Metagenomic Analysis of Lung Microbiome in Patients With Interstitial Lung Diseases and Sarcoidosis: An Experimental Study

Background and Aims: Interactions between the lung microbiome and pulmonary epithelium plays a pivotal role in shaping immunity in the lung. Idiopathic pulmonary fibrosis (IPF) is the most common interstitial lung disease (ILD). Some patients with IPF develop episodic acute exacerbations often associated with microbial dysbiosis in the lungs. This study aimed to investigate etiologic agents as well as the lung microbiome in patients with ILDs and sarcoidosis. Methods: This study analyzed 31 patients divided into the IPF (IPF-stable, n = 12), acute exacerbation of ILDs (AE-ILDs, n = 6), and sarcoidosis (n = 13) groups. Bronchoalveolar lavage fluid (BALF) samples were analyzed by RNA-based metagenomic next-generation sequencing (NGS) on an Illumina platform. Results: In total, 87 pathogens were detected using metagenomic NGS at the genus level. Prevotella, Streptococcus, and Veillonella dominated the BALF microbial communities, and sequence reads of these bacteria were abundant, especially in the sarcoidosis group. Conversely, only a small number of bacterial reads were detected in the AE-ILDs group, and the overall proportion of microbial composition differed from that of the other groups. No significant difference was found in community diversity (α-diversity) among the groups, whereas the structural similarity of the microflora (β-diversity) differed significantly between the AE-ILDs and sarcoidosis groups. Conclusions: Bacterial sequence reads in BALF were smaller in both the IPF-stable and AE-ILD groups than in the sarcoidosis group. Dysbiosis in the lung microbiome has been observed in patients with AE-ILD and may be related to the progression of inflammation.