Morphological changes and gene expression in aged lung tissue. Histological analysis (haemotoxylin and eosin) of 6 month (A) and 18 month (B) old lung tissue from female BALB/c mice revealed enlarged alveolar ducts and decreased tissue integrity (arrow). Sirius red staining revealed the collagen deposition in adult (C) and aged (D) lung tissue (arrows). Histology was representative of 5 animals from each age group. Analysis of the expression of the protein-coding genes Col1a1, Col3a1 and Col6a3 was performed by RT-PCR (E). Data is represented as the mean ΔCT +/- S.E.M. (CT value of gene – CT value of 18 s), therefore the higher the expression the smaller the ΔCT value. All three genes exhibited statistical significance following 6 months and 18 months comparison, according to Student's t-test (*p < 0.05).