1. Department of Microbiology; Jichi Medical School; Tochigi 329-04 Japan
2. Department of Microbiology and Immunology; Showa University School of Medicine; Shinagawa-ku Tokyo 142 Japan
3. Facuity of Science; Osaka University; Suita Osaka 560 Japan
4. Department of Pathology; Oita Medical University; Oita 879S6 Japan