Oral supplementation of gut microbial metabolite indole-3-acetate alleviates diet-induced steatosis and inflammation in mice

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in Western countries. There is growing evidence that dysbiosis of the intestinal microbiota and disruption of microbiota-host interactions contribute to the pathology of NAFLD. We previously demonstrated that gut microbiota-derived tryptophan metabolite indole-3-acetate (I3A) was decreased in both cecum and liver of high-fat diet-fed mice and attenuated the expression of inflammatory cytokines in macrophages and Tnfa and fatty acid-induced inflammatory responses in an aryl-hydrocarbon receptor (AhR)-dependent manner in hepatocytes. In this study, we investigated the effect of orally administered I3A in a mouse model of diet-induced NAFLD. Western diet (WD)-fed mice given sugar water (SW) with I3A showed dramatically decreased serum ALT, hepatic triglycerides (TG), liver steatosis, hepatocyte ballooning, lobular inflammation, and hepatic production of inflammatory cytokines, compared to WD-fed mice given only SW. Metagenomic analysis show that I3A administration did not significantly modify the intestinal microbiome, suggesting that I3A's beneficial effects likely reflect the metabolite's direct actions on the liver. Administration of I3A partially reversed WD-induced alterations of liver metabolome and proteome, notably, decreasing expression of several enzymes in hepatic lipogenesis and β-oxidation. Mechanistically, we also show that AMP-activated protein kinase (AMPK) mediates the anti-inflammatory effects of I3A in macrophages. The potency of I3A in alleviating liver steatosis and inflammation clearly demonstrates its potential as a therapeutic modality for preventing the progression of steatosis to non-alcoholic steatohepatitis (NASH).

Indole Propionic Acid Increases T Regulatory Cells and Decreases T Helper 17 Cells and Blood Pressure in Mice with Salt-Sensitive Hypertension

Hypertension affects over a billion adults worldwide and is a major risk factor for cardiovascular disease. Studies have reported that the microbiota and its metabolites regulate hypertension pathophysiology. Recently, tryptophan metabolites have been identified to contribute to and inhibit the progression of metabolic disorders and cardiovascular diseases, including hypertension. Indole propionic acid (IPA) is a tryptophan metabolite with reported protective effects in neurodegenerative and cardiovascular diseases; however, its involvement in renal immunomodulation and sodium handling in hypertension is unknown. In the current study, targeted metabolomic analysis revealed decreased serum and fecal IPA levels in mice with L-arginine methyl ester hydrochloride (L-NAME)/high salt diet-induced hypertension (LSHTN) compared to normotensive control mice. Additionally, kidneys from LSHTN mice had increased T helper 17 (Th17) cells and decreased T regulatory (Treg) cells. Dietary IPA supplementation in LSHTN mice for 3 weeks resulted in decreased systolic blood pressure, along with increased total 24 h and fractional sodium excretion. Kidney immunophenotyping demonstrated decreased Th17 cells and a trend toward increased Treg cells in IPA-supplemented LSHTN mice. In vitro, naïve T cells from control mice were skewed into Th17 or Treg cells. The presence of IPA decreased Th17 cells and increased Treg cells after 3 days. These results identify a direct role for IPA in attenuating renal Th17 cells and increasing Treg cells, leading to improved sodium handling and decreased blood pressure. IPA may be a potential metabolite-based therapeutic option for hypertension.

Engineering live attenuated vaccines: Old dogs learning new tricks

Autoimmune diseases such as rheumatoid arthritis and type 1 diabetes are increasingly common global problems. Concerns about increases in the prevalence of such diseases and the limited efficacy of conventional treatment regimens necessitates new therapies to address these challenges. Autoimmune disease severity and dysbiosis are interconnected. Although probiotics have been established as a therapy to rebalance the microbiome and suppress autoimmune symptoms, these microbes tend to lack a number of advantageous qualities found in non-commensal bacteria. Through attenuation and genetic manipulation, these non-commensal bacteria have been engineered into recombinant forms that offer malleable platforms capable of addressing the immune imbalances found in RA and T1D. Such bacteria have been engineered to express valuable gene products known to suppress autoimmunity such as anti-inflammatory cytokines, autoantigens, and enzymes synthesizing microbial metabolites. This review will highlight current and emerging trends in the field and discuss how they may be used to prevent and control autoimmune diseases.

NAC1 modulates autoimmunity by suppressing regulatory T cell-mediated tolerance

We report here that nucleus accumbens-associated protein-1 (NAC1), a nuclear factor of the Broad-complex, Tramtrack, Bric-a-brac/poxvirus and zinc finger (BTB/POZ) gene family, is a negative regulator of FoxP3 in regulatory T cells (Tregs) and a critical determinant of immune tolerance. Phenotypically, NAC1-/- mice showed substantial tolerance to the induction of autoimmunity and generated a larger amount of CD4+ Tregs that exhibit a higher metabolic profile and immune-suppressive activity, increased acetylation and expression of FoxP3, and slower turnover of this transcription factor. Treatment of Tregs with the proinflammatory cytokines interleukin-1β or tumor necrosis factor-α induced a robust up-regulation of NAC1 but evident down-regulation of FoxP3 as well as the acetylated FoxP3. These findings imply that NAC1 acts as a trigger of the immune response through destabilization of Tregs and suppression of tolerance induction, and targeting of NAC1 warrants further exploration as a potential tolerogenic strategy for treatment of autoimmune disorders.

Macrophage Polarization in Atherosclerosis

The implication of the heterogeneous spectrum of pro- and anti-inflammatory macrophages (Macs) has been an important area of investigation over the last decade. The polarization of Macs alters their functional phenotype in response to their surrounding microenvironment. Macs are the major immune cells implicated in the pathogenesis of atherosclerosis. A hallmark pathology of atherosclerosis is the accumulation of pro-inflammatory M1-like macrophages in coronary arteries induced by pro-atherogenic stimuli; these M1-like pro-inflammatory macrophages are incapable of digesting lipids, thus resulting in foam cell formation in the atherosclerotic plaques. Recent findings suggest that the progression and stability of atherosclerotic plaques are dependent on the quantity of infiltrated Macs, the polarization state of the Macs, and the ratios of different types of Mac populations. The polarization of Macs is defined by signature markers on the cell surface, as well as by factors in intracellular and intranuclear compartments. At the same time, pro- and anti-inflammatory polarized Macs also exhibit different gene expression patterns, with differential cellular characteristics in oxidative phosphorylation and glycolysis. Macs are reflective of different metabolic states and various types of diseases. In this review, we discuss the major differences between M1-like Macs and M2-like Macs, their associated metabolic pathways, and their roles in atherosclerosis.

