1. Department of Microbiology and Immunology, Keio University School of Medicine 35 Shinanomachi, Shinjuku‐ku Tokyo 160‐8582 Japan
2. Department of Microbiology, Tokyo Metropolitan Institute of Medical Science, Honkomagome, Bunkyo‐ku Tokyo 113‐8613 Japan
3. Discovery Laboratories, Pharmaceutical Research Laboratories, Ajinomoto Co., Inc. 1‐1 Suzuki‐cho, Kawasaki‐ku Kawasaki 210‐0681 Japan
4. Exploratory Research Laboratories, Fujisawa Pharmaceutical Co., Ltd, Tokodai, Tsukuba Ibaraki 300‐2698 Japan
5. Department of Cell and Developmental Biology, Graduate School of Biostudies, Kyoto University, Sakyo‐ku Kyoto 606‐8502 Japan