Understanding How Minerals Contribute to Optimal Immune Function

Sufficient mineral supply is vital not only for the innate immune system but also for the components of the adaptive immune defense, which encompass defense mechanisms against pathogens and the delicate balance of pro- and anti-inflammatory regulation in the long term. Generally, a well-balanced diet is capable of providing the necessary minerals to support the immune system. Nevertheless, specific vulnerable populations should be cautious about obtaining adequate amounts of minerals such as magnesium, zinc, copper, iron, and selenium. Inadequate levels of these minerals can temporarily impair immune competence and disrupt the long-term regulation of systemic inflammation. Therefore, comprehending the mechanisms and sources of these minerals is crucial. In exceptional circumstances, mineral deficiencies may necessitate supplementation; however, excessive intake of supplements can have adverse effects on the immune system and should be avoided. Consequently, any supplementation should be approved by medical professionals and administered in recommended doses. This review emphasizes the crucial significance of minerals in promoting optimal functioning of the immune system. It investigates the indispensable minerals required for immune system function and the regulation of inflammation. Moreover, it delves into the significance of maintaining an optimized intake of minerals from a nutritional standpoint.

Reprogramming of tumor-associated macrophages by polyaniline-coated iron oxide nanoparticles applied to treatment of breast cancer

Breast cancer is the most commonly diagnosed type of cancer among the female population worldwide. It is a disease with a high incidence and geographic distribution that negatively impacts global public health and deleteriously affect the quality of life of cancer patients. Among the new approaches, cancer immunotherapy is the most promising trend in oncology by stimulating the host's own immune system to efficiently destroy cancer cells. Recent evidence has indicated that iron oxide nanoparticles can promote the reprograming of M2 into M1 macrophages with anti-tumor effects in the tumor microenvironment. Thus, the aim of the present work was to evaluate the ability of polyaniline-coated maghemite (Pani/γ-Fe₂O₃) nanoparticles to modulate human macrophages in 2D monolayers and 3D multicellular breast cancer models. It was observed that Pani/γ-Fe₂O₃ NPs re-educated IL-10-stimulated macrophages towards a pro-inflammatory profile, decreasing the proportion of CD163⁺ and increasing the CD86⁺ proportion in 2D models. NPs were successfully taken-up by macrophages presented in the 3D model and were also able to induce an increasing in their CD86⁺ proportion in triple MCTs model. Overall, our findings open new perspectives on the use of Pani/γ-Fe₂O₃ NPs as an immunomodulatory therapy for macrophage reprogramming towards an anti-tumor M1 phenotype, providing a new tool for breast cancer immunotherapies.

Clinical significance of plasma-free amino acids and tryptophan metabolites in patients with non-small cell lung cancer receiving PD-1 inhibitor: a pilot cohort study for developing a prognostic multivariate model

Background

Amino acid metabolism is essential for tumor cell proliferation and regulation of immune cell function. However, the clinical significance of free amino acids (plasma-free amino acids (PFAAs)) and tryptophan-related metabolites in plasma has not been fully understood in patients with non-small cell lung cancer (NSCLC) who receive immune checkpoint inhibitors.

Methods

We conducted a single cohort observational study. Peripheral blood samples were collected from 53 patients with NSCLC before treatment with PD-1 (Programmed cell death-1) inhibitors. The plasma concentrations of 21 PFAAs, 14 metabolites, and neopterin were measured by liquid chromatography–mass spectrometry. Using Cox hazard analysis with these variables, a multivariate model was established to stratify patient overall survival (OS). Gene expression in peripheral blood mononuclear cells (PBMCs) was compared between the high-risk and low-risk patients by this multivariate model.

Results

On Cox proportional hazard analysis, higher concentrations of seven PFAAs (glycine, histidine, threonine, alanine, citrulline, arginine, and tryptophan) as well as lower concentrations of three metabolites (3h-kynurenine, anthranilic acid, and quinolinic acid) and neopterin in plasma were significantly correlated with better OS (p<0.05). In particular, the multivariate model, composed of a combination of serine, glycine, arginine, and quinolinic acid, could most efficiently stratify patient OS (concordance index=0.775, HR=3.23, 95% CI 2.04 to 5.26). From the transcriptome analysis in PBMCs, this multivariate model was significantly correlated with the gene signatures related to immune responses, such as CD8 T-cell activation/proliferation and proinflammatory immune responses, and 12 amino acid-related genes were differentially expressed between the high-risk and low-risk groups.

Conclusions

The multivariate model with PFAAs and metabolites in plasma might be useful for stratifying patients who will benefit from PD-1 inhibitors.

The impact of metal availability on immune function during infection

Nutrient transition metals are required cofactors for many proteins to perform functions necessary for life. As such, the concentration of nutrient metals is carefully maintained to retain critical biological processes while limiting toxicity. During infection, invading bacterial pathogens must acquire essential metals, such as zinc, manganese, iron, and copper, from the host to colonize and cause disease. To combat this, the host exploits the essentiality and toxicity of nutrient metals by producing factors that limit metal availability, thereby starving pathogens or accumulating metals in excess to intoxicate the pathogen in a process termed 'nutritional immunity'. As a result of inflammation, a heterogeneous environment containing both metal-replete and -deplete niches is created, in which nutrient metal availability may have an underappreciated role in regulating immune cell function during infection. How the host manipulates nutrient metal availability during infection, and the downstream effects that nutrient metals and metal-sequestering proteins have on immune cell function, are discussed in this review.

Baseline iron status and presence of anaemia determine the course of systemic Salmonella infection following oral iron supplementation in mice

BACKGROUND

Iron deficiency anaemia (IDA) is a major health concern. However, preventive iron supplementation in regions with high burden of infectious diseases resulted in an increase of infection related morbidity and mortality.

METHODS

We fed male C57BL/6N mice with either an iron deficient or an iron adequate diet. Next, they received oral iron supplementation or placebo followed by intraperitoneal infection with Salmonella Typhimurium (S.Tm).

FINDINGS

We found that mice with IDA had a poorer clinical outcome than mice on an iron adequate diet. Interestingly, iron supplementation of IDA mice resulted in higher bacterial burden in organs and shortened survival. Increased transferrin saturation and non-transferrin bound iron in the circulation together with low expression of ferroportin facilitated the access of the pathogen to iron and promoted bacterial growth. Anaemia, independent of iron supplementation, was correlated with reduced neutrophil counts and cytotoxic T cells. With iron supplementation, anaemia additionally correlated with increased splenic levels of the cytokine IL-10, which is suggestive for a weakened immune control to S.Tm infection.

INTERPRETATION

Supplementing iron to anaemic mice worsens the clinical course of bacterial infection. This can be traced back to increased iron delivery to bacteria along with an impaired anti-microbial immune response. Our findings may have important implications for iron supplementation strategies in areas with high endemic burden of infections, putting those individuals, who potentially profit most from iron supplementation for anaemia, at the highest risk for infections.

FUNDING

Financial support by the Christian Doppler Laboratory for Iron Metabolism and Anemia Research.

Cytokine-Mediated Regulation of ARG1 in Macrophages and Its Impact on the Control of Salmonella enterica Serovar Typhimurium Infection

Arginase 1 (ARG1) is a cytosolic enzyme that cleaves L-arginine, the substrate of inducible nitric oxide synthase (iNOS), and thereby impairs the control of various intracellular pathogens. Herein, we investigated the role of ARG1 during infection with Salmonella enterica serovar Typhimurium (S.tm). To study the impact of ARG1 on Salmonella infections in vitro, bone marrow-derived macrophages (BMDM) from C57BL/6N wild-type, ARG1-deficient Tie2Cre+/-ARG1fl/fl and NRAMPG169 C57BL/6N mice were infected with S.tm. In wild-type BMDM, ARG1 was induced by S.tm and further upregulated by the addition of interleukin (IL)-4, whereas interferon-γ had an inhibitory effect. Deletion of ARG1 did not result in a reduction in bacterial numbers. In vivo, Arg1 mRNA was upregulated in the spleen, but not in the liver of C57BL/6N mice following intraperitoneal S.tm infection. The genetic deletion of ARG1 (Tie2Cre+/-ARG1fl/fl) or its pharmacological inhibition with CB-1158 neither affected the numbers of S.tm in spleen, liver and blood nor the expression of host response genes such as iNOS, IL-6 or tumour necrosis factor (TNF). Furthermore, ARG1 was dispensable for pathogen control irrespective of the presence or absence of the phagolysosomal natural resistance-associated macrophage protein 1 (NRAMP1). Thus, unlike the detrimental function of ARG1 seen during infections with other intraphagosomal microorganisms, ARG1 did not support bacterial survival in systemic salmonellosis, indicating differential roles of arginine metabolism for host immune response and microbe persistence depending on the type of pathogen.

