Department of Liver Disease, The Research Center for Hepatitis and Immunology, National Center for Global Health and Medicine, Ichikawa, Japan. Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. Department of Liver Disease, The Research Center for Hepatitis and Immunology, National Center for Global Health and Medicine, Ichikawa, Japan. sachiyo@hospk.ncgm.go.jp. Department of Gastroenterological Surgery I, Hokkaido University Graduate School of Medicine, Sapporo, Japan. Department of Immunology, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan. Department of Epidemiology, Infectious Disease Control and Prevention, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan. Department of Liver Disease, The Research Center for Hepatitis and Immunology, National Center for Global Health and Medicine, Ichikawa, Japan. kantot@hospk.ncgm.go.jp.