1. Department of Internal Medicine, Seoul National University College of Medicine, Seoul 110-799, Korea.
2. Institute of Allergy and Clinical Immunology, Seoul National University Medical Research Center, Seoul 110-799, Korea.
3. Department of Internal Medicine, Pusan National University College of Medicine, Busan 602-739, Korea.
4. Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam 463-707, Korea.