Dendritic cells (DC) play a pivotal immunoregulatory role in the Th1, Th2, and Th3 cell balance and are present throughout the gastrointestinal tract. Thus, DC may be targets for modulation by gut microbes, including ingested probiotics. In the present study, we tested the hypothesis that species of Lactobacillus, important members of the gut flora, differentially activate DC. Bone marrow-derived murine DC were exposed to various lethally irradiated Lactobacillus spp. and resultant culture supernatants were analyzed for IL-6, IL-10, IL-12, and TNF-α. Substantial differences were found among strains in the capacity to induce IL-12 and TNF-α production in the DC. Similar but less pronounced differences were observed among lactobacilli in the induction of IL-6 and IL-10. Although all strains up-regulated surface MHC class II and B7-2 (CD86), which is indicative of DC maturation, those lactobacilli with greatest capacity to induce IL-12 were most effective. Remarkably, Lactobacillus reuteri DSM12246, a poor IL-12 inducer, inhibited IL-12, IL-6, and TNF-α induction by the otherwise strong cytokine inducer L. casei CHCC3139, while IL-10 production remained unaltered. In analogous fashion, L. reuteri reduced L. casei-induced up-regulation of B7-2. These results suggest that different species of Lactobacillus exert very different DC activation patterns and, furthermore, at least one species may be capable of inhibiting activities of other species in the genus. Thus, the potential exists for Th1/Th2/Th3-driving capacities of the gut DC to be modulated according to composition of gut microflora, including ingested probiotics.

Objective To investigate whether a whole grain diet alters the gut microbiome and insulin sensitivity, as well as biomarkers of metabolic health and gut functionality. Design 60 Danish adults at risk of developing metabolic syndrome were included in a randomised cross-over trial with two 8-week dietary intervention periods comprising whole grain diet and refined grain diet, separated by a washout period of ≥6 weeks. The response to the interventions on the gut microbiome composition and insulin sensitivity as well on measures of glucose and lipid metabolism, gut functionality, inflammatory markers, anthropometry and urine metabolomics were assessed. Results 50 participants completed both periods with a whole grain intake of 179±50 g/day and 13±10 g/day in the whole grain and refined grain period, respectively. Compliance was confirmed by a difference in plasma alkylresorcinols (p<0.0001). Compared with refined grain, whole grain did not significantly alter glucose homeostasis and did not induce major changes in the faecal microbiome. Also, breath hydrogen levels, plasma short-chain fatty acids, intestinal integrity and intestinal transit time were not affected. The whole grain diet did, however, compared with the refined grain diet, decrease body weight (p<0.0001), serum inflammatory markers, interleukin (IL)-6 (p=0.009) and C-reactive protein (p=0.003). The reduction in body weight was consistent with a reduction in energy intake, and IL-6 reduction was associated with the amount of whole grain consumed, in particular with intake of rye. Conclusion Compared with refined grain diet, whole grain diet did not alter insulin sensitivity and gut microbiome but reduced body weight and systemic low-grade inflammation. Trial registration number NCT01731366; Results.

Saponins are naturally occurring amphiphilic molecules and have been associated with many biological activities. The aim of the present study was to investigate whether soya saponins trigger the onset of soyabean-induced enteritis in Atlantic salmon (Salmo salar L.), and to examine if dietary soya saponins increase the epithelial permeability of the distal intestine in Atlantic salmon. Seven experimental diets containing different levels of soya saponins were fed to seawater-adapted Atlantic salmon for 53 d. The diets included a fishmeal-based control diet, two fishmeal-based diets with different levels of added soya saponins, one diet containing 25 % lupin kernel meal, two diets based on 25 % lupin kernel meal with different levels of added soya saponins, and one diet containing 25 % defatted soyabean meal. The effect on intestinal morphology, intestinal epithelial permeability and faecal DM content was examined. Fish fed 25 % defatted soyabean meal displayed severe enteritis, whereas fish fed 25 % lupin kernel meal had normal intestinal morphology. The combination of soya saponins and fishmeal did not induce morphological changes but fish fed soya saponins in combination with lupin kernel meal displayed significant enteritis. Increased epithelial permeability was observed in fish fed 25 % defatted soyabean meal and in fish fed soya saponin concentrate independent of the protein source in the feed. The study demonstrates that soya saponins, in combination with one or several unidentified components present in legumes, induce an inflammatory reaction in the distal intestine of Atlantic salmon. Soya saponins increase the intestinal epithelial permeability but do not, per se, induce enteritis.

