A novel subset of putative stem/progenitor CD34(+)Oct-4(+) cells is the major target for SARS coronavirus in human lung

Chen, Yongxiong; Chan, Vera Sau-Fong; Zheng, Bojian; Chan, Kelvin Yuen-Kwong; Xu, Xiaoning; To, Leo Yuk-Fai; Huang, Fang-Ping; Khoo, Ui-Soon; Lin, Chen-Lung Steve

leukocytes infi ltrating in the lung. Results showed that the SARS Ï© cells did not express tryptase, defensins 1/2/3, CD15, CD68, CD57, CD45RO, CD3, and CD20, indicating that they were not mast cells, neutrophils, macrophages/monocytes, NK, T, or B cells (Fig. S5 , available at http://www.jem.org/ cgi/content/full/jem.20070462/DC1). We next examined the markers for other cell types. CD34 is expressed by hematopoietic progenitors in the circulation ( 19 ) and also by bone marrow stromal cell precursors ( 20 ) . By a four-color sequential IHC and simultaneous fl uorescence in situ hybridization (FISH) and ISH study, we demonstrated that SARS Ï© cells ( Fig. 2 a , red) were distinct from cells expressing the macrophage/monocyte-specifi c marker CD68 ( Fig. 2 a , brown) , and the SARS Ï© cells expressed the only known functional receptor ACE2 ( Fig. 2 b , green) as well as the stem/progenitor cell marker CD34 ( Fig. 2 c , purple). Similar observations were made in the bronchioles, i.e., SARS Ï© cells expressed both ACE2 and CD34 (Fig. S6 ). In a separate sequential IHC/ FISH/ISH study, SARS Ï© cells ( Fig. 2 i , red) expressed CD34 ( Fig. 2 j , green) and another stem/progenitor cell marker, Oct-4 ( Fig. 2 k , purple). Oct-4 is a transcription factor, and its activity is essential for maintaining pluripotency of the some of previous reports the identity of the SARS Ï© cells was judged by morphology or location alone without colocalization with specifi c markers to confi rm the phenotype ( 6, 7, 10 ) . In addition, these reports used avidin -biotin complex for SARS-CoV or cytokeratin staining ( 6, 7, 10 ) . Biotin is widely dispersed in mammalian tissues ( 15 -17 ) , and the presence of endogenous biotin is likely to result in false-positive readings, even after blocking procedures before immunodetection ( 18 ) . Experiences with this problem have also been encountered in our lab (Fig. S4 , available at http://www.jem.org/cgi/content/ full/jem.20070462/DC1). In other reports, the double-color results for colocalization either could not be clearly diff erentiated from single-color staining ( 8, 9 ) or were interfered by autofl uorescence ( 11, 12 ) or by hematoxylin counterstaining ( 9 ) . It is also a concern that none of these reports demonstrates the colocalization of ACE2 expression with the SARS Ï© cells.