SPP1 and Langerhans cell histiocytosis: OPN also plays an important role in the pathogenesis of interstitial pneumonia associated with cigarette smoking, as shown in an experiment by Prasse et al. OPN levels were examined in bronchoalveolar lavage (BAL) cells from 11 patients with Langerhans cell histiocytosis (PLCH), 15 patients with desquamative interstitial pneumonia (DIP), 10 patients with idiopathic pulmonary fibrosis and 5 patients with sarcoidosis, and, additionally, 13 healthy smokers and 19 non-smokers were examined.