Characterization of cultured lung fibroblasts. Lung fibroblasts isolated from BLM-treated GFP BM chimera mice were analyzed by fluorescence microscopy (a–f). The cells showed typical fibroblast morphology, many being stellate or spindle-shaped (a). An average 80% of these cells expressed GFP (green fluorescence in a, at ×100; inset at ×400). Cells were stained with both anti-GFP (green) and anti–Col I (red) antibodies in b–d. The same microscopic field was photographed with the green (b) or red (c) filter only, or both simultaneously (d). Colocalization of both GFP and Col I expression resulted in a yellow color in d. Inset in d shows the cells stained with anti-GFP antibody (green) and isotype-matched control IgG for Col I (red). Cells were also stained with both anti-GFP (green) and anti–α-SMA (red) antibodies (e). Colocalization of GFP and α-SMA should appear yellow, but the two α-SMA⁺ cells in this field did not appear to express GFP (e). Finally, cells were also stained with anti-GFP (green) and anti-TERT (red) antibodies. Colocalization of GFP and TERT appeared yellow, and most of the cells in this field expressed both TERT and GFP (f). Magnification was ×200 for b–f. A representative example of at least three independent experiments is shown.