1. Department of Microbiology and Immunology Minato-ku, Institute of Medical Science, University of Tokyo; 4-6-1, Shirokanedai, Minato-ku Tokyo 108-8639 Japan
2. Department of Biosciences, Teikyo University; 1-1 Toyosatodai Utsunomiya 320-8551 Japan
3. Department of Basic Medical Sciences, Institute of Medical Science, University of Tokyo; 4-6-1, Shirokanedai, Minato-ku Tokyo 108-8639 Japan
4. Nippon Institute for Biological Science; 9-2221-1, Shinmachi, Ome Tokyo 198-0024 Japan
5. Department of Bacterial Toxicology, Research Institute for Microbial Diseases, Osaka University; 3-1, Yamadaoka, Suita Osaka 565-0871 Japan