Novel Role of Ghrelin Receptor in Gut Dysbiosis and Experimental Colitis in Aging

Chronic low-grade inflammation is a hallmark of aging, which is now coined as inflamm-aging. Inflamm-aging contributes to many age-associated diseases such as obesity, type 2 diabetes, cardiovascular disease, and inflammatory bowel disease (IBD). We have shown that gut hormone ghrelin, via its receptor growth hormone secretagogue receptor (GHS-R), regulates energy metabolism and inflammation in aging. Emerging evidence suggests that gut microbiome has a critical role in intestinal immunity of the host. To determine whether microbiome is an integral driving force of GHS-R mediated immune-metabolic homeostasis in aging, we assessed the gut microbiome profiles of young and old GHS-R global knockout (KO) mice. While young GHS-R KO mice showed marginal changes in Bacteroidetes and Firmicutes, aged GHS-R KO mice exhibited reduced Bacteroidetes and increased Firmicutes, featuring a disease-susceptible microbiome profile. To further study the role of GHS-R in intestinal inflammation in aging, we induced acute colitis in young and aged GHS-R KO mice using dextran sulfate sodium (DSS). The GHS-R KO mice showed more severe disease activity scores, higher proinflammatory cytokine expression, and decreased expression of tight junction markers. These results suggest that GHS-R plays an important role in microbiome homeostasis and gut inflammation during aging; GHS-R suppression exacerbates intestinal inflammation in aging and increases vulnerability to colitis. Collectively, our finding reveals for the first time that GHS-R is an important regulator of intestinal health in aging; targeting GHS-R may present a novel therapeutic strategy for prevention/treatment of aging leaky gut and inflammatory bowel disease.

Elongation factor-2 kinase is a critical determinant of the fate and antitumor immunity of CD8+ T cells

eEF-2K has important roles in stress responses and cellular metabolism. We report here a previously unappreciated but critical role of eEF-2K in regulating the fate and cytocidal activity of CD8+ T cells. CD8+ T cells from eEF-2K KO mice were more proliferative but had lower survival than their wild-type counterparts after their activation, followed by occurrence of premature senescence and exhaustion. eEF-2K KO CD8+ T cells were more metabolically active and showed hyperactivation of the Akt-mTOR-S6K pathway. Loss of eEF-2K substantially impaired the activity of CD8+ T cells. Furthermore, the antitumor efficacy and tumor infiltration of the CAR-CD8+ T cells lacking eEF-2K were notably reduced as compared to the control CAR-CD8+ T cells. Thus, eEF-2K is critically required for sustaining the viability and function of cytotoxic CD8+ T cells, and therapeutic augmentation of this kinase may be exploited as a novel approach to reinforcing CAR-T therapy against cancer.

A metabolically engineered bacterium controls autoimmunity and inflammation by remodeling the pro-inflammatory microenvironment

Immunotherapy has led to impressive advances in the treatment of autoimmune and pro-inflammatory disorders; yet, its clinical outcomes remain limited by a variety of factors including the pro-inflammatory microenvironment (IME). Discovering effective immunomodulatory agents, and the mechanisms by which they control disease, will lead to innovative strategies for enhancing the effectiveness of current immunotherapeutic approaches. We have metabolically engineered an attenuated bacterial strain (i.e., Brucella melitensis 16M ∆vjbR, Bm∆vjbR::tnaA) to produce indole, a tryptophan metabolite that controls the fate and function of regulatory T (Treg) cells. We demonstrated that treatment with Bm∆vjbR::tnaA polarized macrophages (Mφ) which produced anti-inflammatory cytokines (e.g., IL-10) and promoted Treg function; moreover, when combined with adoptive cell transfer (ACT) of Treg cells, a single treatment with our engineered bacterial strain dramatically reduced the incidence and score of autoimmune arthritis and decreased joint damage. These findings show how a metabolically engineered bacterium can constitute a powerful vehicle for improving the efficacy of immunotherapy, defeating autoimmunity, and reducing inflammation by remodeling the IME and augmenting Treg cell function.

Live attenuated bacterium limits cancer resistance to CAR-T therapy by remodeling the tumor microenvironment

The tumor microenvironment (TME) is characterized by the activation of immune checkpoints, which limit the ability of immune cells to attack the growing cancer. To overcome immune suppression in the clinic, antigen-expressing viruses and bacteria have been developed to induce antitumor immunity. However, the safety and targeting specificity are the main concerns of using bacteria in clinical practice as antitumor agents. In our previous studies, we have developed an attenuated bacterial strain (Brucella melitensis 16M ∆vjbR, henceforth Bm∆vjbR) for clinical use, which is safe in all tested animal models and has been removed from the select agent list by the Centers for Disease Control and Prevention. In this study, we demonstrated that Bm∆vjbR homed to tumor tissue and improved the TME in a murine model of solid cancer. In addition, live Bm∆vjbR promoted proinflammatory M1 polarization of tumor macrophages and increased the number and activity of CD8+ T cells in the tumor. In a murine colon adenocarcinoma model, when combined with adoptive transfer of tumor-specific carcinoembryonic antigen chimeric antigen receptor CD8+ T cells, tumor cell growth and proliferation was almost completely abrogated, and host survival was 100%. Taken together, these findings demonstrate that the live attenuated bacterial treatment can defeat cancer resistance to chimeric antigen receptor T-cell therapy by remodeling the TME to promote macrophage and T cell-mediated antitumor immunity.

Common Metabolites in Two Different Hypertensive Mouse Models: A Serum and Urine Metabolome Study

Recent metabolomics studies have identified a wide array of microbial metabolites and metabolite pathways that are significantly altered in hypertension. However, whether these metabolites play an active role in pathogenesis of hypertension or are altered because of this has yet to be determined. In the current study, we hypothesized that metabolite changes common between hypertension models may unify hypertension's pathophysiology with respect to metabolites. We utilized two common mouse models of experimental hypertension: L-arginine methyl ester hydrochloride (L-NAME)/high-salt-diet-induced hypertension (LSHTN) and angiotensin II induced hypertension (AHTN). To identify common metabolites that were altered across both models, we performed untargeted global metabolomics analysis in serum and urine and the resulting data were analyzed using MetaboAnalyst software and compared to control mice. A total of 41 serum metabolites were identified as being significantly altered in any hypertensive model compared to the controls. Of these compounds, 14 were commonly changed in both hypertensive groups, with 4 significantly increased and 10 significantly decreased. In the urine, six metabolites were significantly altered in any hypertensive group with respect to the control; however, none of them were common between the hypertensive groups. These findings demonstrate that a modest, but potentially important, number of serum metabolites are commonly altered between experimental hypertension models. Further studies of the newly identified metabolites from this untargeted metabolomics analysis may lead to a greater understanding of the association between gut dysbiosis and hypertension.

