SLAM is a microbial sensor that regulates bacterial phagosome functions in macrophages

Integrative and comparative genomic analyses of mammalian macrophage responses to intracellular mycobacterial pathogens

Mycobacterium tuberculosis, the causative agent of human tuberculosis (hTB), is a close evolutionary relative of Mycobacterium bovis, which causes bovine tuberculosis (bTB), one of the most damaging infectious diseases to livestock agriculture. Previous studies have shown that the pathogenesis of bTB disease is comparable to hTB disease, and that the bovine and human alveolar macrophage (bAM and hAM, respectively) transcriptomes are extensively reprogrammed in response to infection with these intracellular mycobacterial pathogens. In this study, a multi-omics integrative approach was applied with functional genomics and GWAS data sets across the two primary hosts (Bos taurus and Homo sapiens) and both pathogens (M. bovis and M. tuberculosis). Four different experimental infection groups were used: 1) bAM infected with M. bovis, 2) bAM infected with M. tuberculosis, 3) hAM infected with M. tuberculosis, and 4) human monocyte-derived macrophages (hMDM) infected with M. tuberculosis. RNA-seq data from these experiments 24 h post-infection (24 hpi) was analysed using three computational pipelines: 1) differentially expressed genes, 2) differential gene expression interaction networks, and 3) combined pathway analysis. The results were integrated with high-resolution bovine and human GWAS data sets to detect novel quantitative trait loci (QTLs) for resistance to mycobacterial infection and resilience to disease. This revealed common and unique response macrophage pathways for both pathogens and identified 32 genes (12 bovine and 20 human) significantly enriched for SNPs associated with disease resistance, the majority of which encode key components of the NF-κB signalling pathway and that also drive formation of the granuloma.

CD150-dependent hematopoietic stem cell sensing of Brucella instructs myeloid commitment

So far, hematopoietic stem cells (HSC) are considered the source of mature immune cells, the latter being the only ones capable of mounting an immune response. Recent evidence shows HSC can also directly sense cytokines released upon infection/inflammation and pathogen-associated molecular pattern interaction while keeping a long-term memory of previously encountered signals. Direct sensing of danger signals by HSC induces early myeloid commitment, increases myeloid effector cell numbers, and contributes to an efficient immune response. Here, by using specific genetic tools on both the host and pathogen sides, we show that HSC can directly sense B. abortus pathogenic bacteria within the bone marrow via the interaction of the cell surface protein CD150 with the bacterial outer membrane protein Omp25, inducing efficient functional commitment of HSC to the myeloid lineage. This is the first demonstration of direct recognition of a live pathogen by HSC via CD150, which attests to a very early contribution of HSC to immune response.

SLAM-family receptors come of age as a potential molecular target in cancer immunotherapy

The signaling lymphocytic activation molecule (SLAM) family receptors were discovered in immune cells for the first time. The SLAM-family receptors are a significant player in cytotoxicity, humoral immune responses, autoimmune diseases, lymphocyte development, cell survival, and cell adhesion. There is growing evidence that SLAM-family receptors have been involved in cancer progression and heralded as a novel immune checkpoint on T cells. Previous studies have reported the role of SLAMs in tumor immunity in various cancers, including chronic lymphocytic leukemia, lymphoma, multiple myeloma, acute myeloid leukemia, hepatocellular carcinoma, head and neck squamous cell carcinoma, pancreas, lung, and melanoma. Evidence has deciphered that the SLAM-family receptors may be targeted for cancer immunotherapy. However, our understanding in this regard is not complete. This review will discuss the role of SLAM-family receptors in cancer immunotherapy. It will also provide an update on recent advances in SLAM-based targeted immunotherapies.

Beclin 1 regulates astrocyte phagocytosis and phagosomal recruitment of retromer

Phagocytosis plays an important role in maintaining brain homeostasis and when impaired can result in the accumulation of unwanted cellular material. While microglia are traditionally considered the phagocytes of the brain, astrocytes are also capable of phagocytosis and are the most numerous cells in the brain. In Alzheimer's disease (AD), astrocytes can be found surrounding β-amyloid (Aβ) plaques yet they seem unable to eliminate these deposits, suggesting phagocytosis may be impaired in AD. Mechanisms that might diminish astrocyte phagocytosis in AD are currently unclear. Here, we demonstrate that the autophagy protein beclin 1, which is reduced in AD, plays a role in regulating astrocyte phagocytosis. Specifically, we show that reducing beclin 1 in C6 astrocytes impairs the phagocytosis of latex beads, reduces retromer levels, and impairs retromer recruitment to the phagosomal membrane. Furthermore, we show that these beclin 1-mediated changes are accompanied by reduced expression of the phagocytic receptor Scavenger Receptor Class B type I (SR-BI). Collectively, these findings suggest a critical role for the protein beclin 1 in both receptor trafficking and receptor-mediated phagocytosis in astrocytes. Moreover, these findings provide insight into mechanisms by which astrocytes may become impaired in AD.

SLAMF7 regulates the inflammatory response in macrophages during polymicrobial sepsis

Uncontrolled inflammation occurred in sepsis results in multiple organ injuries and shock, which contributes to the death of patients with sepsis. However, the regulatory mechanisms that restrict excessive inflammation are still elusive. Here, we identified an Ig-like receptor called signaling lymphocyte activation molecular family 7 (SLAMF7) as a key suppressor of inflammation during sepsis. We found that the expression of SLAMF7 on monocytes/macrophages was significantly elevated in patients with sepsis and in septic mice. SLAMF7 attenuated TLR-dependent MAPK and NF-κB signaling activation in macrophages by cooperating with Src homology 2-containing inositol-5'‑phosphatase 1 (SHIP1). Furthermore, SLAMF7 interacted with SHIP1 and TNF receptor-associated factor 6 (TRAF6) to inhibit K63 ubiquitination of TRAF6. In addition, we found that tyrosine phosphorylation sites within the intracellular domain of SLAMF7 and the phosphatase domain of SHIP1 were indispensable for the interaction between SLAMF7, SHIP1, and TRAF6 and SLAMF7-mediated modulation of cytokine production. Finally, we demonstrated that SLAMF7 protected against lethal sepsis and endotoxemia by downregulating macrophage proinflammatory cytokines and suppressing inflammation-induced organ damage. Taken together, our findings reveal a negative regulatory role of SLAMF7 in polymicrobial sepsis, thus providing sights into the treatment of sepsis.

Signaling Lymphocytic Activation Molecule Family Member 1 Inhibits Porcine Reproductive and Respiratory Syndrome Virus Replication

The porcine reproductive and respiratory syndrome virus (PRRSV) causes a highly contagious disease in domestic swine. Signaling lymphocytic activation molecule family member 1 (SLAMF1) is a costimulatory factor that is involved in innate immunity, inflammation, and infection. Here, we demonstrate that overexpression of the SLAMF1 gene inhibited PRRSV replication significantly and reduced the levels of key signaling pathways, including MyD88, RIG-I, TLR2, TRIF, and inflammatory factors IL-6, IL-1β, IL-8, TNF-β, TNF-α, and IFN-α in vitro. However, the knockdown of the SLAMF1 gene could enhance replication of the PRRSV and the levels of key signaling pathways and inflammatory factors. Overall, our results identify a new, to our knowledge, antagonist of the PRRSV, as well as a novel antagonistic mechanism evolved by inhibiting innate immunity and inflammation, providing a new reference and direction for PRRSV disease resistance breeding.

Safety assessment of compliant, highly invasive, lipid A-altered, O-antigen-defected Salmonella strains as prospective vaccine delivery systems

In the present study, two prospective Salmonella delivery strains, JOL2782 and JOL2837, were developed by gene deletions of lon and cpxR, which are related to cellular adhesion and intracellular survival. Additionally, sifA deletion was introduced for JOL2782, which confers immune susceptibility and improves antigen delivery. Similarly, the rfaL deletion and lpxE substitution for pagL were accomplished in JOL2837 to reduce virulence and endotoxicity. Thus, enhanced adhesion and invasion and reduced intracellular survival were attained. Furthermore, aspartic acid auxotrophic (asd) was deleted to impose Darwinian selection on retention of the foreign antigen-expressing plasmid. Both delivery strains induced sufficient cytokine expression, but the level was significantly lower than that of the wild-type strain; the lowest cytokine expression was induced by the JOL2837 strain, indicating reduced endotoxicity. In parallel, IgG production was significantly enhanced by both delivery strains. Thus, the innate and adaptive immunogenicity of the strains was ensured. The environmental safety of these strains was ascertained through faecal dissemination assays. The nonpathogenicity of these strains to the host was confirmed by body weight monitoring, survival assays, and morphological and histological assessments of the vital organs. The in vitro assay in murine and human cell lines and in vivo safety assessments in mice suggest that these novel strains possess safety, invasiveness, and immunogenicity, making them ideal delivery strains. Overall, the results clearly showed that strain JOL2782 with sifA deletion had higher invasiveness, demonstrating superior vaccine deliverability, while JOL2837 with lpxE substitution for pagL and rfaL deletion had outstanding safety potential with drastically abridged endotoxicity.

