Monocytes from cystic fibrosis patients are locked in an LPS tolerance state: down-regulation of TREM-1 as putative underlying mechanism

Endotoxin tolerance and trained immunity: breaking down immunological memory barriers

For decades, innate immune cells were considered unsophisticated first responders, lacking the adaptive memory of their T and B cell counterparts. However, mounting evidence demonstrates the surprising complexity of innate immunity. Beyond quickly deploying specialized cells and initiating inflammation, two fascinating phenomena - endotoxin tolerance (ET) and trained immunity (TI) - have emerged. ET, characterized by reduced inflammatory response upon repeated exposure, protects against excessive inflammation. Conversely, TI leads to an enhanced response after initial priming, allowing the innate system to mount stronger defences against subsequent challenges. Although seemingly distinct, these phenomena may share underlying mechanisms and functional implications, blurring the lines between them. This review will delve into ET and TI, dissecting their similarities, differences, and the remaining questions that warrant further investigation.

Neuropsychiatric adverse effects from CFTR modulators deserve a serious research effort

PURPOSE OF REVIEW

This review highlights the problem of neuropsychiatric adverse effects (AEs) associated with elexacaftor/tezacaftor/ivacaftor (ETI), current suboptimal mitigation approaches, a novel testable mechanistic hypothesis, and potential solutions requiring further research.

RECENT FINDINGS

Studies show that a minority of persons with cystic fibrosis (PwCF) initiating cystic fibrosis transmembrane conductance regulator (CFTR) modulators experience neuropsychiatric AEs including worsening mood, cognition, anxiety, sleep, and suicidality. The GABA-A receptor is a ligand-gated chloride channel, and magnetic resonance spectroscopy neuroimaging studies have shown that reduced GABA expression in rostral anterior cingulate cortex is associated with anxiety and depression. Recent research details the impact of peripheral inflammation and the gut-brain axis on central neuroinflammation. Plasma ETI concentrations and sweat chloride have been evaluated in small studies of neuropsychiatric AEs but not validated to guide dose titration or correlated with pharmacogenomic variants or safety/efficacy.

SUMMARY

Although ETI is well tolerated by most PwCF, some experience debilitating neuropsychiatric AEs. In some cases, these AEs may be driven by modulation of CFTR and chloride transport within the brain. Understanding biological mechanisms is a critical next step in identifying which PwCF are likely to experience AEs, and in developing evidence-based strategies to mitigate them, while retaining modulator efficacy.

Update on Innate and Adaptive Immunity in Cystic Fibrosis

Cystic fibrosis (CF) pathophysiology is hallmarked by excessive inflammation and the inability to resolve lung infections, contributing to morbidity and eventually mortality. Paradoxically, despite a robust inflammatory response, CF lungs fail to clear bacteria and are susceptible to chronic infections. Impaired mucociliary transport plays a critical role in chronic infection but the immune mechanisms contributing to the adaptation of bacteria to the lung microenvironment is not clear. CFTR modulator therapy has advanced CF life expectancy opening up the need to understand changes in immunity as CF patients age. Here, we have summarized the current understanding of immune dysregulation in CF.

The Impact of Highly Effective Modulator Therapy on Cystic Fibrosis Microbiology and Inflammation

Highly effective cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulator therapy (HEMT) corrects the underlying molecular defect causing CF disease. HEMT decreases symptom burden and improves clinical metrics and quality of life for most people with CF (PwCF) and eligible cftr mutations. Improvements in measures of pulmonary health suggest that restoration of function of defective CFTR anion channels by HEMT not only enhances airway mucociliary clearance, but also reduces chronic pulmonary infection and inflammation. This article reviews the evidence for how HEMT influences the dynamic and interdependent processes of infection and inflammation in the CF airway, and what questions remain unanswered.

Paeoniflorin Attenuated TREM-1-Mediated Inflammation in THP-1 Cells

Sepsis is caused by bacterial infections or viral infections. Clinically, there exist confirmed or highly suspected infection foci. Mortality caused by septic shock remains in a high rate even though antibiotic treatment works effectively. In this study, we treat THP-1 cells with 1 ug/mL LPS (lipopolysaccharide) and add paeoniflorin or LR-12 inhibitor. TREM-1 (triggering receptor expressed on myeloid cells-1), IL-6, IL-1β, and TNF-α (tumour necrosis factor alpha (a)-cachectin) were detected by ELISA and qRT-PCR, and western blotting is performed to detect related proteins in the NF-κB signaling pathway. As a result, paeoniflorin can significantly reduce the production of LPS-stimulated TREM-1 as well as inflammatory factors and attenuate the phosphorylation of NF-κB signaling pathway-related factors, such as p65 and IκBα. At the same time, the combined effect of paeoniflorin and LR-12 is more significant. The results of this study solidly prove that paeoniflorin plays a role in inhibiting TREM-1-mediated inflammation and the NF-κB pathway could be a potential mechanism of action.

