Faculty Bibliography

The role of the gut microbiome in models of inflammatory and autoimmune disease is now well characterized. Renewed interest in the human microbiome and its metabolites, as well as notable advances in host mucosal immunology, has opened multiple avenues of research to potentially modulate inflammatory responses. The complexity and interdependence of these diet-microbe-metabolite-host interactions are rapidly being unraveled. Importantly, most of the progress in the field comes from new knowledge about the functional properties of these microorganisms in physiology and their effect in mucosal immunity and distal inflammation. This review summarizes the preclinical and clinical evidence on how dietary, probiotic, prebiotic, and microbiome based therapeutics affect our understanding of wellness and disease, particularly in autoimmunity.

The objective of the study is to determine the risk factors for the development of reactive arthritis (ReA) and examine the factors associated with the persistence of symptoms. Patients with a new diagnosis of ReA and controls with a gastrointestinal (GI), urogenital, or sexually transmitted infection in the 3-6 months prior to study entry were prospectively enrolled in Guatemala City. ReA patients fulfilled the Assessment in Spondyloarthritis International Society criteria for peripheral spondyloarthropathy (SpA). Patients underwent history, examination, Achilles tendon ultrasound, and blood draw. Human leukocyte antigen (HLA) type and serum biomarkers were measured. t tests and nonparametric equivalents were used to examine the association of clinical, laboratory, and imaging factors with ReA. Patients were contacted 2 years later to assess for persistence of symptoms. Study subjects included patients with ReA (N = 32) and controls (N = 32). ReA patients were most frequently infected in April whereas controls were most frequently infected in August. Two ReA patients and two controls were HLA-B27-positive. Serum cathepsin K and C-reactive protein were higher in ReA patients compared to controls (p = 0.03 for both), while total cholesterol and low-density lipoprotein were lower (p = 0.008 and 0.045, respectively). Among those with ReA, 15 (47%) patients had continued symptoms at 2 years. These patients had a lower matrix metalloproteinase-3 level at diagnosis than patients for whom ReA resolved (p = 0.004). HLA-B27 was not associated with development of ReA in Guatemala; however, the month of infection was associated with ReA. The most striking finding was the persistence of arthritis at 2 years in nearly half of the patients.

OBJECTIVE: Reactive arthritis (ReA) is an inflammatory disorder occurring several weeks after gastrointestinal or genitourinary infections. HLA-B27 positivity is considered a risk factor, though not necessarily predictive of disease incidence. Among non-genetic factors, the intestinal microbiome may play a role in disease susceptibility. The objective of this study was to characterize the gut microbiota and host gene interactions in ReA and post-infectious spondyloarthritis. METHODS: Adult peripheral spondyloarthritis and control subjects with preceding infections that did not develop arthritis were prospectively recruited from a highly prevalent geographic region. Clinical variables, HLA status, and 16S rRNA gene sequencing of intestinal microbiota were analyzed. RESULTS: ReA subjects showed no significant differences from controls in gut bacterial richness or diversity. However, there was a significantly higher abundance of Erwinia and Pseudomonas, and increased prevalence of typical enteropathogens associated with ReA. Subjects with ultrasound evidence of enthesitis were enriched in Campylobacter, while subjects with uveitis and radiographic sacroiliitis were respectively enriched in Erwinia and unclassified Ruminococcaceae, and both enriched in Dialister. Host genetics, particularly HLA-A24, were associated with differences in gut microbiota diversity irrespective of disease status. We determined several co-occurring taxa that were also predictive of HLA-A24 status. CONCLUSION: This is the first culture-independent study characterizing the gut microbial community of post-infectious arthritis. Although bacterial factors correlated with disease presence and clinical features of ReA, host genetics also appeared to be a major independent driver of intestinal community composition. Understanding of these gut microbiota host-genetic relationships may further clarify the pathogenesis of post-infectious spondyloarthropathies.

Perturbations of the intestinal microbiome have been observed in patients with new-onset and chronic autoimmune inflammatory arthritis. However, it is currently unknown whether these alterations precede the development of arthritis or are rather a consequence of disease. Modulation of intestinal microbiota by oral antibiotics or germ-free condition can prevent arthritis in mice. Yet, the therapeutic potential of modulation of the microbiota after the onset of arthritis is not well characterized. We here show that the intestinal microbial community undergoes marked changes in the preclinical phase of collagen induced arthritis (CIA). The abundance of the phylum Bacteroidetes, specifically families S24-7 and Bacteroidaceae was reduced, whereas Firmicutes and Proteobacteria, such as Ruminococcaceae, Lachnospiraceae and Desulfovibrinocaceae, were expanded during the immune-priming phase of arthritis. In addition, we found that the abundance of lamina propria Th17, but not Th1, cells is highly correlated with the severity of arthritis. Elimination of the intestinal microbiota during established arthritis specifically reduced intestinal Th17 cells and attenuated arthritis. These effects were associated with reduced serum amyloid A expression in ileum and synovial tissue. Our observations suggest that intestinal microbiota perturbations precede arthritis, and that modulation of the intestinal microbiota after the onset of arthritis may offer therapeutic opportunities.