Immune evasion by Helicobacter pylori is mediated by induction of macrophage arginase II

Biochemistry, pharmacology, and in vivo function of arginases

The enzyme arginase catalyzes the hydrolysis of l-arginine into l-ornithine and urea. The 2 existing isoforms Arg1 and Arg2 exhibit different cellular localizations and metabolic functions. Arginase activity is crucial for nitrogen detoxification in the urea cycle, synthesis of polyamines, and control of l-arginine bioavailability and nitric oxide (NO) production. Despite significant progress in the understanding of the biochemistry and function of arginases, several open questions remain. Recent studies have revealed that the regulation and function of Arg1 and Arg2 are cell type-specific, species-specific, and profoundly different in mice and humans. The main differences are in the distribution and function of Arg1 and Arg2 in immune and erythroid cells. Contrary to what was previously thought, Arg1 activity appears to be only partially related to vascular NO signaling under homeostatic conditions in the vascular wall, but its expression is increased under disease conditions and may be targeted by treatment with arginase inhibitors. Arg2 appears to be mainly a catabolic enzyme involved in the synthesis of l-ornithine, polyamine, and l-proline but may play a putative role in blood pressure control, at least in mice. The immunosuppressive role of arginase-mediated arginine depletion is a promising target for cancer treatment. This review critically revises and discusses the biochemistry, pharmacology, and in vivo function of arginases, focusing on the insights gained from the analysis of cell-specific Arg1 and Arg2 knockout mice and human studies using arginase inhibitors or pegylated recombinant arginase. SIGNIFICANCE STATEMENT: Further basic and translational research is needed to deepen our understanding of the regulation of Arg1 and Arg2 in different cell types in consideration of their localization, species-specificity, and multiple biochemical and physiological roles. This will lead to better pharmacological strategies to target arginase activity in liver, cardiovascular, hematological, immune/infectious diseases, and cancer.

Effects and mechanisms of Helicobacter pylori on cancers development and immunotherapy

Tumor immunotherapy has been widely used in clinical treatment of various cancers. However, some patients of these cancers do not respond to immunotherapy effectively. And H. pylori infection has been considered to be related to the efficacy of immunotherapy. This review aims to summarize the different effects and mechanisms of H. pylori infection on immunotherapy in different kinds of cancers. We searched the relevant literature on H. pylori and tumor immunotherapy, and summarized to form a review. Generally, H. pylori infection plays a role in affecting kinds of cancers' development, besides gastric cancer. Current evidence suggests that H. pylori infection may reduce the efficacy of immunotherapy for colorectal cancer, non-small cell lung cancer and melanoma, but due to the lack of sufficient evidence, more data is needed to prove that. While for gastric cancer, the effects remain controversial. The H. pylori regulation effects and metabolisms involved in systematic related cancers should be paid attention to. Whether H. pylori should be eradicated when immunotherapy performed may be a critical consideration for some kinds of tumors.

The role of nitric oxide synthase/ nitric oxide in infection-related cancers: Beyond antimicrobial activity

As a free radical and endogenous effector molecule, mammalian endogenous nitric oxide (NO) is mainly derived from nitric oxide synthase (NOS) via L-arginine. NO participates in normal physiological reactions and provides immune responses to prevent the invasion of foreign bacteria. However, NO also has complex and contradictory biological effects. Abnormal NO signaling is involved in the progression of many diseases, such as cancer. In the past decades, cancer research has been closely linked with NOS/ NO, and many tumors with poor prognosis are associated with high expression of NOS. In this review, we give a overview of the biological effects of NOS/ NO. Then we focus on the oncogenic role of iNOS/ NO in HPV, HBV, EBV and H. pylori related tumors. In fact, there is growing evidence that iNOS could be used as a potential therapeutic target in cancer therapy. We emphasize that the pro-tumor effect of NOS/ NO is greater than the anti-tumor effect.

Polyamines: the pivotal amines in influencing the tumor microenvironment

Cellular proliferation, function and survival is reliant upon maintaining appropriate intracellular polyamine levels. Due to increased metabolic needs, cancer cells elevate their polyamine pools through coordinated metabolism and uptake. High levels of polyamines have been linked to more immunosuppressive tumor microenvironments (TME) as polyamines support the growth and function of many immunosuppressive cell types such as MDSCs, macrophages and regulatory T-cells. As cancer cells and other pro-tumorigenic cell types are highly dependent on polyamines for survival, pharmacological modulation of polyamine metabolism is a promising cancer therapeutic strategy. This review covers the roles of polyamines in various cell types of the TME including both immune and stromal cells, as well as how competition for nutrients, namely polyamine precursors, influences the cellular landscape of the TME. It also details the use of polyamines as biomarkers and the ways in which polyamine depletion can increase the immunogenicity of the TME and reprogram tumors to become more responsive to immunotherapy.

Effect of metabolic reprogramming on the immune microenvironment in gastric cancer

Gastric cancer (GC) is a malignant tumor of the gastrointestinal tract with a high mortality rate worldwide, a low early detection rate and a poor prognosis. The rise of metabolomics has facilitated the early detection and treatment of GC. Metabolism in the GC tumor microenvironment (TME) mainly includes glucose metabolism, lipid metabolism and amino acid metabolism, which provide energy and nutrients for GC cell proliferation and migration. Abnormal tumor metabolism can influence tumor progression by regulating the functions of immune cells and immune molecules in the TME, thereby contributing to tumor immune escape. Thus, in this review, we summarize the impact of metabolism on the TME during GC progression. We also propose novel strategies to modulate antitumor immune responses by targeting metabolism.

Helicobacter pylori antigens as immunomodulators of immune system

Helicobacter pylori (H. pylori) is one of the most prevalent human pathogens and the leading cause of chronic infection in almost half of the population in the world (~59%). The bacterium is a major leading cause of chronic gastritis, gastric and duodenal ulcers, and two type of malignancies, gastric adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma. Despite the immune responses mounted by the host, the bacteria are not cleared from the body resulting in a chronic infection accompanied by a chronic inflammation. Herein, a review of the literature discussing H. pylori antigens modulating the immune responses is presented. The mechanisms that are involved in the modulation of innate immune response, include modulation of recognition by pattern recognition receptors (PRRs) such as modulation of recognition by toll like receptors (TLR)4 and TLR5, modulation of phagocytic function, and modulation of phagocytic killing mediated by reactive oxygen species (ROS) and nitric oxide (NO). On the other hands, H. pylori modulates acquired immune response by the induction of tolerogenic dendritic cells (DCs), modulation of apoptosis, induction of regulatory T cells, modulation of T helper (Th)1 response, and modulation of Th17 response.

BRD4 Regulates Glycolysis-Dependent Nos2 Expression in Macrophages Upon H pylori Infection

BACKGROUND & AIMS

Metabolic reprogramming is essential for the activation and functions of macrophages, including bacterial killing and cytokine production. Bromodomain-containing protein 4 (BRD4) has emerged as a critical regulator of innate immune response. However, the potential role of BRD4 in the metabolic reprogramming of macrophage activation upon Helicobacter pylori infection remains unclear.

METHODS

Bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Brd4-myeloid deletion conditional knockout (Brd4-CKO) mice were infected with H pylori. RNA sequencing was performed to evaluate the differential gene expression between WT and Brd4-deficient BMDMs upon infection. An in vivo model of H pylori infection using WT and Brd4-CKO mice was used to confirm the role of BRD4 in innate immune response to infection.

