Monocyte-mediated defense against bacteria, fungi, and parasites

VX-702 Ameliorates the Severity of Sepsis-Associated Acute Kidney Injury by Downregulating Inflammatory Factors in Macrophages

Purpose

Sepsis-associated acute kidney injury (S-AKI) contributes to high mortality, but it is lack of specific treatments. We aimed to investigate the underlying mechanism of S-AKI and to identify target drugs to alleviate AKI.

Methods

We establish a stable mouse model of S-AKI by Pseudomonas aeruginosa incision infection. Based on high-throughput sequencing and bioinformatics analysis, we investigated the underlying mechanism and selected the target drug (VX-702) for S-AKI. An in vitro model established by co-cultured of kidney tubular epithelial cell line (TCMK-1) cells with lipopolysaccharide (LPS)-induced leukemic monocyte/macrophage cells (RAW264.7), we explored the effect of VX-702 on S-AKI.

Results

The data showed interleukin (IL)-6 and IL-1β were the hub genes, and the mitogen-activated protein kinase (MAPK) signaling pathway was the main pathway involved in S-AKI. Administration of VX-702 by oral gavage decreased the elevated concentrations of IL-6, IL-1β, serum creatinine, and blood urea nitrogen in mice with S-AKI. Moreover, VX-702 reduced the number of apoptotic cells in damaged kidney tissues. Cell viability was decreased, and the number of apoptotic cells was increased in TCMK-1 cells co-cultured with LPS-induced RAW264.7 cells compared to LPS-induced TCMK-1 cells. VX-702 treatment reversed this effect. VX-702 treatment reduced the levels of phosphorylated p38 MAPK and proinflammatory cytokines in RAW264.7 cells and the supernatant. VX-702 could bind IL-6, IL-1β and MAPK, and affect the binding of IL-1β and its receptor, as demonstrated by molecular docking.

Conclusion

VX-702 ameliorated S-AKI by inhibiting the release of proinflammatory cytokines from macrophages, indicating its potential as a novel therapeutic for S-AKI treatment.

Dynamic mRNA network profiles in macrophages challenged with lipopolysaccharide

OBJECTIVES

To elucidate the transcriptome of macrophages in an inflammation model induced by lipopolysaccharide (LPS), providing insight into the molecular basis of inflammation.

METHODS

We utilized RNA sequencing (RNA-seq) to analyze dynamic changes in gene expression in RAW264.7 macrophages treated with LPS at multiple time points. Differentially expressed genes (DEGs) were identified using the edgeR package. Short Time-series Expression Miner (STEM) and KEGG pathway enrichment analyses were conducted to determine temporal expression patterns during inflammation.

RESULTS

We identified 2,512 DEGs, with initial inflammatory responses occurring in two distinct phases at 1 h and 3 h. Venn diagram analysis revealed 78 consistently dysregulated genes throughout the inflammatory process. A key module of 18 dysregulated genes was identified, including Irg1, which may exert an inhibitory effect on inflammation. Further, a second metabolic shift in activated macrophages was observed at the late middle stage (12 h). Multi-omics analysis highlighted the ribosome's potential regulatory role in the inflammatory response.

CONCLUSIONS

This study provides a detailed view of the molecular mechanisms underlying inflammation in macrophages and reveals a dynamic genetic landscape crucial for further research. Our findings underscore the complex interaction between gene expression, metabolic shifts, and ribosomal functions in response to LPS-induced inflammation.

Photobiomodulation with 630-nm LED Inhibits M1 Macrophage Polarization via STAT1 Pathway Against Sepsis-Induced Acute Lung Injury

Background: Sepsis-induced acute lung injury (ALI) is a clinical syndrome characterized by excessive uncontrolled inflammation. Photobiomodulation such as light-emitting diode (LED) irradiation has been used to attenuate inflammatory disease. Objective: The protective effect of 630 nm LED irradiation on sepsis-induced ALI remains unknown. The purpose of this study was to investigate the role of 630 nm LED irradiation in sepsis-induced ALI and its underlying mechanism. Methods and results: C57BL/6 mice were performed cecal ligation and puncture (CLP) for 12 h to generate experimental sepsis models. Histopathology analysis showed that alveolar injury, inflammatory cells infiltration, and hemorrhage were suppressed in CLP mice after 630 nm LED irradiation. The ratio of wet/dry weigh of lung tissue was significantly inhibited by irradiation. The number of leukocytes was reduced in bronchoalveolar lavage fluid. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) results and enzyme-linked immunosorbent assay showed that 630 nm LED irradiation significantly inhibited the mRNA and protein levels of M1 macrophage-related genes in the lung of CLP-induced septic mice. Meanwhile, LED irradiation significantly inhibited signal transducer and activator of transcription 1 (STAT1) phosphorylation in the lung of septic mice. In vitro experiments showed that 630 nm LED irradiation significantly inhibited M1 genes mRNA and protein expression in THP-1-derived M1 macrophages without affecting the cell viability. LED irradiation also significantly inhibited the level of STAT1 phosphorylation in THP-1-derived M1 macrophages. Conclusions: We concluded that 630 nm LED is promising as a treatment against ALI through inhibiting M1 macrophage polarization, which is associated with the downregulation of STAT1 phosphorylation.

Macrophage-derived exosomal miRNA-141 triggers endothelial cell pyroptosis by targeting NLRP3 to accelerate sepsis progression

Sepsis, critical condition marked by severe organ dysfunction from uncontrolled infection, involves the endothelium significantly. Macrophages, through paracrine actions, play a vital role in sepsis, but their mechanisms in sepsis pathogenesis remain elusive. Objective: We aimed to explore how macrophage-derived exosomes with low miR-141 expression promote pyroptosis in endothelial cells (ECs). Exosomes from THP-1 cell supernatant were isolated and characterized. The effects of miR-141 mimic/inhibitor on apoptosis, proliferation, and invasion of Human Umbilical Vein Endothelial Cells (HUVECs) were assessed using flow cytometry, CCK-8, and transwell assays. Key pyroptosis-related proteins, including caspase-1, IL-18, IL-1β, NLR Family Pyrin Domain Containing 3 (NLRP3), ASC, and cleaved-GSDMD, were analyzed via Western blot. The interaction between miR-141 and NLRP3 was studied using RNAhybrid v2.2 and dual-Luciferase reporter assays. The mRNA and protein level of NLRP3 after exosomal miR-141 inhibitor treatment was detected by qPCR and Western blot, respectively. Exosomes were successfully isolated. miR-141 mimic reduced cell death and pyroptosis-related protein expression in HUVECs, while the inhibitor had opposite effects, increasing cell death, and enhancing pyroptosis protein expression. Additionally, macrophage-derived exosomal miR-141 inhibitor increased cell death and pyroptosis-related proteins in HUVECs. miR-141 inhibits NLRP3 transcription. Macrophages facilitate sepsis progression by secreting miR-141 decreased exosomes to activate NLRP3-mediated pyroptosis in ECs, which could be a potentially valuable target of sepsis therapy.

Risk factors and clinical outcomes of carbapenem-resistant Klebsiella pneumoniae bacteraemia in children: a retrospective study

OBJECTIVES

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is increasingly being identified in children, but data on the clinical outcomes in this population are limited. This study aimed to characterise the risk factors for 30-day mortality with CRKP bloodstream infection (BSI) in children.

