1. Laboratory of Laboratory Animal Science and Medicine, School of Veterinary Medicine, Kitasato University, 35-1 Higashi-23, Towada 034-8628, Japan
2. Department of Laboratory Animal Medicine, Research Institute, National Center for Global Health and Medicine, Tokyo 162-8655, Japan
3. Laboratory of Veterinary Pathology, School of Veterinary Medicine, Kitasato University, 35-1 Higashi-23, Towada 034-8628, Japan