RESULTS

Depletion of Brd4 in BMDMs showed impaired H pylori-induced glycolysis. In addition, H pylori-induced expression of glycolytic genes, including Slc2a1 and Hk2, was decreased in Brd4-deficient BMDMs. BRD4 was recruited to the promoters of Slc2a1 and Hk2 via hypoxia-inducible factor-1α, facilitating their expression. BRD4-mediated glycolysis stabilized H pylori-induced nitric oxide synthase (Nos2) messenger RNA to produce nitric oxide. The NO-mediated killing of H pylori decreased in Brd4-deficient BMDMs, which was rescued by pyruvate. Furthermore, Brd4-CKO mice infected with H pylori showed reduced gastric inflammation and increased H pylori colonization with reduced inducible NO synthase expression in gastric macrophages.

CONCLUSIONS

Our study identified BRD4 as a key regulator of hypoxia-inducible factor-1α-dependent glycolysis and macrophage activation. Furthermore, we show a novel regulatory role of BRD4 in innate immunity through glycolysis to stabilize Nos2 messenger RNA for NO production to eliminate H pylori infection.

Gastric precancerous lesions:occurrence, development factors, and treatment

Patients with gastric precancerous lesions (GPL) have a higher risk of gastric cancer (GC). However, the transformation of GPL into GC is an ongoing process that takes several years. At present, several factors including H.Pylori (Hp), flora imbalance, inflammatory factors, genetic variations, Claudin-4, gastric stem cells, solute carrier family member 26 (SLC26A9), bile reflux, exosomes, and miR-30a plays a considerable role in the transformation of GPL into GC. Moreover, timely intervention in the event of GPL can reduce the risk of GC. In clinical practice, GPL is mainly treated with endoscopy, acid suppression therapy, Hp eradication, a cyclooxygenase-2 inhibitor, aspirin, and diet. Currently, the use of traditional Chinese medicine (TCM) or combination with western medication to remove Hp and the use of TCM to treat GPL are common in Asia, particularly China, and have also demonstrated excellent clinical efficacy. This review thoroughly discussed the combining of TCM and Western therapy for the treatment of precancerous lesions as conditions allow. Consequently, this review also focuses on the causes of the development and progression of GPL, as well as its current treatment. This may help us understand GPL and related treatment.

Determination of Heterogeneous Proteomic and Metabolomic Response in anti-TNF and anti-IL-6 Treatment of Patients with Rheumatoid Arthritis

Reduction in tumor necrosis factor (αTNF) and interleukin-6 (IL-6) activities is a widely utilized strategy for the treatment of rheumatoid arthritis (RA) with a high success rate. Despite both schemes targeting the deprivation of inflammatory reactions caused by the excessive activity of cytokines, their mechanisms of action and the final output are still unequal. This was a comparative longitudinal study that lasted for 24 weeks and aimed to find the answer to why the two schemes of therapy can pass out of proportion in attitude of their efficiency. What are the differences in metabolic and proteomic responses among patients who were being treated by either the anti-TNF or anti-IL-6 strategy? We found increased levels of immunoglobulins A and G (more than 2-fold in anti-IL-6 and more than 4-5-fold in anti-TNF groups) at the final stage (24 weeks) of monitoring but the most profound increase was determined for µ-chains of immunoglobulins in both groups of study. Metabolomic changes displayed main alterations with regard to arginine metabolism and collagen maintenance, where arginine increased 8.86-fold (p < 0.001) in anti-TNF and 5.71-fold (p < 0.05) in anti-IL-6 groups but patients treated by the anti-TNF scheme suffered a higher depletion of arginine before the start of therapy. Some indicators of matrix and bone tissue degradation also increased 4-hydroxyproline (4-HP) more than 6-fold (p < 0.001) in anti-TNF and more than 2-fold (p < 0.05) in the anti-IL-6 group, but the growth dynamics in the anti-IL6 group was delayed (gradually raised at week 24) compared to the anti-TNF group (raised at week 12) following a smooth reduction. The ELISA analysis of IL-6 and TNFα concentration in the study population supported proteomic and metabolomic data. A positive correlation between ΔCDAI and ΔDAS28 indicators and ESR and CRP was established for the majority of patients after 24 weeks of treatment where ESR and CRP reduced by 20% and 40% finally, respectively. A regression model using the Forest Plot was estimated to elucidate the impact of the most significant clinical, biochemical, and anthropometric indicators for the evaluation of differences between considered anti-TNF and anti-IL-6 schemes of therapy.

Host M-CSF induced gene expression drives changes in susceptible and resistant mice-derived BMdMs upon Leishmania major infection

Leishmaniases are a group of diseases with different clinical manifestations. Macrophage-Leishmania interactions are central to the course of the infection. The outcome of the disease depends not only on the pathogenicity and virulence of the parasite, but also on the activation state, the genetic background, and the underlying complex interaction networks operative in the host macrophages. Mouse models, with mice strains having contrasting behavior in response to parasite infection, have been very helpful in exploring the mechanisms underlying differences in disease progression. We here analyzed previously generated dynamic transcriptome data obtained from Leishmania major (L. major) infected bone marrow derived macrophages (BMdMs) from resistant and susceptible mouse. We first identified differentially expressed genes (DEGs) between the M-CSF differentiated macrophages derived from the two hosts, and found a differential basal transcriptome profile independent of Leishmania infection. These host signatures, in which 75% of the genes are directly or indirectly related to the immune system, may account for the differences in the immune response to infection between the two strains. To gain further insights into the underlying biological processes induced by L. major infection driven by the M-CSF DEGs, we mapped the time-resolved expression profiles onto a large protein-protein interaction (PPI) network and performed network propagation to identify modules of interacting proteins that agglomerate infection response signals for each strain. This analysis revealed profound differences in the resulting responses networks related to immune signaling and metabolism that were validated by qRT-PCR time series experiments leading to plausible and provable hypotheses for the differences in disease pathophysiology. In summary, we demonstrate that the host's gene expression background determines to a large degree its response to L. major infection, and that the gene expression analysis combined with network propagation is an effective approach to help identifying dynamically altered mouse strain-specific networks that hold mechanistic information about these contrasting responses to infection.

Targeting cancer-specific metabolic pathways for developing novel cancer therapeutics

Cancer is a heterogeneous disease characterized by various genetic and phenotypic aberrations. Cancer cells undergo genetic modifications that promote their proliferation, survival, and dissemination as the disease progresses. The unabated proliferation of cancer cells incurs an enormous energy demand that is supplied by metabolic reprogramming. Cancer cells undergo metabolic alterations to provide for increased energy and metabolite requirement; these alterations also help drive the tumor progression. Dysregulation in glucose uptake and increased lactate production via "aerobic glycolysis" were described more than 100 years ago, and since then, the metabolic signature of various cancers has been extensively studied. However, the extensive research in this field has failed to translate into significant therapeutic intervention, except for treating childhood-ALL with amino acid metabolism inhibitor L-asparaginase. Despite the growing understanding of novel metabolic alterations in tumors, the therapeutic targeting of these tumor-specific dysregulations has largely been ineffective in clinical trials. This chapter discusses the major pathways involved in the metabolism of glucose, amino acids, and lipids and highlights the inter-twined nature of metabolic aberrations that promote tumorigenesis in different types of cancer. Finally, we summarise the therapeutic interventions which can be used as a combinational therapy to target metabolic dysregulations that are unique or common in blood, breast, colorectal, lung, and prostate cancer.

