Li Taisheng, Qiu Zhifeng, Han Yang, Zhang Hongwei, Wang Zhong, Liu Zhengyin, Fan Hongwei, Lu Wei, Yu Ying, Wang Huanling, Zhang Huiyuan, Xie Jing, Zhou Baotong, Ma Xiaojun, Ni Anping, Wang Aixia, Deng Guohua.

Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China

 Background: There has been an outbreak of the severe acute respiratory syndrome (SARS) worldwide. At present time, SARS is threatening more and more people in world, especially in Beijing, China.

In order to decrease mortality maximum, it is necessary to explore pathological mechanism of SARS. Here we report the severest loss of peripheral T lymphocytes in 30 cases of patients with SARS.

Methods: From March to May 2003, 61 patients were diagnosed as SARS in Peking Union Medical College (PUMC) Hospital, Chinese Academy of Medical Sciences & PUMC, after exposure to the try-out diagnosis criterion made by the Ministry of Public Health, China. The percentages and absolute numbers of CD4+ and CD8+ T lymphocytes in peripheral blood from 61 cases of patients with SARS in fever-phase and 56 cases of healthy donors were detected by immunoflourescent staining. The data is also compared with other viral infections including HIV, CMV and EBV.

Results: Compared with healthy donors, the subsets of CD4+ and CD8+ T lymphocytes both have a sharp decrease in term of relative percentage and absolute count in all cases of SARS patients. Their peripheral CD4+ and CD8+ T lymphocyte absolute counts were (（251129/mm3 and 246156 cells/mm3, respectively）. Such loss of T cells could be much severer than those happen in patients with other viral infection including HIV, CMV and EBV.

Conclusions: Severest deficiency of peripheral T cells is key characteristic in fever-phase of patients with SARS, which might lead to subsequently large amount of replication of SARS virus and severe invasion into body. Therefore, application of immunopotentiator in early stage of infection of SARS virus could be a suitable strategy. Besides, severe loss of peripheral T cells could be an impotent biomarker for early diagnosis of SARS.