1. Institute of Laboratory Animals, Mie University School of Medicine, 2–174 Edobashi, Tsu, Mie 514, Japan
2. Department of Pathology, Tohoku University School of Medicine, 2-1 Seiryo, Aoba, Sendai 980-77, Japan
3. Department of Microbiology, Mie University School of Medicine, 2–174 Edobashi, Tsu, Mie 514, Japan