Effects of helicobacter pylori on tumor microenvironment and immunotherapy responses

Helicobacter pylori is closely associated with gastric cancer. During persistent infection, Helicobacter pylori can form a microenvironment in gastric mucosa which facilitates the survival and colony formation of Helicobacter pylori. Tumor stromal cells are involved in this process, including tumor-associated macrophages, mesenchymal stem cells, cancer-associated fibroblasts, and myeloid-derived suppressor cells, and so on. The immune checkpoints are also regulated by Helicobacter pylori infection. Helicobacter pylori virulence factors can also act as immunogens or adjuvants to elicit or enhance immune responses, indicating their potential applications in vaccine development and tumor immunotherapy. This review highlights the effects of Helicobacter pylori on the immune microenvironment and its potential roles in tumor immunotherapy responses.

Innate Immunity Crosstalk with Helicobacter pylori: Pattern Recognition Receptors and Cellular Responses

Helicobacter pylori is one of the most successful gastric pathogens that has co-existed with human for centuries. H. pylori is recognized by the host immune system through human pattern recognition receptors (PRRs), such as toll-like receptors (TLRs), C-type lectin like receptors (CLRs), NOD-like receptors (NLRs), and RIG-I-like receptors (RLRs), which activate downstream signaling pathways. Following bacterial recognition, the first responders of the innate immune system, including neutrophils, macrophages, and dendritic cells, eradicate the bacteria through phagocytic and inflammatory reaction. This review provides current understanding of the interaction between the innate arm of host immunity and H. pylori, by summarizing H. pylori recognition by PRRs, and the subsequent signaling pathway activation in host innate immune cells.

Monocytic-Myeloid Derived Suppressor Cells Suppress T-Cell Responses in Recovered SARS CoV2-Infected Individuals

Coronavirus disease 2019 (COVID-19) caused by SARS Coronavirus 2 (CoV2) is associated with massive immune activation and hyperinflammatory response. Acute and severe CoV2 infection is characterized by the expansion of myeloid derived suppressor cells (MDSC) because of cytokine storm, these MDSC suppress T cell functions. However, the presence of MDSC and its effect on CoV2 antigen specific T cell responses in individuals long after first detection of CoV2 and recovery from infection has not been studied. We and others have previously shown that CD11b+CD33+CD14+HLA-DR-/lo monocytic MDSC (M-MDSC) are present in individuals with clinical recovery from viral infection. In this study, we compared the frequency, functional and transcriptional signatures of M-MDSC isolated from CoV2 infected individuals after 5-months of the first detection of the virus (CoV2+) and who were not infected with CoV2 (CoV2-). Compared to CoV2- individuals, M-MDSC were present in CoV2+ individuals at a higher frequency, the level of M-MDSC correlated with the quantity of IL-6 in the plasma. Compared to CoV2-, increased frequency of PD1+, CD57+ and CX3CR1+ T effector memory (TEM) cell subsets was also present in CoV2+ individuals, but these did not correlate with M-MDSC levels. Furthermore, depleting M-MDSC from peripheral blood mononuclear cells (PBMC) increased T cell cytokine production when cultured with the peptide pools of immune dominant spike glycoprotein (S), membrane (M), and nucleocapsid (N) antigens of CoV2. M-MDSC suppressed CoV2 S- antigen-specific T cell in ROS, Arginase, and TGFβ dependent manner. Our gene expression, RNA-seq and pathway analysis studies further confirm that M-MDSC isolated from CoV2+ individuals are enriched in pathways that regulate both innate and adaptive immune responses, but the genes regulating these functions (HLA-DQA1, HLA-DQB1, HLA-B, NLRP3, IL1β, CXCL2, CXCL1) remained downregulated in M-MDSC isolated from CoV2+ individuals. These results demonstrate that M-MDSC suppresses recall responses to CoV2 antigens long after recovery from infection. Our findings suggest M-MDSC as novel regulators of CoV2 specific T cell responses, and should be considered as target to augment responses to vaccine.

Cystathionine γ-lyase exacerbates Helicobacter pylori immunopathogenesis by promoting macrophage metabolic remodeling and activation

Macrophages play a crucial role in the inflammatory response to the human stomach pathogen Helicobacter pylori, which infects half of the world's population and causes gastric cancer. Recent studies have highlighted the importance of macrophage immunometabolism in their activation state and function. We have demonstrated that the cysteine-producing enzyme cystathionine γ-lyase (CTH) is upregulated in humans and mice with H. pylori infection. Here, we show that induction of CTH in macrophages by H. pylori promoted persistent inflammation. Cth-/- mice had reduced macrophage and T cell activation in H. pylori-infected tissues, an altered metabolome, and decreased enrichment of immune-associated gene networks, culminating in decreased H. pylori-induced gastritis. CTH is downstream of the proposed antiinflammatory molecule, S-adenosylmethionine (SAM). Whereas Cth-/- mice exhibited gastric SAM accumulation, WT mice treated with SAM did not display protection against H. pylori-induced inflammation. Instead, we demonstrated that Cth-deficient macrophages exhibited alterations in the proteome, decreased NF-κB activation, diminished expression of macrophage activation markers, and impaired oxidative phosphorylation and glycolysis. Thus, through altering cellular respiration, CTH is a key enhancer of macrophage activation, contributing to a pathogenic inflammatory response that is the universal precursor for the development of H. pylori-induced gastric disease.

The Efficacy of Cancer Immunotherapies Is Compromised by Helicobacter pylori Infection

Helicobacter pylori infects the gastric mucosa of a large number of humans. Although asymptomatic in the vast majority of cases, H pylori infection can lead to the development of peptic ulcers gastric adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma. Using a variety of mechanisms, H pylori locally suppresses the function of the host immune system to establish chronic infection. Systemic immunomodulation has been observed in both clinical and pre-clinical studies, which have demonstrated that H pylori infection is associated with reduced incidence of inflammatory diseases, such as asthma and Crohn’s disease. The introduction of immunotherapies in the arsenal of anti-cancer drugs has revealed a new facet of H pylori-induced immune suppression. In this review, we will describe the intimate interactions between H pylori and its host, and formulate hypothtyeses describing the detrimental impact of H pylori infection on the efficacy of cancer immunotherapies.

Transcriptome analysis of Echinococcus granulosus sensu stricto protoscoleces reveals differences in immune modulation gene expression between cysts found in cattle and sheep

Cystic Echinococcosis (CE), a zoonotic parasitic disease, is caused by the cestode Echinococcus granulosus sensu lato. CE inflicts severe damage in cattle, sheep, and human hosts worldwide. Fertile CE cysts are characterized by the presence of viable protoscoleces. These parasite forms are studied with minimal contamination with host molecules. Hosts, cattle and sheep, show differences in their CE cyst fertility. The effect of the host in protoscolex transcriptome is not known. We genotyped and performed transcriptomic analysis on sheep protoscoleces obtained from liver and lung CE cysts. The transcriptomic data of Echinococcus granulosus sensu stricto protoscoleces from 6 lung CE cysts and 6 liver CE cysts were Collected. For host comparison analysis, 4 raw data files belonging to Echinococcus granulosus sensu stricto protoscoleces from cattle liver CE cysts were obtained from the NCBI SRA database. Principal component and differential expression analysis did not reveal any statistical differences between protoscoleces obtained from liver or lung cysts, either within the same sheep or different sheep hosts. Conversely, there are significant differences between cattle and sheep protoscolex samples. We found differential expression of immune-related genes. In cattle, 7 genes were upregulated in protoscoleces from liver cysts. In sheep, 3 genes were upregulated in protoscoleces from liver and lung CE cysts. Noteworthy, are the differential expression of antigen B, tegument antigen, and arginase-2 in samples obtained from sheep CE cysts, and basigin in samples from cattle CE cysts. These findings suggest that the host species is an important factor involved in the differential expression of immune related genes, which in turn is possibly related to the fertility of Echinococcus granulosus sensu stricto cysts.