CFTR-mediated monocyte/macrophage dysfunction revealed by cystic fibrosis proband-parent comparisons

Cystic fibrosis (CF) is an inherited disorder caused by biallelic mutations of the CF transmembrane conductance regulator (CFTR) gene. Converging evidence suggests that CF carriers with only 1 defective CFTR copy are at increased risk for CF-related conditions and pulmonary infections, but the molecular mechanisms underpinning this effect remain unknown. We performed transcriptomic profiling of peripheral blood mononuclear cells (PBMCs) of CF child-parent trios (proband, father, and mother) and healthy control (HC) PBMCs or THP-1 cells incubated with the plasma of these participants. Transcriptomic analyses revealed suppression of cytokine-enriched immune-related genes (IL-1β, CXCL8, CREM), implicating lipopolysaccharide tolerance in innate immune cells (monocytes) of CF probands and their parents. These data suggest that a homozygous as well as a heterozygous CFTR mutation can modulate the immune/inflammatory system. This conclusion is further supported by the finding of lower numbers of circulating monocytes in CF probands and their parents, compared with HCs, and the abundance of mononuclear phagocyte subsets, which correlated with Pseudomonas aeruginosa infection, lung disease severity, and CF progression in the probands. This study provides insight into demonstrated CFTR-related innate immune dysfunction in individuals with CF and carriers of a CFTR mutation that may serve as a target for personalized therapy.

Secondary Immunodeficiency Related to Kidney Disease (SIDKD)-Definition, Unmet Need, and Mechanisms

Kidney disease is a known risk factor for poor outcomes of COVID-19 and many other serious infections. Conversely, infection is the second most common cause of death in patients with kidney disease. However, little is known about the underlying secondary immunodeficiency related to kidney disease (SIDKD). In contrast to cardiovascular disease related to kidney disease, which has triggered countless epidemiologic, clinical, and experimental research activities or interventional trials, investments in tracing, understanding, and therapeutically targeting SIDKD have been sparse. As a call for more awareness of SIDKD as an imminent unmet medical need that requires rigorous research activities at all levels, we review the epidemiology of SIDKD and the numerous aspects of the abnormal immunophenotype of patients with kidney disease. We propose a definition of SIDKD and discuss the pathogenic mechanisms of SIDKD known thus far, including more recent insights into the unexpected immunoregulatory roles of elevated levels of FGF23 and hyperuricemia and shifts in the secretome of the intestinal microbiota in kidney disease. As an ultimate goal, we should aim to develop therapeutics that can reduce mortality due to infections in patients with kidney disease by normalizing host defense to pathogens and immune responses to vaccines.

Soluble Triggering Receptor on Myeloid Cell-1 and its Predictive Factors in Patients With End-Stage Kidney Disease on Hemodialysis

Triggering receptor expressed on myeloid cells (TREM)-1 is a potent and early amplifier of the inflammatory response expressed on neutrophils and monocytes/macrophages. TREM-1, and its soluble form (sTREM-1), are increased in sepsis and other noninfectious inflammatory conditions. However, virtually no data are available in kidney disease. To determine serum sTREM-1 and its associated variables in patients on hemodialysis (HD), cross-sectional study including 264 HD patients and 148 controls. sTREM-1 was measured by quantitative sandwich enzyme immunoassay; soluble tumor necrosis factor receptor-1 (sTNF-R1), interleukin-6 (IL-6), and C-reactive protein (CRP) were also measured. All inflammation markers were significantly higher in HD patients than controls. Median (IQR) sTREM-1 was 1,006 (613-1,650) pg/mL but undetectable in controls. Considering only HD patients, sTREM-1 was positively correlated with IL-6 (r = 0.19, p = 0.008), and its levels were significantly higher in patients with arteriovenous fistula than in those with temporary catheter (1,226 vs. 743 pg/mL), in patients with 3 HD sessions/week than in those with 2 sessions/week (1,150 vs. 646 pg/mL), and in patients with >1 year on HD than in those with ≤1 year (1,100 vs. 948 pg/mL), whereas they were not different regarding age or presence of infection. Serum sTREM-1, sTNF-R1, IL-6, and CRP were higher in HD patients compared to controls. In HD patients, sTREM-1 displayed higher levels in individuals with arteriovenous fistula, 3 sessions/week and longer vintage, but not in those with infection or older age; in multivariate analysis, only the first two variables significantly predicted higher sTREM-1 levels.