Immunosuppressive Mechanisms in Brucellosis in Light of Chronic Bacterial Diseases

Brucellosis is considered one of the major zoonoses worldwide, constituting a critical livestock and human health concern with a huge socio-economic burden. Brucella genus, its etiologic agent, is composed of intracellular bacteria that have evolved a prodigious ability to elude and shape host immunity to establish chronic infection. Brucella’s intracellular lifestyle and pathogen-associated molecular patterns, such as its specific lipopolysaccharide (LPS), are key factors for hiding and hampering recognition by the immune system. Here, we will review the current knowledge of evading and immunosuppressive mechanisms elicited by Brucella species to persist stealthily in their hosts, such as those triggered by their LPS and cyclic β-1,2-d-glucan or involved in neutrophil and monocyte avoidance, antigen presentation impairment, the modulation of T cell responses and immunometabolism. Attractive strategies exploited by other successful chronic pathogenic bacteria, including Mycobacteria, Salmonella, and Chlamydia, will be also discussed, with a special emphasis on the mechanisms operating in brucellosis, such as granuloma formation, pyroptosis, and manipulation of type I and III IFNs, B cells, innate lymphoid cells, and host lipids. A better understanding of these stratagems is essential to fighting bacterial chronic infections and designing innovative treatments and vaccines.

Oxidative stress activates transcription of Salmonella pathogenicity island-2 genes in macrophages

The type III secretion system encoded in the Salmonella pathogenicity island-2 (SPI-2) gene cluster facilitates intracellular growth of nontyphoidal Salmonella by interfering with the maturation of Salmonella-containing vacuoles along the degradative pathway. SPI-2 gene products also protect Salmonella against the antimicrobial activity of reactive oxygen species (ROS) synthesized by the phagocyte NADPH oxidase 2 (NOX2). However, a potential relationship between inflammatory ROS and the activation of transcription of SPI-2 genes by intracellular Salmonella is unclear. Here, we show that ROS engendered in the innate host response stimulate SPI-2 gene transcription. We found that the expression of SPI-2 genes in Salmonella-sustaining oxidative stress conditions involves DksA, a protein otherwise known to regulate the stringent response of bacteria to nutritional stress. We also demonstrate that the J and zinc-2-oxidoreductase domains of DnaJ as well as the ATPase activity of the DnaK chaperone facilitate loading of DksA onto RNA polymerase complexed with SPI-2 promoters. Furthermore, the DksA-driven transcription of SPI-2 genes in Salmonella experiencing oxidative stress is contingent on upstream OmpR, PhoP, and SsrB signaling events that participate in the removal of nucleoid proteins while simultaneously recruiting RNA polymerase to SPI-2 promoter regions. Taken together, our results suggest the activation of SPI-2 gene transcription in Salmonella subjected to ROS produced by the respiratory burst of macrophages protects this intracellular pathogen against NOX2-mediated killing. We propose that Salmonella have co-opted inflammatory ROS to induce SPI-2-mediated protective responses against NOX2 host defenses.

Soluble C-Type Lectin-Receptor Ligands Stimulate ROS Production in Dendritic Cells and Potentiate Killing of MRSA as Well as the MRSA Induced IL-12 Production

Methicillin resistant Staphylococcus aureus (MRSA) has developed resistance to most β-lactam antibiotics leaving few treatment options against infections with MRSA. Through mannose receptors, mannan potentiates IL-12 production induced by Gram-positive bacteria, a cytokine crucial in the clearance of S. aureus infection. We investigated the IL-12 potentiating effect of mannan pre-treatment of bone marrow-derived dendritic cells prior to stimulation with clinical MRSA strains. Mannan almost doubled IL-12 as well as IFN-β production in response to USA300, also when USA300 was treated with the β-lactam cefoxitin. The MRSA-induced IL-12 production was dependent on bacterial uptake and reactive oxygen species (ROS). Mannan alone induced ROS production, and in combination with USA300, the ROS produced corresponded to the sum induced by mannan and USA300. Addition of a monoclonal antibody against the mannose receptor likewise enhanced USA300-induced IL-12 and induced ROS production. Mannan addition further increased the endocytosis as well as the rate of endosomal killing of bacteria. Pre-treatment with soluble β-glucans also induced ROS and potentiated the USA300-induced IL-12 indicating that other C-type receptors may play a similar role. In the presence of the pro-inflammatory mediators, GM-CSF or IFN-γ, the mannan-enhanced IL-12 production increased further. The USA300-induced and the mannan-facilitated enhanced IFN-β and IL-12 showed same dependency on MAPK c-Jun N-terminal kinase signaling, suggesting that mannan enhances the signals already induced by the bacteria, rather than changing them. We suggest that the C-type lectin-induced ROS production is a key factor in the IFN-β and IL-12 potentiation.

SLAMF1 Is Dispensable for Vaccine-Induced T Cell Development but Required for Resistance to Fungal Infection

Homotypic signaling lymphocyte activation molecule (SLAM) receptor-ligand cell surface interactions between myeloid and lymphoid cells regulate innate and adaptive immune responses. In this article, we report that SLAMF1 is indispensable for host resistance to primary and vaccine-induced protection against fungal infection. Because vaccine immunity is dependent on cell-mediated immunity, we investigated the development of Ag-specific T cells. We studied the T cell-intrinsic and -extrinsic role of SLAMF1. We generated SLAMF1^-/- TCR transgenic mice and analyzed the responses of adoptively transferred T cells. We also tracked endogenous Ag-specific T cells by using a tetramer. Intrinsic and extrinsic SLAMF1 signaling was dispensable for the development of antifungal Th1 and Th17 cells, which are requisite for the acquisition of vaccine-induced immunity. Despite intact T cell development, vaccinated SLAMF1^-/- mice failed to control fungal infection. Failed accumulation of Ag-specific T cells in the lung on infection of vaccinated mice was due to uncontrolled early infection and inflammation, revealing a role for SLAMF1 in innate host immunity.

Shedding Light on Autophagy During Human Tuberculosis. A Long Way to Go

Immunity against Mycobacterium tuberculosis (Mtb) is highly complex, and the outcome of the infection depends on the role of several immune mediators with particular temporal dynamics on the host microenvironment. Autophagy is a central homeostatic mechanism that plays a role on immunity against intracellular pathogens, including Mtb. Enhanced autophagy in macrophages mediates elimination of intracellular Mtb through lytic and antimicrobial properties only found in autolysosomes. Additionally, it has been demonstrated that standard anti-tuberculosis chemotherapy depends on host autophagy to coordinate successful antimicrobial responses to mycobacteria. Notably, autophagy constitutes an anti-inflammatory mechanism that protects against endomembrane damage triggered by several endogenous components or infectious agents and precludes excessive inflammation. It has also been reported that autophagy can be modulated by cytokines and other immunological signals. Most of the studies on autophagy as a defense mechanism against Mycobacterium have been performed using murine models or human cell lines. However, very limited information exists about the autophagic response in cells from tuberculosis patients. Herein, we review studies that face the autophagy process in tuberculosis patients as a component of the immune response of the human host against an intracellular microorganism such as Mtb. Interestingly, these findings might contribute to recognize new targets for the development of novel therapeutic tools to combat Mtb. Actually, either as a potential successful vaccine or a complementary immunotherapy, efforts are needed to further elucidate the role of autophagy during the immune response of the human host, which will allow to achieve protective and therapeutic benefits in human tuberculosis.