METHODS

A retrospective study was performed from January 2018 to December 2021 at the First Affiliated Hospital of Zhengzhou University. Patients aged < 18 years and with CRKP BSI were included. Multivariable Cox and logistic regression were performed to determine risk factors for death and the development of septic shock following CRKP infection, respectively.

RESULTS

This study identified 33 neonates aged 0-4 weeks and 37 older children. The 30-day mortality rate was 39.4% in neonates and 43.2% in older children. In the neonatal population, a higher Pitt bacteremia score (HR 1.694; 95% CI 1.313-2.186; P < 0.001) was an independent risk factor for 30-day mortality. In the non-neonatal population, higher platelet count (HR 0.990; 95% CI 0.982-0.998; P = 0.010), the use of carbapenems (HR 0.212; 95% CI 0.064-0.702; P = 0.011) and appropriately targeted antimicrobial treatment (HR 0.327; 95% CI 0.111-0.969; P = 0.044) were associated with decreased 30-day mortality. Monocyte count < 0.1 × 109 cells/L (OR 3.615; 95% CI 1.165-11.444; P = 0.026) and a higher Pitt bacteremia score (OR 1.330; 95% CI 1.048-1.688; P = 0.019) were identified as risk factors for the development of septic shock.

CONCLUSIONS

Carbapenem-resistant Klebsiella pneumoniae BSI was associated with high mortality in children. Appropriate antimicrobial treatment is important to improve survival, but more work is needed to assess the efficacy of specific treatment regimens in children.

The TLR-NF-kB axis contributes to the monocytic inflammatory response against a virulent strain of Lichtheimia corymbifera, a causative agent of invasive mucormycosis

Invasive mucormycosis (IM) is a life-threatening infection caused by the fungal order Mucorales, its diagnosis is often delayed, and mortality rates range from 40-80% due to its rapid progression. Individuals suffering from hematological malignancies, diabetes mellitus, organ transplantations, and most recently COVID-19 are particularly susceptible to infection by Mucorales. Given the increase in the occurrence of these diseases, mucormycosis has emerged as one of the most common fungal infections in the last years. However, little is known about the host immune response to Mucorales. Therefore, we characterized the interaction among L. corymbifera—one of the most common causative agents of IM—and human monocytes, which are specialized phagocytes that play an instrumental role in the modulation of the inflammatory response against several pathogenic fungi. This study covered four relevant aspects of the host-pathogen interaction: i) The recognition of L. corymbifera by human monocytes. ii) The intracellular fate of L. corymbifera. iii) The inflammatory response by human monocytes against the most common causative agents of mucormycosis. iv) The main activated Pattern-Recognition Receptors (PRRs) inflammatory signaling cascades in response to L. corymbifera. Here, we demonstrate that L. corymbifera exhibits resistance to intracellular killing over 24 hours, does not germinate, and inflicts minimal damage to the host cell. Nonetheless, viable fungal spores of L. corymbifera induced early production of the pro-inflammatory cytokine IL-1β, and late release of TNF-α and IL-6 by human monocytes. Moreover, we revealed that IL-1β production predominantly depends on Toll-like receptors (TLRs) priming, especially via TLR4, while TNF-α is secreted via C-type lectin receptors (CTLs), and IL-6 is produced by synergistic activation of TLRs and CTLs. All these signaling pathways lead to the activation of NF-kB, a transcription factor that not only regulates the inflammatory response but also the apoptotic fate of monocytes during infection with L. corymbifera. Collectively, our findings provide new insights into the host-pathogen interactions, which may serve for future therapies to enhance the host inflammatory response to L. corymbifera.

Neutrophils as regulators of macrophage-induced inflammation in a setting of allogeneic bone marrow transplantation

Clinical data reveal that patients with allogeneic hematopoietic stem cell transplantation (HSCT) are vulnerable to infection and prone to developing severe sepsis, which greatly compromises the success of transplantation, indicating a dysregulation of inflammatory immune response in this clinical setting. Here, by using a mouse model of haploidentical bone marrow transplantation (haplo-BMT), we found that uncontrolled macrophage inflammation underlies the pathogenesis of both LPS- and E.coli-induced sepsis in recipient animals with graft-versus-host disease (GVHD). Deficient neutrophil maturation in GVHD mice post-haplo-BMT diminished modulation of macrophage-induced inflammation, which was mechanistically dependent on MMP9-mediated activation of TGF-β1. Accordingly, adoptive transfer of mature neutrophils purified from wild-type donor mice inhibited both sterile and infectious sepsis in GVHD mice post-haplo-BMT. Together, our findings identify a novel mature neutrophil-dependent regulation of macrophage inflammatory response in a haplo-BMT setting and provide useful clues for developing clinical strategies for patients suffering from post-HSCT sepsis.

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Macrophage inflammation leads to the development of post-haplo-BMT sepsis

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Impaired neutrophil maturation diminishes regulation of macrophage inflammation

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Extramedullary granulopoiesis fails to support neutrophil maturation after haplo-BMT

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Neutrophils regulate macrophage inflammation via MMP9-mediated TGF-β1 activation

Reprogramming Macrophage Metabolism and its Effect on NLRP3 Inflammasome Activation in Sepsis

Sepsis, the most common life-threatening multi-organ dysfunction syndrome secondary to infection, lacks specific therapeutic strategy due to the limited understanding of underlying mechanisms. It is currently believed that inflammasomes play critical roles in the development of sepsis, among which NLRP3 inflammasome is involved to most extent. Recent studies have revealed that dramatic reprogramming of macrophage metabolism is commonly occurred in sepsis, and this dysregulation is closely related with the activation of NLRP3 inflammasome. In view of the fact that increasing evidence demonstrates the mechanism of metabolism reprogramming regulating NLRP3 activation in macrophages, the key enzymes and metabolites participated in this regulation should be clearer for better interpreting the relationship of NLRP3 inflammasome and sepsis. In this review, we thus summarized the detail mechanism of the metabolic reprogramming process and its important role in the NLRP3 inflammasome activation of macrophages in sepsis. This mechanism summarization will reveal the applicational potential of metabolic regulatory molecules in the treatment of sepsis.

Associations between differences in anemia-related blood cell parameters and short-term exposure to ambient particle pollutants in middle-aged and elderly residents in Beijing, China

Anemia is a highly prevalent disease among older populations, with multiple adverse health outcomes, and particles exposure is a potential risk factor for anemia. However, evidence on associations of exposure to particles with small size with anemia-related blood cell parameters levels in the elderly is limited, and the underlying mechanisms are unclear. Based on a panel study in Beijing, we found that in 135 elderly participants, mass concentrations of particle with an aerodynamic diameter ≤ 2.5 μm (PM_2.5), black/elemental carbon (BC/EC, particle size range: 0-2.5 μm), and number concentrations of ultrafine particles (UFPs, particle size range: 5.6-93.1 nm) and accumulated mode particles (Acc, size range: 93.1-560 nm) were significantly associated with levels of red blood cell count (RBC), hemoglobin (HGB), hematocrit (HCT), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC). The mean ± SD for PM_2.5, UFPs, Acc, BC, OC, and EC were 69.7 ± 61.1 μg/m³, 12.5 ± 4.3 × 10³/cm³, 1.6 ± 1.2 × 10³/cm³, 3.0 ± 2.0 μg/m³, 8.7 ± 6.7 μg/m³, and 2.1 ± 1.6 μg/m³, respectively. Cotinine (higher than 50 ng/mL) is used as an indicator of smoking exposure. The association between MCHC difference and per interquartile range (IQR) increase in average UFPs concentration 14 d before clinical visits was -0.7% (95% CI: -1.1% to -0.3%). Significant associations of UFPs and Acc exposure with MCHC and MCH levels remain robust after adjustment for other pollutants. Furthermore, 25.2% (95% CI: 7.4% to 64.8%) and 29.8% (95% CI: 5.3% to 214.4%) of the difference in MCHC associated with average UFPs and Acc concentrations 14 d before clinical visits were mediated by the level of tumor necrosis factor α (TNF α), a biomarker of systemic inflammation. Our findings for the first time provide the evidence that short-term UFPs and Acc exposure contributed to the damage of anemia-related blood cell in the elderly, and systemic inflammation was a potential internal mediator.

