1. College of Veterinary Medicine, Seoul National University, Seoul 151-742, Korea.
2. School of Agricultural Biotechnology, Seoul National University, Seoul 151-742, Korea.
3. Medical Research Center, MizMedi Hospital, Seoul, 135-280, Korea.
4. Gachon Medical School, Incheon, 417-840, Korea.
5. College of Medicine, Seoul National University, Seoul, 110-744, Korea.