Characterization of primary human breast cancer epithelial cells (HBCEC). A. Scanning electron micrographs of human breast cancer-derived cell cultures. The cells are squamous with many short and thin processes and grow upon each other. B. Ultrathin sections of two human breast cancer-derived cells, which partially overlap and are connected by desmosomes. The cells contain bundles of intermediate filaments and cytoplasmic vacuoles, whereas organelles are almost absent. In the right transmission micrograph, two squamous cell processes are connected by desmosomes and bundles of intermediate filaments are orientated in parallel to the cell surface. C. Immunofluorescence of intermediate filaments. Nuclei became visual using DAPI and the intermediate filament proteins cytokeratin (green) and vimentin (red) were detected by FITC-conjugated mouse anti-cytokeratin and mouse anti-vimentin antibody, respectively. D. Quantification of cytokeratin, vimentin and desmin expression by flow cytometric analysis. About 99% of the HBCEC population stained positive for cytokeratin, whereof some were positive for both, cytokeratin and vimentin intermediate filament proteins. Expression of desmin intermediate filaments remained undetectable. The FITC-labeled IgG control and the secondary antibody control served as background staining balance.