Potential molecular targets of Leishmania pathways in developing novel antileishmanials

The illness known as leishmaniasis has not become a household name like malaria, although it stands as the second-largest parasitic disease, surpassed only by malaria. As no licensed vaccine is available, treatment for leishmaniasis mostly relies on chemotherapy. Inefficiency and drug resistance are the major impediments in current therapeutics. In this scenario, identification of novel molecular drug candidates is indispensable to develop robust antileishmanials. The exploration of structure-based drugs to target enzymes/molecules of Leishmania which differ structurally/functionally from their equivalents in mammalian hosts not only helps in developing a new class of antileishmanials, but also paves the way to understand Leishmania biology. This review provides a comprehensive overview on possible drug candidates relating to various Leishmania molecular pathways.

Molecular identification and expression analysis of natural resistance-associated macrophage protein (Nramp) gene from yellow catfish Pelteobagrus fulvidraco (Siluriformes: Bagridae)

Natural resistance associated macrophage protein genes (Nramp) is one of the important candidate genes responsible for regulating immune response against pathogen infection. The aim of the present was to quantify expression of Nramp gene in response to pathogen infection. Here, a Nramp was identified and molecularly characterized from Pelteobagrus fulvidraco (PfNramp). The obtained 3134 bp cDNA fragment of PfNramp comprised a 5'-untranslated region (UTR) of 81 bp, a 3'-UTR of 1403 bp and an open reading frame (ORF) of 1650 bp, encoding a polypeptide of 549 amino acids that contained a typical structural features of Nramp domain (Pfam01566). BLAST analysis exhibited that PfNramp shared sequence similarity to other organisms, in particular to Ictalurus furcatus (92%), Danio rerio (82%), and Homo sapiens (77%). Phylogenetic analysis revealed that PfNramp is close to Teleostei. Real-time quantitative reverse transcription-PCR (qRT-PCR) analysis showed that PfNramp was expressed in all examined tissues, with the highest abundance in liver. The mRNA expression of PfNramp was remarkably increased at different time points after lipopolysaccharide (LPS), and polyriboinosinic polyribocytidylic acid (poly I:C) challenge. These results suggest that PfNramp is an inducible protein in the innate immune reactions of P. fulvidraco and probably in other fish species.

c-Src kinase is involved in the tyrosine phosphorylation and activity of SLC11A1 in differentiating macrophages

Studies have demonstrated that the solute carrier family 11 member 1 (SLC11A1) is heavily glycosylated and phosphorylated in macrophages. However, the mechanisms of SLC11A1 phosphorylation, and the effects of phosphorylation on SLC11A1 activity remain largely unknown. Here, the tyrosine phosphorylation of SLC11A1 is observed in SLC11A1-expressing U937 cells when differentiated into macrophages by phorbol myristate acetate (PMA). The phosphorylation of SLC11A1 is almost completely blocked by treatment with PP2, a selective inhibitor of Src family kinases. Furthermore, we found that SLC11A1 is a direct substrate for active c-Src kinase and siRNA-mediated knockdown of cellular Src (c-Src) expression results in a significant decrease in tyrosine phosphorylation. We found that PMA induces the interaction of SLC11A1 with c-Src kinase. We demonstrated that SLC11A1 is phosphorylated by Src family kinases at tyrosine 15 and this type of phosphorylation is required for SLC11A1-mediated modulation of NF-κB activation and nitric oxide (NO) production induced by LPS. Our results demonstrate important roles for c-Src tyrosine kinase in phosphorylation and activation of SLC11A1 in macrophages.

Function of Macrophage and Parasite Phosphatases in Leishmaniasis

The kinetoplastid protozoan parasites belonging to the genus Leishmania are the causative agents of different clinical forms of leishmaniasis, a vector-borne infectious disease with worldwide prevalence. The protective host immune response against Leishmania parasites relies on myeloid cells such as dendritic cells and macrophages in which upon stimulation by cytokines (e.g., interferon-γ) a complex network of signaling pathways is switched on leading to strong antimicrobial activities directed against the intracellular parasite stage. The regulation of these pathways classically depends on post-translational modifications of proteins, with phosphorylation events playing a cardinal role. Leishmania parasites deactivate their phagocytic host cells by inducing specific mammalian phosphatases that are capable to impede signaling. On the other hand, there is now also evidence that Leishmania spp. themselves express phosphatases that might target host cell molecules and thereby facilitate the intracellular survival of the parasite. This review will present an overview on the modulation of host phosphatases by Leishmania parasites as well as on the known families of Leishmania phosphatases and their possible function as virulence factors. A more detailed understanding of the role of phosphatases in Leishmania–host cell interactions might open new avenues for the treatment of non-healing, progressive forms of leishmaniasis.

