The intestinal microbiome in spondyloarthritis

Abstract

Purpose of review: Microbial dysbiosis in the gut is emerging as a common component in various inflammatory disorders including spondyloarthritis (SpA). The depth of this influence has begun to be realized with next-generation sequencing of the gut microbiome providing unbiased assessment of previously uncharted bacterial populations.

Recent findings: Decreased numbers of Firmicutes, a major phyla of gut commensals, especially the species Faecalibacterium prausnitzii and Clostridium leptum have been found in various inflammatory disorders including SpA and inflammatory bowel disease (IBD), and could be an important link between SpA and gut inflammation. Multiple studies in ankylosing spondylitis, psoriatic arthritis, juvenile SpA, and animal models of SpA are revealing common bacterial associations among these diseases as well as IBD.

Summary: We are beginning to appreciate the complex relationship between the gut microbiome and host immune regulation and dysregulation in health and disease. Potentially important differences have been revealed in SpA, but cause and effect relationships remain far from established. Many critical questions remain to be answered before we can apply new knowledge to improve therapeutics in SpA.

Figure 1

Host genetics, environmental triggers or inflammation may all trigger changes to the intestinal microbiota (dysbiosis). Importantly, changes to the intestinal microbiota itself may cause or contribute to inflammation. Host genetics may either create niches that promote dysbiosis, or directly alter immune responses to the ‘normal’ microbiota. These altered immune responses may manifest in hyper-active innate and adaptive immune responses that promote inflammation. Due to intimate epithelial-microbiota interactions, dysbiosis may also disrupt barrier function and intestinal homeostasis leading to inflammation, a process itself that may impair barrier integrity. Environmental triggers of dysbiosis are incompletely understood, but include diet and antibiotic use.