1. Department of Immunology, The Fourth Military Medical University, Xincheng District, Xi’an, Shaanxi, P. R. China
2. Department of Microbiology, The Fourth Military Medical University, Xi’an, P. R. China
3. Center for Infectious Diseases, Tangdu Hospital, The Fourth Military Medical University, Xi’an, Shaanxi, P. R. China
4. Eighth Hospital of Xi’an, Xi’an, Shaanxi, P. R. China