Abstract MP40: Microbiome-associated Metabolites Are Altered In Mouse Models Of Hypertension

Recent studies suggest that the microbiome plays a key role in hypertension and associated inflammation. Microbiota produce metabolites that may lead to activated pro-inflammatory immune cells and contribute to hypertension; however, the altered metabolites in multiple models of hypertension is currently unknown. We hypothesized that there are significant differences in metabolomic profiles between normotensive and hypertensive mice. We utilized two mouse models of hypertension: L-arginine methyl ester hydrochloride (L-NAME)/high salt diet induced hypertension (LSHTN) and angiotensin II induced hypertension (A2HTN). Serum and fecal samples were collected at the end of the treatment period. Ultra-high performance liquid chromatography and tandem mass spectrometry were performed to identify the biochemical composition of each sample. Random Forest Analysis was performed to classify each sample based on similarities and differences in metabolite composition. These procedures were performed by Metabolon, Inc. A total of 1,066 and 1,028 biochemicals were measured in serum and feces, respectively. There were 263 biochemicals in LSHTN serum and 122 biochemicals in A2HTN serum that were statistically different from controls (p≤0.05). There were 298 biochemicals in LSHTN feces and 64 biochemicals in A2HTN feces that were statistically different from controls (p≤0.05). Five biochemical metabolite groups were shown to have significant differences between hypertensive groups and controls: aromatic amino acids, bile acids and sterols, benzoates, fatty acids, and diacylglycerols. Tryptophan metabolites were significantly reduced in the serum of LSHTN mice but not in the serum of A2HTN mice. Serum tyrosine and benzoate metabolites showed varied differences between the two hypertensive groups. Serum fatty acid beta oxidation metabolites were significantly reduced in both hypertensive models but were significantly increased in the feces of mice with LSHTN. In conclusion, this study provided significant analysis of metabolite changes in two hypertension mouse models. Further investigation of the roles these metabolites play in hypertension may lead to targeted therapeutic interventions.

Assessment of microbiological correlates and immunostimulatory potential of electron beam inactivated metabolically active yet non culturable (MAyNC) Salmonella Typhimurium

This study investigates the microbiological and immunological basis underlying the efficacy of electron beam-inactivated immune modulators. The underlying hypothesis is that exposure to eBeam-based ionization reactions inactivate microorganisms without modifying their antigenic properties and thereby creating immune modulators. The immunological correlates of protection induced by such eBeam based Salmonella Typhimurium (EBST) immune modulators in dendritic cell (DC) (in vitro) and mice (in vivo) models were assessed. The EBST stimulated innate pro inflammatory response (TNFα) and maturation (MHC-II, CD40, CD80 and CD86) of DC. Immuno-stimulatory potential of EBST was on par with both a commercial Salmonella vaccine, and live Salmonella cells. The EBST cells did not multiply under permissive in vitro and in vivo conditions. However, EBST cells remained metabolically active. EBST immunized mice developed Salmonella-specific CD4+ T-cells that produced the Th1 cytokine IFNγ at a level similar to that induced by the live attenuated vaccine (AroA^- ST) formulation. The EBST retained stable immunogenic properties for several months at room temperature, 4°C, and -20°C as well as after lyophilization. Therefore, such eBeam-based immune modulators have potential as vaccine candidates since they offer the safety of a “killed” vaccine, while retaining the immunogenicity of an “attenuated” vaccine. The ability to store eBeam based immune modulators at room temperature without loss of potency is also noteworthy.

A Comprehensive High-Efficiency Protocol for Isolation, Culture, Polarization, and Glycolytic Characterization of Bone Marrow-Derived Macrophages

Macrophages are among the most important antigen-presenting cells. Many subsets of macrophages have been identified with unique metabolic signatures. Macrophages are commonly classified as M1-like (inflammatory) and M2-like (anti-inflammatory) subtypes. M1-like macrophages are pro-inflammatory macrophages that get activated by LPS and/or pro-inflammatory cytokines such as INF-γ, IL-12 & IL-2. M1-like polarized macrophages are involved in various diseases by mediating the host's defense to a variety of bacteria and viruses. That is very important to study LPS induced M1-like macrophages and their metabolic states in inflammatory diseases. M2-like macrophages are considered anti-inflammatory macrophages, activated by anti-inflammatory cytokines and stimulators. Under the pro-inflammatory state, macrophages show increased glycolysis in glycolytic function. The glycolytic function has been actively investigated in the context of glycolysis, glycolytic capacity, glycolytic reserve, compensatory glycolysis, or non-glycolytic acidification using extracellular flux (XF) analyzers. This paper demonstrates how to assess the glycolytic states in real-time with easy-to-follow steps when the bone marrow-derived macrophages (BMDMs) are respiring, consuming, and producing energy. Using specific inhibitors and activators of glycolysis in this protocol, we show how to obtain a systemic and complete view of glycolytic metabolic processes in the cells and provide more accurate and realistic results. To be able to measure multiple glycolytic phenotypes, we provide an easy, sensitive, DNA-based normalization method for polarization assessment of BMDMs. Culturing, activation/polarization and identification of the phenotype and metabolic state of the BMDMs are crucial techniques that can help to investigate many different types of diseases. In this paper, we polarized the naïve M0 macrophages to M1-like and M2-like macrophages with LPS and IL4, respectively, and measured a comprehensive set of glycolytic parameters in BMDMs in real-time and longitudinally over time, using extracellular flux analysis and glycolytic activators and inhibitors.

Environmental Chemical Diethylhexyl Phthalate Alters Intestinal Microbiota Community Structure and Metabolite Profile in Mice

Exposure to environmental chemicals during windows of development is a potentially contributing factor in gut microbiota dysbiosis and linked to chronic diseases and developmental disorders. We used a community-level model of microbiota metabolism to investigate the effects of diethylhexyl phthalate (DEHP), a ubiquitous plasticizer implicated in neurodevelopmental disorders, on the composition and metabolite outputs of gut microbiota in young mice. Administration of DEHP by oral gavage increased the abundance of Lachnoclostridium, while decreasing Clostridium sensu stricto Addition of DEHP to in vitro-cultured cecal microbiota increased the abundance of Paenibacillus and Lachnoclostridium Untargeted metabolomics showed that DEHP broadly altered the metabolite profile in the culture. Notably, DEHP enhanced the production of p-cresol while inhibiting butyrate synthesis. Metabolic model-guided correlation analysis indicated that the likely sources of p-cresol are Clostridium species. Monoculture of Lachnoclostridium bolteae confirmed that it is capable of producing p-hydroxyphenylacetic acid, the immediate precursor of p-cresol, and that the species' growth is enhanced upon DEHP exposure. Taken together, these findings suggest a model where DEHP increases production of p-cresol, a bacterial metabolite linked with neurodevelopmental disorders, by expanding the abundance of species that synthesize the metabolite's precursor.IMPORTANCE Several previous studies have pointed to environmental chemical exposure during windows of development as a contributing factor in neurodevelopmental disorders and correlated these disorders with microbiota dysbiosis; however, little is known about how the chemicals specifically alter the microbiota to interfere with development. The findings reported in this paper unambiguously establish that a pollutant linked with neurodevelopmental disorders can directly modify the microbiota to promote the production of a potentially toxic metabolite (p-cresol) that has also been correlated with neurodevelopmental disorders. Furthermore, we used a novel modeling strategy to identify the responsible enzymes and bacterial sources of this metabolite. To the best of our knowledge, the present study is the first to characterize the functional consequence of phthalate exposure on a developed microbiota. Our results suggest that specific bacterial pathways could be developed as diagnostic and therapeutic targets against health risks posed by ingestion of environmental chemicals.