Inflammatory Monocytes Promote Granuloma-Mediated Control of Persistent Salmonella Infection

Persistent infections generally involve a complex balance between protective immunity and immunopathology. We used a murine model to investigate the role of inflammatory monocytes in immunity and host defense against persistent salmonellosis. Mice exhibit increased susceptibility to persistent infection when inflammatory monocytes cannot be recruited into tissues or when they are depleted at specific stages of persistent infection. Inflammatory monocytes contribute to the pathology of persistent salmonellosis and cluster with other cells in pathogen-containing granulomas. Depletion of inflammatory monocytes during the chronic phase of persistent salmonellosis causes regression of already established granulomas with resultant pathogen growth and spread in tissues. Thus, inflammatory monocytes promote granuloma-mediated control of persistent salmonellosis and may be key to uncovering new therapies for granulomatous diseases.

Biochemical Analysis of Leukocytes after In Vitro and In Vivo Activation with Bacterial and Fungal Pathogens Using Raman Spectroscopy

Biochemical information from activated leukocytes provide valuable diagnostic information. In this study, Raman spectroscopy was applied as a label-free analytical technique to characterize the activation pattern of leukocyte subpopulations in an in vitro infection model. Neutrophils, monocytes, and lymphocytes were isolated from healthy volunteers and stimulated with heat-inactivated clinical isolates of Candida albicans, Staphylococcus aureus, and Klebsiella pneumoniae. Binary classification models could identify the presence of infection for monocytes and lymphocytes, classify the type of infection as bacterial or fungal for neutrophils, monocytes, and lymphocytes and distinguish the cause of infection as Gram-negative or Gram-positive bacteria in the monocyte subpopulation. Changes in single-cell Raman spectra, upon leukocyte stimulation, can be explained with biochemical changes due to the leukocyte’s specific reaction to each type of pathogen. Raman spectra of leukocytes from the in vitro infection model were compared with spectra from leukocytes of patients with infection (DRKS-ID: DRKS00006265) with the same pathogen groups, and a good agreement was revealed. Our study elucidates the potential of Raman spectroscopy-based single-cell analysis for the differentiation of circulating leukocyte subtypes and identification of the infection by probing the molecular phenotype of those cells.

Hydrogen alleviates cell damage and acute lung injury in sepsis via PINK1/Parkin-mediated mitophagy

BACKGROUND

Multiple organ failure (MOF) is the main cause of early death in septic shock. Lungs are among the organs that are affected in MOF, resulting in acute lung injury. Inflammation is an important factor that causes immune cell dysfunction in the pathogenesis of sepsis. Autophagy is involved in the process of inflammation and also occurs in response to cell and tissue injury in several diseases. We previously demonstrated that hydrogen alleviated the inflammation-induced cell injury and organ damage in septic mice.

AIM

The focus of the present study was to elucidate whether mitophagy mediates the inflammatory response or oxidative injury in sepsis in vitro and in vivo. Furthermore, we evaluated the role of mitophagy in the protective effects of hydrogen against cell injury or organ dysfunction in sepsis.

METHOD

RAW 264.7 macrophages induced by lipopolysaccharide (LPS) were used as an in vitro model for inflammation, and cecal ligation and puncture (CLP)-induced acute lung injury mice were used as an in vivo model for sepsis. The key protein associated with mitophagy, PTEN-induced putative kinase 1 (PINK1), was knocked down by PINK1 shRNA transfection in RAW 264.7 macrophages or mice.

RESULTS

Hydrogen ameliorated cell injury and enhanced mitophagy in macrophages stimulated by LPS. PINK1 was required for the mitigation of the cell impairment in LPS-stimulated macrophages by hydrogen treatment. PINK1 knockdown abrogated the beneficial effects of hydrogen on mitophagy in LPS-stimulated macrophages. Hydrogen inhibited acute lung injury in CLP mice via activation of PINK1-mediated mitophagy.

CONCLUSION

These results suggest that PINK1-mediated mitophagy plays a key role in the protective effects of hydrogen against cell injury in LPS-induced inflammation and CLP-induced acute lung injury.

A Scoring System for Predicting the Prognosis of Late-Onset Severe Pneumonia after Allogeneic Hematopoietic Stem Cell Transplantation

Late-onset severe pneumonia (LOSP) is defined as severe pneumonia developing during the late phase of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Because of the high mortality in patients with LOSP, it is important to identify prognostic factors. In this study, we aimed to develop a risk score system with broad applicability that can help predict the risk of LOSP-associated mortality. We retrospectively analyzed 100 patients with LOSP after allo-HSCT between June 2009 and July 2017. The assessment variables included immune, nutritional, and metabolic parameters at the onset of LOSP. Of these 100 patients, 45 (45%) eventually died, and 55 (55%) were positive for organisms, most commonly viruses. In the multivariate analysis, higher monocyte count (≥0.20 × 10⁹/L versus <0.20 × 10⁹/L; P = .001), higher albumin level (≥30.5 g/L versus <30.5 g/L; P = .044), lower lactic dehydrogenase level (<250 U/L versus ≥250 U/L; P = .008) and lower blood urea nitrogen concentration (<7.2 mmol/L versus ≥7.2 mmol/L; P = .026) at the onset of LOSP were significantly associated with better 60-day survival. A risk score system based on the foregoing results showed that the probability of 60-day survival decreased with increasing risk factors, from 96.3% in the low-risk group to 49.1% in the intermediate-risk group and 12.5% in the high-risk group. Our results indicate that this scoring system using 4 variables can stratify patients with different probabilities of survival after LOSP, which suggests that patients' immune, nutritional, and metabolic status are crucial factors in determining outcome.

Potential biomarkers of immune protection in human leishmaniasis

Leishmaniasis is a vector-borne neglected tropical disease endemic in over 100 countries around the world. Available control measures are not always successful, therapeutic options are limited, and there is no vaccine available against human leishmaniasis, although several candidate antigens have been evaluated over the last decades. Plenty of studies have aimed to evaluate the immune response development and a diverse range of host immune factors have been described to be associated with protection or disease progression in leishmaniasis; however, to date, no comprehensive biomarker(s) have been identified as surrogate marker of protection or exacerbation, and lack of enough information remains a barrier for vaccine development. Most of the current understanding of the role of different markers of immune response in leishmaniasis has been collected from experimental animal models. Although the data generated from the animal models are crucial, it might not always be extrapolated to humans. Here, we briefly review the events during Leishmania invasion of host cells and the immune responses induced against Leishmania in animal models and humans and their potential role as a biomarker of protection against human leishmaniasis.