A Family of Salmonella Type III Secretion Effector Proteins Selectively Targets the NF-κB Signaling Pathway to Preserve Host Homeostasis

Microbial infections usually lead to host innate immune responses and inflammation. These responses most often limit pathogen replication although they can also result in host-tissue damage. The enteropathogenic bacteria Salmonella Typhimurium utilizes a type III secretion system to induce intestinal inflammation by delivering specific effector proteins that stimulate signal transduction pathways resulting in the production of pro-inflammatory cytokines. We show here that a family of related Salmonella Typhimurium effector proteins PipA, GogA and GtgA redundantly target components of the NF-κB signaling pathway to inhibit transcriptional responses leading to inflammation. We show that these effector proteins are proteases that cleave both the RelA (p65) and RelB transcription factors but do not target p100 (NF-κB2) or p105 (NF-κB1). A Salmonella Typhimurium strain lacking these effectors showed increased ability to stimulate NF-κB and increased virulence in an animal model of infection. These results indicate that bacterial pathogens can evolve determinants to preserve host homeostasis and that those determinants can reduce the pathogen’s virulence.

The inflammatory response to microbial pathogens usually limits their replication but it can also cause tissue damage. The enteropathogenic bacteria Salmonella Typhimurium stimulate host signal transduction pathways that result in inflammation. We show here that a family of related Salmonella Typhimurium effector proteins, PipA, GogA and GtgA, which are delivered by its type III secretion systems, specifically and redundantly target components of the NF-κB signaling pathway to inhibit transcriptional responses leading to host inflammation. We show that these effector proteins are proteases that cleave both the RelA (p65) and RelB transcription factors, which are central components of the NF-κB signaling pathway, but do not target p100 (NF-κB2) or p105 (NF-κB1). A Salmonella Typhimurium mutant strain lacking these effector proteins showed increased ability to stimulate NF-κB and increased virulence in an animal model of infection. These results indicate that bacterial pathogens can evolve determinants to preserve host homeostasis.

Nramp1 and Other Transporters Involved in Metal Withholding during Infection

During the course of infection, many natural defenses are set up along the boundaries of the host-pathogen interface. Key among these is the host response to withhold metals to restrict the growth of invading microbes. This simple act of nutritional warfare, starving the invader of an essential element, is an effective means of limiting infection. The physiology of metal withholding is often referred to as "nutritional immunity," and the mechanisms of metal transport that contribute to this host response are the focus of this review.

Manganese homeostasis and utilization in pathogenic bacteria

Manganese (Mn) is a required cofactor for all forms of life. Given the importance of Mn to bacteria, the host has devised strategies to sequester Mn from invaders. In the macrophage phagosome, NRAMP1 removes Mn and other essential metals to starve intracellular pathogens; in the extracellular space, calprotectin chelates Mn and Zn. Calprotectin-mediated Mn sequestration is a newly appreciated host defense mechanism, and recent findings are highlighted herein. In order to acquire Mn when extracellular concentrations are low, bacteria have evolved efficient Mn acquisition systems that are under elegant transcriptional control. To counteract Mn overload, some bacteria possess Mn-specific export systems that are important in vivo, presumably for control of intracellular Mn levels. Mn transporters, their transcriptional regulators and some Mn-requiring enzymes are necessary for virulence of certain bacterial pathogens, as revealed by animal models of infection. Furthermore, Mn is an important facet of the cellular response to oxidative stress, a host antibacterial strategy. The battle for Mn between host and pathogen is now appreciated to be a major determinant of the outcome of infection. In this MicroReview, the contribution of Mn to the host-pathogen interaction is reviewed, and key questions are proposed for future study.

