1. Department of Microbiology; Asahikawa Medical College; Asahikawa 078-8510 Japan
2. Animal Laboratory for Medical Research; Asahikawa Medical College; Asahikawa 078-8510 Japan
3. RIKEN Brain Science Institute; Wako Saitama 351-0198 Japan
4. Department of Immunology; Graduate School of Pharmaceutical Sciences, Osaka University; Suita Osaka 565-0871 Japan