SLAMF8 Downregulates Mouse Macrophage Microbicidal Mechanisms via PI3K Pathways

Signaling lymphocytic activation molecule family 8 (SLAMF8) is involved in the negative modulation of NADPH oxidase activation. However, the impact of SLAMF8 downregulation on macrophage functionality and the microbicide mechanism remains elusive. To study this in depth, we first analyzed NADPH oxidase activation pathways in wild-type and SLAMF8-deficient macrophages upon different stimulus. Herein, we describe increased phosphorylation of the Erk1/2 and p38 MAP kinases, as well as increased phosphorylation of NADPH oxidase subunits in SLAMF8-deficient macrophages. Furthermore, using specific inhibitors, we observed that specific PI3K inhibition decreased the differences observed between wild-type and SLAMF8-deficient macrophages, stimulated with either PMA, LPS, or Salmonella typhimurium infection. Consequently, SLAMF8-deficient macrophages also showed increased recruitment of small GTPases such as Rab5 and Rab7, and the p47^phox subunit to cytoplasmic Salmonella, suggesting an impairment of Salmonella-containing vacuole (SCV) progression in SLAMF8-deficient macrophages. Enhanced iNOS activation, NO production, and IL-6 expression were also observed in the absence of SLAMF8 upon Salmonella infection, either in vivo or in vitro, while overexpression of SLAMF8 in RAW264.7 macrophages showed the opposite phenotype. In addition, SLAMF8-deficient macrophages showed increased activation of Src kinases and reduced SHP-1 phosphate levels upon IFNγ and Salmonella stimuli in comparison to wild-type macrophages. In agreement with in vitro results, Salmonella clearance was augmented in SLAMF8-deficient mice compared to that in wild-type mice. Therefore, in conclusion, SLAMF8 intervention upon bacterial infection downregulates mouse macrophage activation, and confirmed that SLAMF8 receptor could be a potential therapeutic target for the treatment of severe or unresolved inflammatory conditions.

The Manifold Roles of Sphingolipids in Viral Infections

Sphingolipids are essential components of eukaryotic cells. In this review, we want to exemplarily illustrate what is known about the interactions of sphingolipids with various viruses at different steps of their replication cycles. This includes structural interactions during entry at the plasma membrane or endosomal membranes, early interactions leading to sphingolipid-mediated signal transduction, interactions with internal membranes and lipids during replication, and interactions during virus assembly and budding. Targeted interventions in sphingolipid metabolism - as far as they can be tolerated by cells and organisms - may open novel possibilities to support antiviral therapies. Human immunodeficiency virus type 1 (HIV-1) infections have intensively been studied, but for other viral infections, such as influenza A virus (IAV), measles virus (MV), hepatitis C virus (HCV), dengue virus, Ebola virus, and severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), investigations are still in their beginnings. As many inhibitors of sphingolipid metabolism are already in clinical use against other diseases, repurposing studies for applications in some viral infections appear to be a promising approach.

Myeloid-Derived Suppressor Cells in Trypanosoma cruzi Infection

Myeloid-derived suppressor cells (MDSCs) are immature heterogeneous myeloid cells that expand in pathologic conditions as cancer, trauma, and infection. Although characterization of MDSCs is continuously revisited, the best feature is their suppressor activity. There are many markers for MDSC identification, it is distinctive that they express inducible nitric oxide synthase (iNOS) and arginase 1, which can mediate immune suppression. MDSCs can have a medullary origin as a result of emergency myelopoiesis, but also can have an extramedullary origin. Early studies on Trypanosoma cruzi infection showed severe immunosuppression, and several mechanisms involving parasite antigens and host cell mediators were described as inhibition of IL-2 and IL-2R. Another mechanism of immunosuppression involving tumor necrosis factor/interferon γ-dependent nitric oxide production by inducible nitric oxide synthase was also described. Moreover, other studies showed that nitric oxide was produced by CD11b⁺ Gr-1⁺ MDSCs in the spleen, and later iNOS and arginase 1 expressed in CD11b⁺Ly6C⁺Ly6G^lo monocytic MDSC were found in spleen and heart of T. cruzi infected mice that suppressed T cell proliferation. Uncontrolled expansion of monocytic MDSCs leads to L-arginine depletion which hinders nitric oxide production leading to death. Supplement of L-arginine partially reverts L-arginine depletion and survival, suggesting that L-arginine could be administered along with anti-parasitical drugs. On the other hand, pharmacological inhibition of MDSCs leads to death in mice, suggesting that some expansion of MDSCs is needed for an efficient immune response. The role of signaling molecules mediating immune suppression as reactive oxygen species, reactive nitrogen species, as well as prostaglandin E2, characteristics of MDSCs, in T. cruzi infection is not fully understood. We review and discuss the role of these reactive species mediators produced by MDSCs. Finally, we discuss the latest results that link the SLAMF1 immune receptor with reactive oxygen species. Interaction of the parasite with the SLAMF1 modulates parasite virulence through myeloid cell infectivity and reactive oxygen species production. We discuss the possible strategies for targeting MDSCs and SLAMF1 receptor in acute Trypanosoma cruzi infection in mice, to evaluate a possible translational application in human acute infections.

Sphingolipids: Effectors and Achilles Heals in Viral Infections?

As viruses are obligatory intracellular parasites, any step during their life cycle strictly depends on successful interaction with their particular host cells. In particular, their interaction with cellular membranes is of crucial importance for most steps in the viral replication cycle. Such interactions are initiated by uptake of viral particles and subsequent trafficking to intracellular compartments to access their replication compartments which provide a spatially confined environment concentrating viral and cellular components, and subsequently, employ cellular membranes for assembly and exit of viral progeny. The ability of viruses to actively modulate lipid composition such as sphingolipids (SLs) is essential for successful completion of the viral life cycle. In addition to their structural and biophysical properties of cellular membranes, some sphingolipid (SL) species are bioactive and as such, take part in cellular signaling processes involved in regulating viral replication. It is especially due to the progress made in tools to study accumulation and dynamics of SLs, which visualize their compartmentalization and identify interaction partners at a cellular level, as well as the availability of genetic knockout systems, that the role of particular SL species in the viral replication process can be analyzed and, most importantly, be explored as targets for therapeutic intervention.

Single-cell transcriptomic landscape reveals tumor specific innate lymphoid cells associated with colorectal cancer progression

Innate lymphoid cells (ILCs) are tissue-resident lymphocytes differing from conventional T lymphocytes in having no antigen-specific receptors. ILCs include natural killer (NK) cells, helper-like ILC1s, ILC2s, and ILC3s, and lymphoid tissue-inducer (LTi) cells. Tumor ILCs are frequently found in various cancers, but their roles in cancer immunity and immunotherapy remain largely unclear. We report here the single-cell characterization of blood and gut helper-like ILC subsets in healthy conditions and in colorectal cancer (CRC). The healthy gut contains ILC1s, ILC3s, and ILC3/NKs, but no ILC2s. Additional tumor-specific ILC1-like and ILC2 subsets were identified in CRC patients. Signaling lymphocytic activation molecule family member 1 (SLAMF1) was found to be selectively expressed on tumor-specific ILCs, and higher levels of SLAMF1⁺ ILCs were observed in the blood of CRC patients. The SLAMF1-high group of CRC patients had a significantly higher survival rate than the SLAMF1-low group, suggesting that SLAMF1 is an anti-tumor biomarker in CRC.

Healthy gut contains ILC1s, ILC3s, and ILC3/NKs, but no ILC2s

Blood and tumor ILCs from CRC patients have unique transcriptomic features

Tumor tissue from CRC patients contains a tumor specific ILC1-like subset and ILC2s

SLAMF1 is identified as an anti-tumor biomarker in CRC

Knockdown of VDAC1 alleviates the cognitive dysfunction secondary to sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a serious and diffuse cerebral dysregulation with a high morbidity and mortality caused by sepsis. Mitophagy plays an important role in SAE, and microglial phagocytosis of apoptotic cells (efferocytosis) is the core of the brain regenerative response. Voltage dependent anion channel (VDAC1) is an important regulator of mitophagy. However, it remains unknown whether VDAC1 influences SAE progression by regulating mitophagy and efferocytosis. Herein, we explored the mechanism where knockdown of VDAC1 alleviated the cognitive dysfunction caused by sepsis-associated encephalopathy and further elucidated the underlying molecular mechanisms. SAE model in mice was established through caecal ligation and puncture (CLP). The increased mitophagy and decreased efferocytosis were observed by the transmission electron microscope (TEM) in the SAE model. Besides, immunoblot tests showed an interaction between autophagy and efferocytosis. Further behavior tests and TEM results indicated that knockdown of VDAC1 alleviated the cognitive dysfunction by decreasing the autophagy and increasing the efferocytosis in a PINK1/Parkin-dependent manner. Based on these results, we conclude that knockdown of VDAC1 alleviates the cognitive dysfunction in the CLP-induced SAE mouse model.

