1. Center for Gastroenterology, Kobayashi Hospital, Hokkaido 090-8567, Japan
2. Department of Internal Medicine, Kin-ikyo Chuo Hospital, Hokkaido 007-0870, Japan
3. Immunology Division and Division of Molecular Virology, Jichi Medical School, Tochigi-Ken 329-0498, Japan
4. Department of Pediatrics, Jichi Medical School, Tochigi-Ken 329-0498, Japan
5. Japanese Red Cross Saitama Blood Center, Saitama-Ken 360-0806, Japan