Under exponential growth conditions (cells grown in 10% FCS, i.e. actively dividing cells), IPF-derived lung fibroblasts demonstrated a 4.72 to 11.29 fold elevation of cyclin D1 mRNA expression (average of 10.10 fold increase) compared to the CCD8LU normal lung fibroblast cell line (p < 0.05). This evidence concerns the gene CCND1 and idiopathic pulmonary fibrosis.