1. Department of Immunology, Basic Medicine School, Air-Force Medical University (the Fourth Military Medical University) , Xi’an, Shaanxi, 86-710032 , P.R. China
2. Institute of AIDS Prevention and Control,Shaanxi Provincial Center for Disease Control and Prevention , Xi’an, Shaanxi, 86-710054 , P.R. China
3. Department of Internal Medicine, Tangshan Sannvhe Airport Hospital , Tangshan, Hebei, 86-063000 , P.R. China
4. Department of Epidemiology, Public Health School, Air-Force Medical University (the Fourth Military Medical University) , Xi’an, Shaanxi, 86-710032 , P.R. China