Fan et al. BMC Cancer 2011, 11:320 http://www.biomedcentral.com/1471-2407/11/320 Page 3 of 8 Figure 1 Immunohistochemical staining of CD133 in normal human liver tissues. CD133 expression was found mainly on the apical membrane surface of bile ducts of different sizes in normal liver tissue. (A) Normal small bile ducts, original magnification 200×; (B) Reactive bile ducts, original magnification 200×; (C) Large bile duct, original magnification 400×. In addition, CD133-positive cellular debris in the glandular lumina was observed in some normal bile ducts (B, arrow). The subcellular localization of the CD133 protein was investigated and three staining patterns, i.e. apical mem- brane, cytoplasm or both, were identified in CC (Figure 2D-F). In addition, some normal bile ducts (Figure 1B) and most CD133-positive tumors showed the shedding of CD133 positive cellular debris into the glandular lumina (Figure 2E). The Expression and Different Subcellular Localization of CD133 Correlate with the Differentiation Status of CC Tumors In the well, moderately and poorly differentiated CC, the numbers of CD133 positive cases were 19 (19 of 21, 90%), 10 (10 of 12, 83%) and 11 (11 of 21, 52%) respec- tively. Spearman correlation test showed that the Figure 2 The expression and different subcellular localization of CD133 in CC. Among the CD133-positive cholangiocarcinoma, three staining patterns were identified: the well-differentiated tumors (A) were stained mostly on the apical membrane (D) or both membrane and cytoplasm (E) but the majority of moderately (B) and poorly differentiated (C) tumors were stained in the cytoplasm (F) or both membrane and cytoplasm, original magnification 400×. Also, in some cases, CD133-positive cellular debris was observed in the malignant glandular lumina (E).