1. Department of Senescence Biology, Kyoto University, Kyoto 606
2. Department of Immunology, Chest Disease Research Institute, Kyoto University, Kyoto 606
3. Oral and Maxillofacial Surgery, Faculty of Medicine, Kyoto University, Kyoto 606
4. Department of Preventive Medicine, Kyoto Prefectural University of Medicine, Kyoto 602, Japan