Clec12a tempers inflammation while restricting expansion of a colitogenic commensal.

Regulation of the microbiota is critical to intestinal health yet the mechanisms employed by innate immunity remain unclear. Here we show that mice deficient in the C-Type-lectin receptor, Clec12a developed severe colitis, which was dependent on the microbiota. Fecal-microbiota-transplantation (FMT) studies into germfree mice revealed a colitogenic microbiota formed within Clec12a -/- mice that was marked by expansion of the gram-positive organism, Faecalibaculum rodentium . Treatment with F. rodentium was sufficient to worsen colitis in wild-type mice. Macrophages within the gut express the highest levels of Clec12a. Cytokine and sequencing analysis in Clec12a -/- macrophages revealed heighten inflammation but marked reduction in genes associated with phagocytosis. Indeed, Clec12a -/- macrophages are impaired in their ability to uptake F. rodentium. Purified Clec12a had higher binding to gram-positive organisms such as F. rodentium . Thus, our data identifies Clec12a as an innate immune surveillance mechanism to control expansion of potentially harmful commensals without overt inflammation.

CD11c+ myeloid cell exosomes reduce intestinal inflammation during colitis.

Intercellular communication is critical for homeostasis in mammalian systems, including the gastrointestinal (GI) tract. Exosomes are nanoscale lipid extracellular vesicles that mediate communication between many cell types. Notably, the roles of immune cell exosomes in regulating GI homeostasis and inflammation are largely uncharacterized. By generating mouse strains deficient in cell-specific exosome production, we demonstrate deletion of the small GTPase Rab27A in CD11c+ cells exacerbated murine colitis, which was reversible through administration of DC-derived exosomes. Profiling RNAs within colon exosomes revealed a distinct subset of miRNAs carried by colon- and DC-derived exosomes. Among antiinflammatory exosomal miRNAs, miR-146a was transferred from gut immune cells to myeloid and T cells through a Rab27-dependent mechanism, targeting Traf6, IRAK-1, and NLRP3 in macrophages. Further, we have identified a potentially novel mode of exosome-mediated DC and macrophage crosstalk that is capable of skewing gut macrophages toward an antiinflammatory phenotype. Assessing clinical samples, RAB27A, select miRNAs, and RNA-binding proteins that load exosomal miRNAs were dysregulated in ulcerative colitis patient samples, consistent with our preclinical mouse model findings. Together, our work reveals an exosome-mediated regulatory mechanism underlying gut inflammation and paves the way for potential use of miRNA-containing exosomes as a novel therapeutic for inflammatory bowel disease.

Epithelial-myeloid exchange of MHC class II constrains immunity and microbiota composition.

Intestinal epithelial cells (IECs) have long been understood to express high levels of major histocompatibility complex class II (MHC class II) molecules but are not considered canonical antigen-presenting cells, and the impact of IEC-MHC class II signaling on gut homeostasis remains enigmatic. As IECs serve as the primary barrier between underlying host immune cells, we reasoned that IEC-intrinsic antigen presentation may play a role in responses toward the microbiota. Mice with an IEC-intrinsic deletion of MHC class II (IECΔMHC class II) are healthy but have fewer microbial-bound IgA, regulatory T cells (Tregs), and immune repertoire selection. This was associated with increased interindividual microbiota variation and altered proportions of two taxa in the ileum where MHC class II on IECs is highest. Intestinal mononuclear phagocytes (MNPs) have similar MHC class II transcription but less surface MHC class II and are capable of acquiring MHC class II from IECs. Thus, epithelial-myeloid interactions mediate development of adaptive responses to microbial antigens within the gastrointestinal tract.

Fiber Puts Lactobacillus to SLEep.

Few studies have analyzed how diet-induced changes in the microbiota influence lupus. In this issue of Cell Host & Microbe, Zegarra-Ruiz et al. (2019) find that translocation of Lactobacillus reuteri from the gut to systemic organs worsens lupus. However, diets with resistant starch restrict L. reuteri growth and ameliorate disease.

A member of the gut mycobiota modulates host purine metabolism exacerbating colitis in mice.