Effect of the Electromagnetic Field (EMF) Radiation on Transcriptomic Profile of Pig Myometrium during the Peri-Implantation Period-An In Vitro Study

The electromagnetic field (EMF) affects the physiological processes in mammals, but the molecular background of the observed alterations remains not well established. In this study was tested the effect of short duration (2 h) of the EMF treatment (50 Hz, 8 mT) on global transcriptomic alterations in the myometrium of pigs during the peri-implantation period using next-generation sequencing. As a result, the EMF treatment affected the expression of 215 transcript active regions (TARs), and among them, the assigned gene protein-coding biotype possessed 90 ones (differentially expressed genes, DEGs), categorized mostly to gene ontology terms connected with defense and immune responses, and secretion and export. Evaluated DEGs enrich the KEGG TNF signaling pathway, and regulation of IFNA signaling and interferon-alpha/beta signaling REACTOME pathways. There were evaluated 12 differentially expressed long non-coding RNAs (DE-lnc-RNAs) and 182 predicted single nucleotide variants (SNVs) substitutions within RNA editing sites. In conclusion, the EMF treatment in the myometrium collected during the peri-implantation period affects the expression of genes involved in defense and immune responses. The study also gives new insight into the mechanisms of the EMF action in the regulation of the transcriptomic profile through lnc-RNAs and SNVs.

Klebsiella pneumoniae Lipopolysaccharides Serotype O2afg Induce Poor Inflammatory Immune Responses Ex Vivo

Currently, Klebsiella pneumoniae is a pathogen of clinical relevance due to its plastic ability of acquiring resistance genes to multiple antibiotics. During K. pneumoniae infections, lipopolysaccharides (LPS) play an ambiguous role as they both activate immune responses but can also play a role in immune evasion. The LPS O2a and LPS O2afg serotypes are prevalent in most multidrug resistant K. pneumoniae strains. Thus, we sought to understand if those two particular LPS serotypes were involved in a mechanism of immune evasion. We have extracted LPS (serotypes O1, O2a and O2afg) from K. pneumoniae strains and, using human monocytes ex vivo, we assessed the ability of those LPS antigens to induce the production of pro-inflammatory cytokines and chemokines. We observed that, when human monocytes are incubated with LPS serotypes O1, O2a or O2afg strains, O2afg and, to a lesser extent, O2a but not O1 failed to elicit the production of pro-inflammatory cytokines and chemokines, which suggests a role in immune evasion. Our preliminary data also shows that nuclear translocation of NF-κB, a process which regulates an immune response against infections, occurs in monocytes incubated with LPS O1 and, to a smaller extent, with LPS O2a, but not with the LPS serotype O2afg. Our results indicate that multidrug resistant K. pneumoniae expressing LPS O2afg serotypes avoid an initial inflammatory immune response and, consequently, are able to systematically spread inside the host unharmed, which results in the several pathologies associated with this bacterium.

Clinical characteristics and long-term outcome of E. coli-associated granulomatous ileocolitis in dogs: five cases (2010-2014)

OBJECTIVES

To describe the clinical characteristics and long-term outcome of Escherichia coli-associated granulomatous ileocolitis in dogs.

METHODS

Retrospective review of medical records from dogs with periodic acid-Schiff positive (PAS+) granulomatous ileocolitis and mucosally invasive E. coli in the ileum and colon. Initial bacterial colonisation was evaluated using fluorescence in situ hybridization (FISH) in all dogs and corroborated with colonic and/or ileal culture, when performed.

RESULTS

Four boxer dogs and 1 French Bulldog with PAS+ granulomatous ileocolitis (GIC) were evaluated. All dogs had chronic diarrhoea refractory to empirical therapy. Ileocolonoscopy revealed mucosal haemorrhage and ulceration in the ileum (3/4) and colon (5/5). E. coli were visualised as clusters within the ileal and colonic mucosa. Complete (CR, 4/5) or partial (PR, 1/5) clinical response to fluoroquinolones was noted in all dogs within 30 days. CR was sustained in three of four dogs (median disease-free interval 40 months, range 16 to 60). Two dogs relapsed while receiving fluoroquinolones. Repeat biopsy isolated multidrug-resistant, mucosally invasive E. coli in the ileum (1/2) and colon (2/2). Targeted antimicrobial therapy was associated with long-term PR (78 months) in both dogs.

CLINICAL SIGNIFICANCE

Concurrent E. coli-associated granulomatous inflammation in the ileum and colon did not impart a poor clinical outcome or lack of response to the conventional standard of care for granulomatous colitis in dogs that were aggressively diagnosed and treated. Clinical outcome was influenced by antimicrobial resistance, with response dependent upon antimicrobial therapy informed by susceptibility testing.

Gold Nanoparticles and Graphene Oxide Flakes Synergistic Partaking in Cytosolic Bactericidal Augmentation: Role of ROS and NOX2 Activity

Gold nanoparticles (GNPs) and graphene oxide flakes (GOFs) exerted significantly (p < 0.0001) supportive roles on the phagocytosis bioactivity of the immune cells of phagocytic nature against the Gram-positive and Gram-negative human pathogenic bacteria Staphylococcus aureus and Escherichia coli. Under experimental conditions, upon bacterial exposure, the combined GNPs and GOFs induced significant clearance of bacteria through phagosome maturation (p < 0.0001) from time-points of 6 to 30 min and production of reactive oxygen species (ROS, p < 0.0001) through the NADPH oxidase 2 (NOX2, p < 0.0001)-based feedback mechanism. The effects of the combined presence of GNPs and GOFs on phagocytosis (p < 0.0001) suggested a synergistic action underway, also achieved through elevated signal transduction activity in the bone-marrow-derived macrophages (BMDM, p < 0.0001). The current study demonstrated that GNPs’ and GOFs’ bactericidal assisting potentials could be considered an effective and alternative strategy for treating infections from both positive and negative bacterial strains.

The Manifold Roles of Sphingolipids in Viral Infections

Sphingolipids are essential components of eukaryotic cells. In this review, we want to exemplarily illustrate what is known about the interactions of sphingolipids with various viruses at different steps of their replication cycles. This includes structural interactions during entry at the plasma membrane or endosomal membranes, early interactions leading to sphingolipid-mediated signal transduction, interactions with internal membranes and lipids during replication, and interactions during virus assembly and budding. Targeted interventions in sphingolipid metabolism - as far as they can be tolerated by cells and organisms - may open novel possibilities to support antiviral therapies. Human immunodeficiency virus type 1 (HIV-1) infections have intensively been studied, but for other viral infections, such as influenza A virus (IAV), measles virus (MV), hepatitis C virus (HCV), dengue virus, Ebola virus, and severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), investigations are still in their beginnings. As many inhibitors of sphingolipid metabolism are already in clinical use against other diseases, repurposing studies for applications in some viral infections appear to be a promising approach.

Escherichia coli-associated granulomatous colitis in dogs treated according to antimicrobial susceptibility profiling

Background

Eradication of intramucosal Escherichia coli correlates with remission of periodic acid‐Schiff‐positive E coli‐associated granulomatous colitis (GC). Treatment failures attributed to multidrug resistant (MDR) bacteria necessitate alternative approaches.

Hypothesis/objectives

Determine clinical outcome of E coli‐associated GC in dogs treated based on antimicrobial susceptibility profiling and characterize E coli phylogeny and resistance mechanisms.

Animals

Twenty Boxers and 4 French Bulldogs with E coli‐associated GC.

Methods

Culture, antimicrobial susceptibility profiling, and molecular characterization of E coli were performed and response to treatment was evaluated.

Results

Initial biopsy sample culture yielded fluoroquinolone‐sensitive (FQ‐S) E coli from 9/24 dogs and fluoroquinolone‐resistant (FQ‐R) E coli from 15/24. All but 1 FQ‐R E coli were MDR with susceptibility to macrophage‐penetrating antimicrobials restricted to carbapenems in 13/15 dogs. Of 22/24 treated based on susceptibility profiling, 8/9 FQ‐S dogs had complete initial clinical response (CR) during fluoroquinolone (FQ) treatment, whereas 9/13 FQ‐R dogs had complete or partial response (PR) during meropenem or doxycycline treatment. In 5/9 FQ‐S and 12/13 FQ‐R dogs with follow‐up ≥3 months, CR was sustained in 5/5 FQ‐S (median, 25 months; range, 4‐46) whereas 6/12 FQ‐R had long‐term CR (median, 59 months; range 15‐102), 4/12 PR (median, 19 months; range, 5‐65), and 2/12 had no response (NR). Four dogs with long‐term follow‐up died within 4 years of diagnosis, including 2 euthanized for refractory colitis. Escherichia coli were genetically diverse. Fluoroquinolone resistance was associated with mutations in gyrA and parC, with plasmid‐mediated resistance less common.