SARS-CoV-2 Proteins Induce Endotoxin Tolerance Hallmarks: A Demonstration in Patients with COVID-19

According to a large number of reported cohorts, sepsis has been observed in nearly all deceased patients with COVID-19. We and others have described sepsis, among other pathologies, to be an endotoxin tolerance (ET)-related disease. In this study, we demonstrate that the culture of human blood cells from healthy volunteers in the presence of SARS-CoV-2 proteins induced ET hallmarks, including impairment of proinflammatory cytokine production, low MHC class II (HLA-DR) expression, poor T cell proliferation, and enhancing of both phagocytosis and tissue remodeling. Moreover, we report the presence of SARS-CoV-2 blood circulating proteins in patients with COVID-19 and how these levels correlate with an ET status, the viral RNA presence of SARS-CoV-2 in plasma, as well as with an increase in the proportion of patients with secondary infections.

Effect of purine-rich box1 on proliferation of fibroblasts

Fibroblasts are pleomorphic cells that have a multi-directional effect on organ morphogenesis, tissue homeostasis, and immune response. In fibrotic diseases, fibroblasts synthesize large amounts of extracellular matrix (ECM), leading to scarring and organ failure. Purine-rich box1 (PU.1) is a specific transcription factor of hematopoietic cell and belongs to the E26 transformation specificity (ETS) family. Recently, it was found that the transcription factor PU.1 is an important regulatory factor of the profibrotic gene expression program. TGF-β had been proved to play an important role in many ocular tissue fibrosis diseases, and up-regulated the expression of PU.1 in fibroblasts producing ECM in a Smad-3 dependent manner. We explore the effect of PU.1 on fibrosis of different ocular tissues from this perspective. This article reviews the role of PU.1 and its effects on fibrosis of ocular tissue and other tissues.

CFTR Modulator Therapy Enhances Peripheral Blood Monocyte Contributions to Immune Responses in People With Cystic Fibrosis

Background

CFTR modulators decrease some etiologies of CF airway inflammation; however, data indicate that non-resolving airway infection and inflammation persist in individuals with CF and chronic bacterial infections. Thus, identification of therapies that diminish airway inflammation without allowing unrestrained bacterial growth remains a critical research goal. Novel strategies for combatting deleterious airway inflammation in the CFTR modulator era require better understanding of cellular contributions to chronic CF airway disease, and how inflammatory cells change after initiation of CFTR modulator therapy. Peripheral blood monocytes, which traffic to the CF airway, can develop both pro-inflammatory and inflammation-resolving phenotypes, represent intriguing cellular targets for focused therapies. This therapeutic approach, however, requires a more detailed knowledge of CF monocyte cellular programming and phenotypes.

Material and Methods

In order to characterize the inflammatory phenotype of CF monocytes, and how these cells change after initiation of CFTR modulator therapy, we studied adults (n=10) with CF, chronic airway infections, and the CFTR-R117H mutations before and 7 days after initiation of ivacaftor. Transcriptomes of freshly isolated blood monocytes were interrogated by RNA-sequencing (RNA-seq) followed by pathway-based analyses. Plasma concentrations of cytokines and chemokines were evaluated by multiplex ELISA.

Results

RNAseq identified approximately 50 monocyte genes for which basal expression was significantly changed in all 10 subjects after 7 days of ivacaftor. Of these, the majority were increased in expression post ivacaftor, including many genes traditionally associated with enhanced inflammation and immune responses. Pathway analyses confirmed that transcriptional programs were overwhelmingly up-regulated in monocytes after 7 days of ivacaftor, including biological modules associated with immunity, cell cycle, oxidative phosphorylation, and the unfolded protein response. Ivacaftor increased plasma concentrations of CXCL2, a neutrophil chemokine secreted by monocytes and macrophages, and CCL2, a monocyte chemokine.

Conclusions

Our results demonstrate that ivacaftor causes acute changes in blood monocyte transcriptional profiles and plasma chemokines, and suggest that increased monocyte inflammatory signals and changes in myeloid cell trafficking may contribute to changes in airway inflammation in people taking CFTR modulators. To our knowledge, this is the first report investigating the transcriptomic response of circulating blood monocytes in CF subjects treated with a CFTR modulator.