Gut Microbiota-Derived Tryptophan Metabolites Modulate Inflammatory Response in Hepatocytes and Macrophages

The gut microbiota plays a significant role in the progression of fatty liver disease; however, the mediators and their mechanisms remain to be elucidated. Comparing metabolite profile differences between germ-free and conventionally raised mice against differences between mice fed a low- and high-fat diet (HFD), we identified tryptamine and indole-3-acetate (I3A) as metabolites that depend on the microbiota and are depleted under a HFD. Both metabolites reduced fatty-acid- and LPS-stimulated production of pro-inflammatory cytokines in macrophages and inhibited the migration of cells toward a chemokine, with I3A exhibiting greater potency. In hepatocytes, I3A attenuated inflammatory responses under lipid loading and reduced the expression of fatty acid synthase and sterol regulatory element-binding protein-1c. These effects were abrogated in the presence of an aryl-hydrocarbon receptor (AhR) antagonist, indicating that the effects are AhR dependent. Our results suggest that gut microbiota could influence inflammatory responses in the liver through metabolites engaging host receptors.

Interactions between gut microbiota and non-alcoholic liver disease: The role of microbiota-derived metabolites

There is increasing evidence that the intestinal microbiota plays a mechanistic role in the etiology of non-alcoholic fatty liver disease (NAFLD). Animal and human studies have linked small molecule metabolites produced by commensal bacteria in the gut contribute to not only intestinal inflammation, but also to hepatic inflammation. These immunomodulatory metabolites are capable of engaging host cellular receptors, and may mediate the observed association between gut dysbiosis and NAFLD. This review focuses on the effects and potential mechanisms of three specific classes of metabolites that synthesized or modified by gut bacteria: short chain fatty acids, amino acid catabolites, and bile acids. In particular, we discuss their role as ligands for cell surface and nuclear receptors regulating metabolic and inflammatory pathways in the intestine and liver. Studies reveal that the metabolites can both agonize and antagonize their cognate receptors to reduce or exacerbate liver steatosis and inflammation, and that the effects are metabolite- and context-specific. Further studies are warranted to more comprehensively understand bacterial metabolite-mediated gut-liver in NAFLD. This understanding could help identify novel therapeutics and therapeutic targets to intervene in the disease through the gut microbiota.

PNAG-specific equine IgG1 mediates significantly greater opsonization and killing of Prescottella equi (formerly Rhodococcus equi) than does IgG4/7

Prescottella equi (formerly Rhodococcus equi) is a facultative intracellular bacterial pathogen that causes severe pneumonia in foals 1-6 months of age, whereas adult horses are highly resistant to infection. We have shown that vaccinating pregnant mares against the conserved surface polysaccharide capsule, β-1 → 6-linked poly-N-acetyl glucosamine (PNAG), elicits opsonic killing antibody that transfers via colostrum to foals and protects them against experimental infection with virulent. R. equi. We hypothesized that equine IgG1 might be more important than IgG4/7 for mediating protection against R. equi infection in foals. To test this hypothesis, we compared complement component 1 (C1) deposition and polymorphonuclear cell-mediated opsonophagocytic killing (OPK) mediated by IgG1 or IgG4/7 enriched from either PNAG hyperimmune plasma (HIP) or standard plasma. Subclasses IgG1 and IgG4/7 from PNAG HIP and standard plasma were precipitated onto a diethylaminoethyl ion exchange column, then further enriched using a protein G Sepharose column. We determined C1 deposition by enzyme-linked immunosorbent assay (ELISA) and estimated OPK by quantitative microbiologic culture. Anti-PNAG IgG1 deposited significantly (P < 0.05) more C1 onto PNAG than did IgG4/7 from PNAG HIP or subclasses IgG1 and IgG4/7 from standard plasma. In addition, IgG1 from PNAG HIP mediated significantly (P < 0.05) greater OPK than IgG4/7 from PNAG HIP or IgG1 and IgG4/7 from standard plasma. Our findings indicate that anti-PNAG IgG1 is a correlate of protection against R. equi in foals, which has important implications for understanding the immunopathogenesis of R. equi pneumonia, and as a tool for assessing vaccine efficacy and effectiveness when challenge is not feasible.

Shift work cycle-induced alterations of circadian rhythms potentiate the effects of high-fat diet on inflammation and metabolism

Based on genetic models with mutation or deletion of core clock genes, circadian disruption has been implicated in the pathophysiology of metabolic disorders. Thus, we examined whether circadian desynchronization in response to shift work-type schedules is sufficient to compromise metabolic homeostasis and whether inflammatory mediators provide a key link in the mechanism by which alterations of circadian timekeeping contribute to diet-induced metabolic dysregulation. In high-fat diet (HFD)-fed mice, exposure to chronic shifts of the light-dark cycle (12 h advance every 5 d): 1) disrupts photoentrainment of circadian behavior and modulates the period of spleen and macrophage clock gene rhythms; 2) potentiates HFD-induced adipose tissue infiltration and activation of proinflammatory M1 macrophages; 3) amplifies macrophage proinflammatory cytokine expression in adipose tissue and bone marrow-derived macrophages; and 4) exacerbates diet-induced increases in body weight, insulin resistance, and glucose intolerance in the absence of changes in total daily food intake. Thus, complete disruption of circadian rhythmicity or clock gene function as transcription factors is not requisite to the link between circadian and metabolic phenotypes. These findings suggest that macrophage proinflammatory activation and inflammatory signaling are key processes in the physiologic cascade by which dysregulation of circadian rhythmicity exacerbates diet-induced systemic insulin resistance and glucose intolerance.-Kim, S.-M., Neuendorff, N., Alaniz, R. C., Sun, Y., Chapkin, R. S., Earnest, D. J. Shift work cycle-induced alterations of circadian rhythms potentiate the effects of high-fat diet on inflammation and metabolism.

The microbiota metabolite indole inhibits Salmonella virulence: Involvement of the PhoPQ two-component system

The microbial community present in the gastrointestinal tract is an important component of the host defense against pathogen infections. We previously demonstrated that indole, a microbial metabolite of tryptophan, reduces enterohemorrhagic Escherichia coli O157:H7 attachment to intestinal epithelial cells and biofilm formation, suggesting that indole may be an effector/attenuator of colonization for a number of enteric pathogens. Here, we report that indole attenuates Salmonella Typhimurium (Salmonella) virulence and invasion as well as increases resistance to colonization in host cells. Indole-exposed Salmonella colonized mice less effectively compared to solvent-treated controls, as evident by competitive index values less than 1 in multiple organs. Indole-exposed Salmonella demonstrated 160-fold less invasion of HeLa epithelial cells and 2-fold less invasion of J774A.1 macrophages compared to solvent-treated controls. However, indole did not affect Salmonella intracellular survival in J774A.1 macrophages suggesting that indole primarily affects Salmonella invasion. The decrease in invasion was corroborated by a decrease in expression of multiple Salmonella Pathogenicity Island-1 (SPI-1) genes. We also identified that the effect of indole was mediated by both PhoPQ-dependent and independent mechanisms. Indole also synergistically enhanced the inhibitory effect of a short chain fatty acid cocktail on SPI-1 gene expression. Lastly, indole-treated HeLa cells were 70% more resistant to Salmonella invasion suggesting that indole also increases resistance of epithelial cells to colonization. Our results demonstrate that indole is an important microbiota metabolite that has direct anti-infective effects on Salmonella and host cells, revealing novel mechanisms of pathogen colonization resistance.