Leishmania and the macrophage: a multifaceted interaction

ABSTRACT 

Leishmania, the causative agent of leishmaniases, is an intracellular parasite of macrophages, transmitted to humans via the bite of its sand fly vector. This protozoan organism has evolved strategies for efficient uptake into macrophages and is able to regulate phagosome maturation in order to make the phagosome more hospitable for parasite growth and to avoid destruction. As a result, macrophage defenses such as oxidative damage, antigen presentation, immune activation and apoptosis are compromised whereas nutrient availability is improved. Many Leishmania survival factors are involved in shaping the phagosome and reprogramming the macrophage to promote infection. This review details the complexity of the host–parasite interactions and summarizes our latest understanding of key events that make Leishmania such a successful intracellular parasite.

Global H3K4me3 genome mapping reveals alterations of innate immunity signaling and overexpression of JMJD3 in human myelodysplastic syndrome CD34+ cells

The molecular bases of myelodysplastic syndromes (MDS) are not fully understood. Trimethylated histone 3 lysine 4 (H3K4me3) is present in promoters of actively transcribed genes and has been shown to be involved in hematopoietic differentiation. We performed a genome-wide H3K4me3 CHIP-Seq (chromatin immunoprecipitation coupled with whole genome sequencing) analysis of primary MDS bone marrow (BM) CD34+ cells. This resulted in the identification of 36 genes marked by distinct higher levels of promoter H3K4me3 in MDS. A majority of these genes are involved in nuclear factor (NF)-κB activation and innate immunity signaling. We then analyzed expression of histone demethylases and observed significant overexpression of the JmjC-domain histone demethylase JMJD3 (KDM6b) in MDS CD34+ cells. Furthermore, we demonstrate that JMJD3 has a positive effect on transcription of multiple CHIP-Seq identified genes involved in NF-κB activation. Inhibition of JMJD3 using shRNA in primary BM MDS CD34+ cells resulted in an increased number of erythroid colonies in samples isolated from patients with lower-risk MDS. Taken together, these data indicate the deregulation of H3K4me3 and associated abnormal activation of innate immunity signals have a role in the pathogenesis of MDS and that targeting these signals may have potential therapeutic value in MDS.

Solute carrier 11A1 is expressed by innate lymphocytes and augments their activation

Solute carrier 11A1 (SLC11A1) is a divalent ion transporter formerly known as the natural resistance-associated macrophage protein (NRAMP1) and the Bcg/Lsh/Ity locus. SLC11A1 was thought to be exclusively expressed in monocyte/macrophages and to have roles in phagosome maturation and cell activation. We characterized the expression of SLC11A1 in the majority of human and bovine γδ T cells and NK cells and in human CD3(+)CD45RO(+) T cells. Consistent with a role for iron-dependent inhibition of protein tyrosine phosphatases, SLC11A1(+) lymphocytes were more prone to activation and retained tyrosine phosphorylation. Transfection of SLC11A1 into a human γδ T cell-like line rendered the cells more prone to activation. Nonadherent splenocytes from wild-type mice expressed significantly greater IFN-γ compared with cells from Sv/129 (SLC11A1(-/-)) mice. Our data suggest that SLC11A1 has a heretofore unknown role in activation of a large subset of innate lymphocytes that are critical sources of IFN-γ. SLC11A1(+) animals have enhanced innate IFN-γ expression in response to Salmonella infection compared with SLC11A1(-) mice, which include commonly used inbred laboratory mice. Expression of SLC11A1 in innate lymphocytes and its role in augmenting their activation may account for inconsistencies in studies of innate lymphocytes in different animal models.

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.

Identification and functional characterization of Leishmania donovani secretory peroxidase: delineating its role in NRAMP1 regulation

Leishmania silently evades host immune system and establish in the hostile environment of host macrophage phagolysosomes. For differentiation, growth and division parasite acquires divalent cations especially iron from the host nutritive pool. Natural resistance associated with macrophage protein1 (NRAMP1), a cation transporter that effluxes out divalent cations specifically iron from phagosomal milieu to the cytosol, to create ions deprived status for pathogenic microorganisms. The mechanisms of NRAMP1 regulation are largely unknown in leishmanial infections. In the present study, we identified a secretory Leishmania donovani peroxidase (Prx) that showed peroxidoxin like peroxidase activity and significantly reduced H₂O₂, O₂.⁻ and NO levels in LPS activated macrophages. Further, we also observed down regulated Nramp1 expression and concomitantly declined labile iron pool in activated macrophages treated with identified peroxidase. Prx also decreased levels of TNF-α, IFN-γ and IL-12 in LPS activated macrophages. These observations indicate a bifunctional protective role of secretory Prx; first it reduces redox activation of macrophages, and secondly it allows iron access to Leishmania by down regulating NRAMP1 expression.

