Histochem Cell Biol (2010) 134:205–213 209 Fig. 2 ATII cell distribution changes with aging in HPS dou- ble mutant mice. Representative prosurfactant C-stained (brown precipitate) lung sections using IHC from HPS mice at a 2 months, b 5 months, c 9 months, and d WT and e CHS at the age of 12 months. The ATII cells in HPS and CHS mu- tants are both enlarged com- pared with WT mice. Panel f shows the average ATII cell number per photomicrograph in HPS double mutant mice at the age of 2, 5, and 9 months. ATII cell number at 5 months of age is signiWcantly lower than those at 2 and 9 months old (asterisk). Panel g shows the average ATII cell number per photomicro- graph in WT and CHS mice from 2 months to 17 months of age. The cell density was con- stant in WT mice, but showed a non-signiWcant decrease in CHS mice In addition to their distribution, the morphology of ATII cells in HPS changed with aging. These cells were elon- gated along the alveolar walls in the double mutant at 1 year old and beyond (Fig. 3a, b), when it was not possible to assess the number of ATII cells/alveolus in HPS. ATII cells in WT and CHS lungs showed no obvious changes in shape (data not shown). The aggregation and dysmorphism of HPS ATII cells at later ages suggested an EMT process in this cell type. How- ever, the dual stainings for ATII cell marker surfactant C and myoWbroblast marker -SMA did not exhibit co-stain- ing (Fig. 4). Instead, the possible myoWbroblasts with -SMA staining and clusters of ATII cells both appeared around the thickened alveolar walls and Wbrotic patches (Fig. 4a, b). TGF 1 in HPS double mutant mice As seen in Fig. 5a, signiWcantly higher levels of TGF 1 in HPS BAL supernatants were found at all ages tested, 123