The commensal microbiota has an important impact on host health, which is only beginning to be elucidated. Despite the presence of fungal, archaeal, and viral members, most studies have focused solely on the bacterial microbiota. Antibodies against the yeast Saccharomyces cerevisiae are found in some patients with Crohn's disease (CD), suggesting that the mycobiota may contribute to disease severity. We report that S. cerevisiae exacerbated intestinal disease in a mouse model of colitis and increased gut barrier permeability. Transcriptome analysis of colon tissue from germ-free mice inoculated with S. cerevisiae or another fungus, Rhodotorula aurantiaca, revealed that S. cerevisiae colonization affected the intestinal barrier and host metabolism. A fecal metabolomics screen of germ-free animals demonstrated that S. cerevisiae colonization enhanced host purine metabolism, leading to an increase in uric acid production. Treatment with uric acid alone worsened disease and increased gut permeability. Allopurinol, a clinical drug used to reduce uric acid, ameliorated colitis induced by S. cerevisiae in mice. In addition, we found a positive correlation between elevated uric acid and anti-yeast antibodies in human sera. Thus, yeast in the gut may be able to potentiate metabolite production that negatively affects the course of inflammatory bowel disease.

Evaluation of a high avidity anti-dsDNA IgG enzyme-linked immunosorbent assay for the diagnosis of systemic lupus erythematosus.

The high avidity (HA) anti-dsDNA IgG ELISA is considered highly specific for the diagnosis of systemic lupus erythematosus (SLE). The main objective of this study was to determine the performance of this test with existing assays for detecting anti-dsDNA IgG antibodies as well as assess its analytical characteristics. For method comparison studies, we investigated the correlation between the HA ELISA with 8 other assays for the detection of dsDNA IgG antibodies namely; six anti-dsDNA IgG ELISA, the Crithidia luciliae immunofluorescence test (CLIFT) and an in-house developed Farr radioimmunoassay (RIA). Overall, 125 patient (100 ANA-positive, 25 CLIFT-tested) and 100 healthy control samples were tested. The assay was also evaluated for imprecision, lot-to-lot consistency and the effect of interfering substances using commercial quality control materials based on the manufacturer's claims unless otherwise stated. Of the 100 ANA positive samples, 18 were positive in the HA ELISA with significant levels of antibodies in the six ELISAs and CLIFT. The HA ELISA had a specificity of 100% with an overall agreement of 84% with the RIA. Intra - and inter-assay imprecision ranged from 13.9-16.5% and the reproducibility between lots based on qualitative interpretation was 100%. Hemoglobin, bilirubin and lipemia showed variable interference with assay performance based on the manufacturer's claims and our in-house protocol. Our data suggest that the HA ELISA although less sensitive than the other dsDNA IgG assays evaluated, is specific and predicts high levels of anti-dsDNA IgG antibodies.

Significant differences in the analytic concordance between anti-dsDNA IgG antibody assays for the diagnosis of systemic lupus erythematosus--implications for inter-laboratory testing.

BACKGROUND: Anti-double stranded DNA (anti-dsDNA) autoantibodies are considered hallmark of systemic lupus erythematosus (SLE). METHODS: To determine concordance between assays for the detection of this marker, we analyzed 100 antinuclear antibody (ANA) positive sera with a homogeneous pattern and titers≥1:160 by indirect immunofluorescence assay (IFA) on HEp-2 cells, 100 consecutive anti-dsDNA IgG ELISA-negative as well as 100 healthy control samples using six commercial ELISAs and the Crithidia luciliae immunofluorescence test (CLIFT). RESULTS: The positivity rates for the ELISAs in the ANA positive group ranged from 55.0 to 88.0% with specificities from 84.0 to 98.0%. The CLIFT had a positivity rate of 68.0% and specificity of 84%. In the previously screened anti-dsDNA IgG-negative group, the positivity rates ranged from 1 to 19%. The overall correlations between the ELISAs ranged from 73.0 to 89.5% and varied from 70.0 to 80.0% among specific ELISAs and CLIFT. CONCLUSIONS: Our data show variable degree of concordance between anti-dsDNA IgG ELISAs which may significantly impact inter-laboratory testing as well as the diagnosis and management of SLE patients. Although some of the ELISAs show comparable performance to the CLIFT, the degree of concordance between these assays at high antibody levels suggests that CLIFT is still a relevant confirmatory tool.