Comparative biology of γδ T cell function in humans, mice, and domestic animals

γδ T cells are a functionally heterogeneous population and contribute to many early immune responses. The majority of their activity is described in humans and mice, but the immune systems of all jawed vertebrates include the γδ T cell lineage. Although some aspects of γδ T cells vary between species, critical roles in early immune responses are often conserved. Common features of γδ T cells include innate receptor expression, antigen presentation, cytotoxicity, and cytokine production. Herein we compare studies describing these conserved γδ T cell functions and other, potentially unique, functions. γδ T cells are well documented for their potential immunotherapeutic properties; however, these proposed therapies are often focused on human diseases and the mouse models thereof. This review consolidates some of these studies with those in other animals to provide a consensus for the current understanding of γδ T cell function across species.

Proteomic identification of plasma protein tyrosine phosphatase alpha and fibronectin associated with liver fluke, Opisthorchis viverrini, infection

Opisthorchiasis caused by Opisthorchis viverrini induces periductal fibrosis via host immune/inflammatory responses. Plasma protein alteration during host-parasite interaction-mediated inflammation may provide potential diagnostic and/or prognostic biomarkers. To search for target protein changes in O. viverrini-infected hamsters, a 1-D PAGE gel band was trypsin-digested and analyzed by a LC-MS/MS-based proteomics approach in the plasma profile of infected hamsters, and applied to humans. Sixty seven proteins were selected for further analysis based on at least two unique tryptic peptides with protein ID score >10 and increased expression at least two times across time points. These proteins have not been previously identified in O. viverrini-associated infection. Among those, proteins involved in structural (19%), immune response (13%), cell cycle (10%) and transcription (10%) were highly expressed. Western blots revealed an expression level of protein tyrosine phosphatase alpha (PTPα) which reached a peak at 1 month and subsequently tended to decrease. Fibronectin significantly increased at 1 month and tended to increase with time, supporting proteomic analysis. PTPα was expressed in the cytoplasm of inflammatory cells, while fibronectin was observed mainly in the cytoplasm of fibroblasts and the extracellular matrix at periductal fibrosis areas. In addition, these protein levels significantly increased in the plasma of O. viverrini-infected patients compared to healthy individuals, and significantly decreased at 2-months post-treatment, indicating their potential as disease markers. In conclusion, our results suggest that plasma PTPα and fibronectin may be associated with opisthorchiasis and the hamster model provides the basis for development of novel diagnostic markers in the future.

Leishmaniasis: current status of available drugs and new potential drug targets

The control of Leishmania infection relies primarily on chemotherapy till date. Resistance to pentavalent antimonials, which have been the recommended drugs to treat cutaneous and visceral leishmaniasis, is now widespread in Indian subcontinents. New drug formulations like amphotericin B, its lipid formulations, and miltefosine have shown great efficacy to treat leishmaniasis but their high cost and therapeutic complications limit their usefulness. In addition, irregular and inappropriate uses of these second line drugs in endemic regions like state of Bihar, India threaten resistance development in the parasite. In context to the limited drug options and unavailability of either preventive or prophylactic candidates, there is a pressing need to develop true antileishmanial drugs to reduce the disease burden of this debilitating endemic disease. Notwithstanding significant progress of leishmanial research during last few decades, identification and characterization of novel drugs and drug targets are far from satisfactory. This review will initially describe current drug regimens and later will provide an overview on few important biochemical and enzymatic machineries that could be utilized as putative drug targets for generation of true antileishmanial drugs.

Iron homeostasis and the inflammatory response

Iron and its homeostasis are intimately tied to the inflammatory response. The adaptation to iron deficiency, which confers resistance to infection and improves the inflammatory condition, underlies what is probably the most obvious link: the anemia of inflammation or chronic disease. A large number of stimulatory inputs must be integrated to tightly control iron homeostasis during the inflammatory response. In order to understand the pathways of iron trafficking and how they are regulated, this article presents a brief overview of iron homeostasis. A major focus is on the regulation of the peptide hormone hepcidin during the inflammatory response and how its function contributes to the process of iron withdrawal. The review also summarizes new and emerging information about other iron metabolic regulators and effectors that contribute to the inflammatory response. Potential benefits of treatment to ameliorate the hypoferremic condition promoted by inflammation are also considered.