Heme oxygenase-1 inhibition promotes IFNγ- and NOS2-mediated control of Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) infection induces pulmonary expression of the heme-degrading enzyme heme oxygenase-1 (HO-1). We have previously shown that pharmacological inhibition of HO-1 activity in experimental tuberculosis results in decreased bacterial loads and unexpectedly that this outcome depends on the presence of T lymphocytes. Here, we extend these findings by demonstrating that IFNγ production by T lymphocytes and NOS2 expression underlie this T-cell requirement and that HO-1 inhibition potentiates IFNγ-induced NOS2-dependent control of Mtb by macrophages in vitro. Among the products of heme degradation by HO-1 (biliverdin, carbon monoxide, and iron), only iron supplementation reverted the HO-1 inhibition-induced enhancement of bacterial control and this reversal was associated with decreased NOS2 expression and NO production. In addition, we found that HO-1 inhibition results in decreased labile iron levels in Mtb-infected macrophages in vitro and diminished iron accumulation in Mtb-infected lungs in vivo. Together these results suggest that the T-lymphocyte dependence of the therapeutic outcome of HO-1 inhibition on Mtb infection reflects the role of the enzyme in generating iron that suppresses T-cell-mediated IFNγ/NOS2-dependent bacterial control. In broader terms, our findings highlight the importance of the crosstalk between iron metabolism and adaptive immunity in determining the outcome of infection.

Iron in immune cell function and host defense

The control over iron availability is crucial under homeostatic conditions and even more in the case of an infection. This results from diverse properties of iron: first, iron is an important trace element for the host as well as for the pathogen for various cellular and metabolic processes, second, free iron catalyzes Fenton reaction and is therefore producing reactive oxygen species as a part of the host defense machinery, third, iron exhibits important effects on immune cell function and differentiation and fourth almost every immune activation in turn impacts on iron metabolism and spatio-temporal iron distribution. The central importance of iron in the host and microbe interplay and thus for the course of infections led to diverse strategies to restrict iron for invading pathogens. In this review, we focus on how iron restriction to the pathogen is a powerful innate immune defense mechanism of the host called "nutritional immunity". Important proteins in the iron-host-pathogen interplay will be discussed as well as the influence of iron on the efficacy of innate and adaptive immunity. Recently described processes like ferritinophagy and ferroptosis are further covered in respect to their impact on inflammation and infection control and how they impact on our understanding of the interaction of host and pathogen.

Modulation of Inflammation and Immune Responses by Heme Oxygenase-1: Implications for Infection with Intracellular Pathogens

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme molecules releasing equimolar amounts of biliverdin, iron and carbon monoxide. Its expression is induced in response to stress signals such as reactive oxygen species and inflammatory mediators with antioxidant, anti-inflammatory and immunosuppressive consequences for the host. Interestingly, several intracellular pathogens responsible for major human diseases have been shown to be powerful inducers of HO-1 expression in both host cells and in vivo. Studies have shown that this HO-1 response can be either host detrimental by impairing pathogen control or host beneficial by limiting infection induced inflammation and tissue pathology. These properties make HO-1 an attractive target for host-directed therapy (HDT) of the diseases in question, many of which have been difficult to control using conventional antibiotic approaches. Here we review the mechanisms by which HO-1 expression is induced and how the enzyme regulates inflammatory and immune responses during infection with a number of different intracellular bacterial and protozoan pathogens highlighting mechanistic commonalities and differences with the goal of identifying targets for disease intervention.

Iron in infection and immunity

Iron is an essential micronutrient for virtually all living cells. In infectious diseases, both invading pathogens and mammalian cells including those of the immune system require iron to sustain their function, metabolism and proliferation. On the one hand, microbial iron uptake is linked to the virulence of most human pathogens. On the other hand, the sequestration of iron from bacteria and other microorganisms is an efficient strategy of host defense in line with the principles of 'nutritional immunity'. In an acute infection, host-driven iron withdrawal inhibits the growth of pathogens. Chronic immune activation due to persistent infection, autoimmune disease or malignancy however, sequesters iron not only from infectious agents, autoreactive lymphocytes and neoplastic cells but also from erythroid progenitors. This is one of the key mechanisms which collectively result in the anemia of chronic inflammation. In this review, we highlight the most important interconnections between iron metabolism and immunity, focusing on host defense against relevant infections and on the clinical consequences of anemia of inflammation.

Impact of small RNA RaoN on nitrosative-oxidative stress resistance and virulence of Salmonella enterica serovar Typhimurium

RaoN is a Salmonella-specific small RNA that is encoded in the cspH-envE intergenic region on Salmonella pathogenicity island-11. We previously reported that RaoN is induced under conditions of acid and oxidative stress combined with nutrient limitation, contributing to the intramacrophage growth of Salmonella enterica serovar Typhimurium. However, the role of RaoN in nitrosative stress response and virulence has not yet been elucidated. Here we show that the raoN mutant strain has increased susceptibility to nitrosative stress by using a nitric oxide generating acidified nitrite. Extending previous research on the role of RaoN in oxidative stress resistance, we found that NADPH oxidase inhibition restores the growth of the raoN mutant in LPS-treated J774A.1 macrophages. Flow cytometry analysis further revealed that the inactivation of raoN leads to an increase in the intracellular level of reactive oxygen species (ROS) in Salmonella-infected macrophages, suggesting that RaoN is involved in the inhibition of NADPH oxidase-mediated ROS production by mechanisms not yet resolved. Moreover, we evaluated the effect of raoN mutation on the virulence in murine systemic infection and determined that the raoN mutant is less virulent than the wild-type strain following oral inoculation. In conclusion, small regulatory RNA RaoN controls nitrosative-oxidative stress resistance and is required for virulence of Salmonella in mice.

The Role of Iron Regulation in Immunometabolism and Immune-Related Disease

Immunometabolism explores how the intracellular metabolic pathways in immune cells can regulate their function under different micro-environmental and (patho-)-physiological conditions (Pearce, 2010; Buck et al., 2015; O'Neill and Pearce, 2016). In the last decade great advances have been made in studying and manipulating metabolic programs in immune cells. Immunometabolism has primarily focused on glycolysis, the TCA cycle and oxidative phosphorylation (OXPHOS) as well as free fatty acid synthesis and oxidation. These pathways are important for providing the energy needs of cell growth, membrane rigidity, cytokine production and proliferation. In this review, we will however, highlight the specific role of iron metabolism at the cellular and organismal level, as well as how the bioavailability of this metal orchestrates complex metabolic programs in immune cell homeostasis and inflammation. We will also discuss how dysregulation of iron metabolism contributes to alterations in the immune system and how these novel insights into iron regulation can be targeted to metabolically manipulate immune cell function under pathophysiological conditions, providing new therapeutic opportunities for autoimmunity and cancer.

Associations between the presence of specific antibodies to the West Nile Virus infection and candidate genes in Romanian horses from the Danube delta

The West Nile virus (WNV) is a mosquito-borne flavivirus causing meningoencephalitis in humans and animals. Due to their particular susceptibility to WNV infection, horses serve as a sentinel species. In a population of Romanian semi-feral horses living in the Danube delta region, we have analyzed the distribution of candidate polymorphic genetic markers between anti WNV-IgG seropositive and seronegative horses. Thirty-six SNPs located in 28 immunity-related genes and 26 microsatellites located in the MHC and LY49 complex genomic regions were genotyped in 57 seropositive and 32 seronegative horses. The most significant association (p_corr < 0.0002) was found for genotypes composed of markers of the SLC11A1 and TLR4 genes. Markers of five other candidate genes (ADAM17, CXCR3, IL12A, MAVS, TNFA), along with 5 MHC class I and LY49-linked microsatellites were also associated with the WNV antibody status in this model horse population. The OAS1 gene, previously associated with WNV-induced clinical disease, was not associated with the presence of anti-WNV antibodies.

