1. H. Suzuki, M. Fujiwara, S. Koyasu, Department of Immunology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan. Y. Terauchi, Y. Yazaki, T. Kadowaki, Department of Internal Medicine, University of Tokyo, Graduate School of Medicine, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan. S. Aizawa, Department of Morphogenesis, Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kumamoto 860, Japan.