Global Reprogramming of Host Kinase Signaling in Response to Fungal Infection

Cryptococcus neoformans (Cn) is a deadly fungal pathogen whose intracellular lifestyle is important for virulence. Host mechanisms controlling fungal phagocytosis and replication remain obscure. Here, we perform a global phosphoproteomic analysis of the host response to Cryptococcus infection. Our analysis reveals numerous and diverse host proteins that are differentially phosphorylated following fungal ingestion by macrophages, thereby indicating global reprogramming of host kinase signaling. Notably, phagocytosis of the pathogen activates the host autophagy initiation complex (AIC) and the upstream regulatory components LKB1 and AMPKα, which regulate autophagy induction through their kinase activities. Deletion of Prkaa1, the gene encoding AMPKα1, in monocytes results in resistance to fungal colonization of mice. Finally, the recruitment of AIC components to nascent Cryptococcus-containing vacuoles (CnCVs) regulates the intracellular trafficking and replication of the pathogen. These findings demonstrate that host AIC regulatory networks confer susceptibility to infection and establish a proteomic resource for elucidating host mechanisms that regulate fungal intracellular parasitism.

Empirical modeling of T cell activation predicts interplay of host cytokines and bacterial indole

Adoptive transfer of anti-inflammatory FOXP3+ Tregs has gained attention as a new therapeutic strategy for auto-inflammatory disorders such as Inflammatory Bowel Disease. The isolated cells are conditioned in vitro to obtain a sufficient number of anti-inflammatory FOXP3+ Tregs that can be reintroduced into the patient to potentially reduce the pathologic inflammatory response. Previous evidence suggests that microbiota metabolites can potentially condition cells during the in vitro expansion/differentiation step. However, the number of combinations of cytokines and metabolites that can be varied is large, preventing a purely experimental investigation which would determine optimal cell therapeutic outcomes. To address this problem, a combined experimental and modeling approached is investigated here: an artificial neural network model was trained to predict the steady-state T cell population phenotype after differentiation with a variety of host cytokines and the microbial metabolite indole. This artificial neural network model was able to both reliably predict the phenotype of these T cell populations and also uncover unexpected conditions for optimal Treg differentiation that were subsequently verified experimentally. Biotechnol. Bioeng. 2017;114: 2660-2667. © 2017 Wiley Periodicals, Inc.

Salmonella Typhimurium and Multidirectional Communication in the Gut

The mammalian digestive tract is home to trillions of microbes, including bacteria, archaea, protozoa, fungi, and viruses. In monogastric mammals the stomach and small intestine harbor diverse bacterial populations but are typically less populated than the colon. The gut bacterial community (microbiota hereafter) varies widely among different host species and individuals within a species. It is influenced by season of the year, age of the host, stress and disease. Ideally, the host and microbiota benefit each other. The host provides nutrients to the microbiota and the microbiota assists the host with digestion and nutrient metabolism. The resident microbiota competes with pathogens for space and nutrients and, through this competition, protects the host in a phenomenon called colonization resistance. The microbiota participates in development of the host immune system, particularly regulation of autoimmunity and mucosal immune response. The microbiota also shapes gut–brain communication and host responses to stress; and, indeed, the microbiota is a newly recognized endocrine organ within mammalian hosts. Salmonella enterica serovar Typhimurium (S. Typhimurium hereafter) is a food-borne pathogen which adapts to and alters the gastrointestinal (GI) environment. In the GI tract, S. Typhimurium competes with the microbiota for nutrients and overcomes colonization resistance to establish infection. To do this, S. Typhimurium uses multiple defense mechanisms to resist environmental stressors, like the acidic pH of the stomach, and virulence mechanisms which allow it to invade the intestinal epithelium and disseminate throughout the host. To coordinate gene expression and disrupt signaling within the microbiota and between host and microbiota, S. Typhimurium employs its own chemical signaling and may regulate host hormone metabolism. This review will discuss the multidirectional interaction between S. Typhimurium, host and microbiota as well as mechanisms that allow S. Typhimurium to succeed in the gut.

Outer membrane vesicles in service as protein shuttles, biotic defenders, and immunological doppelgängers

Characterization of host microbial interactions typically occurs on the cellular or protein level. Recently, a more thorough and accurate appreciation of cellular interactions has come into better focus with improved understanding of membrane vesicles (OMV). While OMVs are documented primarily in Gram-negative bacteria, certain Gram-positive species generate these structures, despite the obvious physical limitations of the cell envelope. Here, we briefly review the current understanding of OMVs in content and function, their role in pathogenesis, and the consequences of somatic cell gene expression on these events.

The microbiota-derived metabolite indole decreases mucosal inflammation and injury in a murine model of NSAID enteropathy

Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most frequently used classes of medications in the world. Unfortunately, NSAIDs induce an enteropathy associated with high morbidity and mortality. Although the pathophysiology of this condition involves the interaction of the gut epithelium, microbiota, and NSAIDs, the precise mechanisms by which microbiota influence NSAID enteropathy are unclear. One possible mechanism is that the microbiota may attenuate the severity of disease by specific metabolite-mediated regulation of host inflammation and injury. The microbiota-derived tryptophan-metabolite indole is abundant in the healthy mammalian gut and positively influences intestinal health. We thus examined the effects of indole administration on NSAID enteropathy. Mice (n = 5 per group) were treated once daily for 7 days with an NSAID (indomethacin; 5 mg/kg), indole (20 mg/kg), indomethacin plus indole, or vehicle only (control). Outcomes compared among groups included: microscopic pathology; fecal calprotectin concentration; proportion of neutrophils in the spleen and mesenteric lymph nodes; fecal microbiota composition and diversity; small intestinal mucosal transcriptome; and, fecal tryptophan metabolites. Co-administration of indole with indomethacin: significantly reduced mucosal pathology scores, fecal calprotectin concentrations, and neutrophilic infiltration of the spleen and mesenteric lymph nodes induced by indomethacin; modulated NSAID-induced perturbation of the microbiota, fecal metabolites, and inferred metagenome; and, abrogated a pro-inflammatory gene expression profile in the small intestinal mucosa induced by indomethacin. The microbiota-derived metabolite indole attenuated multiple deleterious effects of NSAID enteropathy, including modulating inflammation mediated by innate immune responses and altering indomethacin-induced shift of the microbiota.