Innate Immunity in Diabetic Wound Healing: Focus on the Mastermind Hidden in Chronic Inflammatory

A growing body of evidence suggests that the interaction between immune and metabolic responses is essential for maintaining tissue and organ homeostasis. These interacting disorders contribute to the development of chronic diseases associated with immune-aging such as diabetes, obesity, atherosclerosis, and nonalcoholic fatty liver disease. In Diabetic wound (DW), innate immune cells respond to the Pathogen-associated molecular patterns (PAMAs) and/or Damage-associated molecular patterns (DAMPs), changes from resting to an active phenotype, and play an important role in the triggering and maintenance of inflammation. Furthermore, the abnormal activation of innate immune pathways secondary to immune-aging also plays a key role in DW healing. Here, we review studies of innate immune cellular molecular events that identify metabolic disorders in the local microenvironment of DW and provide a historical perspective. At the same time, we describe some of the recent progress, such as TLR receptor-mediated intracellular signaling pathways that lead to the activation of NF-κB and the production of various pro-inflammatory mediators, NLRP3 inflammatory via pyroptosis, induction of IL-1β and IL-18, cGAS-STING responds to mitochondrial injury and endoplasmic reticulum stress, links sensing of metabolic stress to activation of pro-inflammatory cascades. Besides, JAK-STAT is also involved in DW healing by mediating the action of various innate immune effectors. Finally, we discuss the great potential of targeting these innate immune pathways and reprogramming innate immune cell phenotypes in DW therapy.

Impaired DNA repair in mouse monocytes compared to macrophages and precursors

Previously we showed that human monocytes isolated from peripheral blood display downregulation of several DNA repair proteins, including XRCC1, ligase III, PARP-1 and DNA-PK_CS, resulting in a deficiency of DNA repair, while in macrophages derived from monocytes the repair protein expression and DNA repair is restored. To see whether this is a specific phenomenon of human monocytes and macrophages, we assessed the expression of these repair genes in mice. We also addressed the question at which differentiation step in bone marrow cells downregulation of DNA repair gene expression occurs. The study revealed that mouse monocytes, similar to human, lack the expression of XRCC1, ligase III, PARP-1 and DNA-PK_CS. If mice were treated with total body irradiation, they showed significant apoptosis in bone marrow monocytes, but not in peritoneal macrophages. This was also observed after treatment with the methylating anticancer drug temozolomide, resulting in high death rate of monocytes, but not macrophages. Monocytes arise from hematopoietic stem cells. Even the early stem cell fraction (LT-HSC) expressed detectable amounts of XRCC1, which was transiently upregulated, achieving the highest expression level in CMP (common myeloid progenitor) and, during the subsequent differentiation process, downregulated up to a non-detectable level in monocytes. The immediate monocyte precursor GMP also expressed ligase III, PARP-1 and DNA-PK_CS. All these repair genes lacking in monocytes were upregulated again in macrophages. The sensitivity of monocytes, macrophages and precursor cells roughly correlated with their XRCC1 expression level. Monocytes, but not macrophages, also displayed strong γH2AX focal staining, indicating the presence of non-repaired DNA double-strand breaks following total body irradiation. Overall, the data revealed that murine monocytes exhibit the same DNA repair-impaired phenotype and high sensitivity compared to macrophages as observed in human. Therefore, the repair deficiency previously described for human monocytes appears to be a general property of this cell type.

Intestinal Macrophages in Resolving Inflammation

Macrophages not only regulate intestinal homeostasis by recognizing pathogens to control enteric infections but also employ negative feedback mechanisms to prevent chronic inflammation. Hence, macrophages are intriguing targets for immune-mediated therapies, especially when barrier function in the gut is compromised to trigger aberrant inflammatory responses, most notably during inflammatory bowel diseases. Recently, there has been considerable progress in our understanding of human macrophage biology in different tissues, including the intestines. In this review, we discuss some new findings on the properties of distinct populations of intestinal macrophages, how resolution of inflammation and tissue repair by macrophages could be promoted by type 2 cytokines as well as other therapeutic interventions, and highlight some challenges for translating these findings into the future for this exciting area of immunology research.

Immune Exhaustion of T Cells in Alveolar Echinococcosis Patients and Its Reversal by Blocking Checkpoint Receptor TIGIT in a Murine Model

BACKGROUND AND AIMS

The cestode Echinococcus multilocularis infection, a serious health problem worldwide, causes alveolar echinococcosis (AE), a tumor-like disease predominantly located in the liver and able to spread to any organs. Until now, there have been few studies that explore how T-cell exhaustion contributes to the parasite's escape from immune attack and how it might be reversed.

APPROACH AND RESULTS

In this study, we found that liver T-cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) expression was significantly enhanced and positively correlated with lesion activity in AE patients. High TIGIT expression in both liver-infiltrating and blood T cells was associated with their functional exhaustion, and its ligand CD155 was highly expressed by hepatocytes surrounding the infiltrating lymphocytes. In co-culture experiments using human blood T cells and hepatic cell line HL-7702, CD155 induced functional impairment of TIGIT⁺ T cells, and in vitro blockade with TIGIT antibody restored the function of AE patients' T cells. Similar TIGIT-related functional exhaustion of hepatic T cells and an abundant CD155 expression on hepatocytes were observed in E. multilocularis-infected mice. Importantly, in vivo blocking TIGIT prevented T-cell exhaustion and inhibited disease progression in E. multilocularis-infected mice. Mechanistically, CD4⁺ T cells were totally and CD8⁺ T cells partially required for anti-TIGIT-induced regression of parasite growth in mice.

CONCLUSIONS

This study demonstrates that E. multilocularis can induce T-cell exhaustion through inhibitory receptor TIGIT, and that blocking this checkpoint may reverse the functional impairment of T cells and represent a possible approach to immunotherapy against AE.

A quantitativeex vivostudy of the interactions between reconstituted high-density lipoproteins and human leukocytes

Knowledge of the interactions between nanoparticles and immune cells is required for optimal design of nanoparticle-based drug delivery systems, either when aiming to avoid phagocytic clearance of the nanoparticles or promote an immune response by delivering therapeutic agents to specific immune cells. Several studies have suggested that reconstituted high-density lipoproteins (rHDL) are attractive drug delivery vehicles. However, detailed studies of rHDL interactions with circulating leukocytes are limited. Here, we evaluated the association of discoidal rHDL with leukocytes in human whole blood (HWB) using quantitative approaches. We found that while the rHDL of various lipid compositions associated preferentially with monocytes, the degree of association depended on the lipid composition. However, consistent with the long circulation half-life of rHDL, we show that only a minor fraction of the rHDL associated with the leukocytes. Furthermore, we used three-dimensional fluorescence microscopy and imaging flow cytometry to evaluate the possible internalization of rHDL cargo into the cells, and we show increased internalization of rHDL cargo in monocytes relative to granulocytes. The preferential rHDL association with monocytes and the internalization of rHDL cargo could possibly be mediated by the scavenger receptor class B type 1 (SR-BI), which we show is expressed to a higher extent on monocytes than on the other major leukocyte populations. Our work implies that drug-loaded rHDL can deliver its cargo to monocytes in circulation, which could lead to some off-target effects when using rHDL for systemic drug delivery, or it could pave the way for novel immunotherapeutic treatments aiming to target the monocytes.

We used novel quantitative methods to study the interactions between reconstituted high-density lipoproteins (rHDL) and human leukocytes – showing that rHDL cargo are preferentially taken up by monocytes.

