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

were subjected to triple-color sequential immunohistochemistry (IHC) and immunofl uorescence staining on the same section. We found that the SARS antigen could be detected in six patients who died within 11 d after illness onset, but not in the other three patients who died 21, 24, or 27 d after disease onset ( Table I ) , which is consistent with a recent report showing that SARS antigen or RNA could not be detected in patients who died Ͼ2 wk after disease onset ( 11 ) . In samples where SARS antigen was detected, as many as 42 SARS ϩ cells in a microscopic fi eld (400ϫ) were identifi ed ( Table I ) . By location, SARS ϩ cells were found in the alveoli ( Fig. 1 , a and b, and d and e , red) and the bronchiolar lining layer ( Fig. 1 , j and k , red). By morphology, SARS ϩ cells were round or oval in shape and rich in cytoplasm ( Fig. 1, b , d, e, j, and k ). Furthermore, SARS ϩ cells did not express surfactant A, a type II pneumocyte marker ( Fig. 1, a, b , d, and j , brown), or cytokeratin ( Fig. 1 , e and k , green). SARS ϩ cells did not express surfactant C (also a type II pneumocyte marker) or T1 ␣ (a type I pneumocyte marker) either (Fig. S2 , available at http://www .jem.org/cgi/content/full/jem.20070462/DC1). Because bronchial/bronchiolar lining layers are composed of multiple cell types that are compactly arranged, some SARS ϩ cells were " overlapping " with adjacent cytokeratin ϩ cells (e.g., one indicated by a circle, Fig. 1 k and Fig. S3 ), which could be mistakenly interpreted as " colocalized " on two-dimensional images. However, they could be carefully distinguished by adjusting the focus under the microscope.