STAT1-/- mammary tumor cells display a luminal epithelial cell phenotype. (A) Gating procedure used for the analysis of cell surface markers. Disaggregated mammary glands or mammary tumors were collected by an LSRII flow cytometer and analyzed by using FlowJo. Cells were first selected on the basis of size by using forward and side scatter (left panel). Single cells were then selected by forward scatter (FSC)-A and FSC-W (middle panel). Live cells (DAPI-) and lineage- cells (Ter119-, CD31-, and CD45-) were gated for the analysis depicted in (B). (B) Expression of CD49f and CD24 on STAT1-/- mammary epithelial cells (MECs), mammary intraepithelial neoplasia (MIN), and carcinoma. Representative images from five STAT1-/- mice are shown. Myoepithelial (myo) and luminal epithelial (lum) are highlighted. (C) Immunohistochemical analysis of primary STAT1-/- mammary tumors for cytokeratin (CK) 5, 14, 8/18, and 19. Mammary tumor cells were stained positive for CK19 and CK8/18 (luminal epithelial markers) but negative for CK5 and CK14 (myoepithelial markers). Scale bar = 100 μm. DAPI, 4'-6-diamidino-2-phenylindole.