Triggering receptor expressed on myeloid cells-1 (TREM-1) as a therapeutic target in infectious and noninfectious disease: a critical review

The triggering receptor expressed on myeloid cells-1 (TREM-1) is an innate immune receptor found in the surface of several immune and non-immune cells. Since its first description in 2000, this molecule and its soluble form (sTREM-1) have been implicated in many diseases with infectious and noninfectious origins. As an amplifier of inflammation, the membrane-associated TREM-1 (mTREM-1) isoform induces the production of pro-inflammatory mediators, thus contributing to the pathogenesis of diseases such as sepsis, arthritis, colitis and infections. In this context, many studies have used molecules capable of inhibiting TREM-1 activity as anti-inflammatory drugs. In this regard, a few peptides have been showing promising results in the amelioration of detrimental immune responses. Some commercially available drugs, including corticosteroids and antibiotics, with known anti-inflammatory effects, have also shown activity in TREM-1 signaling. Therefore, considering the potential of this receptor as a therapeutic target, the present review encompasses the main compounds explored so far in TREM-1 modulation, highlighting and critically discussing its effects and major drawbacks of such approaches.

Ivacaftor decreases monocyte sensitivity to interferon-γ in people with cystic fibrosis

This study demonstrates that initiation of the CFTR modulator ivacaftor in people with cystic fibrosis and susceptible CFTR mutations causes an acute reduction in blood monocyte sensitivity to the key proinflammatory cytokine IFN-γ http://bit.ly/2TeI6LG.

Salivary biomarkers in the context of gingival inflammation in children with cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) is a life-threatening chronic inflammatory disease in children due to respiratory complications. Saliva could serve as a reservoir of bacterial colonization and potentially reflect systemic inflammation. This study investigated whether salivary triggering receptor expressed on myeloid cells 1 (TREM-1), peptidoglycan recognition protein 1 (PGLYRP1), interleukin (IL)-1β, and calprotectin are associated with CF or reflect concomitant gingival inflammation.

METHODS

Ten CF (aged 3 to 12 years) and 10 systemically healthy (SH) age- and sex-matched children (C) were enrolled in the study. Individuals with CF underwent routine laboratory determinations. Probing depth, gingival index (GI), plaque index (PI), and bleeding on probing (BOP) were recorded on fully erupted teeth and saliva samples collected. Salivary TREM-1, PGLYRP1, IL-1β, and calprotectin were analyzed by enzyme-linked immunosorbent assay.

RESULTS

Children with CF had significantly higher BOP scores (P = 0.001) and calprotectin levels (P = 0.017) compared with the C group. TREM-1, PGLYRP1, and IL-1β could not distinguish between CF and SH but showed positive correlation with GI, PI, and BOP in both groups. Calprotectin levels positively correlated with procalcitonin (P = 0.014), thrombocyte counts (P = 0.001), mean platelet volume (P = 0.030), and with PGLYRP1 (P = 0.019) and IL-1β (P = 0.013) in CF children. Receiver operating characteristic curve analysis for calprotectin (CFvsC) showed an area under the curve of 0.79 (95% CI 0.58 to 0.99, P = 0.034).

CONCLUSIONS

CF children presented with higher gingival inflammation scores and salivary calprotectin levels, that correlated with systemic inflammatory markers. Salivary calprotectin levels were not associated with periodontal parameters. Hence, preliminary data demonstrate that salivary calprotectin might have a chairside diagnostic potential for CF in children.

Strong toll-like receptor responses in cystic fibrosis patients are associated with higher lung function

BACKGROUND

Cystic fibrosis (CF) airways disease varies widely among patients with identical cystic fibrosis transmembrane conductance regulator (CFTR) genotypes. Robust airway inflammation is thought to be deleterious in CF; inter-individual variation in Toll-like receptor (TLR)-mediated innate immune inflammatory responses (TMIIR) might account for a portion of the phenotypic variation. We tested if TMIIR in people with CF are different than those of healthy controls, and whether higher TMIIR in people with CF are associated with reduced lung function.

METHODS

We cultured whole blood from clinically stable subjects with CF (n = 76) and healthy controls (n = 45) with TLR agonists, and measured cytokine production and expression of TLR-associated genes. We tested for differences in TLR-stimulated cytokine levels between subjects with CF and healthy subjects, and for associations between cytokine and gene expression levels with baseline lung function (forced expiratory volume in one second percent predicted (FEV₁%)) and decline in FEV₁% over time.

RESULTS

TMIIR in blood from subjects with CF were lower than in healthy controls. Expression of TLR regulators SARM1, TOLLIP, and AKT1 were downregulated in CF. In subjects with CF we found that lower TLR4-agonist-induced IL-8 was associated with lower FEV₁% at enrollment (p<0.001) and with greater five year FEV₁% decline (p<0.001).

CONCLUSIONS

TMIIR were lower in people with CF relative to healthy controls; however, unexpectedly, greater whole blood TMIIR were positively associated with lung function in people with CF. These findings suggest a complex interaction between inflammation and disease in people with CF.

