1. Department of Virology, Osaka City University Medical School, Asahimachi, Abeno-ku, Osaka 545-8585, Japan
2. Department of Pediatrics, Osaka City University Medical School, Asahimachi, Abeno-ku, Osaka 545-8585, Japan
3. Department of Immunology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka 537-8511, Japan
4. Department of Virology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan