1. Department of Microbiology and Immunology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan
2. Department of Oral Medicine, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan
3. Department of Biochemistry, Tokyo Dental College, Mihama, Chiba 261-8502, Japan