ENaC-mediated sodium influx exacerbates NLRP3-dependent inflammation in cystic fibrosis

Cystic Fibrosis (CF) is a monogenic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, resulting in defective CFTR-mediated chloride and bicarbonate transport, with dysregulation of epithelial sodium channels (ENaC). These changes alter fluid and electrolyte homeostasis and result in an exaggerated proinflammatory response driven, in part, by infection. We tested the hypothesis that NLRP3 inflammasome activation and ENaC upregulation drives exaggerated innate-immune responses in this multisystem disease. We identify an enhanced proinflammatory signature, as evidenced by increased levels of IL-18, IL-1β, caspase-1 activity and ASC-speck release in monocytes, epithelia and serum with CF-associated mutations; these differences were reversed by pretreatment with NLRP3 inflammasome inhibitors and notably, inhibition of amiloride-sensitive sodium (Na⁺) channels. Overexpression of β-ENaC, in the absence of CFTR dysfunction, increased NLRP3-mediated inflammation, indicating that dysregulated, ENaC-dependent signalling may drive exaggerated inflammatory responses in CF. These data support a role for sodium in modulating NLRP3 inflammasome activation.

Cystic Fibrosis Plasma Blunts the Immune Response to Bacterial Infection

Cystic fibrosis (CF) is caused by mutations of the gene encoding the CF transmembrane conductance regulator. It remains unclear whether the abnormal immune response in CF involves extrinsic signals released from the external or internal environment. We sought to characterize the peripheral immune signatures in CF and its association with clinical phenotypes. Healthy peripheral blood mononuclear cells (PBMCs) were cultured with plasma from CF probands (CFPs) or healthy control subjects (HCs) followed by nCounter gene and microRNA (miRNA) profiling. A discovery cohort of 12 CFPs and 12 HCs and a validation cohort of 103 CFPs and 31 HCs (our previous microarray data [GSE71799]) were analyzed to characterize the composition of cultured immune cells and establish a miRNA‒mRNA network. Cell compositions and miRNA profiles were associated with clinical characteristics of the cohorts. Significantly differentially expressed genes and abundance of myeloid cells were downregulated in PMBCs after culture with CF plasma (P < 0.05). Top-ranked miRNAs that increased in response to CF plasma (adjusted P < 0.05) included miR-155 and miR-146a, which target many immune-related genes, such as IL-8. Pseudomonas aeruginosa infection was negatively associated with abundance of monocytes and the presence of those regulatory miRNAs. Extrinsic signals in plasma from patients with CF led to monocyte inactivation and miRNA upregulation in PBMCs. An improved understanding of the immune effects of extrinsic factors in CF holds great promise for integrating immunomodulatory cell therapies into current treatment strategies in CF.

Transcriptional consequences of impaired immune cell responses induced by cystic fibrosis plasma characterized via dual RNA sequencing

Background

In cystic fibrosis (CF), impaired immune cell responses, driven by the dysfunctional CF transmembrane conductance regulator (CFTR) gene, may determine the disease severity but clinical heterogeneity remains a major therapeutic challenge. The characterization of molecular mechanisms underlying impaired immune responses in CF may reveal novel targets with therapeutic potential. Therefore, we utilized simultaneous RNA sequencing targeted at identifying differentially expressed genes, transcripts, and miRNAs that characterize impaired immune responses triggered by CF and its phenotypes.

Methods

Peripheral blood mononuclear cells (PBMCs) extracted from a healthy donor were stimulated with plasma from CF patients (n = 9) and healthy controls (n = 3). The PBMCs were cultured (1 × 10⁵ cells/well) for 9 h at 37 ° C in 5% CO₂. After culture, total RNA was extracted from each sample and used for simultaneous total RNA and miRNA sequencing.

Results

Analysis of expression signatures from peripheral blood mononuclear cells induced by plasma of CF patients and healthy controls identified 151 genes, 154 individual transcripts, and 41 miRNAs differentially expressed in CF compared to HC while the expression signatures of 285 genes, 241 individual transcripts, and seven miRNAs differed due to CF phenotypes. Top immune pathways influenced by CF included agranulocyte adhesion, diapedesis signaling, and IL17 signaling, while those influenced by CF phenotypes included natural killer cell signaling and PI3K signaling in B lymphocytes. Upstream regulator analysis indicated dysregulation of CCL5, NF-κB and IL1A due to CF while dysregulation of TREM1 and TP53 regulators were associated with CF phenotype. Five miRNAs showed inverse expression patterns with three target genes relevant in CF-associated impaired immune pathways while two miRNAs showed inverse expression patterns with two target genes relevant to a dysregulated immune pathway associated with CF phenotypes.

