1. Department of Medical Laboratory Science, Faculty of Health Sciences; Hokkaido University; North-12, West-5, Kita-ku Sapporo 060-0812 Japan
2. National Institute of Infectious Diseases; Toyama 1-23-1, Shinjuku-ku Tokyo 162-8640 Japan
3. Division of Biomedical Imaging Research; Juntendo University Graduate School of Medicine; 2-1-1 Hongo, Bunkyo-ku Tokyo 113-8421 Japan
4. Division of Ultrastructural Research; Juntendo University Graduate School of Medicine; 2-1-1 Hongo, Bunkyo-ku Tokyo 113-8421 Japan