1. Department of Virology State Key Laboratory of Pathogen and Biosecurity Beijing Institute of Microbiology and Epidemiology AMMS Beijing 100071 P. R. China
2. Beijing Protein and Antibody R&D Engineering Center Sinocelltech Ltd. Beijing 100176 P. R. China
3. Research Unit of Discovery and Tracing of Natural Focus Diseases Chinese Academy of Medical Sciences Beijing 100071 P. R. China