Conclusions and Clinical Importance

Antimicrobial treatment guided by susceptibility profiling was associated with positive long‐term outcomes in >80% of cases. Fluoroquinolone‐resistance was widespread and not clonal. Further study is required to optimize treatment for dogs with MDR E coli‐associated GC.

Microbiota-Derived Short-Chain Fatty Acids Promote LAMTOR2-Mediated Immune Responses in Macrophages

ABSRTACTKlebsiella pneumoniae is a common cause of human-pneumonia-derived sepsis with high morbidity and mortality. The microbiota promotes and maintains host immune homeostasis. The mechanisms by which the gut microbiota affects the host defenses in the respiratory system systematically, however, remain poorly understood. Here, we show that gut microbiota depletion increases susceptibility to extracellular K. pneumoniae infections in terms of increased bacterial burdens in lung and decreased survival rates. Oral supplementation with gut microbiota-derived short-chain fatty acids (SCFAs), subsequently activating G protein-coupled receptor 43 (GPCR43), enhances a macrophage's capacity to phagocytose invading K. pneumoniae Furthermore, SCFAs and GPR43 increase macrophage bacterial clearance by upregulating LAMTOR2, which is further identified as an antibacterial effector and elucidated to facilitate phagosome-lysosome fusion and extracellular signal-regulated kinase (ERK) phosphorylation. Lastly, conditional ablation of Lamtor2 in macrophages decreases their antimicrobial activity, even though mice were pretreated with exogenous SCFA supplementation.IMPORTANCE These observations highlight that SCFAs promote macrophage elimination of K. pneumoniae via a LAMTOR2-dependent signal pathway and suggest that it is possible to intervene in K. pneumoniae pneumonia by targeting the gut microbiota.

Neutrophil autophagy during human active tuberculosis is modulated by SLAMF1

Neutrophils infected with Mycobacterium tuberculosis (Mtb) predominate in tuberculosis patients' lungs. Neutrophils phagocytose the pathogen, but the mechanism of pathogen elimination is controversial. Macroautophagy/autophagy, a crucial mechanism for several neutrophil functions, can be modulated by immunological mediators. The costimulatory molecule SLAMF1 can act as a microbial sensor in macrophages being also able to interact with autophagy-related proteins. Here, we demonstrate for the first time that human neutrophils express SLAMF1 upon Mtb-stimulation. Furthermore, SLAMF1 was found colocalizing with LC3B⁺ vesicles, and activation of SLAMF1 increased neutrophil autophagy induced by Mtb. Finally, tuberculosis patients' neutrophils displayed reduced levels of SLAMF1 and lower levels of autophagy against Mtb as compared to healthy controls. Altogether, these results indicate that SLAMF1 participates in neutrophil autophagy during active tuberculosis.Abbreviations: AFB: acid-fast bacilli; BafA1: bafilomycin A₁; CLL: chronic lymphocytic leukemia; DPI: diphenyleneiodonium; EVs: extracellular vesicles; FBS: fetal bovine serum; HD: healthy donors; HR: high responder (tuberculosis patient); IFNG: interferon gamma; IL1B: interleukin 1 beta; IL17A: interleukin 17A; IL8: interleukin 8; LR: low responder (tuberculosis patient); mAb: monoclonal antibody; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAPK: mitogen-activated protein kinase; MAPK1/ERK2: mitogen-activated protein kinase 1; MAPK14/p38: mitogen-activated protein kinase 14; Mtb: Mycobacterium tuberculosis; Mtb-Ag: Mycobacterium tuberculosis, Strain H37Rv, whole cell lysate; NETs: neutrophils extracellular traps; PPD: purified protein derivative; ROS: reactive oxygen species; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; SLAMF1: signaling lymphocytic activation molecule family member 1; TB: tuberculosis; TLR: toll like receptor.

SLAMF1 signaling induces Mycobacterium tuberculosis uptake leading to endolysosomal maturation in human macrophages

Tuberculosis dates back to ancient times but it is not a problem of the past. Each year, millions of people die from tuberculosis. After inhalation of infectious droplet nuclei, Mycobacterium tuberculosis reaches the lungs where it can manipulate the immune system and survive within host macrophages, establishing a persistent infection. The signaling lymphocytic activation molecule family member 1 (SLAMF1) is a self-ligand receptor that can internalize gram-negative bacteria and regulate macrophages' phagosomal functions. In tuberculosis, SLAMF1 promotes Th1-protective responses. In this work, we studied the role of SLAMF1 on macrophages' functions during M. tuberculosis infection. Our results showed that both M. tuberculosis and IFN-γ stimulation induce SLAMF1 expression in macrophages from healthy donor and Tohoku Hospital Pediatrcs-1 cells. Costimulation through SLAMF1 with an agonistic antibody resulted in an enhanced internalization of M. tuberculosis by macrophages. Interestingly, we found that SLAMF1 interacts with M. tuberculosis and colocalizes with the bacteria and with early and late endosomes/lysosomes markers (EEA1 and LAMP2), suggesting that SLAMF1 recognize M. tuberculosis and participate in the endolysosomal maturation process. Notably, increased levels of SLAMF1 were detected in CD14 cells from pleural effusions of tuberculosis patients, indicating that SLAMF1 might have an active function at the site of infection. Taken together, our results provide evidence that SLAMF1 improves the uptake of M. tuberculosis by human monocyte-derived macrophages.

Interaction of Signaling Lymphocytic Activation Molecule Family 1 (SLAMF1) receptor with Trypanosoma cruzi is strain-dependent and affects NADPH oxidase expression and activity

The receptor Signaling Lymphocyte-Activation Molecule Family 1 (SLAMF1) controls susceptibility to Infection by the lethal Trypanosoma cruzi Y strain. To elucidate whether genetic diversity of the parasite was related with disease susceptibility, we further analyzed the role of SLAMF1 using 6 different Trypanosoma cruzi strains including Y. The interaction of SLAMF1 receptor with T. cruzi was evidenced by fluorescence microscopy, flow cytometry and quantitative PCR. All the strains, except VFRA, showed a decrease in parasite load in infected macrophages in Slamf1^-/- compared to BALB/c. In macrophages gene expression NADPH oxidase (NOX2), and reactive oxygen species (ROS) production increased in Slamf1^-/- compared to BALB/c in 5 out of 6 strains. However, Slamf1^-/-macrophages infected with VFRA strain exhibited a divergent behavior, with higher parasite load, lower NOX2 expression and ROS production compared to BALB/c. Parasitological and immunological studies in vivo with Y strain showed that in the absence of SLAMF1 the immune response protected mice from the otherwise lethal Y infection favoring a proinflammatory response likely involving CD4, CD8, dendritic cells and classically activated macrophages. In the case of VFRA, no major changes were observed in the absence of SLAMF1. Thus, the results suggest that the T. cruzi affects SLAMF1-dependent ROS production, controlling parasite replication in macrophages and affecting survival in mice in a strain-dependent manner. Further studies will focus in the identification of parasite molecules involved in SLAMF1 interaction to explain the immunopathogenesis of the disease.

Chagas disease, caused by Trypanosoma cruzi, is characterized by an acute phase, with low mortality, and after many years without any sign of disease, patients develop a symptomatic chronic phase, characterized by cardiomyopathy and/or digestive mega syndromes. These differences have been attributed to the high genetic variability of this parasite. We have shown that the receptor Signaling Lymphocyte-Activation Molecule Family 1 (SLAMF1) controls susceptibility to Infection by the lethal T. cruzi Y strain. Here we studied in detail the immunopathogenic role of SLAMF1 using 6 genetically diverse strains of T. cruzi using in vitro and in vivo approaches. Our results indicate an important role of SLAMF1 in T. cruzi infection which is parasite strain-dependent. We found that parasites interact with SLAMF1 in macrophages affecting NADPH oxidase (NOX2) expression and reactive oxygen species (ROS) production 5 out of 6 strains tested. Y and VFRA strains showed a divergent behavior in vitro and the role of SLAMF1 in the in vivo infection was also strikingly different. The Y strain caused 70% mortality in BALB/c mice but not in Slamf1^-/- mice. The proinflammatory response was stronger in the last, suggesting that SLAMF1 was repressing protective immune responses of mice infected with the Y strain. In contrast, for VFRA, SLAMF1 deficiency resulted in 100% survival of BALB/c mice, without major changes in the immune response in the absence of SLAMF1. Thus, the results indicate that SLAMF1 receptor interacts with T. cruzi, affecting parasite replication and ROS production in macrophages as well as the adaptive immune response in mice in a parasite strain-dependent manner. Future studies will focus in understanding the immunopathogenic role of SLAMF1 during T. cruzi infection.