Arginine Signaling and Cancer Metabolism

Arginine is an amino acid critically involved in multiple cellular processes including the syntheses of nitric oxide and polyamines, and is a direct activator of mTOR, a nutrient-sensing kinase strongly implicated in carcinogenesis. Yet, it is also considered as a non- or semi-essential amino acid, due to normal cells' intrinsic ability to synthesize arginine from citrulline and aspartate via ASS1 (argininosuccinate synthase 1) and ASL (argininosuccinate lyase). As such, arginine can be used as a dietary supplement and its depletion as a therapeutic strategy. Strikingly, in over 70% of tumors, ASS1 transcription is suppressed, rendering the cells addicted to external arginine, forming the basis of arginine-deprivation therapy. In this review, we will discuss arginine as a signaling metabolite, arginine's role in cancer metabolism, arginine as an epigenetic regulator, arginine as an immunomodulator, and arginine as a therapeutic target. We will also provide a comprehensive summary of ADI (arginine deiminase)-based arginine-deprivation preclinical studies and an update of clinical trials for ADI and arginase. The different cell killing mechanisms associated with various cancer types will also be described.

Notch Signaling Ligand Jagged1 Enhances Macrophage-Mediated Response to Helicobacter pylori

Helicobacter pylori (H. pylori) is one of the gram-negative bacteria that mainly colonize the stomach mucosa and cause many gastrointestinal diseases, such as gastritis, peptic ulcer, and gastric cancer. Macrophages play a key role in eradicating H. pylori. Recent data have shown that Notch signaling could modulate the activation and bactericidal activities of macrophages. However, the role of Notch signaling in macrophages against H. pylori remains unclear. In the present study, in the co-culture model of macrophages with H. pylori, the inhibition of Notch signaling using γ-secretase decreased the expression of inducible nitric oxide synthase (iNOS) and its product, nitric oxide (NO), and downregulated the secretion of pro-inflammatory cytokine and attenuated phagocytosis and bactericidal activities of macrophages to H. pylori. Furthermore, we identified that Jagged1, one of Notch signaling ligands, was both upregulated in mRNA and protein level in activated macrophages induced by H. pylori. Clinical specimens showed that the number of Jagged1⁺ macrophages in the stomach mucosa from H. pylori-infected patients was significantly higher than that in healthy control. The overexpression of Jagged1 promoted bactericidal activities of macrophages against H. pylori and siRNA-Jagged1 presented the opposite effect. Besides, the addition of exogenous rJagged1 facilitated the pro-inflammatory mediators of macrophages against H. pylori, but the treatment of anti-Jagged1 neutralizing antibody attenuated it. Taken together, these results suggest that Jagged1 is a promoting molecule for macrophages against H. pylori, which will provide insight for exploring Jagged1 as a novel therapeutic target for the control of H. pylori infection.

The role of polyamines in gastric cancer

Advancements in our understanding of polyamine molecular and cellular functions have led to increased interest in targeting polyamine metabolism for anticancer therapeutic benefits. The polyamines putrescine, spermidine, and spermine are polycationic alkylamines commonly found in all living cells and are essential for cellular growth and survival. This review summarizes the existing research on polyamine metabolism and function, specifically the role of polyamines in gastric immune cell and epithelial cell function. Polyamines have been implicated in a multitude of cancers, but in this review, we focus on the role of polyamine dysregulation in the context of Helicobacter pylori-induced gastritis and subsequent progression to gastric cancer. Due to the emerging implication of polyamines in cancer development, there is an increasing number of promising clinical trials using agents to target the polyamine metabolic pathway for potential chemoprevention and anticancer therapy.

Promotion of Anti-Tuberculosis Macrophage Activity by L-Arginine in the Absence of Nitric Oxide

Macrophages are indispensable immune cells tasked at eliminating intracellular pathogens. Mycobacterium tuberculosis (Mtb), one of the most virulent intracellular bacterial pathogens known to man, infects and resides within macrophages. While macrophages can be provoked by extracellular stimuli to inhibit and kill Mtb bacilli, these host defense mechanisms can be blocked by limiting nutritional metabolites, such as amino acids. The amino acid L-arginine has been well described to enhance immune function, especially in the context of driving macrophage nitric oxide (NO) production in mice. In this study, we aimed to establish the necessity of L-arginine on anti-Mtb macrophage function independent of NO. Utilizing an in vitro system, we identified that macrophages relied on NO for only half of their L-arginine-mediated host defenses and this L-arginine-mediated defense in the absence of NO was associated with enhanced macrophage numbers and viability. Additionally, we observed macrophage glycolysis to be driven by both L-arginine and mechanistic target of rapamycin (mTOR), and inhibition of glycolysis or mTOR reduced macrophage control of Mtb as well as macrophage number and viability in the presence of L-arginine. Our data underscore L-arginine as an essential nutrient for macrophage function, not only by fueling anti-mycobacterial NO production, but also as a central regulator of macrophage metabolism and additional host defense mechanisms.

Metabolism in tumour-associated macrophages: a quid pro quo with the tumour microenvironment

Lung cancer is the leading cause of death from cancer worldwide. Recent studies demonstrated that the tumour microenvironment (TME) is pivotal for tumour progression, providing multiple targeting opportunities for therapeutic strategies. As one of the most abundant stromal cell types in the TME, tumour-associated macrophages (TAMs) exhibit high plasticity. Malignant cells alter their metabolic profiles to adapt to the limited availability of oxygen and nutrients in the TME, resulting in functional alteration of TAMs. The metabolic features of TAMs are strongly associated with their functional plasticity, which further impacts metabolic profiling in the TME and contributes to tumourigenesis and progression. Here, we review the functional determination of the TME by TAM metabolic alterations, including glycolysis as well as fatty acid and amino acid metabolism, which in turn are influenced by environmental changes. Additionally, we discuss metabolic reprogramming of TAMs to a tumouricidal phenotype as a potential antitumoural therapeutic strategy.

Tumour-associated macrophages (TAMs) display a high level of functional plasticity and altered metabolism symbolised by high sensitivity to the surrounding tumour microenvironment. The metabolism of TAMs provides novel therapeutic opportunities to treat cancer.https://bit.ly/31OqHhe

Myeloid Cell-Derived Arginase in Cancer Immune Response

Amino acid metabolism is a critical regulator of the immune response, and its modulating becomes a promising approach in various forms of immunotherapy. Insufficient concentrations of essential amino acids restrict T-cells activation and proliferation. However, only arginases, that degrade L-arginine, as well as enzymes that hydrolyze L-tryptophan are substantially increased in cancer. Two arginase isoforms, ARG1 and ARG2, have been found to be present in tumors and their increased activity usually correlates with more advanced disease and worse clinical prognosis. Nearly all types of myeloid cells were reported to produce arginases and the increased numbers of various populations of myeloid-derived suppressor cells and macrophages correlate with inferior clinical outcomes of cancer patients. Here, we describe the role of arginases produced by myeloid cells in regulating various populations of immune cells, discuss molecular mechanisms of immunoregulatory processes involving L-arginine metabolism and outline therapeutic approaches to mitigate the negative effects of arginases on antitumor immune response. Development of potent arginase inhibitors, with improved pharmacokinetic properties, may lead to the elaboration of novel therapeutic strategies based on targeting immunoregulatory pathways controlled by L-arginine degradation.