Pathological alteration and therapeutic implications of sepsis-induced immune cell apoptosis

Sepsis is a life-threatening organ dysfunction syndrome caused by dysregulated host response to infection that leads to uncontrolled inflammatory response followed by immunosuppression. However, despite the high mortality rate, no specific treatment modality or drugs with high efficacy is available for sepsis to date. Although improved treatment strategies have increased the survival rate during the initial state of excessive inflammatory response, recent trends in sepsis show that mortality occurs at a period of continuous immunosuppressive state in which patients succumb to secondary infections within a few weeks or months due to post-sepsis “immune paralysis.” Immune cell alteration induced by uncontrolled apoptosis has been considered a major cause of significant immunosuppression. Particularly, apoptosis of lymphocytes, including innate immune cells and adaptive immune cells, is associated with a higher risk of secondary infections and poor outcomes. Multiple postmortem studies have confirmed that sepsis-induced immune cell apoptosis occurs in all age groups, including neonates, pediatric, and adult patients, and it is considered to be a primary contributing factor to the immunosuppressive pathophysiology of sepsis. Therapeutic perspectives targeting apoptosis through various strategies could improve survival in sepsis. In this review article, we will focus on describing the major apoptosis process of immune cells with respect to physiologic and molecular mechanisms. Further, advances in apoptosis-targeted treatment modalities for sepsis will also be discussed.

Innate and Adaptive Immune Responses during Listeria monocytogenes Infection

It could be argued that we understand the immune response to infection with Listeria monocytogenes better than the immunity elicited by any other bacteria. L. monocytogenes are Gram-positive bacteria that are genetically tractable and easy to cultivate in vitro, and the mouse model of intravenous (i.v.) inoculation is highly reproducible. For these reasons, immunologists frequently use the mouse model of systemic listeriosis to dissect the mechanisms used by mammalian hosts to recognize and respond to infection. This article provides an overview of what we have learned over the past few decades and is divided into three sections: "Innate Immunity" describes how the host initially detects the presence of L. monocytogenes and characterizes the soluble and cellular responses that occur during the first few days postinfection; "Adaptive Immunity" discusses the exquisitely specific T cell response that mediates complete clearance of infection and immunological memory; "Use of Attenuated Listeria as a Vaccine Vector" highlights the ways that investigators have exploited our extensive knowledge of anti-Listeria immunity to develop cancer therapeutics.

Repetitive Exposure of IL-17 Into the Murine Air Pouch Favors the Recruitment of Inflammatory Monocytes and the Release of IL-16 and TREM-1 in the Inflammatory Fluids

The infiltration of Th17 cells in tissues and organs during the development of many autoimmune diseases is considered a key step toward the establishment of chronic inflammation. Indeed, the localized and prolonged release of IL-17 in specific tissues has been associated with an increased severity of the inflammatory response that remains sustained over time. The cellular and molecular mechanisms behind these effects are far from being clear. In this study we investigated the effects of two repetitive administration of recombinant IL-17 into the murine air pouch to simulate a scenario where IL-17 is released over time in a pre-inflamed tissue. Consistent with our previous observations, mice receiving a single dose of IL-17 showed a transitory influx of neutrophils into the air pouch that peaked at 24 h and declined at 48 h. Conversely, mice receiving a double dose of the cytokine—one at time 0 and the second after 24 h—showed a more dramatic inflammatory response with almost 2-fold increase in the number of infiltrated leukocytes and significant higher levels of TNF-α and IL-6 in the inflammatory fluids. Further analysis of the exacerbated inflammatory response of double-injected IL-17 mice showed a unique cellular and biochemical profile with inflammatory monocytes as the second main population emigrating to the pouch and IL-16 and TREM-1 as the most upregulated cytokines found in the inflammatory fluids. Most interestingly, mice receiving a double injection of IL-1β did not show any change in the cellular or biochemical inflammatory response compared to those receiving a single injection or just vehicle. Collectively these results shed some light on the function of IL-17 as pro-inflammatory cytokine and provide possible novel ways to target therapeutically the pathogenic effects of IL-17 in autoimmune conditions.

Human Pathogenic Entomophthorales

The pathogenic entomophthoralean fungi cause infection in insects and mammalian hosts. Basidiobolus and Conidiobolus species can be found in soil and insect, reptile, and amphibian droppings in tropical and subtropical areas. The life cycles of these fungi occur in these environments where infecting sticky conidia are developed. The infection is acquired by insect bite or contact with contaminated environments through open skin. Conidiobolus coronatus typically causes chronic rhinofacial disease in immunocompetent hosts, whereas some Conidiobolus species can be found in immunocompromised patients. Basidiobolus ranarum infection is restricted to subcutaneous tissues but may be involved in intestinal and disseminated infections. Its early diagnosis remains challenging due to clinical similarities to other intestinal diseases. Infected tissues characteristically display eosinophilic granulomas with the Splendore-Höeppli phenomenon. However, in immunocompromised patients, the above-mentioned inflammatory reaction is absent. Laboratory diagnosis includes wet mount, culture serological assays, and molecular methodologies. The management of entomophthoralean fungi relies on traditional antifungal therapies, such as potassium iodide (KI), amphotericin B, itraconazole, and ketoconazole, and surgery. These species are intrinsically resistant to some antifungals, prompting physicians to experiment with combinations of therapies. Research is needed to investigate the immunology of entomophthoralean fungi in infected hosts. The absence of an animal model and lack of funding severely limit research on these fungi.

A new biomarker candidate for spinal muscular atrophy: Identification of a peripheral blood cell population capable of monitoring the level of survival motor neuron protein

Spinal muscular atrophy (SMA) is a severe genetic neuromuscular disorder caused by insufficiency of functional survival motor neuron (SMN) protein. Several clinical trials have been conducted with the aim of upregulating the expression of the SMN protein in SMA patients. In order to evaluate the efficiency of these SMN-targeted approaches, it has become necessary to verify SMN protein levels in the cells of SMA patients. Accordingly, we have developed a method allowing the evaluation of the functional SMN protein with < 1.5 mL of peripheral blood using imaging flow cytometry. The expression of SMN protein in CD3⁺, CD19⁺, and CD33⁺⁺ cells obtained from SMA patients, was significantly reduced compared with that in cells from control subjects. In spot analysis of CD33⁺⁺ cells, the intensities of SMN spots were significantly reduced in SMA subjects, when compared with that in controls. Therefore, SMN spots implied the presence of functional SMN protein in the cell nucleus. To our knowledge, our results are the first to demonstrate the presence of functional SMN protein in freshly isolated peripheral blood cells. We anticipate that SMN spot analysis will become the primary endpoint assay for the evaluation and monitoring of therapeutic intervention, with SMN serving as a reliable biomarker of therapeutic efficacy in SMA patients.

fMLP-dependent activation of Akt and ERK1/2 through ROS/Rho A pathways is mediated through restricted activation of the FPRL1 (FPR2) receptor

OBJECTIVE AND DESIGN

The objective of this study is to uncover the signal transduction pathways of N-formyl methionyl-leucyl-phenylalanine (fMLP) in monocyte.

MATERIALS OR SUBJECTS

Freshly isolated human peripheral blood monocytes (PBMC) were used for in vitro assessment of signal transduction pathways activated by fMLP.

TREATMENT

Time-course and dose-response experiments were used to evaluate the effect of fMLP along with the specific inhibitors/stimulators on the activation of downstream signaling kinases.