SLAMF1 contributes to cell survival through the AKT signaling pathway in Farage cells

SLAMF1 is often overexpressed in Epstein Barr virus (EBV)-infected B cell tumors. However, its role in the pathogenesis of EBV-infected B cell tumors remains largely unknown. Here, we generated SLAMF1-deficient EBV+ tumor cells and examined the effect of its deficiency on cell proliferation and cell survival. There were no significant differences in cell proliferation and cell cycle distribution for short periods between the SLAMF1-deficient and wild-type cells. However, the deficient cells were more resistant to an AKT inhibitor (MK-2206). When the both cells were co-cultured and repeatedly exposed to the limitations in nutrition and growth factors, the SLAMF1-deficient cells were gradually decreased. We observed that levels of phospho-AKT were differentially regulated according to the nutritional status between the SLAMF1-deficient and wild-type cells. A decrease in phospho-AKT was observed in SLAMF1-deficient cells as well as an increase in pro-apoptotic Bim just before cell passage, which may have been due to the loss of SLAMF1 under poor growth condition. Overall, SLAMF1 is not a strong survival factor, but it seems to be necessary for cell survival in unfavorable growth condition.

Molecular and Phenotypic Characterization of Escherichia coli Associated with Granulomatous Colitis of Boxer Dogs

Invasive Escherichia coli is causally associated with granulomatous colitis (GC) of Boxer dogs and French Bulldogs. The virulence determinants of GC E. coli are unclear. E. coli isolated from 16 GC (36 strains) and 17 healthy control (HC: 33 strains) dogs were diverse in phylogeny, genotype, and serotype and lacked diarrheagenic genes. Genes encoding type II (gsp), IV (traC), and VI (hcp) secretion systems, long polar fimbriae (lpfA154/141), and iron acquisition (fyuA, chuA) were frequent in GC and HC. E. coli from 14/15 GC and 10/11 HC invaded Caco-2 better than non-pathogenic E. coli strain DH5α, with invasion correlated with motility and presence of chuA and colV. E. coli from all GC and 10/11 HC survived better than DH5α in J774 macrophages, with adherent-invasive E. coli (AIEC) in 60% GC and 73% HC. AIEC replicated in monocyte derived macrophages from a GC Boxer with CD48/SLAM risk haplotype but not the HC. Fluroquinolone resistant E. coli were less motile and invasive than fluoroquinolone sensitive (p < 0.05), and only 1/8 resistant strains met criteria for AIEC. In conclusion GC E. coli are diverse, resemble extraintestinal pathogenic E. coli (ExPEC), including AIEC, and can replicate in GC-susceptible macrophages. They are likely resident pathosymbionts that can opportunistically persist within macrophages of a GC-susceptible dog.

Signalling lymphocyte activation molecule family member 9 is found on select subsets of antigen-presenting cells and promotes resistance to Salmonella infection

Signalling lymphocyte activation molecule family member 9 (SLAMF9) is an orphan receptor of the CD2/SLAM family of leucocyte surface proteins. Examination of SLAMF9 expression and function indicates that SLAMF9 promotes inflammation by specialized subsets of antigen‐presenting cells. Within healthy liver and circulating mouse peripheral blood mononuclear cells, SLAMF9 is expressed on CD11b⁺, Ly6C⁻, CD11c^low, F4/80^low, MHC‐II⁺, CX₃CR1⁺ mononuclear phagocytes as well as plasmacytoid dendritic cells. In addition, SLAMF9 can be found on peritoneal B1 cells and small (F4/80^low), but not large (F4/80^high), peritoneal macrophages. Upon systemic challenge with Salmonella enterica Typhimurium, Slamf9^−/− mice were impaired in their ability to clear the infection from the liver. In humans, SLAMF9 is up‐regulated upon differentiation of monocytes into macrophages, and lipopolysaccharide stimulation of PMA‐differentiated, SLAMF9 knockdown THP‐1 cells showed an essential role of SLAMF9 in production of granulocyte–macrophage colony‐stimulating factor, tumour necrosis factor‐α, and interleukin‐1β. Taken together, these data implicate SLAMF9 in the initiation of inflammation and clearance of bacterial infection.

SLAM Family Receptor Signaling in Viral Infections: HIV and Beyond

The signaling lymphocytic activation molecule (SLAM) family of receptors are expressed on the majority of immune cells. These receptors often serve as self-ligands, and play important roles in cellular communication and adhesion, thus modulating immune responses. SLAM family receptor signaling is differentially regulated in various immune cell types, with responses generally being determined by the presence or absence of two SLAM family adaptor proteins-Ewing's sarcoma-associated transcript 2 (EAT-2) and SLAM-associated adaptor protein (SAP). In addition to serving as direct regulators of the immune system, certain SLAM family members have also been identified as direct targets for specific microbes and viruses. Here, we will discuss the known roles for these receptors in the setting of viral infection, with special emphasis placed on HIV infection. Because HIV causes such complex dysregulation of the immune system, studies of the roles for SLAM family receptors in this context are particularly exciting.

Mannan Enhances IL-12 Production by Increasing Bacterial Uptake and Endosomal Degradation in L. acidophilus and S. aureus Stimulated Dendritic Cells

The mannose receptor (MR) is a C-type lectin involved in endocytosis and with a poorly defined ability to modulate cellular activation. We investigated the effect of mannan treatment prior to stimulation of murine bone marrow-derived dendritic cells with the Gram-positive bacteria Lactobacillus acidophilus NCFM (L. acidophilus) on the induction of Interleukin (IL)-12. Mannan enhanced the IL-12 production induced by L. acidophilus in a dose dependent manner (up to 230% enhancement). Additionally, mannan-enhanced IL-12 induction was also demonstrated with another Gram-positive bacteria, Staphylococcus aureus (S. aureus), while an IL-12 reducing effect was seen on Escherichia coli stimulated cells. Furthermore, the expression of Interferon β (Ifnb) was increased in cells treated with mannan prior to stimulation with L. acidophilus. The addition of mannan but not of bacteria led to endocytosis of MR, while addition of mannan prior to L. acidophilus or S. aureus resulted in increased endocytosis of bacteria, a faster killing of endocytosed bacteria, and increased reactive oxygen species production. Expression of signaling lymphocytic activation molecule (SLAMF)1 shown previously to be involved in the facilitation of endosomal degradation was upregulated by mannan but not by L. acidophilus and S. aureus. The IL-12 enhancement by mannan but not the IL-12 induced by the bacteria was abrogated by addition of inhibitors of clathrin coated pits (chlorpromazine and monodansylcadaverine). Furthermore, the addition of acid sphingomyelinase, a facilitator of ceramide raft formation, prior to addition of L. acidophilus enhanced the IL-12 production and the endocytosis of bacteria. In summary, our results show that mannan increases the IL-12 production induced by some Gram-positive bacteria through MR-endocytosis, which increases bacterial endocytosis and endosomal killing. The differential effect of MR activation on the IL-12 production induced by Gram-positive and Gram-negative bacteria may influence the immune response toward allergens and other glycoproteins.

Proteomics of intracellular Salmonella enterica reveals roles of Salmonella pathogenicity island 2 in metabolism and antioxidant defense

Intracellular Salmonella enterica serovar Typhimurium (STM) deploy the Salmonella Pathogenicity Island 2-encoded type III secretion system (SPI2-T3SS) for the massive remodeling of the endosomal system for host cells. This activity results in formation of an extensive interconnected tubular network of Salmonella-induced filaments (SIFs) connected to the Salmonella-containing vacuole (SCV). Such network is absent in cells infected with SPI2-T3SS-deficient mutant strains such as ΔssaV. A tubular network with reduced dimensions is formed if SPI2-T3SS effector protein SseF is absent. Previous single cell live microscopy-based analyses revealed that intracellular proliferation of STM is directly correlated to the ability to transform the host cell endosomal system into a complex tubular network. This network may also abrogate host defense mechanisms such as delivery of antimicrobial effectors to the SCV. To test the role of SIFs in STM patho-metabolism, we performed quantitative comparative proteomics of STM recovered from infected murine macrophages. We infected RAW264.7 cells with STM wild type (WT), ΔsseF or ΔssaV strains, recovered bacteria 12 h after infection and determined proteome compositions. Increased numbers of proteins characteristic for nutritional starvation were detected in STM ΔsseF and ΔssaV compared to WT. In addition, STM ΔssaV, but not ΔsseF showed signatures of increased exposure to stress by antimicrobial defenses, in particular reactive oxygen species, of the host cells. The proteomics analyses presented here support and extend the role of SIFs for the intracellular lifestyle of STM. We conclude that efficient manipulation of the host cell endosomal system by effector proteins of the SPI2-T3SS contributes to nutrition, as well as to resistance against antimicrobial host defense mechanisms.

