Biographical note of the first authors: Bao-Yun ZHANG, male, born in 1956, majoring in virus morphology and the mechanism of prion diseases; Chan TIAN, female, born in 1980, Ph.D., majoring in immunology and mechanism of prion diseases. Correspondence should be addressed to Xiao-Ping DONG. Tel: 86-10-83534616. Fax: 86-10-63564478. E-mail:dongxp238@sina.com