METHODS

Freshly isolated human PBMC were stimulated with fMLP for the desired time. Western blot and siRNA analysis were used to evaluate the activated intracellular signaling kinases, and flow analysis was performed to assess the levels of CD11b. Furthermore, luminescence spectrometry was performed to measure the levels of released hydrogen peroxide in the media.

RESULTS

fMLP strongly stimulated the activation of AKT and ERK1/2 through a RhoA-GTPase-dependent manner and also induced H₂O₂ release by monocytes. Furthermore, fMLP mediated its effects through restricted activation of formylpeptide receptor-like 1 (FPRL1/FPR2), but independently of either EGFR transactivation or intracellular calcium release. In addition, NAC reversed fMLP- and H₂O₂-induced activation of Akt and RhoA-GTPase.

CONCLUSION

Collectively, these data suggested that fMLP-activated ERK1/2 and Akt pathways through specific activation of the FPRL1/ROS/RoA-GTPase pathway.

Inflammatory and Anti-inflammatory Responses Co-exist Inside Lung Granuloma of Fatal Cases of Coccidioidomycosis: A Pilot Report

Coccidioidomycosis is a fungal disease caused by Coccidioides immitis or Coccidioides posadasii. These fungi are endemic in the southern USA and northern Mexico. Immunocompromised patients are susceptible to develop severe forms of this fungal infection. Cytokines play an important role in controlling the fungal infection, but little is known about the predominant immunological environment in human lung tissue from fatal cases. Our aim was to analyze the pro-inflammatory and anti-inflammatory cytokines and monocyte/macrophages markers (CD14 and CD206) in the granulomas of six fatal cases of coccidioidomycosis. Cytokines and surface markers were higher in coccidioidomycosis cases when compared to control (P < 0.05). CD14 positive cells were increased inside the coccidioidal granuloma when compared to the outside (P < 0.05). No differences were found in the number of CD206+ cells inside the granuloma when compared to the outer population (P > 0.05). Interestingly, an analysis of stain intensity signals showed an increased signaling of CD14, CD206, IL-10 and TNFα inside the granuloma when compared to the outside (P < 0.05). iNOS and IL-12 gene expression were not detected in coccidioidomycosis cases, while IL-10, IL-6 and TGFβ gene expression were detected, but the differences when compared to healthy lungs were not significant (P > 0.05). TNFα gene expression was lower in coccidioidomycosis cases when compared to healthy lung (P = 0.05). In conclusion, pro- and anti-inflammatory responses co-exist inside of the granulomas of fatal cases of coccidioidomycosis and the absent of iNOS and IL-12 gene expression may be related with patient's outcome.

A novel model to study neonatal Escherichia coli sepsis and the effect of treatment on the human immune system using humanized mice

PROBLEM

Neonatal sepsis is a serious threat especially for preterm infants. As existing in vitro and in vivo models have limitations, we generated a novel neonatal sepsis model using humanized mice and tested the effect of Betamethasone and Indomethacin which are used in the clinic in case of premature birth.

METHOD OF STUDY

Humanized mice were infected with Escherichia coli (E. coli). Subsequently, the effect of the infection itself, and treatment with Betamethasone and Indomethacin on survival, recovery, bacterial burden, leukocyte populations, and cytokine production, was analyzed.

RESULTS

The human immune system in the animals responded with leukocyte trafficking to the site of infection and granulopoiesis in the bone marrow. Treatment with Indomethacin had no pronounced effect on the immune system or bacterial burden. Betamethasone induced a decline of splenocytes.

CONCLUSION

The human immune system in humanized mice responds to the infection, making them a suitable model to study neonatal E. coli sepsis and the immune response of the neonatal immune system. Treatment with Betamethasone could have potential negative long-term effects for the immune system of the child.

Targeting macrophage immunometabolism: Dawn in the darkness of sepsis

Sepsis is known since the time (470 BC) of great Greek physician, Hippocrates. Advancement in modern medicine and establishment of separate branches of medical science dealing with sepsis research have improved its outcome. However, mortality associated with sepsis still remains higher (25-30%) that further increases to 40-50% in the presence of septic shock. For example, sepsis-associated deaths account more in comparison to deaths-associated with myocardial-infarction and certain cancers (i.e. breast and colorectal cancer). However, it is now well established that profound activation of innate immune cells including macrophages play a very important role in the immunopathogenesis of sepsis. Macrophages are sentinel cells of the innate immune system with their location varying from peripheral blood to various target organs including lungs, liver, brain, kidneys, skin, testes, vascular endothelium etc. Thus, profound and dysregulated activation of these cells during sepsis can directly impact the outcome of sepsis. However, the emergence of the concept of immunometabolism as a major controller of immune response has raised a new hope for identifying new targets for immunomodulatory therapeutic approaches. Thus this present review starts with an introduction of sepsis as a major medical problem worldwide and signifies the role of dysregulated innate immune response including macrophages in its immunopathogenesis. Thereafter, subsequent sections describe changes in immunometabolic stage of macrophages (both M1 and M2) during sepsis. The article ends with the discussion of novel macrophage-specific therapeutic targets targeting their immunometabolism during sepsis and epigenetic regulation of macrophage immunometabolism and vice versa.

CCR2+ Inflammatory Monocytes Are Recruited to Yersinia pseudotuberculosis Pyogranulomas and Dictate Adaptive Responses at the Expense of Innate Immunity during Oral Infection

Murine Ly6C^hi inflammatory monocytes (IMs) require CCR2 to leave the bone marrow and enter mesenteric lymph nodes (MLNs) and other organs in response to Yersinia pseudotuberculosis infection. We are investigating how IMs, which can differentiate into CD11c⁺ dendritic cells (DCs), contribute to innate and adaptive immunity to Y. pseudotuberculosis Previously, we obtained evidence that IMs are important for a dominant CD8⁺ T cell response to the epitope YopE_69-77 and host survival using intravenous infections with attenuated Y. pseudotuberculosis Here we challenged CCR2^+/+ or CCR2^-/- mice orally with wild-type Y. pseudotuberculosis to investigate how IMs contribute to immune responses during intestinal infection. Unexpectedly, CCR2^-/- mice did not have reduced survival but retained body weight better and their MLNs cleared Y. pseudotuberculosis faster and with reduced lymphadenopathy compared to controls. Enhanced bacterial clearance in CCR2^-/- mice correlated with reduced numbers of IMs in spleens and increased numbers of neutrophils in livers. In situ imaging of MLNs and spleens from CCR2-GFP mice showed that green fluorescent protein-positive (GFP⁺) IMs accumulated at the periphery of neutrophil-rich Yersinia-containing pyogranulomas. GFP⁺ IMs colocalized with CD11c⁺ cells and YopE_69-77-specific CD8⁺ T cells in MLNs, suggesting that IM-derived DCs prime adaptive responses in Yersinia pyogranulomas. Consistently, CCR2^-/- mice had reduced numbers of splenic DCs, YopE_69-77-specific CD8⁺ T cells, CD4⁺ T cells, and B cells in organs and lower levels of serum antibodies to Y. pseudotuberculosis antigens. Our data suggest that IMs differentiate into DCs in MLN pyogranulomas and direct adaptive responses in T cells at the expense of innate immunity during oral Y. pseudotuberculosis infection.