Genetic susceptibility to West Nile virus infection in Camargue horses

West Nile virus (WNV) is a mosquito-borne zoonotic neurotropic virus capable to cause lethal meningoencephalitis (WNE) in infected hosts such as birds, horses, and humans. Due to their sensitivity, horses serve as sentinel species in areas at risk. We studied a population of Camargue horses living in Southern France in two zones with endemic WNV circulation where WNV outbreaks were recorded in 2000 and 2003-4. Two sets of microsatellite markers located in MHC and Ly49 genomic regions were genotyped as well as multiple SNPs in ten immunity-related candidate gene regions. Associations between genetic polymorphisms and resistance/susceptibility to WNE were tested. While single marker associations were weak, compound two-gene genotypes of SNPs located within the MAVS, NCR2 and IL-10 genes and microsatellites HMS082 and CZM013 were associated with susceptibility to WNE. Combinations of microsatellite markers CZM009, ABGe17402 and ABGe9019 were associated with simple seroconversion without clinical signs of WNE (resistance). In addition, a distribution of polymorphic markers between WNV-IgG seropositive horses and a control group of WNV-IgG seronegative horses was tested. One SNP in the OAS1 gene (NC_009151.3:g.21961328A>G) was significantly associated with the seropositive phenotype (p_corr = 0.023; OR = 40.5 CI (4.28; 383.26); RR = 8.18 CI (1.27; 52.89) in the Camargue breed. In compound genotypes, SNP markers for SLC11A1, MAVS, OAS1, TLR4, ADAM17 and NCR2 genes and ten microsatellites showed non-random distribution between seropositive and seronegative groups of horses. Further analysis of associated markers could contribute to our understanding of anti-WNV defense mechanisms in horses.

Iron and innate antimicrobial immunity-Depriving the pathogen, defending the host

The acute-phase response is triggered by the presence of infectious agents and danger signals which indicate hazards for the integrity of the mammalian body. One central feature of this response is the sequestration of iron into storage compartments including macrophages. This limits the availability of this essential nutrient for circulating pathogens, a host defence strategy known as 'nutritional immunity'. Iron metabolism and the immune response are intimately linked. In infections, the availability of iron affects both the efficacy of antimicrobial immune pathways and pathogen proliferation. However, host strategies to withhold iron from microbes vary according to the localization of pathogens: Infections with extracellular bacteria such as Staphylococcus aureus, Streptococcus, Klebsiella or Yersinia stimulate the expression of the iron-regulatory hormone hepcidin which targets the cellular iron-exporter ferroportin-1 causing its internalization and blockade of iron egress from absorptive enterocytes in the duodenum and iron-recycling macrophages. This mechanism disrupts both routes of iron delivery to the circulation, contributes to iron sequestration in the mononuclear phagocyte system and mediates the hypoferraemia of the acute phase response subsequently resulting in the development of anaemia of inflammation. When intracellular microbes are present, other strategies of microbial iron withdrawal are needed. For instance, in macrophages harbouring intracellular pathogens such as Chlamydia, Mycobacterium tuberculosis, Listeria monocytogenes or Salmonella Typhimurium, ferroportin-1-mediated iron export is turned on for the removal of iron from infected cells. This also leads to reduced iron availability for intra-macrophage pathogens which inhibits their growth and in parallel strengthens anti-microbial effector pathways of macrophages including the formation of inducible nitric oxide synthase and tumour necrosis factor. Iron plays a key role in infectious diseases both as modulator of the innate immune response and as nutrient for microbes. We need to gain a more comprehensive understanding of how the body can differentially respond to infection by extra- or intracellular pathogens. This knowledge may allow us to modulate mammalian iron homeostasis pharmaceutically and to target iron-acquisition systems of pathogens, thus enabling us to treat infections with novel strategies that act independent of established antimicrobials.

Searching for signals of recent natural selection in genes of the innate immune response - ancient DNA study

The last decade has seen sharp progress in the field of human evolutionary genetics and a great amount of genetic evidence of natural selection has been provided so far. Since host-pathogen co-evolution is difficult to trace due to the polygenic nature of human susceptibility to microbial diseases, of particular interest is any signal of natural selection in response to the strong selective pressure exerted by pathogens. Analysis of ancient DNA allows for the direct insight into changes of a gene pool content over time and enables monitoring allele frequency fluctuations. Among pathogenic agents, mycobacteria are proved to have remained in an intimate, long-lasting relation with humans, reflected by the current high level of host resistance. Therefore, we aimed to investigate the prevalence of several polymorphisms within innate immune response genes related to susceptibility to mycobacterial diseases (in SLC11A1, MBL2, TLR2, P2RX7, IL10, TNFA) in time series data from North and East Poland (1st-18th century AD, n = 207). The comparison of allele frequencies over time revealed a predominant role of genetic drift in shaping past gene pool of small, probably isolated groups, which was explained by the high level of population differentiation and limited gene flow. However, the trajectory of frequency fluctuations of two SNPs suggested the possibility of their non-neutral evolution and the results of applied forward simulations further strengthened the hypothesis of natural selection acting on those loci. However, we observed an unusual excess of homozygosity in the profile of several SNPs, which pinpoints to the necessity of further research on temporally and spatially diverse samples to support our inference on non-stochastic evolution, ideally employing pathway-based approaches. Nevertheless, our study confirms that time series data could help to decipher very recent human adaptation to life-threatening pathogens and assisting demographic events.

Investigation of the Role of Genes Encoding Zinc Exporters zntA, zitB, and fieF during Salmonella Typhimurium Infection

The transition metal zinc is involved in crucial biological processes in all living organisms and is essential for survival of Salmonella in the host. However, little is known about the role of genes encoding zinc efflux transporters during Salmonella infection. In this study, we constructed deletion mutants for genes encoding zinc exporters (zntA, zitB, and fieF) in the wild-type (WT) strain Salmonella enterica serovar Typhimurium (S. Typhimurium) 4/74. The mutants 4/74ΔzntA and 4/74ΔzntA/zitB exhibited a dramatic growth delay and abrogated growth ability, respectively, in Luria Bertani medium supplemented with 0.25 mM ZnCl₂ or 1.5 mM CuSO₄ compared to the WT strain. In order to investigate the role of genes encoding zinc exporters on survival of S. Typhimurium inside cells, amoeba and macrophage infection models were used. No significant differences in uptake or survival were detected for any of the mutants compared to the WT during infection of amoebae. In natural resistance-associated macrophage protein 1 (Nramp1)-negative J774.1 murine macrophages, significantly higher bacterial counts were observed for the mutant strains 4/74ΔzntA and 4/74ΔzntA/zitB compared to the WT at 4 h post-infection although the fold net replication was similar between all the strains. All four tested mutants (4/74ΔzntA, 4/74ΔzitB, 4/74ΔfieF, and 4/74ΔzntA/zitB) showed enhanced intracellular survival capacity within the modified Nramp1-positive murine RAW264.7 macrophages at 20 h post-infection. The fold net replication was also significantly higher for 4/74ΔzntA, 4/74ΔzitB, and 4/74ΔzntA/zitB mutants compared to the WT. Intriguingly, the ability to survive and cause infection was significantly impaired in all the three mutants tested (4/74ΔzntA, 4/74ΔzitB, and 4/74ΔzntA/zitB) in C3H/HeN mice, particularly the double mutant 4/74ΔzntA/zitB was severely attenuated compared to the WT in all the three organs analyzed. These findings suggest that these genes encoding zinc exporters, especially zntA, contribute to the resistance of S. Typhimurium to zinc and copper stresses during infection.

Renal association clinical practice guideline on Anaemia of Chronic Kidney Disease

Anaemia is a commonly diagnosed complication among patients suffering with chronic kidney disease. If left untreated, it may affect patient quality of life. There are several causes for anaemia in this patient population. As the kidney function deteriorates, together with medications and dietary restrictions, patients may develop iron deficiency, resulting in reduction of iron supply to the bone marrow (which is the body organ responsible for the production of different blood elements). Chronic kidney disease patients may not be able to utilise their own body's iron stores effectively and hence, many patients, particularly those receiving haemodialysis, may require additional iron treatment, usually provided by infusion.With further weakening of kidney function, patients with chronic kidney disease may need additional treatment with a substance called erythropoietin which drives the bone marrow to produce its own blood. This substance, which is naturally produced by the kidneys, becomes relatively deficient in patients with chronic kidney disease. Any patients will eventually require treatment with erythropoietin or similar products that are given by injection.Over the last few years, several iron and erythropoietin products have been licensed for treating anaemia in chronic kidney disease patients. In addition, several publications discussed the benefits of each treatment and possible risks associated with long term treatment. The current guidelines provide advice to health care professionals on how to screen chronic kidney disease patients for anaemia, which patients to investigate for other causes of anaemia, when and how to treat patients with different medications, how to ensure safe prescribing of treatment and how to diagnose and manage complications associated with anaemia and the drugs used for its treatment.