The facultative intracellular bacterium Salmonella enterica has evolved sophisticated mechanisms to adapt to life inside a pathogen-containing vacuole in mammalian host cells. Intracellular Salmonella manipulate the host cell endosomal system resulting in formation of a complex network of tubular vesicles, termed Salmonella-induced filaments (SIFs). We applied quantitative proteomics to intracellular Salmonella in murine macrophages and compared the wild-type strain to mutant strains with aberrant SIF architecture, or no capacity for induction of SIF. We determined that those mutant strains contain higher amounts of transporters for nutrient uptake, and lower amounts of proteins for central carbon metabolism. These observations indicate response to nutrient restriction in absence of fully established SIF. In addition, the mutant strain unable to induce SIF formation showed increased amounts of proteins required for response to antimicrobial factors of the host cells. These data show that the massive remodeling of the endosomal system of host cells by intracellular Salmonella serves to essential needs, i.e. to enable access to nutrients for efficient proliferation of the pathogen, and to withstand hostile conditions within the pathogen-containing vacuole.

Platelet Factor 4 Attenuates Experimental Acute Liver Injury in Mice

Platelet factor 4 (PF4) is a pleiotropic inflammatory chemokine, which has been implicated in various inflammatory disorders including liver fibrosis. However, its role in acute liver diseases has not yet been elucidated. Here we describe an unexpected, anti-inflammatory role of PF4. Serum concentrations of PF4 were measured in patients and mice with acute liver diseases. Acute liver injury in mice was induced either by carbon tetrachloride or by D-galactosamine hydrochloride and lipopolysaccharide. Serum levels of PF4 were decreased in patients and mice with acute liver diseases. PF4^-/- mice displayed increased liver damage in both models compared to control which was associated with increased apoptosis of hepatocytes and an enhanced pro-inflammatory response of liver macrophages. In this experimental setting, PF4^-/- mice were unable to generate activated Protein C (APC), a protein with anti-inflammatory activities on monocytes/macrophages. In vitro, PF4 limited the activation of liver resident macrophages. Hence, the systemic application of PF4 led to a strong amelioration of experimental liver injury. Along with reduced liver injury, PF4 improved the severity of the pro-inflammatory response of liver macrophages and induced increased levels of APC. PF4 has a yet unidentified direct anti-inflammatory effect in two models of acute liver injury. Thus, attenuation of acute liver injury by systemic administration of PF4 might offer a novel therapeutic approach for acute liver diseases.

Molecular characterization of newly identified Klebsiella PKBSG14 and analysis of its effect on immune response and cell cycle progression using common catfish (Channa punctatus) as a model

Microbial studies on Catfish revealed that Klebsiella is the most common pathogen causing prevalence of ulcers, fin erosion, and other lesions. During this study, a new strain of bacteria was isolated from Channa punctatus, and molecular identification by 16srRNA revealed the strain was Klebsiella PKBSG14 (Accession no KJ162158). The strain was also PCR positive for two virulent gene wcaG (Accession no LN606595) and rmpA (Accession no LN606594) responsible for inflammatory reactions and induction of innate immune response in the host cell. To study innate immune response induced by pathogenic infection the phagocytic interactive process between the spleen macrophages and KlebsiellaPKBSG14 was investigated using optical microscopy. FACS of splenic macrophages revealed that the phagocytic interaction leads to the process of macrophage cell cycle progression. A detailed study on the macrophage DNA content by performing DNA fragmentation and comet allowed us to study simultaneously host cell division as a function of phagocytosis and the findings unveiled the fact that Phagocytosis of KlebsiellaPKBSG14 aided in macrophage cell cycle progression but was less likely to complete mitosis. Here we also report the cytotoxic effect linked to the infection with KlebsiellaPKBSG14 by performing Cell viability assay, intracellular production of ROS, and mitochondrial transmembrane potential where it manifested itself in impaired cellular function. So, in summary, we simultaneously discovered a new strain of bacteria ie. Klebsiella PKBSG14 as well as deliberately attempted to study the immunomodulatory effect of isolated new stain on Channa punctatus by performing host-pathogen phagocytic interactive experiments, the cell cycle state of the host cell and pathogen-mediated cytotoxicity along with genotoxicity, and our results evidence a new immunomodulatory effect of KlebsiellaPKBSG14 infection on fish splenic macrophages.

β-Barrel outer membrane proteins suppress mTORC2 activation and induce autophagic responses

The outer membranes of Gram-negative bacteria and mitochondria contain proteins with a distinct β-barrel tertiary structure that could function as a molecular pattern recognized by the innate immune system. Here, we report that purified outer membrane proteins (OMPs) from different bacterial and mitochondrial sources triggered the induction of autophagy-related endosomal acidification, LC3B lipidation, and p62 degradation. Furthermore, OMPs reduced the phosphorylation and therefore activation of the multiprotein complex mTORC2 and its substrate Akt in macrophages and epithelial cells. The cell surface receptor SlamF8 and the DNA-protein kinase subunit XRCC6 were required for these OMP-specific responses in macrophages and epithelial cells, respectively. The addition of OMPs to mouse bone marrow-derived macrophages infected with Salmonella Typhimurium facilitated bacterial clearance. These data identify a specific cellular response mediated by bacterial and mitochondrial OMPs that can alter inflammatory responses and influence the killing of pathogens.

SLAMF receptors on normal and malignant B cells

The Signaling Lymphocyte Activation Molecule family (SLAMF) is a collection of nine surface receptors expressed mainly on hematopoietic cells, and was found to modulate the behavior of immune cells. SLAMF receptors are expressed on B cells in health and disease. Each SLAM receptor has a unique differential expression pattern during the development and activation of B cells. Furthermore, recent findings have revealed a principal role for this family of receptors in B cell malignancies, emphasizing their importance in the control of malignant cell survival, cell to cell communication within the tumor microenvironment, retention in the supporting niches and regulation of T cell anti-tumor response. This review summarizes the latest studies regarding SLAMF expression and behavior in B cells and in B cell pathologies, and discusses the therapeutic potential of these receptors.

The surreptitious survival of the emerging pathogen Staphylococcus lugdunensis within macrophages as an immune evasion strategy

Staphylococcus lugdunensis is a commensal bacterium that can cause serious infection suggesting an ability to circumvent aspects of host immunity. We demonstrate here that macrophages fail to kill ingested S. lugdunensis and the bacteria persist for extended periods, without replicating, within mature LAMP-1-positive phagolysosomes. Phagocytosed S. lugdunensis also do not intoxicate host cells in contrast to Staphylococcus aureus. Optimal survival of S. lugdunensis requires O-acetylated peptidoglycan because an oatA mutant, which is more sensitive to killing by lysozyme than wild type, survived to a lesser extent in macrophages. In vitro models of macrophage infection reveal that viable intracellular S. lugdunensis bacteria can be made to grow by pharmacologic perturbation of phagosome function or by phagocyte intoxication by S. aureus toxins. Remarkably, replicating S. lugdunensis is not constrained by LAMP-1 and phosphatidylserine-positive endomembranes, which is distinct from S. aureus that replicates within phagolysosomes. In vivo, S. lugdunensis can also reside in the murine Kupffer cell where the bacteria persist without replicating and require oatA to resist killing in vivo. The intracellular environment of the macrophage represents a niche where S. lugdunensis can exist while protected from extracellular immune factors and may serve as a reservoir from which these bacteria could disseminate.

SLAMF1/CD150 in hematologic malignancies: Silent marker or active player?

