1. Department of Immunology; Kyushu University; Fukuoka Fukuoka 812-8582 Japan
2. Department of Virology; Medical Institute of Bioregulation, Kyushu University; Fukuoka Fukuoka 812-8582 Japan
3. Graduate School of Genetic Resources Technology; Kyushu University; Fukuoka Fukuoka 812-8582 Japan
4. Department of Microbiology; Miyazaki Medical College; Miyazaki Japan