The mammalian intestine harbors a remarkable number of microbes and their components and metabolites, which are fundamental for the instigation and development of the host immune system. The intestinal innate and adaptive immunity coordinate and interact with the symbionts contributing to the intestinal homeostasis through establishment of a mutually beneficial relationship by tolerating to symbiotic microbiota and retaining the ability to exert proinflammatory response towards invasive pathogens. Imbalance between the intestinal immune system and commensal organisms disrupts the intestinal microbiological homeostasis, leading to microbiota dysbiosis, compromised integrity of the intestinal barrier, and proinflammatory immune responses towards symbionts. This, in turn, exacerbates the degree of the imbalance. Intestinal adaptive immunity plays a critical role in maintaining immune tolerance towards symbionts and the integrity of intestinal barrier, while the innate immune system regulates the adaptive immune responses to intestinal commensal bacteria. In this review, we will summarize recent findings on the effects and mechanisms of gut microbiota on intestinal adaptive immunity and the plasticity of several immune cells under diverse microenvironmental settings.

and microbial-dependent metabolites and components driven by inulin on physiological indexes disturbed by a high-fat diet. The objective of this study was to evaluate how inulin with different degrees of polymerization modulated gut microbial ecology and host physiology, including mainly biochemical indicators, glucose metabolism and immunity, as well as to assess whether these microbial changes affect the host phenotype in high-fat diet-fed mice. Results Food intake and body and tissue weight. Food intake in the LC (high-fat diet plus long-chain inulin) group was always higher than that of the other three groups (Fig. 1A). The average food intakes in the NCD (normal chow diet), HFD (high-fat diet), SC (high-fat diet plus short-chain inulin) and LC groups were 18.89, 21.07, 21.76 and 27.36 g/week, respectively. The average weekly food intake in the LC group was significantly higher than that in the HFD and SC groups (p < 0.05), whereas no significant difference was observed between the HFD and NCD groups (Fig. 1B, p > 0.05). The body, liver, epididymal fat, abdominal fat, kidney and pancreas weights at the tenth week in the HFD group were significantly higher than those in the NCD group (p < 0.05), whereas there were no significant differences among the HFD, SC and LC groups (Fig. 1C,D, p > 0.05). Biochemical indicators and glycemic metabolism. Biochemical analysis demonstrated that a high-fat diet resulted in a significant increase in serum triacylglycerol (TG), total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C) compared to those in the NCD group (p < 0.05), whereas we observed no significant differences in TG and HDL-C levels among the HFD, SC and LC groups (Fig. 1E, p > 0.05). Moreover, lower TC levels were observed in the LC group than in the SC group (Fig. 1E, p < 0.05). Higher blood glucose levels were observed in the SC group than in the HFD group at 30 and 60 minutes after glucose loading, and blood glucose concentrations in the SC group were higher than those in the LC group at 30 minutes (Fig. 2A, p < 0.01). Furthermore, fasting glucose concentrations and glucose tolerance test area under the glucose curve (GTT AUC) in the HFD group were significantly higher than those in the NCD group (Fig. 2A,B, p < 0.05). No significant differences in fasting glucose levels and glucose tolerance test area under the glucose curve (GTT AUC) were observed among the HFD, SC and LC groups (p > 0.05). In parallel, serum insulin analysis demonstrated a significant decrease in the HFD group compared with that in the NCD group (p < 0.05), and there was no significant difference among the HFD, SC and LC groups (Fig. 2C, p > 0.05).

Three purified polysaccharide fractions designated as PAC-I, PAC-II, and PAC-III were prepared from Aloe vera L. var. chinensis (Haw.) Berg. by membrane fractionation and gel filtration HPLC. The polysaccharide fractions had molecular weights of 10,000 kDa, 1300 kDa, and 470 kDa, respectively. The major sugar residue in the polysaccharide fractions is mannose, which was found to be 91.5% in PAC-I, 87.9% in PAC-II, and 53.7% in PAC-III. The protein contents in the polysaccharide fractions was undetectable. NMR study of PAC-I and PAC-II demonstrated the polysaccharides shared the same structure. The main skeletons of PAC-I and PAC-II are beta-(1-->4)-D linked mannose with acetylation at C-6 of manopyranosyl. The polysaccharide fractions stimulated peritoneal macrophages, splenic T and B cell proliferation, and activated these cells to secrete TNF-alpha, IL-1 beta, INF-gamma, IL-2, and IL-6. The polysaccharides were nontoxic and exhibited potent indirect antitumor response in murine model. PAC-I, which had the highest mannose content and molecular weight, was found to be the most potent biological response modifier of the three fractions. Our results suggested that the potency of aloe polysaccharide fraction increases as mannose content and molecular weight of the polysaccharide fraction increase.