Spermine oxidase mediates Helicobacter pylori-induced gastric inflammation, DNA damage, and carcinogenic signaling

Helicobacter pylori infection is the main risk factor for the development of gastric cancer, the third leading cause of cancer death worldwide. H. pylori colonizes the human gastric mucosa and persists for decades. The inflammatory response is ineffective in clearing the infection, leading to disease progression that may result in gastric adenocarcinoma. We have shown that polyamines are regulators of the host response to H. pylori, and that spermine oxidase (SMOX), which metabolizes the polyamine spermine into spermidine plus H2O2, is associated with increased human gastric cancer risk. We now used a molecular approach to directly address the role of SMOX, and demonstrate that Smox-deficient mice exhibit significant reductions of gastric spermidine levels and H. pylori-induced inflammation. Proteomic analysis revealed that cancer was the most significantly altered functional pathway in Smox-/- gastric organoids. Moreover, there was also less DNA damage and β-catenin activation in H. pylori-infected Smox-/- mice or gastric organoids, compared to infected wild-type animals or gastroids. The link between SMOX and β-catenin activation was confirmed in human gastric organoids that were treated with a novel SMOX inhibitor. These findings indicate that SMOX promotes H. pylori-induced carcinogenesis by causing inflammation, DNA damage, and activation of β-catenin signaling.

Arginase Pathway in Acute Retina and Brain Injury: Therapeutic Opportunities and Unexplored Avenues

Ischemic retinopathies represent a major cause of visual impairment and blindness. They include diabetic retinopathy (DR), acute glaucoma, retinopathy of prematurity (ROP), and central (or branch) retinal artery occlusion (CRAO). These conditions share in common a period of ischemia or reduced blood supply to the retinal tissue that eventually leads to neuronal degeneration. Similarly, acute brain injury from ischemia or trauma leads to neurodegeneration and can have devastating consequences in patients with stroke or traumatic brain injury (TBI). In all of these conditions, current treatment strategies are limited by their lack of effectiveness, adverse effects or short time window for administration. Therefore, there is a great need to identify new therapies for acute central nervous system (CNS) injury. In this brief review article, we focus on the pathway of the arginase enzyme as a novel therapeutic target for acute CNS injury. We review the recent work on the role of arginase enzyme and its downstream components in neuroprotection in both retina and brain acute injury models. Delineating the similarities and differences between the role of arginase in the retina and brain neurodegeneration will allow for better understanding of the role of arginase in CNS disorders. This will also facilitate repurposing the arginase pathway as a new therapeutic target in both retina and brain diseases.

Alveolar Macrophage Chromatin Is Modified to Orchestrate Host Response to Mycobacterium bovis Infection

Bovine tuberculosis is caused by infection with Mycobacterium bovis, which can also cause disease in a range of other mammals, including humans. Alveolar macrophages are the key immune effector cells that first encounter M. bovis and how the macrophage epigenome responds to mycobacterial pathogens is currently not well understood. Here, we have used chromatin immunoprecipitation sequencing (ChIP-seq), RNA-seq and miRNA-seq to examine the effect of M. bovis infection on the bovine alveolar macrophage (bAM) epigenome. We show that H3K4me3 is more prevalent, at a genome-wide level, in chromatin from M. bovis-infected bAM compared to control non-infected bAM; this was particularly evident at the transcriptional start sites of genes that determine programmed macrophage responses to mycobacterial infection (e.g. M1/M2 macrophage polarisation). This pattern was also supported by the distribution of RNA Polymerase II (Pol II) ChIP-seq results, which highlighted significantly increased transcriptional activity at genes demarcated by permissive chromatin. Identification of these genes enabled integration of high-density genome-wide association study (GWAS) data, which revealed genomic regions associated with resilience to infection with M. bovis in cattle. Through integration of these data, we show that bAM transcriptional reprogramming occurs through differential distribution of H3K4me3 and Pol II at key immune genes. Furthermore, this subset of genes can be used to prioritise genomic variants from a relevant GWAS data set.

The role of polyamines in the regulation of macrophage polarization and function

Naturally occurring polyamines are ubiquitously distributed and play important roles in cell development, amino acid and protein synthesis, oxidative DNA damage, proliferation, and cellular differentiation. Macrophages are essential in the innate immune response, and contribute to tissue remodeling. Naïve macrophages have two major potential fates: polarization to (1) the classical pro-inflammatory M1 defense response to bacterial pathogens and tumor cells, and (2) the alternatively activated M2 response, induced in the presence of parasites and wounding, and also implicated in the development of tumor-associated macrophages. ODC, the rate-limiting enzyme in polyamine synthesis, leads to an increase in putrescine levels, which impairs M1 gene transcription. Additionally, spermidine and spermine can regulate translation of pro-inflammatory mediators in activated macrophages. In this review, we focus on polyamines in macrophage activation patterns in the context of gastrointestinal inflammation and carcinogenesis. We seek to clarify mechanisms of innate immune regulation by polyamine metabolism and potential novel therapeutic targets.

African-centric TP53 variant increases iron accumulation and bacterial pathogenesis but improves response to malaria toxin

A variant at amino acid 47 in human TP53 exists predominantly in individuals of African descent. P47S human and mouse cells show increased cancer risk due to defective ferroptosis. Here, we show that this ferroptotic defect causes iron accumulation in P47S macrophages. This high iron content alters macrophage cytokine profiles, leads to higher arginase level and activity, and decreased nitric oxide synthase activity. This leads to more productive intracellular bacterial infections but is protective against malarial toxin hemozoin. Proteomics of macrophages reveal decreased liver X receptor (LXR) activation, inflammation and antibacterial defense in P47S macrophages. Both iron chelators and LXR agonists improve the response of P47S mice to bacterial infection. African Americans with elevated saturated transferrin and serum ferritin show higher prevalence of the P47S variant (OR = 1.68 (95%CI 1.07–2.65) p = 0.023), suggestive of its role in iron accumulation in humans. This altered macrophage phenotype may confer an advantage in malaria-endemic sub-Saharan Africa.

A polymorphism in human TP53 (P47S) that predominantly exists in individuals of African descent affects ferroptosis. Here, the authors show that this results in iron accumulation in macrophages leading to more productive infection by intracellular bacteria but improved anti-inflammatory response to the malarial toxin hemozoin.

Immunometabolism of Phagocytes During Mycobacterium tuberculosis Infection

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) remains as a leading killer among infectious diseases worldwide. The nature of the host immune response dictates whether the initial Mtb infection is cleared or progresses toward active disease, and is ultimately determined by intricate host-pathogen interactions that are yet to be fully understood. The early immune response to infection is mediated by innate immune cells, including macrophages and neutrophils that can phagocytose Mtb and mount an antimicrobial response. However, Mtb can exploit these innate immune cells for its survival and dissemination. Recently, it has become clear that the immune response and metabolic remodeling are interconnected, which is highlighted by the rapid evolution of the interdisciplinary field of immunometabolism. It has been proposed that the net outcome to Mtb infection—clearance or chronic disease—is likely a result of combined immunologic and metabolic activities of the immune cells. Indeed, host cells activated by Mtb infection have strikingly different metabolic requirements than naïve/non-infected cells. Macrophages activated by Mtb-derived molecules or upon phagocytosis acquire a phenotype similar to M1 with elevated production of pro-inflammatory molecules and rely on glycolysis and pentose phosphate pathway to meet their bioenergetic and metabolic requirements. In these macrophages, oxidative phosphorylation and fatty acid oxidation are dampened. However, the non-infected/naive, M2-type macrophages are anti-inflammatory and derive their energy from oxidative phosphorylation and fatty acid oxidation. Similar metabolic adaptations also occur in other phagocytes, including dendritic cells, neutrophils upon Mtb infection. This metabolic reprogramming of innate immune cells during Mtb infection can differentially regulate their effector functions, such as the production of cytokines and chemokines, and antimicrobial response, all of which can ultimately determine the outcome of Mtb-host interactions within the granulomas. In this review, we describe key immune cells bolstering host innate response and discuss the metabolic reprogramming in these phagocytes during Mtb infection. We focused on the major phagocytes, including macrophages, dendritic cells and neutrophils and the key regulators involved in metabolic reprogramming, such as hypoxia-inducible factor-1, mammalian target of rapamycin, the cellular myelocytomatosis, peroxisome proliferator-activator receptors, sirtuins, arginases, inducible nitric acid synthase and sphingolipids.