Oral Administration of Electron-Beam Inactivated Rhodococcus equi Failed to Protect Foals against Intrabronchial Infection with Live, Virulent R. equi

There is currently no licensed vaccine that protects foals against Rhodococcus equi–induced pneumonia. Oral administration of live, virulent R. equi to neonatal foals has been demonstrated to protect against subsequent intrabronchial challenge with virulent R. equi. Electron beam (eBeam)-inactivated R. equi are structurally intact and have been demonstrated to be immunogenic when administered orally to neonatal foals. Thus, we investigated whether eBeam inactivated R. equi could protect foals against developing pneumonia after experimental infection with live, virulent R. equi. Foals (n = 8) were vaccinated by gavaging with eBeam-inactivated R. equi at ages 2, 7, and 14 days, or gavaged with equal volume of saline solution (n = 4), and subsequently infected intrabronchially with live, virulent R. equi at age 21 days. The proportion of vaccinated foals that developed pneumonia following challenge was similar among the vaccinated (7/8; 88%) and unvaccinated foals (3/4; 75%). This vaccination regimen did not appear to be strongly immunogenic in foals. Alternative dosing regimens or routes of administration need further investigation and may prove to be immunogenic and protective.

Insulin-Like Growth Factor (IGF)-I Modulates Endothelial Blood-Brain Barrier Function in Ischemic Middle-Aged Female Rats

In comparison with young females, middle-aged female rats sustain greater cerebral infarction and worse functional recovery after stroke. These poorer stroke outcomes in middle-aged females are associated with an age-related reduction in IGF-I levels. Poststroke IGF-I treatment decreases infarct volume in older females and lowers the expression of cytokines in the ischemic hemisphere. IGF-I also reduces transfer of Evans blue dye to the brain, suggesting that this peptide may also promote blood-brain barrier function. To test the hypothesis that IGF-I may act at the blood-brain barrier in ischemic stroke, 2 approaches were used. In the first approach, middle-aged female rats were subjected to middle cerebral artery occlusion and treated with IGF-I after reperfusion. Mononuclear cells from the ischemic hemisphere were stained for CD4 or triple-labeled for CD4/CD25/FoxP3 and subjected to flow analyses. Both cohorts of cells were significantly reduced in IGF-I-treated animals compared with those in vehicle controls. Reduced trafficking of immune cells to the ischemic site suggests that blood-brain barrier integrity is better maintained in IGF-I-treated animals. The second approach directly tested the effect of IGF-I on barrier function of aging endothelial cells. Accordingly, brain microvascular endothelial cells from middle-aged female rats were cultured ex vivo and subjected to ischemic conditions (oxygen-glucose deprivation). IGF-I treatment significantly reduced the transfer of fluorescently labeled BSA across the endothelial monolayer as well as cellular internalization of fluorescein isothiocyanate-BSA compared with those in vehicle-treated cultures, Collectively, these data support the hypothesis that IGF-I improves blood-brain barrier function in middle-aged females.

Microbiota metabolite regulation of host immune homeostasis: a mechanistic missing link

Metazoans predominantly co-exist with symbiotic microorganisms called the microbiota. Metagenomic surveys of the microbiota reveal a diverse ecosystem of microbes particularly in the gastrointestinal (GI) tract. Perturbations in the GI microbiota in higher mammals (i.e., humans) are linked to diseases with variegated symptomology including inflammatory bowel disease, asthma, and auto-inflammatory disorders. Indeed, studies using germ-free mice (lacking a microbiota) confirm that host development and homeostasis are dependent on the microbiota. A long-known key feature of the GI tract microbiota is metabolizing host indigestible dietary matter for maximum energy extraction; however, host signaling pathways are greatly influenced by the microbiota as well. In line with these observations, recent research has revealed that metabolites produced strictly by select microbiota members are mechanistic regulators of host cell functions. In this review, we discuss two major classes of microbiota-produced metabolites: short-chain fatty acids and tryptophan metabolites. We describe the known important roles for these metabolites in shaping host immunity and comment on the current status and future directions for microbiota metabolomics research.

Altered host immune responses to membrane vesicles from Salmonella and Gram-negative pathogens

Membrane vesicles (MVs), discrete nano-structures produced from the outer membrane of Gram-negative bacteria such as Salmonella enterica Typhimurium (S. Typhimurium), strongly activate dendritic cells (DCs), contain major antigens (Ags) recognized by Salmonella-specific B-cells and CD4+ T-cells, and provide protection against S. Typhimurium challenge in a mouse model. With this in mind, we hypothesized that alterations to the gene expression profile of bacteria will be reflected in the immunologic response to MVs. To test this, we assessed the ability of MVs from wild-type (WT) S. Typhimurium or a strain with a phenotype mimicking the intracellular-phase of S. Typhimurium (PhoP(c)) to activate dendritic cells and initiate a strong inflammatory response. MVs, isolated from wild-type and PhoP(c)S. Typhimurium (WTMVs and PhoPcMVs, respectively) had pro-inflammatory properties consistent with the parental bacterial strains: PhoPcMVs were less stimulatory for DC activation in vitro and were impaired for subsequent inflammatory responses compared to WTMVs. Interestingly, the reduced pro-inflammatory properties of PhoPcMVs did not completely rely on signals through TLR4, the receptor for LPS. Nonetheless, both WTMVs and PhoPcMVs contained abundant immunogenic antigens capable of being recognized by memory-immune CD4+ T-cells from mice previously infected with S. Typhimurium. Furthermore, we analyzed a suite of pathogenic Gram-negative bacteria and their purified MVs for their ability to activate DCs and stimulate inflammation in a manner consistent with the known inflammatory properties of the parental strains, as shown for S. Typhimurium. Finally, analysis of the potential vaccine utility of S. Typhimurium MVs revealed their capacity to encapsulate an exogenous model antigen and stimulate antigen-specific CD4+ and CD8+ T-cell responses. Taken together, our results demonstrate the dependence of bacterial cell gene expression for MV immunogenicity and subsequent in vitro immunologic response, as well as their potential utility as a vaccine platform.

Myeloid cell-specific disruption of Period1 and Period2 exacerbates diet-induced inflammation and insulin resistance

The circadian clockworks gate macrophage inflammatory responses. Given the association between clock dysregulation and metabolic disorders, we conducted experiments to determine the extent to which over-nutrition modulates macrophage clock function and whether macrophage circadian dysregulation is a key factor linking over-nutrition to macrophage proinflammatory activation, adipose tissue inflammation, and systemic insulin resistance. Our results demonstrate that 1) macrophages from high fat diet-fed mice are marked by dysregulation of the molecular clockworks in conjunction with increased proinflammatory activation, 2) global disruption of the clock genes Period1 (Per1) and Per2 recapitulates this amplified macrophage proinflammatory activation, 3) adoptive transfer of Per1/2-disrupted bone marrow cells into wild-type mice potentiates high fat diet-induced adipose and liver tissue inflammation and systemic insulin resistance, and 4) Per1/2-disrupted macrophages similarly exacerbate inflammatory responses and decrease insulin sensitivity in co-cultured adipocytes in vitro. Furthermore, PPARγ levels are decreased in Per1/2-disrupted macrophages and PPARγ2 overexpression ameliorates Per1/2 disruption-associated macrophage proinflammatory activation, suggesting that this transcription factor may link the molecular clockworks to signaling pathways regulating macrophage polarization. Thus, macrophage circadian clock dysregulation is a key process in the physiological cascade by which diet-induced obesity triggers macrophage proinflammatory activation, adipose tissue inflammation, and insulin resistance.