Protein tyrosine phosphatases are regulated by mononuclear iron dicitrate

The involvement of macrophages (Mvarphis) as host, accessory, and effector cells in the development of infectious diseases, together with their central role in iron homeostasis, place these immune cells as key players in the interface between iron and infection. Having previously shown that the functional expression of NRAMP-1 results in increased protein phosphorylation mediated in part by an iron-dependent inhibition of Mvarphi protein-tyrosine phosphatase (PTP) activity, we sought to study the mechanism(s) underlying this specific event. Herein we have identified the mononuclear dicitrate iron complex [Fe(cit)(2)H(4-x)]((1+x)-) as the species responsible for the specific inhibition of Mvarphi PTP activity. By using biochemical and computational approaches, we show that [Fe(cit)(2)](5-) targets the catalytic pocket of the PTP SHP-1, competitively inhibiting its interaction with an incoming phosphosubstrate. In vitro and in vivo inhibition of PTP activity by iron-citrate results in protein hyperphosphorylation and enhanced MAPK signaling in response to LPS stimulation. We propose that iron-citrate-mediated PTP inhibition represents a novel and biologically relevant regulatory mechanism of signal transduction.

Leishmania GP63 alters host signaling through cleavage-activated protein tyrosine phosphatases

With more than 12 million people affected worldwide, 2 million new cases occurring per year, and the rapid emergence of drug resistance and treatment failure, leishmaniasis is an infectious disease for which research on drug and vaccine development, host-pathogen, and vector-parasite interactions are current international priorities. Upon Leishmania-macrophage interaction, activation of the protein tyrosine phosphatase (PTP) SHP-1 rapidly leads to the down-regulation of Janus kinase and mitogen-activated protein kinase signaling, resulting in the attenuation of host innate inflammatory responses and of various microbicidal macrophage functions. We report that, in addition to SHP-1, the PTPs PTP1B and TCPTP are activated and posttranslationally modified in infected macrophages, and we identify an essential role for PTP1B in the in vivo progression of Leishmania infection. The mechanism underlying PTP modulation involves the proteolytic activity of the Leishmania surface protease GP63. Access of GP63 to macrophage PTP1B, TCPTP, and SHP-1 is mediated in part by a lipid raft-dependent mechanism, resulting in PTP cleavage and stimulation of phosphatase activity. Collectively, our data present a mechanism of cleavage-dependent activation of macrophage PTPs by an obligate intracellular pathogen and show that internalization of GP63, a key Leishmania virulence factor, into host macrophages is a strategy the parasite uses to interact and survive within its host.

Protein tyrosine phosphatases regulate asthma development in a murine asthma model

Allergic asthma is a chronic inflammatory disease characterized by Th2-type inflammation. Although the cellular interactions are now well studied, the intracellular signaling involved in asthma development is still a developing field. Protein tyrosine kinases are one focus of such research and their inhibition shows improvement of asthmatic features. Interestingly, very little attention was given to protein tyrosine phosphatases (PTPs), the counterparts to protein tyrosine kinases, in the development of asthma. Previous studies from our laboratory showed that pharmacological inhibition of PTPs induced a transient Th1 response in the spleen. Therefore, we hypothesized that modulation of PTPs could influence asthma development. To assess PTP functions, we used the PTP inhibitor bis-peroxovanadium bpV(phen) in a murine model of asthma during either allergen sensitization or challenge. Inhibition of PTPs during allergen sensitization resulted in the reduction of key features of allergic asthma: serum IgE levels, lung tissue inflammation, eosinophilia, and airway hyperresponsiveness. Of utmost interest, PTP inhibition at allergen challenge resulted in a very similar improvement of asthmatic features. Of further importance, we observed that bpV(phen) treatment modulated cytokine expression in the spleen and, more specifically, favored Th1 cytokines while inhibiting Th2 cytokines. Collectively, we show for the first time that intact activity of PTPs is required for a complete induction of asthma in a mouse model. This clearly suggests that PTPs have a pivotal regulatory role in the development of asthmatic diseases, which opens the possibility of new therapeutic avenues.

