Microbiome in connective tissue diseases associated interstitial lung disease

Microbiome consists of a large community of bacteria, yeast, protozoa, and viruses that co-exist in symbiosis with human hosts. Changes in microbiome, named "dysbiosis," alter the interplay between microbiome and immune system triggering inflammation and contributing to the pathogenesis of connective tissue diseases (CTD). Interstitial lung diseases (ILD) are a group of pulmonary disorders characterized by lung tissue fibrosis and impaired lung function. The existence of a gut-lung axis is well demonstrated; however, it is not established whether gastrointestinal dysbiosis contributes to ILD development. ILD represent a major cause of morbidity and mortality in CTD patients. Lung microbiome changes and high microbial load are associated with worse prognosis and acute exacerbations in patients with CTD-ILD and especially in those affected by rheumatoid arthritis, systemic sclerosis and dermatomyositis. Probiotics are active microorganisms that normalize the intestinal flora and their use has been proposed as potential supportive treatment of CTD-ILD. Present knowledge of the relationships between dysbiosis and CTD-ILD development is largely incomplete and further studies are needed to validate this issue. Aim of this concise review is to report current knowledge on microbiome in CTD-ILD focusing on clinical lung aspects and therapeutic options.