of allergic diseases [1] . IL-33 Induces Human Eosinophil Activation Maho Suzukawa a, c , Masao Yamaguchi a, c , Rikiya Koketsu a , Motoyasu Iikura d , Hiroyuki Nagase c , Susumu Nakae e , Kenji Matsumoto e , Hirohisa Saito e , Kouji Matsushima b , Tetsuya Adachi c , Ken Ohta c , Kazuhiko Yamamoto a Departments of a Allergy and Rheumatology and b Molecular Preventive Medicine, University of Tokyo Graduate School of Medicine, c Department of Respiratory Medicine, Teikyo University School of Medicine, d Department of Respiratory Medicine, International Medical Center of Japan, and e Department of Allergy and Immunology, National Research Institute for Child Health and Development, Tokyo , Japan Although eosinophils are important effector cells in allergic diseases, it has not been fully clarified how their biological functions are regulated. IL-33 is a recently identified cytokine of the IL-1 family; it augments the production of Th2-associated cytokines and promotes tissue inflammation. However, the action of IL-33 on effector cells including eosinophils has remained unclear. Therefore, we investigated the effect of IL-33 on human eoPublished online: June 3, 2009 © 2009 S. Karger AG, Basel 1018–2438/09/1495–0113$26.00/0 Accessible online at: www.karger.com/iaa Reference 1 Suzukawa M, Koketsu R, Iikura M, Nakae S, Matsumoto K, Nagase H, Saito H, Matsushima K, Ohta K, Yamamoto K, Yamaguchi M: Interleukin-33 enhances adhesion, CD11b expression and survival in human eosinophils. Lab Invest 2008; 88: 1245–1253.