1. Department of Rheumatism and Immunology, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
2. Department of Pulmonary and Critical Care Medicine, Yan'an University Affiliated Hospital, Yan'an, Shaanxi 716000, P.R. China
3. Department of Pulmonary and Critical Care Medicine, Second Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi 710004, P.R. China