1. Department of Respiratory and Critical Care Medicine, Chronic Airways Diseases Laboratory, Nanfang Hospital, Southern Medical University, Guangzhou, Guangdong 510515, China
2. Department of Allergy and Clinical Immunology, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong 510120, China
3. Department of Occupational Health and Occupational Medicine School of Public Health, Southern Medical University, Guangzhou, Guangdong 510515, China.