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, Ewha Womans University School of Medicine, Seoul 158-710, Korea.
4. Department of Internal Medicine, Chung-Ang University Hospital, Seoul 156-755, Korea.