Myofibroblasts and S-100 protein positive cells in idiopathic pulmonary fibrosis and rheumatoid arthritis-associated interstitial pneumonia.

The aim of this study was to investigate whether idiopathic pulmonary fibrosis (IPF) can be distinguished from rheumatoid arthritis (RA)-associated interstitial pneumonia (RA-IP) by means of quantitatively assessing myofibroblasts and S-100 protein positive dendritic cells. Seven patients with IPF and twelve with RA, in whom the pathological findings were consistent with usual interstitial pneumonia (UIP) were studied. Antibodies to vimentin, alpha-smooth muscle actin (alpha-SMA) and S-100 protein were used for immunohistochemical studies performed using the streptavidin/biotin/peroxidase complex method, applied to dewaxed sections from each case. In fibrosis of RA-IP, appearance of both vimentin- and alpha-SMA-positive cells, namely myofibroblasts, was widely observed, together with the pathological patterns of honeycombing, UIP and bronchiolitis obliterans-organizing pneumonia (BOOP). Fibrosis, in cases of chronic IPF, was found to be characterized mainly by vimentin-positive but alpha-SMA-negative fibroblasts. Pulmonary tissues from RA-IP patients especially when associated with a BOOP pattern, contained many cells positive for S-100 protein. However, such cells were generally hard to find in cases of IPF. These findings suggests that idiopathic pulmonary fibrosis and rheumatoid arthritis-associated interstitial pneumonia can be differentiated from each other, to some extent, based on the appearance of myofibroblasts and the presence of S-100-positive dendritic cells.