Conclusions

Our results indicate that miRNAs and individual transcript variants are relevant molecular targets contributing to impaired immune cell responses in CF.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0529-0) contains supplementary material, which is available to authorized users.

Myalgic encephalomyelitis or chronic fatigue syndrome: how could the illness develop?

A model of the development and progression of chronic fatigue syndrome (myalgic encephalomyelitis), the aetiology of which is currently unknown, is put forward, starting with a consideration of the post-infection role of damage-associated molecular patterns and the development of chronic inflammatory, oxidative and nitrosative stress in genetically predisposed individuals. The consequences are detailed, including the role of increased intestinal permeability and the translocation of commensal antigens into the circulation, and the development of dysautonomia, neuroinflammation, and neurocognitive and neuroimaging abnormalities. Increasing levels of such stress and the switch to immune and metabolic downregulation are detailed next in relation to the advent of hypernitrosylation, impaired mitochondrial performance, immune suppression, cellular hibernation, endotoxin tolerance and sirtuin 1 activation. The role of chronic stress and the development of endotoxin tolerance via indoleamine 2,3-dioxygenase upregulation and the characteristics of neutrophils, monocytes, macrophages and T cells, including regulatory T cells, in endotoxin tolerance are detailed next. Finally, it is shown how the immune and metabolic abnormalities of chronic fatigue syndrome can be explained by endotoxin tolerance, thus completing the model.

Transcriptional and functional diversity of human macrophage repolarization

BACKGROUND

Macrophage plasticity allows cells to adopt different phenotypes, a property with important implications in disorders such as cystic fibrosis (CF) and asthma.

OBJECTIVE

We sought to examine the transcriptional and functional significance of macrophage repolarization from an M1 to an M2 phenotype and assess the role of a common human genetic disorder (CF) and a prototypical allergic disease (asthma) in this transformation.

METHODS

Monocyte-derived macrophages were collected from healthy subjects and patients with CF and polarized to an M2 state by using IL-4, IL-10, glucocorticoids, apoptotic PMNs, or azithromycin. We performed transcriptional profiling and pathway analysis for each stimulus. We assessed the ability of M2-repolarized macrophages to respond to LPS rechallenge and clear apoptotic neutrophils and used murine models to determine conserved functional responses to IL-4 and IL-10. We investigated whether M2 signatures were associated with alveolar macrophage phenotypes in asthmatic patients.

RESULTS

We found that macrophages exhibit highly diverse responses to distinct M2-polarizing stimuli. Specifically, IL-10 activated proinflammatory pathways and abrogated LPS tolerance, allowing rapid restoration of LPS responsiveness. In contrast, IL-4 enhanced LPS tolerance, dampening proinflammatory responses after repeat LPS challenge. A common theme observed across all M2 stimuli was suppression of interferon-associated pathways. We found that CF macrophages had intact reparative and transcriptional responses, suggesting that macrophage contributions to CF-related lung disease are primarily shaped by their environment. Finally, we leveraged in vitro-derived signatures to show that allergen provocation induces distinct M2 state transcriptional patterns in alveolar macrophages.

CONCLUSION

Our findings highlight the diversity of macrophage polarization, attribute functional consequences to different M2 stimuli, and provide a framework to phenotype macrophages in disease states.

Pseudomonas aeruginosa colonization causes PD-L1 overexpression on monocytes, impairing the adaptive immune response in patients with cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) is an endotoxin tolerance (ET)-related disease. Given that increased PD-L1 has been reported in ET, its expression and physiological effects on cystic fibrosis monocytes should be studied.

METHODS

We analyzed the phenotype and ex vivo response of immune system cells in 32 patients with CF, 19 of them colonized by Pseudomonas aeruginosa. An in vitro model was developed of Pseudomonas aeruginosa colonization using purified lipopolysaccharides (LPS) from one of the most prevalent strains in patients with CF (a CF-adapted Pseudomonas aeruginosa ST395 clone). Changes in the immune response, including cytokine production and T-lymphocyte proliferation, as well as expression of PD-L1, were evaluated.

RESULTS

PD-L1 was overexpressed in the monocytes of patients with CF compared with healthy volunteers, and levels of this immune checkpoint were associated with Pseudomonas aeruginosa colonization. In addition, patients with Pseudomonas aeruginosa colonization showed a patent ET status, including poor inflammatory response, reduced HLA-DR expression and T-lymphocyte proliferation impairment. PD-L1/PD-1 blocking assays reverted the impaired adaptive response. Ultimately, monocytes from healthy volunteers cultured in the presence of the clinically relevant strain of Pseudomonas aeruginosa or serum collected from patients with CF colonized by Pseudomonas aeruginosa reproduced the previous observed features.