Biphasic Dynamics of Macrophage Immunometabolism during Mycobacterium tuberculosis Infection

Macrophages are the primary targets of Mycobacterium tuberculosis infection; the early events of macrophage interaction with M. tuberculosis define subsequent progression and outcome of infection. M. tuberculosis can alter the innate immunity of macrophages, resulting in suboptimal Th1 immunity, which contributes to the survival, persistence, and eventual dissemination of the pathogen.

Macrophages are the primary targets of Mycobacterium tuberculosis infection; the early events of macrophage interaction with M. tuberculosis define subsequent progression and outcome of infection. M. tuberculosis can alter the innate immunity of macrophages, resulting in suboptimal Th1 immunity, which contributes to the survival, persistence, and eventual dissemination of the pathogen. Recent advances in immunometabolism illuminate the intimate link between the metabolic states of immune cells and their specific functions. In this review, we describe the little-studied biphasic metabolic dynamics of the macrophage response during progression of infection by M. tuberculosis and discuss their relevance to macrophage immunity and M. tuberculosis pathogenicity. The early phase of macrophage infection, which is marked by M1 polarization, is accompanied by a metabolic switch from mitochondrial oxidative phosphorylation to hypoxia-inducible factor 1 alpha (HIF-1α)-mediated aerobic glycolysis (also known as the Warburg effect in cancer cells), as well as by an upregulation of pathways involving oxidative and antioxidative defense responses, arginine metabolism, and synthesis of bioactive lipids. These early metabolic changes are followed by a late adaptation/resolution phase in which macrophages transition from glycolysis to mitochondrial oxidative metabolism, with a consequent dampening of macrophage proinflammatory and antimicrobial responses. Importantly, the identification of upregulated metabolic pathways and/or metabolic regulatory mechanisms with immunomodulatory functions during M1 polarization has revealed novel mechanisms of M. tuberculosis pathogenicity. These advances can lead to the development of novel host-directed therapies to facilitate bacterial clearance in tuberculosis by targeting the metabolic state of immune cells.

Helicobacter pylori Deregulates T and B Cell Signaling to Trigger Immune Evasion

Helicobacter pylori is a prevalent human pathogen that successfully establishes chronic infection, which leads to clinically significant gastric diseases including chronic gastritis, peptic ulcer disease (PUD), and gastric cancer (GC). H. pylori is able to produce a persistent infection due in large part to its ability to hijack the host immune response. The host adaptive immune response is activated to strategically and specifically attack pathogens and normally clears them from the infected host. Since B and T lymphocytes are central mediators of adaptive immunity, in this chapter we review their development and the fundamental mechanisms regulating their activation in order to understand how some of the normal processes are subverted by H. pylori. In this review, we place particular emphasis on the CD4⁺ T cell responses, their subtypes, and regulatory mechanisms because of the expanding literature in this area related to H. pylori. T lymphocyte differentiation and function are finely orchestrated through a series of cell-cell interactions, which include immune checkpoint receptors. Among the immune checkpoint receptor family, there are some with inhibitory properties that are exploited by tumor cells to facilitate their immune evasion. Gastric epithelial cells (GECs), which act as antigen-presenting cells (APCs) in the gastric mucosa, are induced by H. pylori to express immune checkpoint receptors known to sway T lymphocyte function and thus circumvent effective T effector lymphocyte responses. This chapter reviews these and other mechanisms used by H. pylori to interfere with host immunity in order to persist.

The diabetes pandemic and associated infections: suggestions for clinical microbiology

There are 425 million people with diabetes mellitus in the world. By 2045, this figure will grow to over 600 million. Diabetes mellitus is classified among noncommunicable diseases. Evidence points to a key role of microbes in diabetes mellitus, both as infectious agents associated with the diabetic status and as possible causative factors of diabetes mellitus. This review takes into account the different forms of diabetes mellitus, the genetic determinants that predispose to type 1 and type 2 diabetes mellitus (especially those with possible immunologic impact), the immune dysfunctions that have been documented in diabetes mellitus. Common infections occurring more frequently in diabetic vs. nondiabetic individuals are reviewed. Infectious agents that are suspected of playing an etiologic/triggering role in diabetes mellitus are presented, with emphasis on enteroviruses, the hygiene hypothesis, and the environment. Among biological agents possibly linked to diabetes mellitus, the gut microbiome, hepatitis C virus, and prion-like protein aggregates are discussed. Finally, preventive vaccines recommended in the management of diabetic patients are considered, including the bacillus calmette-Guerin vaccine that is being tested for type 1 diabetes mellitus. Evidence supports the notion that attenuation of immune defenses (both congenital and secondary to metabolic disturbances as well as to microangiopathy and neuropathy) makes diabetic people more prone to certain infections. Attentive microbiologic monitoring of diabetic patients is thus recommendable. As genetic predisposition cannot be changed, research needs to identify the biological agents that may have an etiologic role in diabetes mellitus, and to envisage curative and preventive ways to limit the diabetes pandemic.

Endogenous Regulators of the Immune System (sCD100, Malonic Dialdehyde, and Arginase)

Tissue damage in various diseases, hypoxic conditions, and some pathologies are associated with production of endogenous factors such as the soluble form of the surface receptor CD100, malonic dialdehyde, and arginase and their release into circulation. These factors modulate functional state of lymphocytes in the immune system: potentiate activation of B lymphocytes, activate synthesis and secretion of IL-25 and IL-17 cytokines, and suppress proliferative activity of T lymphocytes, thus modulating immunological reactivity of the organism. Reactions of innate and adaptive immunity develop against the background of changed immunological reactivity, which should be taken into account in the development of pathogenetically substantiated therapy.

Human and Helicobacter pylori Interactions Determine the Outcome of Gastric Diseases

The innate immune response is a critical hallmark of Helicobacter pylori infection. Epithelial and myeloid cells produce effectors, including the chemokine CXCL8, reactive oxygen species (ROS), and nitric oxide (NO), in response to bacterial components. Mechanistic and epidemiologic studies have emphasized that dysregulated and persistent release of these products leads to the development of chronic inflammation and to the molecular and cellular events related to carcinogenesis. Moreover, investigations in H. pylori-infected patients about polymorphisms of the genes encoding CXCL8 and inducible NO synthase, and epigenetic control of the ROS-producing enzyme spermine oxidase, have further proven that overproduction of these molecules impacts the severity of gastric diseases. Lastly, the critical effect of the crosstalk between the human host and the infecting bacterium in determining the severity of H. pylori-related diseases has been supported by phylogenetic analysis of the human population and their H. pylori isolates in geographic areas with varying clinical and pathologic outcomes of the infection.