Elemental Ingredients in the Macrophage Cocktail: Role of ZIP8 in Host Response to Mycobacterium tuberculosis

Tuberculosis (TB) is a global epidemic caused by the infection of human macrophages with the world’s most deadly single bacterial pathogen, Mycobacterium tuberculosis (M.tb). M.tb resides in a phagosomal niche within macrophages, where trace element concentrations impact the immune response, bacterial metal metabolism, and bacterial survival. The manipulation of micronutrients is a critical mechanism of host defense against infection. In particular, the human zinc transporter Zrt-/Irt-like protein 8 (ZIP8), one of 14 ZIP family members, is important in the flux of divalent cations, including zinc, into the cytoplasm of macrophages. It also has been observed to exist on the membrane of cellular organelles, where it can serve as an efflux pump that transports zinc into the cytosol. ZIP8 is highly inducible in response to M.tb infection of macrophages, and we have observed its localization to the M.tb phagosome. The expression, localization, and function of ZIP8 and other divalent cation transporters within macrophages have important implications for TB prevention and dissemination and warrant further study. In particular, given the importance of zinc as an essential nutrient required for humans and M.tb, it is not yet clear whether ZIP-guided zinc transport serves as a host protective factor or, rather, is targeted by M.tb to enable its phagosomal survival.

Burkholderia pseudomallei Evades Nramp1 (Slc11a1)- and NADPH Oxidase-Mediated Killing in Macrophages and Exhibits Nramp1-Dependent Virulence Gene Expression

Bacterial survival in macrophages can be affected by the natural resistance-associated macrophage protein 1 (Nramp1; also known as solute carrier family 11 member a1 or Slc11a1) which localizes to phagosome membranes and transports divalent cations, including iron. Little is known about the role of Nramp1 in Burkholderia infection, in particular whether this differs for pathogenic species like Burkholderia pseudomallei causing melioidosis or non-pathogenic species like Burkholderia thailandensis. Here we show that transfected macrophages stably expressing wild-type Nramp1 (Nramp1⁺) control the net replication of B. thailandensis, but not B. pseudomallei. Control of B. thailandensis was associated with increased cytokine responses, and could be abrogated by blocking NADPH oxidase-mediated production of reactive oxygen species but not by blocking generation of reactive nitrogen species. The inability of Nramp1⁺ macrophages to control B. pseudomallei was associated with rapid escape of bacteria from phagosomes, as indicated by decreased co-localization with LAMP1 compared to B. thailandensis. A B. pseudomallei bipB mutant impaired in escape from phagosomes was controlled to a greater extent than the parent strain in Nramp1⁺ macrophages, but was also attenuated in Nramp1⁻ cells. Consistent with reduced escape from phagosomes, B. thailandensis formed fewer multinucleated giant cells in Nramp1⁺ macrophages at later time points compared to B. pseudomallei. B. pseudomallei exhibited elevated transcription of virulence-associated genes of Type VI Secretion System cluster 1 (T6SS-1), the Bsa Type III Secretion System (T3SS-3) and the bimA gene required for actin-based motility in Nramp1⁺ macrophages. Nramp1⁺ macrophages were found to contain decreased iron levels that may impact on expression of such genes. Our data show that B. pseudomallei is able to evade Nramp1- and NADPH oxidase-mediated killing in macrophages and that expression of virulence-associated genes by pathogenic B pseudomallei is enhanced in macrophages expressing wild-type compared to non-functional Nramp1. B. thailandensis has been proposed as surrogate for B. pseudomallei in the study of melioidosis however our study highlights important differences in the interaction of these bacteria with macrophages.

Role of iron in the pathogenesis of respiratory disease

Iron is essential for many biological processes, however, too much or too little iron can result in a wide variety of pathological consequences, depending on the organ system, tissue or cell type affected. In order to reduce pathogenesis, iron levels are tightly controlled in throughout the body by regulatory systems that control iron absorption, systemic transport and cellular uptake and storage. Altered iron levels and/or dysregulated homeostasis have been associated with several lung diseases, including chronic obstructive pulmonary disease, lung cancer, cystic fibrosis, idiopathic pulmonary fibrosis and asthma. However, the mechanisms that underpin these associations and whether iron plays a key role in the pathogenesis of lung disease are yet to be fully elucidated. Furthermore, in order to survive and replicate, pathogenic micro-organisms have evolved strategies to source host iron, including freeing iron from cells and proteins that store and transport iron. To counter these microbial strategies, mammals have evolved immune-mediated defence mechanisms that reduce iron availability to pathogens. This interplay between iron, infection and immunity has important ramifications for the pathogenesis and management of human respiratory infections and diseases. An increased understanding of the role that iron plays in the pathogenesis of lung disease and respiratory infections may help inform novel therapeutic strategies. Here we review the clinical and experimental evidence that highlights the potential importance of iron in respiratory diseases and infections.

Solute carrier protein family 11 member 1 (Slc11a1) activation efficiently inhibits Leishmania donovani survival in host macrophages

Visceral leishmaniasis (kala-azar), a life threatening disease caused by L. donovani, is a latent threat to more than 147 million people living in disease endemic South East Asia region of the Indian subcontinent. The therapeutic option to control leishmanial infections are very limited, and at present comprise only two drugs, an antifungal amphotericin B and an antitumor miltefosine, which are also highly vulnerable for parasitic resistance. Therefore, identification and development of alternate control measures is an exigent requirement to control leishmanial infections. In this study, we report that functionally induced expression of solute carrier protein family 11 member 1 (Slc11a1), a transmembrane divalent cationic transporter recruited on the surface of phagolysosomes after phagocytosis of parasites, effectively inhibits Leishmania donovani growth in host macrophages. Further, the increased Slc11a1 functionality also resulted in increased production of NOx, TNF-α and IL-12 by activated macrophages. The findings of this study signify the importance of interplay between Slc11a1 expression and macrophages activation that can be effectively used to control of Leishmania growth and survival.

Animal Models for Salmonellosis: Applications in Vaccine Research

Salmonellosis remains an important cause of human disease worldwide. While there are several licensed vaccines for Salmonella enterica serovar Typhi, these vaccines are generally ineffective against other Salmonella serovars. Vaccines that target paratyphoid and nontyphoidal Salmonella serovars are very much in need. Preclinical evaluation of candidate vaccines is highly dependent on the availability of appropriate scientific tools, particularly animal models. Many different animal models exist for various Salmonella serovars, from whole-animal models to smaller models, such as those recently established in insects. Here, we discuss various mouse, rat, rabbit, calf, primate, and insect models for Salmonella infection, all of which have their place in research. However, choosing the right model is imperative in selecting the best vaccine candidates for further clinical testing. In this minireview, we summarize the various animal models that are used to assess salmonellosis, highlight some of the advantages and disadvantages of each, and discuss their value in vaccine development.

Macrophages and Iron Metabolism

Iron is a transition metal that due to its inherent ability to exchange electrons with a variety of molecules is essential to support life. In mammals, iron exists mostly in the form of heme, enclosed within an organic protoporphyrin ring and functioning primarily as a prosthetic group in proteins. Paradoxically, free iron also has the potential to become cytotoxic when electron exchange with oxygen is unrestricted and catalyzes the production of reactive oxygen species. These biological properties demand that iron metabolism is tightly regulated such that iron is available for core biological functions while preventing its cytotoxic effects. Macrophages play a central role in establishing this delicate balance. Here, we review the impact of macrophages on heme-iron metabolism and, reciprocally, how heme-iron modulates macrophage function.

