1. Department of Pathology; Kansai Medical University; Moriguchi, Osaka 570
2. Division of Tumor Biology; The Netherlands Cancer Institute; Plesmanlaan 121 1066 CX Amsterdam The Netherlands
3. Institute of Pathological Anatomy; Medical Academy “Carl Gustav Carus” DDR-8019 Dresden; German Democratic Republic
4. Institute for Virus Research; Kyoto University; Kyoto, Kyoto 606