Rational identification of diet-derived postbiotics for improving intestinal microbiota function

The intestinal microbiota plays an important role in a wide range of functions and whole body homeostasis. Recent advances have linked microbiota dysbiosis to conditions ranging from Crohn's disease to cancer. The restoration or strengthening of the intestinal microbiota through diet-based approaches such as probiotics and prebiotics has been proposed for combating the onset or progression of these diseases. In this review, we highlight the importance of postbiotics for the manipulation of the intestinal microbiota, with special emphasis on systems biology computational tools and targeted metabolomics for the rational discovery and identification of these bioactive molecules. The identification of novel postbiotics and the pathways responsible for their production should lead to improved mechanistic understanding of the role that specific probiotics, prebiotics, and postbiotics have in restoring intestinal microbiota composition and function.

Abstract WP93: CD4+ T Helper Cell Mediated Regulation Of Cerebral Ischemia In Vitamin D Deficient Rats

Stroke is the third leading cause of death worldwide, and Vitamin D deficiency is associated with increased stroke risk, severity, and mortality. Vitamin D potently regulates the immune system and the post-stroke inflammatory response plays a critical role in ischemia-induced CNS pathogenesis; and neuroimmune interactions in the CNS and periphery regulate the nature, extent, and duration of inflammation. Previous studies from this lab indicate that Vitamin D deficiency (VDD) exacerbates ischemic cell loss and sensory motor behavioral deficits in adult rats subject to middle cerebral artery occlusion, an experimental stroke model. Changes in inflammatory cytokines post-ischemia included increased TGF-β expression in both groups but significantly higher IL-6 expression in VDD ischemic cortical tissues than control levels. Increased IL-6 levels in the presence of TGF-β is known to induce pathogenic CD4+ Th17 cell development and suppress neuroprotective Treg generation. In the present studies we used flow cytometry to examine Th17 and Treg subsets in ischemic cortical and splenic tissues. Flow cytometry indicated that VDD rats had significantly less activated Treg cells in ischemic cortical and splenic tissue, while Th17 activation was significantly increased in VDD ischemic cortical tissue. Due to the dysregulation of Treg:Th17 subsets in VDD animals post-stroke and the recently recognized role of the spleen and peripheral nervous system in ischemia-associated neurodegeneration we hypothesized that adoptive transfer of CD4+ T cells harvested from the spleen of control animals 2d post-stroke to the VDD group acutely following middle cerebral artery occlusion (4h) may provide key neuroimmune regulatory elements and/or neuroprotective immune cells and secretions. We found that splenic CD4+ adoptive transfer to VDD rats 4h post-stroke markedly improved infarct volume, survival, and behavioral performance as compared with VDD animals injected with vehicle alone. Together, these results suggest that peripheral immune status significantly influences stroke severity and that acute manipulation of the peripheral immune system post-stroke can prevent or ameliorate inflammation-associated neurodegeneration.

Th17 cell accumulation is decreased during chronic experimental colitis by (n-3) PUFA in Fat-1 mice

During colon inflammation, Th17 cells and immunosuppressive regulatory T cells (Treg) are thought to play promotive and preventative roles, respectively. Dietary (n-3) PUFA favorably modulate intestinal inflammation in part by downregulating T-cell activation and functionality. We used the Fat-1 mouse, a genetic model that synthesizes long-chain (n-3) PUFA de novo, to test the hypothesis that (n-3) PUFA protect against colonic inflammation by modulating the polarization of Treg and Th17 cells during colitis. Male and female wild-type (WT) and Fat-1 mice were administered dextran sodium sulfate (DSS) in the drinking water (2.5%) to induce acute (5 d DSS) or chronic (3 cycles DSS) colitis and the percentage of Treg and Th17 cells residing locally [colonic lamina propria (cLP)] and systemically (spleen) was determined by flow cytometry. The percentage of Treg in either tissue site was unaffected by genotype (P > 0.05); however, during chronic colitis, the percentage of Th17 cells residing in both the spleen and cLP was lower in Fat-1 mice compared to WT mice (P < 0.05). Colonic mucosal mRNA expression of critical Th17 cell cytokines and chemokine receptors (IL-17F, IL-21, and CCR6) were lower, whereas expression of the Th17 cell suppressive cytokine, IL-27, was greater in Fat-1 mice compared to WT mice during chronic colitis (P < 0.05). Moreover, colon histological scores were improved in Fat-1 mice (P < 0.05). Collectively, these results demonstrate for the first time, to our knowledge, that (n-3) PUFA can modulate the colonic mucosal microenvironment to suppress Th17 cell accumulation and inflammatory damage following the induction of chronic colitis.

Immunomodulatory action of dietary fish oil and targeted deletion of intestinal epithelial cell PPARδ in inflammation-induced colon carcinogenesis

The ligand-activated transcription factor peroxisome proliferator-activated receptor (PPAR)-δ is highly expressed in colonic epithelial cells; however, the role of PPARδ ligands, such as fatty acids, in mucosal inflammation and malignant transformation has not been clarified. Recent evidence suggests that the anti-inflammatory/chemoprotective properties of fish oil (FO)-derived n-3 polyunsaturated fatty acids (PUFAs) may be partly mediated by PPARδ. Therefore, we assessed the role of PPARδ in modulating the effects of dietary n-3 PUFAs by targeted deletion of intestinal epithelial cell PPARδ (PPARδ(ΔIEpC)). Subsequently, we documented changes in colon tumorigenesis and the inflammatory microenvironment, i.e., local [mesenteric lymph node (MLN)] and systemic (spleen) T cell activation. Animals were fed chemopromotive [corn oil (CO)] or chemoprotective (FO) diets during the induction of chronic inflammation/carcinogenesis. Tumor incidence was similar in control and PPARδ(ΔIEpC) mice. FO reduced mucosal injury, tumor incidence, colonic STAT3 activation, and inflammatory cytokine gene expression, independent of PPARδ genotype. CD8(+) T cell recruitment into MLNs was suppressed in PPARδ(ΔIEpC) mice. Similarly, FO reduced CD8(+) T cell numbers in the MLN. Dietary FO independently modulated MLN CD4(+) T cell activation status by decreasing CD44 expression. CD11a expression by MLN CD4(+) T cells was downregulated in PPARδ(ΔIEpC) mice. Lastly, splenic CD62L expression was downregulated in PPARδ(ΔIEpC) CD4(+) and CD8(+) T cells. These data demonstrate that expression of intestinal epithelial cell PPARδ does not influence azoxymethane/dextran sodium sulfate-induced colon tumor incidence. Moreover, we provide new evidence that dietary n-3 PUFAs attenuate intestinal inflammation in an intestinal epithelial cell PPARδ-independent manner.