The Iron age of host-microbe interactions

Microbes exert a major impact on human health and disease by either promoting or disrupting homeostasis, in the latter instance leading to the development of infectious diseases. Such disparate outcomes are driven by the ever-evolving genetic diversity of microbes and the countervailing host responses that minimize their pathogenic impact. Host defense strategies that limit microbial pathogenicity include resistance mechanisms that exert a negative impact on microbes, and disease tolerance mechanisms that sustain host homeostasis without interfering directly with microbes. While genetically distinct, these host defense strategies are functionally integrated, via mechanisms that remain incompletely defined. Here, we explore the general principles via which host adaptive responses regulating iron (Fe) metabolism impact on resistance and disease tolerance to infection.

iNOS Activity Modulates Inflammation, Angiogenesis, and Tissue Fibrosis in Polyether-Polyurethane Synthetic Implants

There is considerable interest in implantation techniques and scaffolds for tissue engineering and, for safety and biocompatibility reasons, inflammation, angiogenesis, and fibrosis need to be determined. The contribution of inducible nitric oxide synthase (iNOS) in the regulation of the foreign body reaction induced by subcutaneous implantation of a synthetic matrix was never investigated. Here, we examined the role of iNOS in angiogenesis, inflammation, and collagen deposition induced by polyether-polyurethane synthetic implants, using mice with targeted disruption of the iNOS gene (iNOS^−/−) and wild-type (WT) mice. The hemoglobin content and number of vessels were decreased in the implants of iNOS^−/− mice compared to WT mice 14 days after implantation. VEGF levels were also reduced in the implants of iNOS^−/− mice. In contrast, the iNOS^−/− implants exhibited an increased neutrophil and macrophage infiltration. However, no alterations were observed in levels of CXCL1 and CCL2, chemokines related to neutrophil and macrophage migration, respectively. Furthermore, the implants of iNOS^−/− mice showed boosted collagen deposition. These data suggest that iNOS activity controls inflammation, angiogenesis, and fibrogenesis in polyether-polyurethane synthetic implants and that lack of iNOS expression increases foreign body reaction to implants in mice.

Genetic variants of SLC11A1 are associated with both autoimmune and infectious diseases: systematic review and meta-analysis

A systematic review and meta-analyses were undertaken to investigate the association of SLC11A1 genetic variants with disease occurrence. Literature searching indentified 109 publications to include in the meta-analyses assessing the association of 11 SLC11A1 variants with autoimmune and infectious disease. The (GT)n promoter alleles 2 and 3 (rs534448891), which alter SLC11A1 expression, were significantly associated with tuberculosis (OR=1.47 (1.30-1.66), OR=0.76 (0.65-0.89), respectively) and infectious disease (OR=1.25 (1.10-1.42), OR=0.83 (0.74-0.93), respectively). However, although no association was observed with autoimmune disease, a modest significant association was observed with type 1 diabetes (allele 2 OR=0.94 (0.89-0.98)). On the basis of a stronger association of (GT)n allele 2 with tuberculosis, compared with the protective effect of allele 3, we hypothesise that allele 2 is likely the disease-causing variant influencing disease susceptibility. Significant associations were observed between the 469+14G/C polymorphism (rs3731865) and autoimmune disease (OR=1.30 (1.04-1.64)) and rheumatoid arthritis (OR=1.60 (1.20-2.13)) and between the -237C/T polymorphism (rs7573065) and inflammatory bowel disease (OR=0.60 (0.43-0.84)). Further, significant associations were identified between the 469+14G/C, 1730G/A and 1729+55del4 polymorphisms (rs3731865, rs17235409 and rs17235416, respectively) and both infectious disease per se and tuberculosis. These findings show a clear association between variants in the SLC11A1 locus and autoimmune and infectious disease susceptibility.

Macrophage defense mechanisms against intracellular bacteria

Macrophages and neutrophils play a decisive role in host responses to intracellular bacteria including the agent of tuberculosis (TB), Mycobacterium tuberculosis as they represent the forefront of innate immune defense against bacterial invaders. At the same time, these phagocytes are also primary targets of intracellular bacteria to be abused as host cells. Their efficacy to contain and eliminate intracellular M. tuberculosis decides whether a patient initially becomes infected or not. However, when the infection becomes chronic or even latent (as in the case of TB) despite development of specific immune activation, phagocytes have also important effector functions. Macrophages have evolved a myriad of defense strategies to combat infection with intracellular bacteria such as M. tuberculosis. These include induction of toxic anti-microbial effectors such as nitric oxide and reactive oxygen intermediates, the stimulation of microbe intoxication mechanisms via acidification or metal accumulation in the phagolysosome, the restriction of the microbe's access to essential nutrients such as iron, fatty acids, or amino acids, the production of anti-microbial peptides and cytokines, along with induction of autophagy and efferocytosis to eliminate the pathogen. On the other hand, M. tuberculosis, as a prime example of a well-adapted facultative intracellular bacterium, has learned during evolution to counter-balance the host's immune defense strategies to secure survival or multiplication within this otherwise hostile environment. This review provides an overview of innate immune defense of macrophages directed against intracellular bacteria with a focus on M. tuberculosis. Gaining more insights and knowledge into this complex network of host-pathogen interaction will identify novel target sites of intervention to successfully clear infection at a time of rapidly emerging multi-resistance of M. tuberculosis against conventional antibiotics.

'Ride on the ferrous wheel'--the cycle of iron in macrophages in health and disease

Iron homeostasis and macrophage biology are closely interconnected. On the one hand, iron exerts multiple effects on macrophage polarization and functionality. On the other hand, macrophages are central for mammalian iron homeostasis. The phagocytosis of senescent erythrocytes and their degradation by macrophages enable efficient recycling of iron and the maintenance of systemic iron balance. Macrophages express multiple molecules and proteins for the acquisition and utilization of iron and many of these pathways are affected by inflammatory signals. Of note, iron availability within macrophages has significant effects on immune effector functions and metabolic pathways within these cells. This review summarizes the physiological and pathophysiological aspects of macrophage iron metabolism and highlights its relevant consequences on immune function and in common diseases such as infection and atherosclerosis.

Iron at the interface of immunity and infection

Both, mammalian cells and microbes have an essential need for iron, which is required for many metabolic processes and for microbial pathogenicity. In addition, cross-regulatory interactions between iron homeostasis and immune function are evident. Cytokines and the acute phase protein hepcidin affect iron homeostasis leading to the retention of the metal within macrophages and hypoferremia. This is considered to result from a defense mechanism of the body to limit the availability of iron for extracellular pathogens while on the other hand the reduction of circulating iron results in the development of anemia of inflammation. Opposite, iron and the erythropoiesis inducing hormone erythropoietin affect innate immune responses by influencing interferon-gamma (IFN-γ) mediated (iron) or NF-kB inducible (erythropoietin) immune effector pathways in macrophages. Thus, macrophages loaded with iron lose their ability to kill intracellular pathogens via IFN-γ mediated effector pathways such as nitric oxide (NO) formation. Accordingly, macrophages invaded by the intracellular bacterium Salmonella enterica serovar Typhimurium increase the expression of the iron export protein ferroportin thereby reducing the availability of iron for intramacrophage bacteria while on the other side strengthening anti-microbial macrophage effector pathways via increased formation of NO or TNF-α. In addition, certain innate resistance genes such as natural resistance associated macrophage protein function (Nramp1) or lipocalin-2 exert part of their antimicrobial activity by controlling host and/or microbial iron homeostasis. Consequently, pharmacological or dietary modification of cellular iron trafficking enhances host resistance to intracellular pathogens but may increase susceptibility to microbes in the extracellular compartment and vice versa. Thus, the control over iron homeostasis is a central battlefield in host–pathogen interplay influencing the course of an infectious disease in favor of either the mammalian host or the pathogenic invader.

Transition metal ions at the crossroads of mucosal immunity and microbial pathogenesis

Transition metal ions are essential micronutrients for all living organisms. In mammals, these ions are often protein-bound and sequestered within cells, limiting their availability to microbes. Moreover, in response to infection, mammalian hosts further reduce the availability of metal nutrients by activating epithelial cells and recruiting neutrophils, both of which release metal-binding proteins with antimicrobial function. Microorganisms, in turn, have evolved sophisticated systems to overcome these limitations and acquire the metal ions essential for their growth. Here we review some of the mechanisms employed by the host and by pathogenic microorganisms to compete for transition metal ions, with a discussion of how evading “nutritional immunity” benefits pathogens. Furthermore, we provide new insights on the mechanisms of host-microbe competition for metal ions in the mucosa, particularly in the inflamed gut.

