1. Department of Hematology, Tangdu Hospital, Fourth Military Medical University, Xi'an 710038, P. R. China
2. Experiment Teaching Center, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, P. R. China
3. Department of Physiology, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, P. R. China
4. Department of Geratology, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, P. R. China