Spondyloarthritis and the microbiome: new insights from an ancient hypothesis.

The human microbiome, which represents the total collection of microorganisms (and their genes) inhabiting the human body, has increasingly been recognized as a potential key factor in the development of autoimmune disease. Multiple studies suggest that the microbiome has significant influence on immune homeostasis, while disruptions in local microbiome composition can result in a heightened systemic inflammatory response. The intestinal microbiome, in particular, harbors the densest assembly of bacteria and appears to influence the immune system in the context of inflammatory arthropathies. Although studies are still sparse, this review will examine the role of the microbiome in the pathogenesis of spondyloarthritis (SpA), particularly in enteropathic arthritis (EA), reactive arthritis (ReA), ankylosing spondylitis (AS), and psoriatic arthritis (PsA).