SLAMF1/CD150 receptor is a founder of signaling lymphocyte activation molecule (SLAM) family of cell-surface receptors. It is widely expressed on cells within hematopoietic system. In hematologic malignancies CD150 cell surface expression is restricted to cutaneous T-cell lymphomas, few types of B-cell non-Hodgkin's lymphoma, near half of cases of chronic lymphocytic leukemia, Hodgkin's lymphoma, and multiple myeloma. Differential expression among various types of hematological malignancies allows considering CD150 as diagnostical and potential prognostic marker. Moreover, CD150 may be a target for antibody-based or measles virus oncolytic therapy. Due to CD150 signaling properties it is involved in regulation of malignant cell fate decision and tumor microenvironment in Hodgkin's lymphoma and chronic lymphocytic leukemia. This review summarizes evidence for the important role of CD150 in pathogenesis of hematologic malignancies.

Autophagy and lysosomal pathways in nervous system disorders

Autophagy is an evolutionarily conserved pathway for delivering cytoplasmic cargo to lysosomes for degradation. In its classically studied form, autophagy is a stress response induced by starvation to recycle building blocks for essential cellular processes. In addition, autophagy maintains basal cellular homeostasis by degrading endogenous substrates such as cytoplasmic proteins, protein aggregates, damaged organelles, as well as exogenous substrates such as bacteria and viruses. Given their important role in homeostasis, autophagy and lysosomal machinery are genetically linked to multiple human disorders such as chronic inflammatory diseases, cardiomyopathies, cancer, and neurodegenerative diseases. Multiple targets within the autophagy and lysosomal pathways offer therapeutic opportunities to benefit patients with these disorders. Here, I will summarize the mechanisms of autophagy pathways, the evidence supporting a pathogenic role for disturbed autophagy and lysosomal degradation in nervous system disorders, and the therapeutic potential of autophagy modulators in the clinic.

Linking SLAMF1 to autophagy and sensitivity to therapy in chronic lymphocytic leukemia

We recently reported that expression of the costimulatory molecule and microbial sensor SLAMF1 (signaling lymphocytic activation molecule family 1, also known as CD150) is lost in chronic lymphocytic leukemia (CLL) patients characterized by a shorter overall survival. SLAMF1 modulates CLL responses to chemokines and regulates autophagy. Loss of SLAMF1 renders CLL cells relatively unresponsive to autophagy-inducing drugs, including B-cell CLL/lymphoma 2 (BCL2) inhibitors.

SLAMF1 is required for TLR4-mediated TRAM-TRIF-dependent signaling in human macrophages

Yurchenko et al. discover that the Ig-like receptor molecule SLAMF1 enhances production of type I interferon induced by Gram-negative bacteria through modulation of MyD88-independent TLR4 signaling. This makes SLAMF1 a potential target for controlling inflammatory responses against Gram-negative bacteria.

Signaling lymphocytic activation molecule family 1 (SLAMF1) is an Ig-like receptor and a costimulatory molecule that initiates signal transduction networks in a variety of immune cells. In this study, we report that SLAMF1 is required for Toll-like receptor 4 (TLR4)-mediated induction of interferon β (IFNβ) and for killing of Gram-negative bacteria by human macrophages. We found that SLAMF1 controls trafficking of the Toll receptor–associated molecule (TRAM) from the endocytic recycling compartment (ERC) to Escherichia coli phagosomes. In resting macrophages, SLAMF1 is localized to ERC, but upon addition of E. coli, it is trafficked together with TRAM from ERC to E. coli phagosomes in a Rab11-dependent manner. We found that endogenous SLAMF1 protein interacted with TRAM and defined key interaction domains as amino acids 68 to 95 of TRAM as well as 15 C-terminal amino acids of SLAMF1. Interestingly, the SLAMF1–TRAM interaction was observed for human but not mouse proteins. Overall, our observations suggest that SLAMF1 is a new target for modulation of TLR4–TRAM–TRIF inflammatory signaling in human cells.

Signaling Lymphocyte Activation Molecule Family 5 Enhances Autophagy and Fine-Tunes Cytokine Response in Monocyte-Derived Dendritic Cells via Stabilization of Interferon Regulatory Factor 8

Signaling lymphocyte activation molecule family (SLAMF) receptors are essential regulators of innate and adaptive immune responses. The function of SLAMF5/CD84, a family member with almost ubiquitous expression within the hematopoietic lineage is poorly defined. In this article, we provide evidence that in human monocyte-derived dendritic cells (moDCs) SLAMF5 increases autophagy, a degradative pathway, which is highly active in dendritic cells (DCs) and plays a critical role in orchestration of the immune response. While investigating the underlying mechanism, we found that SLAMF5 inhibited proteolytic degradation of interferon regulatory factor 8 (IRF8) a master regulator of the autophagy process by a mechanism dependent on the E3-ubiquitin ligase tripartite motif-containing protein 21 (TRIM21). Furthermore, we demonstrate that SLAMF5 influences the ratio of CD1a⁺ cells in differentiating DCs and partakes in the regulation of IL-1β, IL-23, and IL-12 production in LPS/IFNγ-activated moDCs in a manner that is consistent with its effect on IRF8 stability. In summary, our experiments identified SLAMF5 as a novel cell surface receptor modulator of autophagy and revealed an unexpected link between the SLAMF and IRF8 signaling pathways, both implicated in multiple human pathologies.

S1PR3 Signaling Drives Bacterial Killing and Is Required for Survival in Bacterial Sepsis

RATIONALE

Efficient elimination of pathogenic bacteria is a critical determinant in the outcome of sepsis. Sphingosine-1-phosphate receptor 3 (S1PR3) mediates multiple aspects of the inflammatory response during sepsis, but whether S1PR3 signaling is necessary for eliminating the invading pathogens remains unknown.

OBJECTIVES

To investigate the role of S1PR3 in antibacterial immunity during sepsis.

METHODS

Loss- and gain-of-function experiments were performed using cell and murine models. S1PR3 levels were determined in patients with sepsis and healthy volunteers.

MEASUREMENTS AND MAIN RESULTS

S1PR3 protein levels were up-regulated in macrophages upon bacterial stimulation. S1pr3^-/- mice showed increased mortality and increased bacterial burden in multiple models of sepsis. The transfer of wild-type bone marrow-derived macrophages rescued S1pr3^-/- mice from lethal sepsis. S1PR3-overexpressing macrophages further ameliorated the mortality rate of sepsis. Loss of S1PR3 led to markedly decreased bacterial killing in macrophages. Enhancing endogenous S1PR3 activity using a peptide agonist potentiated the macrophage bactericidal function and improved survival rates in multiple models of sepsis. Mechanically, the reactive oxygen species levels were decreased and phagosome maturation was delayed in S1pr3^-/- macrophages due to impaired recruitment of vacuolar protein-sorting 34 to the phagosomes. In addition, S1RP3 expression levels were elevated in monocytes from patients with sepsis. Higher levels of monocytic S1PR3 were associated with efficient intracellular bactericidal activity, better immune status, and preferable outcomes.

CONCLUSIONS

S1PR3 signaling drives bacterial killing and is essential for survival in bacterial sepsis. Interventions targeting S1PR3 signaling could have translational implications for manipulating the innate immune response to combat pathogens.

ATG-dependent phagocytosis in dendritic cells drives myelin-specific CD4+ T cell pathogenicity during CNS inflammation

Although reactivation and accumulation of autoreactive CD4⁺ T cells within the CNS are considered to play a key role in the pathogenesis of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), the mechanisms of how these cells recognize their target organ and induce sustained inflammation are incompletely understood. Here, we report that mice with conditional deletion of the essential autophagy protein ATG5 in classical dendritic cells (DCs), which are present at low frequencies in the nondiseased CNS, are completely resistant to EAE development following adoptive transfer of myelin-specific T cells and show substantially reduced in situ CD4⁺ T cell accumulation during the effector phase of the disease. Endogenous myelin peptide presentation to CD4⁺ T cells following phagocytosis of injured, phosphatidylserine-exposing oligodendroglial cells is abrogated in the absence of ATG5. Pharmacological inhibition of ATG-dependent phagocytosis by the cardiac glycoside neriifolin, an inhibitor of the Na⁺, K⁺-ATPase, delays the onset and reduces the clinical severity of EAE induced by myelin-specific CD4⁺ T cells. These findings link phagocytosis of injured oligodendrocytes, a pathological hallmark of MS lesions and during EAE, with myelin antigen processing and T cell pathogenicity, and identify ATG-dependent phagocytosis in DCs as a key regulator in driving autoimmune CD4⁺ T cell-mediated CNS damage.