Microbiome and Behçet's disease: a systematic review

The aim of this review was to describe the changes in the microbiota of patients with Behçet's disease (BD) and the mechanisms involved in the relationship between the microbiome and immunity in BD. A systematic search for relevant articles was made on PubMed and the Cochrane Library database using the following terms: "microbiota AND Behçet's disease" or "microbiome AND Behçet's disease". Sixteen articles were included in a qualitative synthesis. This systematic review on the microbiome and Behçet's disease underlines the presence of gut dysbiosis in BD patients. This dysbiosis is marked by (i) a decrease in butyrate-producing bacteria, which could affect T cell differentiation and epigenetic regulation of immune-related genes, (ii) a modification of tryptophan-metabolising bacteria, which could be linked to dysregulated IL-22 secretion, and (iii) a decrease in bacteria known to have anti-inflammatory properties. Regarding oral microbiota, this review underlines the possible role of Streptococcus sanguinis through molecular mimicry and NETosis. Clinical studies of BD have shown that (i) need for dentistry is associated with a more severe course in BD, and (ii) antibiotic-supplemented mouthwash reduces pain and ulcers. Fecal transplantation of BD patients' microbiota into mouse models led to decreased SCFA production, neutrophil activation, and Th1/Th17 responses.Recipient mice showed exacerbated experimental autoimmune uveitis (EAU) and experimental autoimmune encephalomyelitis (EAE). In Herpes Virus Simplex-1 (HSV-1) infected mice mimicking BD, administration of butyrateproducing bacteria improved symptoms and immune variables. The microbiome may thus be involved in BD through immunity regulation and epigenetic modifications.