Gut epithelial barrier dysfunction in lupus triggers a differential humoral response against gut commensals

Detection of Serum IgG Specific for Brachyspira pilosicoli and "Brachyspira canis" in Dogs

Brachyspira pilosicoli (B. pilosicoli) is a pathogen in pigs, poultry, and humans causing colitis, diarrhea, and poor growth rates. Its role as a canine pathogen is controversial, and the seroprevalence of specific IgG antibodies against B. pilosicoli in dogs is unknown. A further, not yet officially recognized Brachyspira species in dogs is "Brachyspira canis" ("B. canis"), which is proposed to be apathogenic. This study evaluates enzyme-linked immunosorbent assays (ELISAs) measuring serum IgG antibodies specific for B. pilosicoli or "B. canis" and investigates levels of specific IgG antibodies against B. pilosicoli and "B. canis" in a cohort of clinical patients presented at an animal referral clinic. These ELISAs use detergent-extracted antigens from B. pilosicoli and "B. canis". To increase analytic specificity, we precipitated the antigens with trichloroacetic acid (TCA) to isolate and concentrate the respective protein fraction. Our results indicate that a large number of serum IgG antibodies bind to shared epitopes of detergent-extracted antigens of the two spirochaetes. Our data also suggest that dogs might not only carry B. pilosicoli but also have "B. canis"-specific serum IgG antibodies.

Interferon subverts an AHR-JUN axis to promote CXCL13+ T cells in lupus

Systemic lupus erythematosus (SLE) is prototypical autoimmune disease driven by pathological T cell-B cell interactions1,2. Expansion of T follicular helper (TFH) and T peripheral helper (TPH) cells, two T cell populations that provide help to B cells, is a prominent feature of SLE3,4. Human TFH and TPH cells characteristically produce high levels of the B cell chemoattractant CXCL13 (refs. 5,6), yet regulation of T cell CXCL13 production and the relationship between CXCL13+ T cells and other T cell states remains unclear. Here, we identify an imbalance in CD4+ T cell phenotypes in patients with SLE, with expansion of PD-1+/ICOS+ CXCL13+ T cells and reduction of CD96hi IL-22+ T cells. Using CRISPR screens, we identify the aryl hydrocarbon receptor (AHR) as a potent negative regulator of CXCL13 production by human CD4+ T cells. Transcriptomic, epigenetic and functional studies demonstrate that AHR coordinates with AP-1 family member JUN to prevent CXCL13+ TPH/TFH cell differentiation and promote an IL-22+ phenotype. Type I interferon, a pathogenic driver of SLE7, opposes AHR and JUN to promote T cell production of CXCL13. These results place CXCL13+ TPH/TFH cells on a polarization axis opposite from T helper 22 (TH22) cells and reveal AHR, JUN and interferon as key regulators of these divergent T cell states.

D-beta-hydroxybutyrate up-regulates Claudin-1 and alleviates the intestinal hyperpermeability in lipopolysaccharide-treated mice

The hyperpermeability of intestinal epithelium is a key contributor to the occurrence and development of systemic inflammation. Although D-beta-hydroxybutyrate (BHB) exhibits various protective effects, whether it affects the permeability of intestinal epithelium in systemic inflammation has not been clarified. In this study, we investigated the effects of BHB on the intestinal epithelial permeability, the epithelial marker E-cadherin and the tight junction protein Claudin-1 in colon in the lipopolysaccharide (LPS)-induced systemic inflammation mouse model. Intraperitoneal injection of LPS was used to induce systemic inflammation and BHB was given by oral administration. The permeability of intestinal epithelium, the morphological changes of colonic epithelium, the distribution and generation of colon E-cadherin, and the Claudin-1 generation and its epithelial distribution in colon were detected. The results confirmed the intestinal epithelial hyperpermeability and inflammatory changes in colonic epithelium, with disturbed E-cadherin distribution in LPS-treated mice. Besides, colon Claudin-1 generation was decreased and its epithelial distribution in colon was weakened in LPS-treated mice. However, BHB treatments alleviated the LPS-induced hyperpermeability of intestinal epithelium, attenuated the colonic epithelial morphological changes and promoted orderly distribution of E-cadherin in colon. Furthermore, BHB up-regulated colon Claudin-1 generation and promoted its colonic epithelial distribution and content in LPS-treated mice. In conclusion, BHB may alleviate the hyperpermeability of intestinal epithelium via up-regulation of Claudin-1 in colon in LPS-treated mice.

Dietary tryptophan and genetic susceptibility expand gut microbiota that promote systemic autoimmune activation

Tryptophan modulates disease activity and the composition of microbiota in the B6.Sle1.Sle2.Sle3 (TC) mouse model of lupus. To directly test the effect of tryptophan on the gut microbiome, we transplanted fecal samples from TC and B6 control mice into germ-free or antibiotic-treated non-autoimmune B6 mice that were fed with a high or low tryptophan diet. The recipient mice with TC microbiota and high tryptophan diet had higher levels of immune activation, autoantibody production and intestinal inflammation. A bloom of Ruminococcus gnavus (Rg), a bacterium associated with disease flares in lupus patients, only emerged in the recipients of TC microbiota fed with high tryptophan. Rg depletion in TC mice decreased autoantibody production and increased the frequency of regulatory T cells. Conversely, TC mice colonized with Rg showed higher autoimmune activation. Overall, these results suggest that the interplay of genetic and tryptophan can influence the pathogenesis of lupus through the gut microbiota.