Background Altered composition of intestinal microbiota in recent-onset rheumatoid arthritis (RA) and possible efficacy of oral antibiotics suggest a role of intestinal microbiota in RA. This study aimed to investigate the involvement of commensal intestinal microbiota in T cell-dependent experimental arthritis.
Methods IL-1 receptor antagonist deficient (IL-1Ra-/-) mice spontaneously developing T cell-driven IL-17-dependent autoimmune arthritis were used. Intestinal and systemic T cell differentiation and arthritis development were studied in conventional and germ-free (GF) mice. Contribution of intestinal microbiota was investigated using oral broad-spectrum and selective antibiotic treatments, combined with recolonization by specific microbiota. Multiplex 454 pyrosequencing of V5 and V6 hyper-variable regions of fecal bacterial 16S rRNA was used to identify specific microbiota associated with arthritis.
Results Compared to wild-type mice, small intestinal lamina propria of IL-1Ra-/- mice contained increased Th17 and to lower extent Th1 percentages, both of which significantly correlated with arthritis severity. Importantly, GF IL-1Ra-/- mice had a marked abrogation of arthritis along with reduced intestinal Th1 and in particular Th17. GF IL-1Ra-/- mice exhibited a notable decrease in IL-1b and IL-17 production by splenocytes upon CD3 and Toll-like receptor stimulations, suggesting abolishment of systemic Th17 response.
Relevance of intestinal microbiota was underlined by significant long-term suppression of arthritis by one-week oral treatment with Metronidazole, Neomycin and Ampicillin (each 1g/l). Interestingly, recolonization of antibiotic-treated IL-1Ra-/- mice by segmented filamentous bacteria, previously reported as a prominent intestinal Th17 inducer, was sufficient to cause full-blown arthritis. Selective elimination of Gram-negative bacteria, but not Gram-positive, suppressed arthritis, indicating members of intestinal Gram-negative commensals may drive arthritis.
High-throughput pyrosequencing revealed lower microbiota abundance (operational taxonomic units) and reduced species richness and diversity (Chao and Shannon indices, resp.) in arthritic IL-1Ra-/- compared to wild-type mice. The genus Helicobacter, belonging to Gram-negative bacteria, was found associated with arthritis severity (0.0% in wild-type versus 1.1% in arthritic mice). Validation of microbiota alterations and studies on T cell-modulatory and disease-inducing characteristics in GF mice are in progress.
Conclusion The presence of commensal intestinal microbiota is critical for the development of autoimmune T cell-driven arthritis, probably via shaping the T cell differentiation by Gram-negative bacteria. Understanding the molecular and cellular mechanisms linking the intestinal T cell response with extra-intestinal disease may help identify novel therapeutic targets in RA.