The complex interplay of iron metabolism, reactive oxygen species, and reactive nitrogen species: insights into the potential of various iron therapies to induce oxidative and nitrosative stress

Production of minute concentrations of superoxide (O2(*-)) and nitrogen monoxide (nitric oxide, NO*) plays important roles in several aspects of cellular signaling and metabolic regulation. However, in an inflammatory environment, the concentrations of these radicals can drastically increase and the antioxidant defenses may become overwhelmed. Thus, biological damage may occur owing to redox imbalance-a condition called oxidative and/or nitrosative stress. A complex interplay exists between iron metabolism, O2(*-), hydrogen peroxide (H2O2), and NO*. Iron is involved in both the formation and the scavenging of these species. Iron deficiency (anemia) (ID(A)) is associated with oxidative stress, but its role in the induction of nitrosative stress is largely unclear. Moreover, oral as well as intravenous (iv) iron preparations used for the treatment of ID(A) may also induce oxidative and/or nitrosative stress. Oral administration of ferrous salts may lead to high transferrin saturation levels and, thus, formation of non-transferrin-bound iron, a potentially toxic form of iron with a propensity to induce oxidative stress. One of the factors that determine the likelihood of oxidative and nitrosative stress induced upon administration of an iv iron complex is the amount of labile (or weakly-bound) iron present in the complex. Stable dextran-based iron complexes used for iv therapy, although they contain only negligible amounts of labile iron, can induce oxidative and/or nitrosative stress through so far unknown mechanisms. In this review, after summarizing the main features of iron metabolism and its complex interplay with O2(*-), H2O2, NO*, and other more reactive compounds derived from these species, the potential of various iron therapies to induce oxidative and nitrosative stress is discussed and possible underlying mechanisms are proposed. Understanding the mechanisms, by which various iron formulations may induce oxidative and nitrosative stress, will help us develop better tolerated and more efficient therapies for various dysfunctions of iron metabolism.

Transcriptional regulation by Ferric Uptake Regulator (Fur) in pathogenic bacteria

In the ancient anaerobic environment, ferrous iron (Fe²⁺) was one of the first metal cofactors. Oxygenation of the ancient world challenged bacteria to acquire the insoluble ferric iron (Fe³⁺) and later to defend against reactive oxygen species (ROS) generated by the Fenton chemistry. To acquire Fe³⁺, bacteria produce low-molecular weight compounds, known as siderophores, which have extremely high affinity for Fe³⁺. However, during infection the host restricts iron from pathogens by producing iron- and siderophore-chelating proteins, by exporting iron from intracellular pathogen-containing compartments, and by limiting absorption of dietary iron. Ferric Uptake Regulator (Fur) is a transcription factor which utilizes Fe²⁺ as a corepressor and represses siderophore synthesis in pathogens. Fur, directly or indirectly, controls expression of enzymes that protect against ROS damage. Thus, the challenges of iron homeostasis and defense against ROS are addressed via Fur. Although the role of Fur as a repressor is well-documented, emerging evidence demonstrates that Fur can function as an activator. Fur activation can occur through three distinct mechanisms (1) indirectly via small RNAs, (2) binding at cis regulatory elements that enhance recruitment of the RNA polymerase holoenzyme (RNAP), and (3) functioning as an antirepressor by removing or blocking DNA binding of a repressor of transcription. In addition, Fur homologs control defense against peroxide stress (PerR) and control uptake of other metals such as zinc (Zur) and manganese (Mur) in pathogenic bacteria. Fur family members are important for virulence within bacterial pathogens since mutants of fur, perR, or zur exhibit reduced virulence within numerous animal and plant models of infection. This review focuses on the breadth of Fur regulation in pathogenic bacteria.

Cell-Type Specific Determinants of NRAMP1 Expression in Professional Phagocytes

The Natural resistance-associated macrophage protein 1 (Nramp1 or Solute carrier 11 member 1, Slc11a1) transports divalent metals across the membrane of late endosomes and lysosomes in professional phagocytes. Nramp1 represents an ancient eukaryotic cell-autonomous defense whereas the gene duplication that yielded Nramp1 and Nramp2 predated the origin of Sarcopterygians (lobe-finned fishes and tetrapods). SLC11A1 genetic polymorphisms associated with human resistance to tuberculosis consist of potential regulatory variants. Herein, current knowledge of the regulation of SLC11A1 gene expression is reviewed and comprehensive analysis of ENCODE data available for hematopoietic cell-types suggests a hypothesis for the regulation of SLC11A1 expression during myeloid development and phagocyte functional polarization. SLC11A1 is part of a 34.6 kb CTCF-insulated locus scattered with predicted regulatory elements: a 3' enhancer, a large 5' enhancer domain and four elements spread around the transcription start site (TSS), including several C/EBP and PU.1 sites. SLC11A1 locus ends appear mobilized by ETS-related factors early during myelopoiesis; activation of both 5' and 3' enhancers in myelo-monocytic cells correlate with transcription factor binding at the TSS. Characterizing the corresponding cis/trans determinants functionally will establish the mechanisms involved and possibly reveal genetic variation that impacts susceptibility to infectious or immune diseases.

Neutrophil gelatinase-associated lipocalin and interleukin-10 regulate intramacrophage Chlamydia pneumoniae replication by modulating intracellular iron homeostasis

Neutrophil gelatinase-associated lipocalin (NGAL/Lipocalin-2/Lcn-2) is a 25 kDa protein which is involved in host defence against certain Gram negative bacteria upon binding of iron loaded bacterial siderophores thereby limiting the availability of this essential nutrient to bacteria resulting in inhibition of their growth and pathogenicity. As iron is important for the growth of the intracellular bacterium Chlamydia pneumoniae we questioned whether Lcn-2 affects the course of this infection. We employed primary peritoneal macrophages obtained from wildtype and Lcn-2 −/− mice and RAW 264.7 cells which were infected with C. pneumoniae. In addition, we studied C. pneumoniae multiplication in vivo in mice receiving diets with varying iron contents. We analyzed C. pneumoniae numbers by immunohistochemistry and RT-PCR and studied the expression of iron metabolism and cytokine genes by RT-PCR, Western blot or ELISA.

Infection with Chlamydiae ex vivo and in vivo revealed a significantly higher bacterial growth in peritoneal macrophages of Lcn-2 −/− than of wildtype mice. These differences were significantly more pronounced upon iron challenge, which stimulated bacterial growth. Accordingly, treatment with an anti-Lnc-2 antibody increased whereas addition of recombinant Lcn-2 reduced bacterial growth in infected macrophages. When investigating the underlying mechanisms we observed partly different expression of several iron metabolism genes between Lcn-2 +/+ and Lcn-2 −/− macrophages and most strikingly an increased formation of the anti-inflammatory cytokine IL-10 by Lcn-2 −/− macrophages. Upon treatment with an anti-IL10 antibody we experienced a significant increase of Chlamydial growth within Lcn-2 −/− macrophages along with a reduction of the major iron storage protein ferritin. Herein we provide first time evidence that Lcn-2 is involved in host defence against Chlamydia presumably by limiting the availability of iron to the pathogen. In the absence of Lcn-2, increased formation of IL-10 exerts protective effects by increasing the intracellular formation of ferritin, thereby reducing the access of iron for bacteria.

Peripheral blood immune cell methylation profiles are associated with nonhematopoietic cancers

BACKGROUND

Blood leukocytes from patients with solid tumors exhibit complex and distinct cancer-associated patterns of DNA methylation. However, the biologic mechanisms underlying these patterns remain poorly understood. Because epigenetic biomarkers offer significant clinical potential for cancer detection, we sought to address a mechanistic gap in recently published works, hypothesizing that blood-based epigenetic variation may be due to shifts in leukocyte populations.

METHODS

We identified differentially methylated regions (DMR) among leukocyte subtypes using epigenome-wide DNA methylation profiling of purified peripheral blood leukocyte subtypes from healthy donors. These leukocyte-tagging DMRs were then evaluated using epigenome-wide blood methylation data from three independent case-control studies of different cancers.