Polyamine- and NADPH-dependent generation of ROS during Helicobacter pylori infection: A blessing in disguise

Helicobacter pylori is a Gram-negative bacterium that specifically colonizes the gastric ecological niche. During the infectious process, which results in diseases ranging from chronic gastritis to gastric cancer, the host response is characterized by the activation of the innate immunity of gastric epithelial cells and macrophages. These cells thus produce effector molecules such as reactive oxygen species (ROS) to counteract the infection. The generation of ROS in response to H. pylori involves two canonical pathways: 1) the NADPH-dependent reduction of molecular oxygen to generate O₂^•-, which can dismute to generate ROS; and 2) the back-conversion of the polyamine spermine into spermidine through the enzyme spermine oxidase, leading to H₂O₂ production. Although these products have the potential to affect the survival of bacteria, H. pylori has acquired numerous strategies to counteract their deleterious effects. Nonetheless, ROS-mediated oxidative DNA damage and mutations may participate in the adaptation of H. pylori to its ecological niche. Lastly, ROS have been shown to play a major role in the development of the inflammation and carcinogenesis. It is the purpose of this review to summarize the literature about the production of ROS during H. pylori infection and their role in this infectious gastric disease.

Role of Dietary Metabolites in Regulating the Host Immune Response in Gastrointestinal Disease

The host immune response to gastrointestinal (GI) infections, hypersensitivity reactions, or GI cancers comprises numerous pathways that elicit responses on different host cells. Some of these include (1) the stimulation of mast cells via their IgE receptor, (2) the production of antibodies leading to antibody-mediated cytotoxic T/natural killer cell killing, (3) the activation of the complement pathway, and (4) the activation of the adaptive immune response via antigen-presenting cell, T cell, and B cell interactions. Within the plethora of these different responses, several host immune cells represent major key players such as those of myeloid lineage (including neutrophils, macrophages, myeloid-derived suppressor cells) or lymphoid lineage (including T and B cells). In this review, we focus on newly identified metabolites and metabolite receptors that are expressed by either myeloid or lymphoid lineages. Irrespective of their source, these metabolites can in certain instances elicit responses on a wide range of cell types. The myeloid-expressed metabolic enzymes and receptors which we will discuss in this review include arginase 2 (Arg2), indoleamine-2,3-dioxygenase 1 (IDO1), hydroxycarboxylic acid receptor 2 (Hcar2; also called GPR109A), and immunoresponsive gene 1 (Irg1). We will also review the role of the lymphoid-expressed metabolite receptor that binds to the sphingosine-1-phosphate (S1P) sphingolipid. Moreover, we will describe the synthesis and metabolism of retinoic acid, and its effect on T cell activation. The review will then discuss the function of these metabolites in the context of GI disease. The review provides evidence that metabolic pathways operate in a disease- and context-dependent manner-either independently or concomitantly-in the GI tract. Therefore, an integrated approach and combinatorial analyses are necessary to devise new therapeutic strategies that can synergistically improve prognoses.

Ornithine decarboxylase regulates M1 macrophage activation and mucosal inflammation via histone modifications

Macrophage activation is a critical step in host responses during bacterial infections. Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine metabolism, has been well studied in epithelial cells and is known to have essential roles in many different cellular functions. However, its role in regulating macrophage function during bacterial infections is not well characterized. We demonstrate that macrophage-derived ODC is a critical regulator of M1 macrophage activation during both Helicobacter pylori and Citrobacter rodentium infection. Myeloid-specific Odc deletion significantly increased gastric and colonic inflammation, respectively, and enhanced M1 activation. Add-back of putrescine, the product of ODC, reversed the increased macrophage activation, indicating that ODC and putrescine are regulators of macrophage function. Odc-deficient macrophages had increased histone 3, lysine 4 (H3K4) monomethylation, and H3K9 acetylation, accompanied by decreased H3K9 di/trimethylation both in vivo and ex vivo in primary macrophages. These alterations in chromatin structure directly resulted in up-regulated gene transcription, especially M1 gene expression. Thus, ODC in macrophages tempers antimicrobial, M1 macrophage responses during bacterial infections through histone modifications and altered euchromatin formation, leading to the persistence and pathogenesis of these organisms.

Oxidative and nitrosative stress defences of Helicobacter and Campylobacter species that counteract mammalian immunity

Helicobacter and Campylobacter species are Gram-negative microaerophilic host-associated heterotrophic bacteria that invade the digestive tract of humans and animals. Campylobacter jejuni is the major worldwide cause of foodborne gastroenteritis in humans, while Helicobacter pylori is ubiquitous in over half of the world's population causing gastric and duodenal ulcers. The colonisation of the gastrointestinal system by Helicobacter and Campylobacter relies on numerous cellular defences to sense the host environment and respond to adverse conditions, including those imposed by the host immunity. An important antimicrobial tool of the mammalian innate immune system is the generation of harmful oxidative and nitrosative stresses to which pathogens are exposed during phagocytosis. This review summarises the regulators, detoxifying enzymes and subversion mechanisms of Helicobacter and Campylobacter that ultimately promote the successful infection of humans.

EGFR regulates macrophage activation and function in bacterial infection

EGFR signaling regulates macrophage function, but its role in bacterial infection has not been investigated. Here, we assessed the role of macrophage EGFR signaling during infection with Helicobacter pylori, a bacterial pathogen that causes persistent inflammation and gastric cancer. EGFR was phosphorylated in murine and human macrophages during H. pylori infection. In human gastric tissues, elevated levels of phosphorylated EGFR were observed throughout the histologic cascade from gastritis to carcinoma. Deleting Egfr in myeloid cells attenuated gastritis and increased H. pylori burden in infected mice. EGFR deficiency also led to a global defect in macrophage activation that was associated with decreased cytokine, chemokine, and NO production. We observed similar alterations in macrophage activation and disease phenotype in the Citrobacter rodentium model of murine infectious colitis. Mechanistically, EGFR signaling activated NF-κB and MAPK1/3 pathways to induce cytokine production and macrophage activation. Although deletion of Egfr had no effect on DC function, EGFR-deficient macrophages displayed impaired Th1 and Th17 adaptive immune responses to H. pylori, which contributed to decreased chronic inflammation in infected mice. Together, these results indicate that EGFR signaling is central to macrophage function in response to enteric bacterial pathogens and is a potential therapeutic target for infection-induced inflammation and associated carcinogenesis.

Upregulation of Soluble HLA-G5 and HLA-G6 Isoforms in the Milder Histopathological Stages of Helicobacter pylori Infection: A Role for Subverting Immune Responses?

The subversion mechanisms employed by Helicobacter pylori (H. pylori) to escape from immune surveillance and to establish persistent infection are poorly understood. Growing evidence indicates that expression of HLA-G, a non-classical major histocompatibility complex molecule, negatively regulates immune responses in pathological conditions, including infectious diseases. In this context, we aimed to evaluate HLA-G expression in the gastric microenvironment of individuals harbouring H. pylori and to correlate it with histological variables. Fifty-four gastric specimens from patients harbouring H. pylori infection were evaluated by immunohistochemistry using anti-HLA-G monoclonal antibody. As a result, HLA-G expression was detected in 43 of 54 specimens harbouring H. pylori. The presence of HLA-G was significantly associated with milder colonization by H. pylori (P < 0.02), milder inflammatory activity (P < 0.02) and bacterium histological location in the gastric antrum. This study is the first to explore HLA-G expression in the context of bacterial infection. Whether the biological role of HLA-G during H. pylori infection is beneficial or hazardous for patients remains to be defined.

