The Lung Mycobiome in Idiopathic Interstitial Pneumonia, Collagen Tissue Disease-related Interstitial Lung Disease, and Sarcoidosis

Dysbiosis of the lung microbiome may be associated with the development and progression of respiratory diseases. As fungal spores invade the lungs more easily than bacteria, it seems likely that fungi colonizing the lungs are also involved in respiratory diseases. In this study, we investigated the relationship between fungal flora (mycobiome) and diffuse lung disease. Of the 185 patients who underwent bronchoalveolar lavage (BAL) during the diagnostic process, 42 with diffuse lung disease were selected for a mycobacterial analysis of BAL fluid. Twenty patients with idiopathic interstitial pneumonia (IIP), 8 with collagen tissue disease-related interstitial lung disease (CTD-ILD), 8 with sarcoidosis, and 6 with other diseases were included. Fungal DNA was extracted, and internal transcribed spacer 2 (ITS2) regions were sequenced. Of the 42 patients, 29 had polymerase chain reaction amplification products in the ITS2 region. Significant differences in alpha diversity (observed species, Shannon, and Simpson indices) were found between the CTD-ILD and sarcoidosis groups, and between the IIP and sarcoidosis groups. A comparison of the mycobiomes of individual patients (beta diversity) showed that the clustering patterns differed among the groups. In particular, BAL fluid samples from patients with sarcoidosis showed a clear clustering pattern of mycobacterial composition. Our results may lead to significant advances in our understanding of the etiology of these diseases.