The F-Box Protein Fbp1 Shapes the Immunogenic Potential of Cryptococcus neoformans

Cryptococcus neoformans is the main etiologic agent of cryptococcal meningitis and causes a significant number of deadly infections per year. Although it is well appreciated that host immune responses are crucial for defense against cryptococcosis, our understanding of factors that control the development of effective immunity to this fungus remains incomplete. In previous studies, we identified the F-box protein Fbp1 as a novel determinant of C. neoformans virulence. In this study, we found that the hypovirulence of the fbp1Δ mutant is linked to the development of a robust host immune response. Infection with the fbp1Δ mutant induces a rapid influx of CCR2⁺ monocytes and their differentiation into monocyte-derived dendritic cells (mo-DCs). Depletion of CCR2⁺ monocytes and their derivative mo-DCs resulted in impaired activation of a protective inflammatory response and the rapid death of mice infected with the fbp1Δ mutant. Mice lacking B and T cells also developed fungal meningitis and succumbed to infection with the fbp1Δ mutant, demonstrating that adaptive immune responses to the fbp1Δ mutant help to maintain the long-term survival of the host. Adaptive immune responses to the fbp1Δ mutant were characterized by enhanced differentiation of Th1 and Th17 CD4⁺ T cells together with diminished Th2 responses compared to the H99 parental strain. Importantly, we found that the enhanced immunogenicity of fbp1Δ mutant yeast cells can be harnessed to confer protection against a subsequent infection with the virulent H99 parental strain. Altogether, our findings suggest that Fbp1 functions as a novel virulence factor that shapes the immunogenicity of C. neoformansIMPORTANCECryptococcus neoformans is the most common cause of deadly fungal meningitis, with over 270,000 infections per year. Immune responses are critically required for the prevention of cryptococcosis, and patients with impaired immunity and low CD4⁺ T cell numbers are at high risk of developing these deadly infections. Although it is well appreciated that the development of protective immunity is shaped by the interactions of the host immune system with fungal cells, our understanding of fungal products that influence this process remains poor. In this study, we found that the activity of F-box protein 1 (Fbp1) in highly virulent C. neoformans clinical strain H99 shapes its immunogenicity and thus affects the development of protective immune responses in the host. The identification of this new mechanism of virulence may facilitate the future development of therapeutic interventions aimed at boosting antifungal host immunity.

Combination of Classifiers Identifies Fungal-Specific Activation of Lysosome Genes in Human Monocytes

Blood stream infections can be caused by several pathogens such as viruses, fungi and bacteria and can cause severe clinical complications including sepsis. Delivery of appropriate and quick treatment is mandatory. However, it requires a rapid identification of the invading pathogen. The current gold standard for pathogen identification relies on blood cultures and these methods require a long time to gain the needed diagnosis. The use of in situ experiments attempts to identify pathogen specific immune responses but these often lead to heterogeneous biomarkers due to the high variability in methods and materials used. Using gene expression profiles for machine learning is a developing approach to discriminate between types of infection, but also shows a high degree of inconsistency. To produce consistent gene signatures, capable of discriminating fungal from bacterial infection, we have employed Support Vector Machines (SVMs) based on Mixed Integer Linear Programming (MILP). Combining classifiers by joint optimization constraining them to the same set of discriminating features increased the consistency of our biomarker list independently of leukocyte-type or experimental setup. Our gene signature showed an enrichment of genes of the lysosome pathway which was not uncovered by the use of independent classifiers. Moreover, our results suggest that the lysosome genes are specifically induced in monocytes. Real time qPCR of the identified lysosome-related genes confirmed the distinct gene expression increase in monocytes during fungal infections. Concluding, our combined classifier approach presented increased consistency and was able to "unmask" signaling pathways of less-present immune cells in the used datasets.

Functions of Murine Dendritic Cells

Dendritic cells (DCs) play critical roles in activating innate immune cells and initiating adaptive immune responses. The functions of DCs were originally obscured by their overlap with other mononuclear phagocytes, but new mouse models have allowed for the selective ablation of subsets of DCs and have helped to identify their non-redundant roles in the immune system. These tools have elucidated the functions of DCs in host defense against pathogens, autoimmunity, and cancer. This review will describe the mouse models generated to interrogate the role of DCs and will discuss how their use has progressively clarified our understanding of the unique functions of DC subsets.

Peripheral monocytosis as a predictive factor for adverse outcome in the emergency department: Survey based on a register study

Monocytosis is associated with chronic infections such as tuberculosis or endocarditis as well as rheumatic and myeloproliferative disorders. Monocytes are also involved in the pathogenesis of atherosclerosis, coronary artery disease, and stroke. The value of monocytosis as a prognostic marker in different diagnostic groups in the emergency setting, however, has not been investigated so far.The aim of the article is to study monocytosis as an outcome factor in the emergency setting.In a Swiss register study, we analyzed monocyte counts in 4238 patients aged >18 years who were admitted to the emergency department of a regional tertiary care hospital. Monocytosis was defined as 0.8×10 cells/L. Diagnoses were grouped into infection, cardiovascular, neurological, metabolic, gastrointestinal, pulmonary, or other. Thirty-day mortality was defined as the primary endpointA total of 1217 patients with monocytosis were identified. Patients with monocytosis at admission suffered more frequently from respiratory symptoms (17.7% vs 8.9%, P <.001) and infection as the final diagnosis (20.8% vs 10.3%, P <.001) while neurological diagnoses were significantly lower in the monocytosis group (15.3% vs 30.9%, P <.001). Patients with monocytosis suffered from more comorbidities such as congestive heart failure, chronic obstructive pulmonary disease, tumor, diabetes, or renal failure but not dementia. When adjusted for age, gender, comorbidities, and main diagnosis, the 30-day mortality (P = .002) and length of stay (P = .001) were significantly higher in patients with monocytosis. The 30-day mortality in patients with monocytosis was most notably influenced by a cardiological diagnosis (odds ratio 3.91).An increased monocyte count predicts adverse outcome in patients admitted to the emergency department. Mechanistic studies will be necessary to specify the potentially detrimental role of monocytosis in critical illness.

Alterations of zinc homeostasis in response to Cryptococcus neoformans in a murine macrophage cell line

Aim: To evaluate alterations of zinc homeostasis in macrophages exposed to Cryptococcus neoformans. Materials & methods: Using a fluorescent zinc probe-based flow cytometry and atomic absorption spectrometry, zinc levels were evaluated in J774.A1 cell lines exposed to C. neoformans H99 cells. The transcription profile of macrophage zinc related homeostasis genes – metallothioneins and zinc transporters (ZnTs) of the SLC30 and SLC39 (Zrt-Irt-protein) families – was analyzed by quantitative PCR. Results: Macrophage intracellular labile zinc levels decreased following exposure to C. neoformans. A significant decrease in transcription levels was detected in specific ZnTs from both the Zrt-Irt-protein and ZnT families, especially 24 h after infection. Conclusion: These findings suggest that macrophages may exhibit zinc depletion in response to C. neoformans infection.

Negative Regulation of Type 2 Immunity

Type 2 immunity encompasses the mechanisms through which the immune system responds to helminths and an array of environmental substances such as allergens. In the developing world, billions of individuals are chronically infected with endemic parasitic helminths. In comparison, in the industrialized world, millions of individuals suffer from dysregulated type 2 immunity, referred to clinically as atopic diseases including asthma, allergic rhinitis, and atopic dermatitis. Thus, type 2 immunity must be carefully regulated to mount protective host responses yet avoid inappropriate activation and immunopathology. In this review, we describe the key players and connections at play in type 2 responses and focus on the emerging mechanisms involved in the negative regulation of type 2 immunity.

