Figure 1

Bronchial biopsy specimen from a COPD current smoker double-stained for both S100A4 (green) and cytokeratin (red). Black arrows showing cells in the basal epithelium and reticular basement membrane (Rbm) and also within the superficial lamina propria, double-stained for both cytokeratin (red, anti-pan-cytokeratin monoclonal antibody, epithelial marker) and S100A4 (green, anti-S100A4 polyclonal antibody, mesenchymal marker). Overall, there are fewer double-stained cells in the Rbm than in the basal epithelium; consistent with loss of epithelial markers as these cells gain mesenchymal markers. Original magnifications 100 ×/1.30 Oil. Scale bar = 50 μm.