These authors contributed equally to this work. These authors contributed equally to this work. Correspondence to: Dr. Qiuping Zhang, Department of Immunology, College of Basic Medical Sciences, Wuhan University, Donghu Road 185, Wuchang, Wuhan 430071, China. Tel: +86-27-6875-9827, Fax: +86-27- 6875-9827, E-mail: qpzhang@whu.edu.cn