Gut microbiota have strong connections with health. Lactulose has been shown to regulate gut microbiota and benefit host health. In this study, the effect of short-term (3 week) intervention of lactulose on gut microbiota was investigated. Gut microbiota were detected from mouse feces by 16S rRNA high-throughput sequencing, and short chain fatty acids (SCFAs) were detected by gas chromatography-mass spectrometry (GC-MS). Lactulose intervention enhanced the α-diversity of the gut microbiota; increased the abundance of hydrogen-producing bacteria Prevotellaceae and Rikenellaceae, probiotics Bifidobacteriaceae and Lactobacillaceae, and mucindegrading bacteria Akkermansia and Helicobacter; decreased the abundance of harmful bacteria Desulfovibrionaceae and branched-chain SCFAs (BCFAs). These results suggest that lactulose intervention effectively increased the diversity and improved the structure of the intestinal microbiota, which may be beneficial for host health. K E Y W O R D S16S rRNA high-throughput sequencing, gut microbiota, prebiotic, probiotics, short chain fatty acids 2 of 8 | ZHAI et Al. enzymes in the intestine, but is metabolized by gut microbiota to short chain fatty acids (SCFAs) in the ileum (Guerra-Ordaz et al., 2014).Lactulose can change the composition of the gut microbiota. For example, Vanhoutte et al. (2006), reported a significant increase in Bifidobacterium adolescentis following lactulose intake. Tuohy et al. (2002) showed that Bifidobacterium spp. were increased, whereas Clostridia and Lactobacilli were decreased after lactulose treatment in humans.SCFAs are main metabolites of gut microbiota, and are divided into straight-chain SCFAs and branched-chain SCFAs (BCFAs). Straightchain SCFAs are mainly produced by microbial fermentation of unabsorbed dietary carbohydrates in the gut. Lactate and succinate can also be metabolized to straight-chain SCFAs, including acetate, propionate, and butyrate (Hasebe et al., 2016;Verbeke et al., 2015). Straight-chain SCFAs have a range of beneficial effects, including regulation of the colonic and intracellular environment (Wong et al. 2006), and modulation of cell proliferation and gene expression. In addition, straightchain SCFAs are able to improve immune function, glucose regulation, and prevent obesity (Polyviou et al., 2016). In contrast, BCFAs are always derived from catabolism of branched-chain amino acids (Zheng et al., 2013), and are major markers of protein fermentation, which is likely to be detrimental to the host (Yang & Rose, 2015).Although some studies have assessed the effects of lactulose on gut microbiota, the gel-or PCR-based methods used limit our ability to evaluate the full extent of the impact of lactulose on the gut microbiotic community. In this study, 16S rRNA high-throughput sequencing and gas chromatography-mass spectrometry (GC-MS) were used to evaluate effect of lactulose on gut microbiota and their metabolites in mice. | MATERIAL S AND ME THODS | Animals and experiment designSix-week-old male C57BL/6J mice were...

The study aimed to analyze the global influences of dietary inulin with different degrees of polymerization (DP) on intestinal microbial communities. Six-week-old male C57BL/6J mice were treated with fructo-oligosaccharides and inulin for 6 weeks. Fecal samples were obtained at time point 0 and 6th week. 16S rRNA sequence analysis was used to measure intestinal microbiota performed on the Illumina MiSeq platform. Influences of dietary inulin on intestinal microbiota were more complex effects than bifidogenic effects, relative abundance of butyrate-producing bacteria increased after interventions. Akkermansia muciniphila, belonging to mucin-degrading species, became a dominant species in Verrucomicrobia phylum after treatment with fructo-oligosaccharides and inulin. Modulation effects of intestinal microbiota were positively correlated with DP. Lower DP interventions exhibited better effects than higher DP treatment on stimulation of probiotics. We hypothesized that Akkermansia muciniphila played an important role on maintaining balance between mucin and short chain fatty acids.

Butyrate, a key metabolite fermented by gut microbiota mainly from undigested carbohydrates such as dietary fibers is widely used as feed additive. However, mechanisms of its contributions in maintaining host health are relatively poorly revealed. The aim of this study was to investigate how butyrate impacts gut microbiota and immunity response in high-fat diet-fed mice. Gut microbial analysis exhibited that butyrate intervention increased SCFAs-producing bacteria and decreased pathogenic bacteria, such as endotoxin-secreting bacteria. Our result also demonstrated that butyrate intervention enhanced fecal SCFAs concentrations, and inhibited endotoxin levels in feces and serum. Correlation analysis indicated positive relation between endotoxin level and Desulfovibrionaceae abundance. Furthermore, butyrate intervention inhibited expressions of IL-1β, IL-6 and MCP1/CCL2 in liver, as well as TLR4 in adipose tissue. Apart from inhibiting expressions of proinflammatory cytokines, butyrate exerted anti-inflammation effect through selectively modulating gut microbiota, such as increasing SCFAs-producing bacteria and decreasing endotoxin-secreting bacteria, as well as via regulating levels of microbiota-dependent metabolites and components, such as SCFAs and endotoxin.

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The health‐promoting effects of phycocyanin (PC) have become widely accepted over the last two decades. In this study, we investigated the effects of different doses of PC in modulating the intestinal microbiota and the intestinal barrier in mice. Six‐week‐old male C57BL/6 mice were treated with PC for 28 days. Fecal samples were collected before and after PC intervention, and the microbiota were analyzed by 16S rRNA high‐throughput sequencing. Bacterial abundance and diversity increased after PC intervention. Saccharolytic bacteria of the families Lachnospiraceae and Ruminococcaceae, which can produce butyric acid, increased after PC treatment. The family Rikenellaceae, which contains hydrogen‐producing bacteria, also increased after PC intervention. The PC treatment reduced intestinal permeability and increased the intestinal barrier function, as demonstrated by hematoxylin–eosin staining and reduced serum lipopolysaccharide levels. The modulating effects on the intestinal microbiota were more favorable in the low‐dose PC group.