Expression analysis of selected immune-relevant genes in channel catfish during Edwardsiella ictaluri infection

Channel catfish Ictalurus punctatus were intraperitoneally challenged with the bacterium Edwardsiella ictaluri (the causative agent of enteric septicemia of catfish), and the expression of genes presumed to function in the inducible innate defense was evaluated. End-binding protein 1 (EB1), beta1-integrin, natural-resistance-associated macrophage protein (Nramp), heat shock protein 70 (Hsp70), serum amyloid P (SAP), and transferrin gene expression profiles were determined using quantitative reverse-transcriptase-polymerase chain reaction on liver, anterior kidney, spleen, and gut. Fish were subsampled at 0, 24, 48, 72, and 96 h after bacterial or phosphate-buffered-saline injection. Posterior kidney sampling demonstrated increasing bacterial counts at 24-48 h postinjection (hpi), followed by a plateau to 96 hpi. The transferrin and SAP transcripts were liver specific. The other genes were expressed in all four tissues. In bacterially infected fish, expression of EB1 (anterior kidney, spleen, and liver), Hsp70 (anterior kidney and spleen), and Nramp (spleen and gut) significantly increased by 48 hpi. Transferrin was strongly up-regulated and SAP was downregulated by 72 hpi, indicating positive and negative acute-phase reactants, respectively. The data indicate a substantial response of innate immunity effector cells by 48 hpi, followed by suppression of bacterial growth and induction of the acute-phase response. This suggests that the 48-72-hpi time frame is critical in our model for evaluating the effectiveness of innate defenses.

Nramp1 drives an accelerated inflammatory response during Salmonella-induced colitis in mice

A recently developed model for enterocolitis in mice involves pre-treatment with the antibiotic streptomycin prior to infection with Salmonella enterica serovar Typhimurium (S. Typhimurium). The contribution of Nramp1/Slc11a1 protein, a critical host defence mechanism against S. Typhimurium, to the development of inflammation in this model has not been studied. Here, we analysed the impact of Nramp1 expression on the early development of colitis using isogenic Nramp1(+/+) and Nramp1(-/-) mice. We hypothesized that Nramp1 acts by rapidly inducing an inflammatory response in the gut mucosa creating an antibacterial environment and limiting spread of S. Typhimurium to systemic sites. We observed that Nramp1(+/+) mice showed lower numbers of S. Typhimurium in the caecum compared with Nramp1(-/-) mice at all times analysed. Acute inflammation was much more pronounced in Nramp1(+/+) mice 1 day after infection. The effect of Nramp1 on development of colitis was characterized by higher secretion of the pro-inflammatory cytokines IFN-gamma, TNF-alpha and MIP-1alpha and a massive infiltration of neutrophils and macrophages, compared with Nramp1(-/-) animals. These data show that an early and rapid inflammatory response results in protection against pathological effects of S. Typhimurium infection in Nramp1(+/+) mice.

Nramp1 expression by dendritic cells modulates inflammatory responses during Salmonella Typhimurium infection

Host resistance against Salmonella enterica serovar Typhimurium (S. Typhimurium) is mediated by natural resistance-associated macrophage protein 1 (Nramp1/Slc11a1). Nramp1 is critical to host defence, as mice lacking Nramp1 fail to control bacterial replication and succumb to low doses of S. Typhimurium. Despite this crucial role, the mechanisms underlying Nramp1's protective effects are unclear. Dendritic cells (DCs) that sample the intestinal lumen are among the first cells encountered by S. Typhimurium following oral infection and act as a conduit for S. Typhimurium to cross the intestinal epithelial barrier. We report that DCs, including intestinal, splenic and bone marrow-derived DCs (BMDCs), express Nramp1 protein. In the small intestine, Nramp1 expression is greater in a subset of DCs (CD11c(+)CD103(-)) characterized by the elevated expression of pro-inflammatory cytokines in response to bacterial products. While Nramp1 expression did not affect S. Typhimurium replication in BMDCs, infected Nramp1+/+ BMDCs and intestinal CD11c(+)CD103(-) DCs secreted more inflammatory cytokines (IL-6, IL-12 and TNF-alpha) than Nramp1-/-, suggesting that Nramp1 expression may promote a more rapid inflammatory response following infection. Collectively, these findings reveal a new role for DCs and Nramp1 in modulating the host inflammatory response to S. Typhimurium.