Gut microbiota and sarcoidosis: a concise review

Microbial involvement in sarcoidosis pathogenesis is suggested by the observation that histological findings in sarcoid granulomas are like those of leprosy, tuberculosis and parasitic infection. Some studies have shown that the lung microbiome in patients with sarcoidosis is different from healthy individuals. Results are conflicting, reporting an abundance or decrease in bacterial and fungal species. The altered composition of the microbiome in sarcoidosis can contribute to the formation of granulomas, typical lesions of the disease, through interactions with the host immune system. However, no single microbe has been clearly demonstrated as a cause of sarcoidosis, several microorganisms have been involved in the formation of granulomas and are under study. In fact, various microorganisms have been detected in sarcoid granulomas and in the tissue of different organs. Microorganisms were demonstrated at the genomic level and only a few studies showed microbial presence using bacteriological or proteomic methods. A possible microbial involvement in sarcoidosis pathogenesis is further supported by studies reporting innate immune system activation and increased inflammatory cytokines secretion. Of note, a meta-analysis involving over 6,000 patients identified a strong association between Cutibacterium acnes and Mycobacterium tuberculosis and sarcoidosis. Interestingly, some studies have compared microbiomes in sarcoidosis with chronic respiratory conditions like chronic obstructive pulmonary disease, asthma, interstitial lung disease, and occupational lung diseases. Little is known whether gut microbiota alteration plays a causal role in the development of these diseases or is a consequence of a shared risk factor profile. However, current evidence does not conclusively support the causative role of microbes in sarcoidosis. Furthermore, research is studying the role of intestinal microbiomes in sarcoidosis with some studies showing that the restoration of the intestinal microbiome could be a possible therapeutic approach. The aims of the review are: (1) to clarify microbial involvement in sarcoidosis pathogenesis, (2) to describe microbiota in lungs of patients with sarcoidosis and to compare the data with other interstitial lung diseases.