Abstract
The interest in the lung microbiome and virome and their contribution to the pathogenesis, perpetuation and progression of idiopathic pulmonary fibrosis (IPF) has been increasing during the last decade. The utilization of high-throughput sequencing to detect microbial and/or viral genetic material in bronchoalveolar lavage fluid or lung tissue samples has amplified the ability to identify and quantify specific microbial and viral populations. In stable IPF, higher microbial burden is associated with worse prognosis but no specific microbe has been identified to contribute to this. Additionally, no causative relation has been established. Regarding viral infections, although in the past they have been associated with IPF, causation has not been proved. Although in the past the diagnosis of acute exacerbation of IPF (AE-IPF) was not considered in patients with overt infection, this was amended in the last few years and infection is considered a cause for exacerbation. Besides this, a higher microbial burden has been found in the lungs of patients with AE-IPF and an association with higher morbidity and mortality has been confirmed. In contrast, an association of AE-IPF with viral infection has not been established. Despite the progress during the last decade, a comprehensive knowledge of the microbiome and virome in IPF and their role in disease pathogenesis are yet elusive. Although association with disease severity, risk for progression and mortality has been established, causation has not been proven and the potential use as a biomarker or the benefits of antimicrobial therapeutic strategies are yet to be determined.
Highlights
Despite its constant exposure to the environment, the lower respiratory tract has been considered sterile for years
This notion is augmented by the recent discovery that mutations in the gene encoding the mucin 5B (MUC5B), which is essential for mucociliary clearance and in host-bacterial defense, and the extracellular matrix, are associated with increased incidence of both sporadic and familial Idiopathic pulmonary fibrosis (IPF) [16,17]
We summarize the available evidence regarding the lung microbiome in IPF patients, the available data regarding its association with the pathogenesis and its role in the clinical course of the disease
Summary
Despite its constant exposure to the environment, the lower respiratory tract has been considered sterile for years. Idiopathic pulmonary fibrosis (IPF) is a devastating interstitial pneumonia of unknown cause, characterized by the fibrotic distortion of normal lung architecture leading to gas exchange abnormalities and respiratory failure and death [7] It affects older, mostly male individuals, with a median age of diagnosis of 66 years and estimates of incidence between 4.6 to 16.3 per 100,000 individuals [8]. The microbiome, the entirety of the symbiotic and pathogenic microorganisms that compose the microbial ecosystem that inhabits our body, has gained attention concerning its relation to the initiation, perpetuation and exacerbation of the fibrotic process in IPF [6,14,15] This notion is augmented by the recent discovery that mutations in the gene encoding the mucin 5B (MUC5B), which is essential for mucociliary clearance and in host-bacterial defense, and the extracellular matrix, are associated with increased incidence of both sporadic and familial IPF [16,17]. A summary of the studies and their main results can be found in Supplement Table S1
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