1. Department of Respiratory Medicine, The First Affiliated Hospital of The Fourth Military Medical University, Xi'an, Shaanxi 710038, P.R. China
2. Medical Oncology Center, Dongguan Kanghua Hospital, Dongguan, Guangdong 523080, P.R. China
3. Department of Basic Microbiology, The Fourth Military Medical University, Xi'an, Shaanxi 710038, P.R. China