1. Department of Pathology II, Kansai Medical University, Moriguchi, Osaka 570-8506, Japan
2. Department of Toxicological Research, Research Laboratories, Maruho Co., Ltd., Kyoto, Kyoto 600-8815, Japan
3. Division of Cytopathology, Kansai Medical University Takii Hospital, Moriguchi, Osaka 570-8507, Japan