CONCLUSIONS

Pseudomonas aeruginosa colonization in patients with CF was associated with PD-L1 overexpression and impaired T cell response, and LPS from this pathogen induced the observed phenotype. Our findings open new avenues for the use of anti-PD-1/PD-L1 immunotherapy in patients with CF who are colonized by Pseudomonas aeruginosa.

Prolonged lipopolysaccharide exposure induces transient immunosuppression in BV2 microglia

Continuous pre-exposure of immune cells to low level of inflammatory stimuli makes them hyporesponsive to subsequent exposure. This pathophysiological adaptation; known as endotoxin tolerance is a general paradigm behind several disease pathogenesis. Current study deals with this immunosuppression with respect to BV2 microglia. We attempted to investigate their immune response under prolonged endotoxin exposure and monitor the same upon withdrawal of the stimuli. BV2 microglia cells were maintained under continual exposure of lipopolysaccharide (LPS) for weeks with regular passage after 72 hr (prolonged LPS exposed cells [PLECs]). PLECs were found to be immunosuppressed with diminished expression of proinflammatory cytokines (IL6, IL1β, TNF-α, and iNOS) and production of nitric oxide, as compared to once LPS exposed cells. Upon remaintenance of cells in normal media without LPS exposure (LPS withdrawal cells [LWCs]), the induced immunosuppression reversed and cells started responding to inflammatory stimuli; revealed by significant expression of proinflammatory cytokines. LWCs showed functional similarities to never LPS exposed cells (NLECs) in phagocytosis activity and their response to anti-inflammatory agents like dexamethasone. Despite their immunoresponsiveness, PLECs were inflamed and showed higher autophagy rate than NLECs. Additionally, we investigated the role of inhibitor of apoptotic proteins (IAPs) in PLECs to understand whether IAPs aids in the survival of microglial cells under stress conditions. Our results revealed that cIAP1 and cIAP2 are induced in PLECs which might play a role in retaining the viability. Furthermore, antagonism of IAPs has significantly induced cell death in PLECs suggesting the role of IAPs in microglial survival under stress condition. Conclusively, our data suggest that continuous exposure of BV2 microglia cells to LPS results in transient immunosuppression and indicates the involvement of IAPs in retaining their viability under inflammatory stress.

Sepsis Diagnostics in the Era of "Omics" Technologies

Sepsis is a multifactorial clinical syndrome with an extremely dynamic clinical course and with high diverse clinical phenotype. Early diagnosis is crucial for the final clinical outcome. Previous studies have not identified a biomarker for the diagnosis of sepsis which would have sufficient sensitivity and specificity. Identification of the infectious agents or the use of molecular biology, next gene sequencing, has not brought significant benefit for the patient in terms of early diagnosis. Therefore, we are currently searching for biomarkers, through "omics" technologies with sufficient diagnostic specificity and sensitivity, able to predict the clinical course of the disease and the patient response to therapy. Current progress in the use of systems biology technologies brings us hope that by using big data from clinical trials such biomarkers will be found.

PKR inhibition mediates endotoxin tolerance in macrophages through inactivation of PI3K/AKT signaling

Following long‑term exposure to endotoxins, macrophages enter an immunosuppressive state that renders them unable respond to subsequent exposures to endotoxin, a phenomenon that is termed 'endotoxin tolerance'. Endotoxin tolerance increases the risks of secondary infection and mortality in patients with sepsis. In endotoxin‑tolerant macrophages, the mixed variation of gene transcription is referred to as macrophage reprogramming. The mechanisms underlying macrophage reprogramming remain unclear at present. Interferon‑induced double‑stranded RNA‑dependent protein kinase (PKR) is a widely expressed serine/threonine protein kinase. In addition to antiviral effects, PKR regulates the transcription of inflammatory cytokines by affecting transcription factors. However, the role of PKR in macrophage reprogramming remains to be elucidated. In the present study, the expression of inflammatory cytokines differed in lipopolysaccharide (LPS)‑tolerant RAW264.7 macrophages compared with LPS‑activated macrophages. Specifically, reverse transcription‑quantitative polymerase chain reaction results demonstrated that the mRNA levels of tumor necrosis factor‑α, interleukin‑1β (IL‑1β), C‑X‑C motif chemokine ligand 11, C‑C motif chemokine ligand (CCL17), CCL22 and suppressor of cytokine signaling 3 were decreased, and mRNAs levels of arginase‑1 (Arg1) and nitric oxide synthase 2 (iNOS) were increased, in LPS‑tolerant macrophages compared with LPS‑activated macrophages. Furthermore, western blot analysis demonstrated that the protein levels of phosphorylated (p)‑PKR were significantly decreased in the LPS‑tolerant cells. PKR activation with rotenone (10 µM) abrogated endotoxin tolerance by increasing the levels of the IL‑1β, CCL17 and CCL22 mRNAs and decreasing the levels of the Arg1 and iNOS mRNAs. Furthermore, western blotting demonstrated that AKT was markedly inactivated in endotoxin‑tolerant cells, as indicated by reduced p‑AKT levels. However, levels of p‑AKT were markedly increased following rotenone‑induced PKR activation in endotoxin‑tolerant cells. Ly294002 (10 µM), a phosphatidylinositol‑4,5‑bisphosphate 3‑kinase (PI3K)/AKT signaling inhibitor, partially reversed the rotenone‑induced alleviation of endotoxin tolerance. These results demonstrated that PKR inhibition mediated endotoxin tolerance in macrophages, and these effects were partially mediated by PI3K/AKT signaling. PKR may be a potential target for the treatment of endotoxin tolerance in patients with sepsis.