Arginase 2 deletion leads to enhanced M1 macrophage activation and upregulated polyamine metabolism in response to Helicobacter pylori infection

We reported that arginase 2 (ARG2) deletion results in increased gastritis and decreased bacterial burden during Helicobacter pylori infection in mice. Our studies implicated a potential role for inducible nitric oxide (NO) synthase (NOS2), as Arg2 (-/-) mice exhibited increased NOS2 levels in gastric macrophages, and NO can kill H. pylori. We now bred Arg2 (-/-) to Nos2 (-/-) mice, and infected them with H. pylori. Compared to wild-type mice, both Arg2 (-/-) and Arg2 (-/-) ;Nos2 (-/-) mice exhibited increased gastritis and decreased colonization, the latter indicating that the effect of ARG2 deletion on bacterial burden was not mediated by NO. While Arg2 (-/-) mice demonstrated enhanced M1 macrophage activation, Nos2 (-/-) and Arg2 (-/-) ;Nos2 (-/-) mice did not demonstrate these changes, but exhibited increased CXCL1 and CXCL2 responses. There was an increased expression of the Th1/Th17 cytokines, interferon gamma and interleukin 17, in gastric tissues and splenic T-cells from Arg2 (-/-), but not Nos2 (-/-) or Arg2 (-/-) ;Nos2 (-/-) mice. Gastric tissues from infected Arg2 (-/-) mice demonstrated increased expression of arginase 1, ornithine decarboxylase, adenosylmethionine decarboxylase 1, spermidine/spermine N (1)-acetyltransferase 1, and spermine oxidase, along with increased spermine levels. These data indicate that ARG2 deletion results in compensatory upregulation of gastric polyamine synthesis and catabolism during H. pylori infection, which may contribute to increased gastric inflammation and associated decreased bacterial load. Overall, the finding of this study is that ARG2 contributes to the immune evasion of H. pylori by restricting M1 macrophage activation and polyamine metabolism.

The Immune Battle against Helicobacter pylori Infection: NO Offense

Helicobacter pylori is a successful pathogen of the human stomach. Despite a vigorous immune response by the gastric mucosa, the bacterium survives in its ecological niche, thus favoring diseases ranging from chronic gastritis to adenocarcinoma. The current literature demonstrates that high-output of nitric oxide (NO) production by the inducible enzyme NO synthase-2 (NOS2) plays major functions in host defense against bacterial infections. However, pathogens have elaborated several strategies to counteract the deleterious effects of NO; this includes inhibition of host NO synthesis and transcriptional regulation in response to reactive nitrogen species, allowing the bacteria to face the nitrosative stress. Moreover, NO is also a critical mediator of inflammation and carcinogenesis. In this context, we review the recent findings on the expression of NOS2 in H. pylori-infected gastric tissues and epithelial cells, the role of NO in H. pylori-related diseases and H. pylori gene expression, and the mechanisms whereby H. pylori regulates NO synthesis by host cells.

Gastric Helicobacter pylori Infection Affects Local and Distant Microbial Populations and Host Responses

Helicobacter pylori is a late-in-life human pathogen with potential early-life benefits. Although H. pylori is disappearing from the human population, little is known about the influence of H. pylori on the host's microbiota and immunity. Studying the interactions of H. pylori with murine hosts over 6 months, we found stable colonization accompanied by gastric histologic and antibody responses. Analysis of gastric and pulmonary tissues revealed increased expression of multiple immune response genes, conserved across mice and over time in the stomach and more transiently in the lungs. Moreover, H. pylori infection led to significantly different population structures in both the gastric and intestinal microbiota. These studies indicate that H. pylori influences the microbiota and host immune responses not only locally in the stomach, but distantly as well, affecting important target organs.

Systems-wide analyses of mucosal immune responses to Helicobacter pylori at the interface between pathogenicity and symbiosis

Helicobacter pylori is the dominant member of the gastric microbiota in over half of the human population of which 5-15% develop gastritis or gastric malignancies. Immune responses to H. pylori are characterized by mixed T helper cell, cytotoxic T cell and NK cell responses. The presence of Tregs is essential for the control of gastritis and together with regulatory CX3CR1+ mononuclear phagocytes and immune-evasion strategies they enable life-long persistence of H. pylori. This H. pylori-induced regulatory environment might contribute to its cross-protective effect in inflammatory bowel disease and obesity. Here we review host-microbe interactions, the development of pro- and anti-inflammatory immune responses and how the latter contribute to H. pylori's role as beneficial member of the gut microbiota. Furthermore, we present the integration of existing and new data into a computational/mathematical model and its use for the investigation of immunological mechanisms underlying initiation, progression and outcomes of H. pylori infection.

Dual role of arginine metabolism in establishing pathogenesis

Arginine is an integral part of host defense when invading pathogens are encountered. The arginine metabolite nitric oxide (NO) confers antimicrobial properties, whereas the metabolite ornithine is utilized for polyamine synthesis. Polyamines are crucial to tissue repair and anti-inflammatory responses. iNOS/arginase balance can determine Th1/Th2 response. Furthermore, the host arginine pool and its metabolites are utilized as energy sources by various pathogens. Apart from its role as an immune modulator, recent studies have also highlighted the therapeutic effects of arginine. This article sheds light upon the roles of arginine metabolism during pathological conditions and its therapeutic potential.

Macrophage polarization in pathology

Macrophages are cells of the innate immunity constituting the mononuclear phagocyte system and endowed with remarkable different roles essential for defense mechanisms, development of tissues, and homeostasis. They derive from hematopoietic precursors and since the early steps of fetal life populate peripheral tissues, a process continuing throughout adult life. Although present essentially in every organ/tissue, macrophages are more abundant in the gastro-intestinal tract, liver, spleen, upper airways, and brain. They have phagocytic and bactericidal activity and produce inflammatory cytokines that are important to drive adaptive immune responses. Macrophage functions are settled in response to microenvironmental signals, which drive the acquisition of polarized programs, whose extremes are simplified in the M1 and M2 dichotomy. Functional skewing of monocyte/macrophage polarization occurs in physiological conditions (e.g., ontogenesis and pregnancy), as well as in pathology (allergic and chronic inflammation, tissue repair, infection, and cancer) and is now considered a key determinant of disease development and/or regression. Here, we will review evidence supporting a dynamic skewing of macrophage functions in disease, which may provide a basis for macrophage-centered therapeutic strategies.

Suppression of cell division-associated genes by Helicobacter pylori attenuates proliferation of RAW264.7 monocytic macrophage cells

Helicobacter pylori at multiplicity of infection (MOI ≥ 50) have been shown to cause apoptosis in RAW264.7 monocytic macrophage cells. Because chronic gastric infection by H. pylori results in the persistence of macrophages in the host's gut, it is likely that H. pylori is present at low to moderate, rather than high numbers in the infected host. At present, the effect of low-MOI H. pylori infection on macrophage has not been fully elucidated. In this study, we investigated the genome-wide transcriptional regulation of H. pylori-infected RAW264.7 cells at MOI 1, 5 and 10 in the absence of cellular apoptosis. Microarray data revealed up- and down-regulation of 1341 and 1591 genes, respectively. The expression of genes encoding for DNA replication and cell cycle-associated molecules, including Aurora-B kinase (AurkB) were down-regulated. Immunoblot analysis verified the decreased expression of AurkB and downstream phosphorylation of Cdk1 caused by H. pylori infection. Consistently, we observed that H. pylori infection inhibited cell proliferation and progression through the G1/S and G2/M checkpoints. In summary, we suggest that H. pylori disrupts expression of cell cycle-associated genes, thereby impeding proliferation of RAW264.7 cells, and such disruption may be an immunoevasive strategy utilized by H. pylori.