TLR10 suppresses the activation and differentiation of monocytes with effects on DC-mediated adaptive immune responses

TLRs are important pattern-recognition receptors involved in the activation of innate immune responses against foreign pathogens. TLR10 is the only TLR family member without a known ligand, signaling pathway, or clear cellular function. Previous work has shown that TLR10 suppresses proinflammatory cytokine production in response to TLR agonists in a mixed human mononuclear cell population. We report that TLR10 is preferentially expressed on monocytes and suppresses proinflammatory cytokine production resulting from either TLR or CD40 stimulation. TLR10 engagement affects both the MAPK and Akt signaling pathways, leading to changes in the transcriptome of isolated human monocytes. Differentiation of monocytes into dendritic cells in the presence of an αTLR10 mAb reduced the expression of maturation markers and the induction of proinflammatory cytokines, again in response to either TLR or CD40 stimulation. Finally, in coculture experiments, TLR10 differentiated dendritic cells exhibited a decreased capacity to activate T cells as measured by IL-2 and IFN-γ production. These data demonstrate that TLR10 is a novel regulator of innate immune responses and of the differentiation of primary human monocytes into effective dendritic cells.

Death of Monocytes through Oxidative Burst of Macrophages and Neutrophils: Killing in Trans

Monocytes and their descendants, macrophages, play a key role in the defence against pathogens. They also contribute to the pathogenesis of inflammatory diseases. Therefore, a mechanism maintaining a balance in the monocyte/macrophage population must be postulated. Our previous studies have shown that monocytes are impaired in DNA repair, rendering them vulnerable to genotoxic stress while monocyte-derived macrophages are DNA repair competent and genotoxic stress-resistant. Based on these findings, we hypothesized that monocytes can be selectively killed by reactive oxygen species (ROS) produced by activated macrophages. We also wished to know whether monocytes and macrophages are protected against their own ROS produced following activation. To this end, we studied the effect of the ROS burst on DNA integrity, cell death and differentiation potential of monocytes. We show that monocytes, but not macrophages, stimulated for ROS production by phorbol-12-myristate-13-acetate (PMA) undergo apoptosis, despite similar levels of initial DNA damage. Following co-cultivation with ROS producing macrophages, monocytes displayed oxidative DNA damage, accumulating DNA single-strand breaks and a high incidence of apoptosis, reducing their ability to give rise to new macrophages. Killing of monocytes by activated macrophages, termed killing in trans, was abolished by ROS scavenging and was also observed in monocytes co-cultivated with ROS producing activated granulocytes. The data revealed that monocytes, which are impaired in the repair of oxidised DNA lesions, are vulnerable to their own ROS and ROS produced by macrophages and granulocytes and support the hypothesis that this is a mechanism regulating the amount of monocytes and macrophages in a ROS-enriched inflammatory environment.

Differences in Inflammatory Response Induced by Two Representatives of Clades of the Pandemic ST258 Klebsiella pneumoniae Clonal Lineage Producing KPC-Type Carbapenemases

ST258-K. pneumoniae (ST258-KP) strains, the most widespread multidrug-resistant hospital-acquired pathogens, belong to at least two clades differing in a 215 Kb genomic region that includes the cluster of capsule genes. To investigate the effects of the different capsular phenotype on host-pathogen interactions, we studied representatives of ST258-KP clades, KKBO-1 and KK207-1, for their ability to activate monocytes and myeloid dendritic cells from human immune competent hosts. The two ST258-KP strains strongly induced the production of inflammatory cytokines. Significant differences between the strains were found in their ability to induce the production of IL-1β: KK207-1/clade I was much less effective than KKBO-1/clade II in inducing IL-1β production by monocytes and dendritic cells. The activation of NLRP3 inflammasome pathway by live cells and/or purified capsular polysaccharides was studied in monocytes and dendritic cells. We found that glibenclamide, a NLRP3 inhibitor, inhibits more than 90% of the production of mature IL-1β induced by KKBO1 and KK207-1. KK207-1 was always less efficient compared to KKBO-1 in: a) inducing NLRP3 and pro-IL-1β gene and protein expression; b) in inducing caspase-1 activation and pro-IL-1β cleavage. Capsular composition may play a role in the differential inflammatory response induced by the ST258-KP strains since capsular polysaccharides purified from bacterial cells affect NLRP3 and pro-IL-1β gene expression through p38MAPK- and NF-κB-mediated pathways. In each of these functions, capsular polysaccharides from KK207-1 were significantly less efficient compared to those purified from KKBO-1. On the whole, our data suggest that the change in capsular phenotype may help bacterial cells of clade I to partially escape innate immune recognition and IL-1β-mediated inflammation.

Dendritic Cells in the Immune System—History, Lineages, Tissues, Tolerance, and Immunity

The aim of this review is to provide a coherent framework for understanding dendritic cells (DCs). It has seven sections. The introduction provides an overview of the immune system and essential concepts, particularly for the nonspecialist reader. Next, the “History” section outlines the early evolution of ideas about DCs and highlights some sources of confusion that still exist today. The “Lineages” section then focuses on five different populations of DCs: two subsets of “classical” DCs, plasmacytoid DCs, monocyte-derived DCs, and Langerhans cells. It highlights some cellular and molecular specializations of each, and also notes other DC subsets that have been proposed. The following “Tissues” section discusses the distribution and behavior of different DC subsets within nonlymphoid and secondary lymphoid tissues that are connected by DC migration pathways between them. In the “Tolerance” section, the role of DCs in central and peripheral tolerance is considered, including their ability to drive the differentiation of different populations of regulatory T cells. In contrast, the “Immunity” section considers the roles of DCs in sensing of infection and tissue damage, the initiation of primary responses, the T-cell effector phase, and the induction of immunological memory. The concluding section provides some speculative ideas about the evolution of DCs. It also revisits earlier concepts of generation of diversity and clonal selection in terms of DCs driving the evolution of T-cell responses. Throughout, this review highlights certain areas of uncertainty and suggests some avenues for future investigation.

LPS-Activated Monocytes Are Unresponsive to T4 Phage and T4-Generated Escherichia coli Lysate

A growing body of data shows that bacteriophages can interact with different kinds of immune cells. The objective of this study was to investigate whether T4 bacteriophage and T4-generated Escherichia coli lysate affect functions of monocytes, the key population of immune cells involved in antibacterial immunity. To that end, we evaluated how T4 and E. coli lysate influence the expression of main costimulatory molecules including CD40, CD80 and CD86, TLR2, TLR4 on monocytes, as well as the production of IL-6 and IL-12 in cultures of peripheral blood mononuclear cells (PBMCs). Separate experiments were performed on unactivated and LPS-activated PBMCs cultures. Both studied preparations significantly increased the percentage of CD14⁺CD16^-CD40⁺ and CD14⁺CD16^-CD80⁺ monocytes in unactivated PBMCs cultures, as well as the concentration of IL-6 and IL-12 in culture supernates. However, neither purified T4 nor E. coli lysate had any significant effect on monocytes in LPS-activated PBMCs cultures. We conclude that LPS-activated monocytes are unresponsive to phages and products of phage-induced lysis of bacteria. This study is highly relevant to phage therapy because it suggests that in patients with infections caused by Gram-negative bacteria the administration of phage preparations to patients and lysis of bacteria by phages are not likely to overly stimulate monocytes.