RESULTS

A substantial proportion of the top 50 leukocyte DMRs were significantly differentially methylated among head and neck squamous cell carcinoma (HNSCC) cases and ovarian cancer cases compared with cancer-free controls (48 and 47 of 50, respectively). Methylation classes derived from leukocyte DMRs were significantly associated cancer case status (P < 0.001, P < 0.03, and P < 0.001) for all three cancer types: HNSCC, bladder cancer, and ovarian cancer, respectively and predicted cancer status with a high degree of accuracy (area under the curve [AUC] = 0.82, 0.83, and 0.67).

CONCLUSIONS

These results suggest that shifts in leukocyte subpopulations may account for a considerable proportion of variability in peripheral blood DNA methylation patterns of solid tumors.

IMPACT

This illustrates the potential use of DNA methylation profiles for identifying shifts in leukocyte populations representative of disease, and that such profiles may represent powerful new diagnostic tools, applicable to a range of solid tumors.

Slc11a1 (Nramp1) impairs growth of Salmonella enterica serovar typhimurium in macrophages via stimulation of lipocalin-2 expression

The expression of the cation transporter Nramp1 (Slc11a1) in late phagolysosomes confers resistance to infection with several intracellular pathogens, such as Salmonella enterica, in mice. The antimicrobial actions of Nramp1 are attributable, in part, to modulation of macrophage immune function and cellular iron metabolism--the latter affecting the availability of the essential nutrient iron for intraphagosomal bacteria. Here, we provide novel evidence that Nramp1 functionality increases the expression of the peptide Lcn2, which exerts its antimicrobial activity by scavenging iron-loaded bacterial siderophores and mediating iron efflux from macrophages. With the use of macrophage cell lines expressing functional or nonfunctional Nramp1, we found significantly elevated Lcn2 mRNA and protein levels in Nramp1-expressing cells. These resulted from Nramp1-mediated alterations in the production of ROS, which stimulated NF-κ B activity and subsequently, Lcn2 transcription. We observed that increased Lcn2 levels in primary Nramp1-positive macrophages resulted in a significant suppression of S. enterica serovar typhimurium growth. Stimulation of Lcn2 expression is a novel mechanism by which Nramp1 confers resistance against infection with the intracellular bacterium S. typhimurium.

High levels of tumor necrosis factor-α downregulate antimicrobial iron transport protein, Nramp1, in chronic hemodialysis patients: a key factor for infection risk

BACKGROUND/AIMS

The susceptibility of patients on maintenance hemodialysis (MHD) to infections is a major cause of mortality and morbidity. Natural resistance-associated macrophage protein 1 (Nramp1) regulates intracellular pathogen proliferation, and its mRNA expression is highest in polymorphonuclear leukocytes (PMNLs). The purpose of this study was to determine the level of Nramp1 in PMNLs from MHD patients and the factors affecting its expression.

METHODS

Twenty MHD patients and 24 healthy volunteers (controls) were recruited. Relative quantitative PCR was used to measure Nramp1 mRNA, and protein levels were semiquantified by means of real-time PCR and Western blot analysis or immunohistochemistry. The effect of tumor necrosis factor-α (TNF-α) or interleukin-6 (IL-6) on Nramp1 expression in PMNLs from controls was also examined.

RESULTS

Nramp1 mRNA and protein levels were substantially lower in PMNLs from MHD than control subjects. Serum TNF-α levels were significantly higher in the MHD group and were inversely correlated with Nramp1 mRNA levels. The addition of TNF-α to PMNLs from control subjects decreased mRNA and protein levels of Nramp1. IL-6 did not alter Nramp1 mRNA or protein expression.

CONCLUSION

We found that Nramp1 was downregulated in the PMNLs of MHD patients, which constitute the first defense barrier against bacterial challenges. High levels of TNF-α may be associated with the downregulation of Nramp1. Our findings indicate that the susceptibility to infection observed in MHD patients could be partly due to the impairment of the intracellular handling of iron and the donation of more iron to the bacteria.

A glycine betaine importer limits Salmonella stress resistance and tissue colonization by reducing trehalose production

Mechanisms by which Salmonella establish chronic infections are not well understood. Microbes respond to stress by importing or producing compatible solutes, small molecules that stabilize proteins and lipids. The Salmonella locus opuABCD (also called OpuC) encodes a predicted importer of the compatible solute glycine betaine. Under stress conditions, if glycine betaine cannot be imported, Salmonella enterica produce the disaccharide trehalose, a highly effective compatible solute. We demonstrate that strains lacking opuABCD accumulate more trehalose under stress conditions than wild-type strains. ΔopuABCD mutant strains are more resistant to high-salt, low-pH and -hydrogen peroxide, conditions that mimic aspects of innate immunity, in a trehalose-dependent manner. In addition, ΔopuABCD mutant strains require the trehalose production genes to out-compete wild-type strains in mice and macrophages. These data suggest that in the absence of opuABCD, trehalose accumulation increases bacterial resistance to stress in broth and mice. Thus, opuABCD reduces bacterial colonization via a mechanism that limits trehalose production. Mechanisms by which microbes limit disease may reveal novel pathways as therapeutic targets.

Nifedipine affects the course of Salmonella enterica serovar Typhimurium infection by modulating macrophage iron homeostasis

BACKGROUND

Iron overload can adversely influence the course of infection by increasing microbial replication and suppressing antimicrobial immune effector pathways. Recently, we have shown that the calcium channel blocker nifedipine can mobilize tissue iron in mouse models of iron overload. We therefore investigated whether nifedipine treatment affects the course of infection with intracellular bacteria via modulation of iron homeostasis.

METHODS

The effect of nifedipine on intramacrophage replication of bacteria and modulation of cellular iron homeostasis was investigated in the murine macrophage cell line RAW264.7, and the impact of nifedipine treatment on the course of systemic infection was investigated in C57BL/6 mice in vivo.

RESULTS

In RAW264.7 cells, nifedipine treatment significantly reduced intracellular bacterial survival of Salmonella enterica serovar Typhimurium and Chlamydophila pneumoniae. This could be attributed to the induction of the iron exporter ferroportin 1, which limited the availability of iron for intracellular Salmonella. When C57BL/6 mice were infected intraperitoneally with Salmonella and subsequently injected with nifedipine for 3 consecutive days, bacterial counts in livers and spleens were significantly reduced and survival of the mice significantly was prolonged compared with solvent-treated littermates. Nifedipine treatment increased expression of ferroportin 1 in the spleen, whereas splenic levels of the iron storage protein ferritin and serum iron concentrations were reduced.

CONCLUSIONS

Our data provide evidence for a novel mechanism whereby nifedipine enhances host resistance to intracellular pathogens via limitation of iron availability.

Cellular aspects of immunity to intracellular Salmonella enterica

Salmonella enterica is a frequent gastrointestinal pathogen with ability to cause diseases ranging from local gastrointestinal inflammation and diarrhea to life-threatening typhoid fever. Salmonella is an invasive, facultative intracellular pathogen that infects various cell types of the host and can survive and proliferate in different populations of immune cells. During pathogenesis, Salmonella is confronted with various lines of immune defense. To successfully colonize host organisms, the pathogen deploys a set of sophisticated mechanisms of immune evasion and direct manipulation of immune cell functions. In addition to resistance against innate immune mechanisms, including the ability to avoid killing by macrophages and dendritic cells (DCs), Salmonella interferes with antigen presentation by DCs and the formation of an efficient adaptive immune response. In this review, we describe the current understanding of Salmonella virulence factors during intracellular life and focus on the recent advances in the understanding of interference of intracellular Salmonella with cellular functions of immune cells.

Evidence of association with type 1 diabetes in the SLC11A1 gene region

BACKGROUND

Linkage and congenic strain analyses using the nonobese diabetic (NOD) mouse as a model for human type 1 autoimmune diabetes (T1D) have identified several NOD mouse Idd (insulin dependent diabetes) loci, including Slc11a1 (formerly known as Nramp1). Genetic variants in the orthologous region encompassing SLC11A1 in human chromosome 2q35 have been reported to be associated with various immune-related diseases including T1D. Here, we have conducted association analysis of this candidate gene region, and then investigated potential correlations between the most T1D-associated variant and RNA expression of the SLC11A1 gene and its splice isoform.

