1. Department of Oral Pathology, Tokyo Dental College, Masago 1-2-2, Chiba City, Chiba 260, Japan
2. Cell Biology Research Laboratory, Tokai University SchaoL of Medicine, Isehara City, Kanagawa 259-11, Japan
3. Department of Pathology, Tokai University SchaoL of Medicine, Isehara City, Kanagawa 259-11, Japan