Salmonella typhimurium coordinately regulates FliC location and reduces dendritic cell activation and antigen presentation to CD4+ T cells

During infection, Salmonella transitions from an extracellular-phase (STEX, growth outside host cells) to an intracellular-phase (STIN, growth inside host cells): changes in gene expression mediate survival in the phagosome and modifies LPS and outer membrane protein expression, including altered production of FliC, an Ag recognized by immune CD4+ T cells. Previously, we demonstrated that systemic STIN bacteria repress FliC below the activation threshold of FliC-specific T cells. In this study, we tested the hypothesis that changes in FliC compartmentalization and bacterial responses triggered during the transition from STEX to STIN combine to reduce the ability of APCs to present FliC to CD4+ T cells. Approximately 50% of the Salmonella-specific CD4+ T cells from Salmonella-immune mice were FliC specific and produced IFN-gamma, demonstrating the potent immunogenicity of FliC. FliC expressed by STEX bacteria was efficiently presented by splenic APCs to FliC-specific CD4+ T cells in vitro. However, STIN bacteria, except when lysed, expressed FliC within a protected intracellular compartment and evaded stimulation of FliC-specific T cells. The combination of STIN-mediated responses that reduced FliC bioavailability were overcome by dendritic cells (DCs), which presented intracellular FliC within heat-killed bacteria; however, this ability was abrogated by live bacterial infection. Furthermore, STIN bacteria, unlike STEX, limited DC activation as measured by increased MHC class II, CD86, TNF-alpha, and IL-12 expression. These data indicate that STIN bacteria restrict FliC bioavailability by Ag compartmentalization, and together with STIN bacterial responses, limit DC maturation and cytokine production. Together, these mechanisms may restrain DC-mediated activation of FliC-specific CD4+ T cells.

CD4+-T-cell responses generated during murine Salmonella enterica serovar Typhimurium infection are directed towards multiple epitopes within the natural antigen FliC

The flagellar filament protein FliC is a natural antigen recognized by memory CD4+ T cells recovered from Salmonella enterica serovar Typhimurium-infected humans and mice. To further investigate T-cell responses to FliC, we derived FliC-specific CD4+-T-cell clones from mice of two different haplotypes following oral S. enterica serovar Typhimurium infection. Using C-terminal truncations of MalE-FliC recombinant fusion proteins, we mapped antigenic activity to four different regions of FliC; three of the four epitope-containing regions were present in both FliC and the alternate flagellin subunit FljB. We determined that two novel FliC epitopes were also present in flagellins from several gram-negative enteric bacterial species: E(k)-restricted FliC 80-94 (amino acids 80 to 94) and A(b)-restricted FliC 455-469. Further mapping confirmed the presence of two previously identified FliC epitopes: A(k)-restricted FliC 339-350 and A(b)-restricted FliC 428-442. Therefore, like the recognition site of the innate immune receptor Toll-like receptor 5, three of four FliC epitopes recognized by CD4+ T cells colocalize in the D0/D1 domains of FliC. Salmonella-infected macrophages and dendritic cells stimulated epitope-specific CD4+-T-cell proliferation; infected dendritic cells also activated T cells to produce gamma interferon. These data demonstrate that Salmonella infection generates murine CD4+-T-cell responses to multiple epitopes in the natural antigen FliC and that recognition of infected phagocytes by FliC-specific CD4+ T cells triggers effector functions known to be essential for protective immunity. Together, these data suggest that FliC-specific CD4+ T cells may contribute to cell-mediated host defenses against Salmonella.

Increased Dendritic Cell Numbers Impair Protective Immunity to Intracellular Bacteria Despite Augmenting Antigen-Specific CD8+T Lymphocyte Responses

Dendritic cells (DCs) reside in tissues, where they function as sentinels, providing an essential link between innate and adaptive immunity. Increasing the numbers of DCs in vivo augments T cell responses, and can cause dramatic CTL-dependent tumor regression. To determine whether greater DC numbers promoted T cell-mediated protection in the context of host defense against intracellular bacteria, we treated mice with Flt3 ligand (Flt3-L) to increase DCs in vivo and challenged them with Listeria monocytogenes. Unexpectedly, after primary challenge with Listeria, the overall control of Listeria infection was impaired in Flt3-L-treated mice, which had greater bacterial burden and mortality than controls. Similar results were obtained when DC numbers were increased by treatment with polyethylene glycol-conjugated GM-CSF rather than Flt3-L and in mice infected with Mycobacterium tuberculosis. Impaired protection was not due to dysfunctional T cell responses, as Flt3-L-treated mice had a greater frequency and absolute number of Ag-specific CD8+ T cells, which produced IFN-gamma, exhibited cytolytic activity, and transferred protection. The increased Listeria burden in Flt3-L-treated mice was preferentially associated with DCs, which were unable to kill Listeria and more resistant to CTL lysis compared with macrophages in vitro. Although we cannot exclude the possibility that other potential effects, in addition to increased numbers of DCs, are shared by Flt3-L and polyethylene glycol-conjugated GM-CSF and contributed to the increase in susceptibility observed in treated mice, these results support the notion that DC numbers must be properly controlled within physiological limits to optimize host defense to intracellular bacterial pathogens.

Dopamine beta-hydroxylase deficiency impairs cellular immunity

Norepinephrine, released from sympathetic neurons, and epinephrine, released from the adrenal medulla, participate in a number of physiological processes including those that facilitate adaptation to stressful conditions. The thymus, spleen, and lymph nodes are richly innervated by the sympathetic nervous system, and catecholamines are thought to modulate the immune response. However, the importance of this modulatory role in vivo remains uncertain. We addressed this question genetically by using mice that lack dopamine beta-hydroxylase (dbh-/- mice). dbh-/- mice cannot produce norepinephrine or epinephrine, but produce dopamine instead. When housed in specific pathogen-free conditions, dbh-/- mice had normal numbers of blood leukocytes, and normal T and B cell development and in vitro function. However, when challenged in vivo by infection with the intracellular pathogens Listeria monocytogenes or Mycobacterium tuberculosis, dbh-/- mice were more susceptible to infection, exhibited extreme thymic involution, and had impaired T cell function, including Th1 cytokine production. When immunized with trinitrophenyl-keyhole limpet hemocyanin, dbh-/- mice produced less Th1 cytokine-dependent-IgG2a antitrinitrophenyl antibody. These results indicate that physiological catecholamine production is not required for normal development of the immune system, but plays an important role in the modulation of T cell-mediated immunity to infection and immunization.