METHODS

Nine SNPs (rs2276631, rs2279015, rs1809231, rs1059823, rs17235409 (D543N), rs17235416 (3'UTR), rs3731865 (INT4), rs7573065 (-237 C → T) and rs4674297) were genotyped using TaqMan genotyping assays and the polymorphic promoter microsatellite (GT)n was genotyped using PCR and fragment length analysis. A maximum of 8,863 T1D British cases and 10,841 British controls, all of white European descent, were used to test association using logistic regression. A maximum of 5,696 T1D families were also tested for association using the transmission/disequilibrium test (TDT). We considered P ≤ 0.005 as evidence of association given that we tested nine variants in total. Upon identification of the most T1D-associated variant, we investigated the correlation between its genotype and SLC11A1 expression overall or with splice isoform ratio using 42 PAXgene whole blood samples from healthy donors by quantitative PCR (qPCR).

RESULTS

Using the case-control collection, rs3731865 (INT4) was identified to be the variant most associated with T1D (P = 1.55 × 10-6). There was also some evidence of association at rs4674297 (P = 1.57 × 10-4). No evidence of disease association was obtained at any of the loci using the family collections (PTDT ≥ 0.13). We also did not observe a correlation between rs3731865 genotypes and SLC11A1 expression overall or with splice isoform expression.

CONCLUSION

We conclude that rs3731685 (INT4) in the SLC11A1 gene may be associated with T1D susceptibility in the European ancestry population studied. We did not observe a difference in SLC11A1 expression at the RNA level based on the genotypes of rs3731865 in whole blood samples. However, a potential correlation cannot be ruled out in purified cell subsets especially monocytes or macrophages.

Nitric oxide and salmonella pathogenesis

Nitric oxide (NO) and its congeners contribute to the innate immune response to Salmonella. This enteric pathogen is exposed to reactive nitrogen species (RNS) in the environment and at different anatomical locations during its infectious cycle in vertebrate hosts. Chemical generation of RNS enhances the gastric barrier to enteropathogenic bacteria, while products of the Salmonella pathogenicity island 1 type III secretion system and Salmonella-associated molecular patterns stimulate transcription of inducible NO synthase (iNOS) by cells of the mononuclear phagocytic cell lineage. The resulting NO, or products that arise from its interactions with oxygen (O₂) or iron and low-molecular weight thiols, are preferentially bacteriostatic against Salmonella, while reaction of NO and superoxide (O2−) generates the bactericidal compound peroxynitrite (ONOO−). The anti-Salmonella activity of RNS emanates from the modification of redox active thiols and metal prosthetic groups of key molecular targets of the electron transport chain, central metabolic enzymes, transcription factors, and DNA and DNA-associated proteins. In turn, Salmonella display a plethora of defenses that modulate the delivery of iNOS-containing vesicles to phagosomes, scavenge and detoxify RNS, and repair biomolecules damaged by these toxic species. Traditionally, RNS have been recognized as important mediators of host defense against Salmonella. However, exciting new findings indicate that Salmonella can exploit the RNS produced during the infection to foster virulence. More knowledge of the primary RNS produced in response to Salmonella infection, the bacterial processes affected by these toxic species, and the adaptive bacterial responses that protect Salmonella from nitrosative and oxidative stress associated with NO will increase our understanding of Salmonella pathogenesis. This information may assist in the development of novel therapeutics against this common enteropathogen.

Candidate gene and genome-wide association studies of Mycobacterium avium subsp. paratuberculosis infection in cattle and sheep: a review

Paratuberculosis (Johne's disease), caused by Mycobacterium avium subspecies paratuberculosis, is responsible for significant economic losses in livestock industries worldwide. This organism is also of public health concern due to an unconfirmed link to Crohn's disease. Susceptibility to paratuberculosis has been suggested to have a genetic component. In livestock, a number of candidate genes have been studied, selected on their association to susceptibility in other mycobacterial diseases, their known role in disease pathogenesis or links to susceptibility of humans to Crohn's disease. These genes include solute carrier family 11 member 1 (SLC11A1, formerly NRAMP1), toll-like receptors, caspase associated recruitment domain 15 (CARD15, formerly NOD2), major histocompatibility complex (MHC) and cytokines (interleukin-10 and interferon-gamma) and their receptors. Genome wide association studies have attempted to confirm associations found and identify new genes involved in pathogenesis and susceptibility. There are a number of limitations and difficulties in these approaches, some peculiar to paratuberculosis but others generally applicable to identification of genetic associations for complex traits. The technical approaches and available information for paratuberculosis have expanded rapidly, particularly relating to sheep and cattle. Here we review the current published evidence for a genetic association with paratuberculosis susceptibility, technological advances that have progressed the field and potential avenues for future research.

SLC11A1 polymorphisms in inflammatory bowel disease and Mycobacterium avium subspecies paratuberculosis status

AIM: To test for association of SLC11A1 with inflammatory bowel disease (IBD) and Mycobacterium avium subspecies paratuberculosis (MAP) status in a Caucasian cohort.

METHODS: Five hundred and seven Crohn’s disease (CD) patients, 474 ulcerative colitis (UC) patients, and 569 healthy controls were genotyped for SLC11A1 1730G>A and SLC11A1 469+14G>C using pre-designed TaqMan^® SNP assays. χ² tests were applied to test for association of single nucleotide polymorphisms (SNPs) with disease, and the presence of MAP DNA.

RESULTS: SLC11A1 1730G>A and SLC11A 1469+14G>C were not associated with CD, UC, or IBD. The SLC11A1 1730A minor allele was over-represented in patients who did not require immunomodulator therapy (P = 0.002, OR: 0.29, 95% CI: 0.13-0.66). The frequency of the SLC11A1 469+14C allele was higher in the subset of study participants who tested positive for MAP DNA (P = 0.02, OR: 1.56, 95% CI: 1.06-2.29). No association of SLC11A1 1730G>A with MAP was observed.

CONCLUSION: Although SLC11A1 was not associated with IBD, association with MAP suggests that SLC11A1 is important in determining susceptibility to bacteria implicated in the etiology of CD.

β 1-4 mannobiose enhances Salmonella-killing activity and activates innate immune responses in chicken macrophages

Salmonella spp. is one of the major causes of food-borne illness in humans, and Salmonella enteritidis (SE) infection in commercial poultry is a world-wide problem. Here we have investigated the in vitro immune-modulating effects of β 1-4 mannobiose (MNB), which was previously found to prevent SE infection in vivo in chickens, using chicken macrophage (MQ-MCSU) cells. Treatment of MQ-NCSU cells with MNB dose-dependently increased both phagocytic activity and Salmonella-killing activity of macrophages, with the highest reduction in SE viability observed at a concentration of 40 μg/ml at 48 h post-infection. Likewise, both hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) production were increased in a dose-dependent manner by MNB. Gene expression analysis of MNB-treated macrophages revealed significant increases in the expression of iNOS, NOX-1, IFN-γ, NRAMP1, and LITAF, genes critical for host defense and antimicrobial activity, when compared to untreated cells. This data confirms that MNB possesses potent innate immune-modulating activities and can up-regulate antibacterial defenses in chicken macrophages.

Slc11a1 limits intracellular growth of Salmonella enterica sv. Typhimurium by promoting macrophage immune effector functions and impairing bacterial iron acquisition

The natural resistance-associated macrophage protein 1, Slc11a1, is a phagolysosomal transporter for protons and divalent ions including iron that confers host protection against diverse intracellular pathogens including Salmonella. We investigated and compared the regulation of iron homeostasis and immune function in RAW264.7 murine phagocytes stably transfected with non-functional Slc11a1 and functional Slc11a1 controls in response to an infection with Salmonella enterica serovar Typhimurium. We report that macrophages lacking functional Slc11a1 displayed an increased expression of transferrin receptor 1, resulting in enhanced acquisition of transferrin-bound iron. In contrast, cellular iron release mediated via ferroportin 1 was significantly lower in Salmonella-infected Slc11a1-negative macrophages in comparison with phagocytes bearing Slc11a1. Lack of Slc11a1 led to intracellular persistence of S. enterica serovar Typhimurium within macrophages, which was paralleled by a reduced formation of nitric oxide, tumour necrosis factor-alpha and interleukin-6 in Slc11a1-negative macrophages following Salmonella infection, whereas interleukin-10 production was increased. Moreover, Slc11a1-negative phagocytes exhibited higher cellular iron content, resulting in increased iron acquisition by intracellular Salmonella. Our observations indicate a bifunctional role for Slc11a1 within phagocytes. Slc11a restricts iron availability, which first augments pro-inflammatory macrophage effector functions and second concomitantly limits microbial iron access.