1. The Peking University Research Center on Aging, Department of Biochemistry and Molecular Biology, Peking University Health Science Center, Beijing, China
2. Department of Microbiology, Peking University Health Science Center, Beijing, China
3. Department of Pathology, Peking University Health Science Center, Beijing, China
4. Department of Histology and Embryology, Peking University Health Science Center, Beijing, China