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, Seoul National University Bundang Hospital, Seongnam 463-707, Korea.
4. Cardiovascular and Respiratory Studies, Castle Hill Hospital, University of Hull, Hull York Medical School, Cottingham HU16 5JQ, UK.