1. Department of Microbiology, Kawasaki Medical School, Kurashiki, Okayama 701-0192, Japan
2. Department of Virology 3, National Institute of Infectious Diseases, Musashi-Murayama, Tokyo 208-0011, Japan
3. Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8566, Japan
4. Department of Immunology and Microbiology, Nihon University School of Medicine, Itabashi-ku, Tokyo 173-8610, Japan
5. Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Kanagawa 228-8555, Japan