Summary: Humans and other mammals coexist with a diverse array of microbes colonizing the intestine, termed the microflora. The relationship is symbiotic, with the microbes benefiting from a stable environment and nutrient supply, and the host gaining competitive exclusion of pathogens and continuously maintenance of the gut immune homeostasis. Here we report novel crosstalk mechanisms between the human enterocyte cell line, Caco2, and underlying human monocyte‐derived DC in a transwell model where Gram‐positive (G⁺) commensals prevent Toll‐like receptor‐4 (TLR4)‐dependent Escherichia coli‐induced semimaturation in a TLR2‐dependent fashion. These findings add to our understanding of the hypo‐responsiveness of the gut epithelium towards the microflora. Gut DC posses a more tolerogenic phenotype than conventional DC. Here we show that Caco2 spent medium (SM) induces tolerogenic DC with lower expression of maturation markers, interleukin (IL)‐12p70, and tumour necrosis factor‐α when matured with G⁺ and Gram‐negative (G^–) commensals, while IL‐10 production is enhanced in DC upon encountering G⁺ commensals and reduced upon encountering G^– bacteria. The Caco2 SM‐induced tolerogenic phenotype is also seen in DC priming of naive T cells with elevated levels of transforming growth factor‐β (TGF‐β) and markedly reduced levels of bacteria‐induced interferon‐γ production. Caco2 cell production of IL‐8, thymic stromal lymphopoietin (TSLP) and TGF‐β increases upon microbial stimulation in a strain dependent manner. TSLP and TGF‐β co‐operate in inducing the tolerogenic DC phenotype but other mediators might be involved.

Adherence to a low-gluten diet has become increasingly common in parts of the general population. However, the effects of reducing gluten-rich food items including wheat, barley and rye cereals in healthy adults are unclear. Here, we undertook a randomised, controlled, cross-over trial involving 60 middle-aged Danish adults without known disorders with two 8-week interventions comparing a low-gluten diet (2 g gluten per day) and a high-gluten diet (18 g gluten per day), separated by a washout period of at least six weeks with habitual diet (12 g gluten per day). We find that, in comparison with a high-gluten diet, a low-gluten diet induces moderate changes in the intestinal microbiome, reduces fasting and postprandial hydrogen exhalation, and leads to improvements in self-reported bloating. These observations suggest that most of the effects of a low-gluten diet in non-coeliac adults may be driven by qualitative changes in dietary fibres.

Summary: Lactobacilli are probiotics that, among other health‐promoting effects, have been ascribed immunostimulating and virus‐preventive properties. Certain Lactobacillus spp. have been shown to possess strong interleukin‐12 (IL‐12) ‐inducing properties. As IL‐12 production depends on the up‐regulation of type I interferons (IFNs), we hypothesized that the strong IL‐12‐inducing capacity of Lactobacillus acidophilus NCFM in murine bone‐marrow‐derived dendritic cells (DCs) is caused by an up‐regulation of IFN‐β, which subsequently induces IL‐12 and the double‐stranded RNA binding Toll‐like receptor‐3 (TLR‐3). The expression of the genes encoding IFN‐β, TLR‐3, IL‐12 and IL‐10 in DCs upon stimulation with L. acidophilus NCFM was determined. Lactobacillus acidophilus NCFM induced a much stronger expression of Ifn‐β, Il‐12 and Il‐10 compared with the synthetic double‐stranded RNA ligand Poly I:C, whereas the levels of expressed Tlr‐3 were similar. Whole genome microarray gene expression analysis revealed that other genes related to viral defence were significantly up‐regulated and among the strongest induced genes in DCs stimulated with L. acidophilus NCFM. The ability to induce IFN‐β was also detected in another L. acidophilus strain (X37), but was not a property of other probiotic strains tested, i.e. Bifidobacterium bifidum Z9 and Escherichia coli Nissle 1917. The IFN‐β expression was markedly reduced in TLR‐2^−/− DCs, dependent on endocytosis, and the major cause of the induction of Il‐12 and Tlr‐3 in DCs stimulated with L. acidophilus NCFM. Collectively, our results reveal that certain lactobacilli trigger the expression of viral defence genes in DCs in a TLR‐2 manner dependent on IFN‐β.