TREM-1 and its potential ligands in non-infectious diseases: from biology to clinical perspectives

Triggering receptor expressed on myeloid cells-1 (TREM-1) is expressed on the majority of innate immune cells and to a lesser extent on parenchymal cells. Upon activation, TREM-1 can directly amplify an inflammatory response. Although it was initially demonstrated that TREM-1 was predominantly associated with infectious diseases, recent evidences shed new light into its role in sterile inflammatory diseases. Indeed, TREM-1 receptor and its signaling pathways contribute to the pathology of several non-infectious acute and chronic inflammatory diseases, including atherosclerosis, ischemia reperfusion-induced tissue injury, colitis, fibrosis and cancer. This review, aims to give an extensive overview of TREM-1 in non-infectious diseases, with the focus on the therapeutic potential of TREM-1 intervention strategies herein. In addition, we provide the reader with a functional enrichment analysis of TREM-1 signaling pathway and potential TREM-1 ligands in these diseases, obtained via in silico approach. We discuss pre-clinical studies which show that TREM-1 inhibition, via synthetic soluble TREM-1 protein mimickers, is effective in treating (preventing) specific inflammatory disorders, without significant effects on antibacterial response. Further research aimed at identifying specific TREM-1 ligands, in different inflammatory disorders, is required to further unravel the role of this receptor, and explore new avenues to modulate its function.

A System Dynamics Model to Predict the Human Monocyte Response to Endotoxins

System dynamics is a powerful tool that allows modeling of complex and highly networked systems such as those found in the human immune system. We have developed a model that reproduces how the exposure of human monocytes to lipopolysaccharides (LPSs) induces an inflammatory state characterized by high production of tumor necrosis factor alpha (TNFα), which is rapidly modulated to enter into a tolerant state, known as endotoxin tolerance (ET). The model contains two subsystems with a total of six states, seven flows, two auxiliary variables, and 14 parameters that interact through six differential and nine algebraic equations. The parameters were estimated and optimized to obtain a model that fits the experimental data obtained from human monocytes treated with various LPS doses. In contrast to publications on other animal models, stimulation of human monocytes with super-low-dose LPSs did not alter the response to a second LPSs challenge, neither inducing ET, nor enhancing the inflammatory response. Moreover, the model confirms the low production of TNFα and increased levels of C-C motif ligand 2 when monocytes exhibit a tolerant state similar to that of patients with sepsis. At present, the model can help us better understand the ET response and might offer new insights on sepsis diagnostics and prognosis by examining the monocyte response to endotoxins in patients with sepsis.

Vitamin D treatment modulates immune activation in cystic fibrosis

Persistent inflammatory response in cystic fibrosis (CF) airways is believed to play a central role in the progression of lung damage. Anti-inflammatory treatment may slow lung disease progression, but adverse side effects have limited its use. Vitamin D has immunoregulatory properties. We randomized 16 CF patients to receive vitamin D2, vitamin D3 or to serve as controls, and investigated the effect of vitamin D supplementation on soluble immunological parameters, myeloid dendritic cells (mDCs) and T cell activation. Three months of vitamin D treatment were followed by two washout months. Vitamin D status at baseline was correlated negatively with haptoglobin, erythrocyte sedimentation rate and immunoglobulin A concentration. Total vitamin D dose per kg bodyweight correlated with the down-modulation of the co-stimulatory receptor CD86 on mDCs. Vitamin D treatment was associated with reduced CD279 (PD-1) expression on CD4⁺ and CD8⁺ T cells, as well as decreased frequency of CD8⁺ T cells co-expressing the activation markers CD38 and human leucocyte antigen D-related (HLA-DR) in a dose-dependent manner. There was a trend towards decreased mucosal-associated invariant T cells (MAIT) cell frequency in patients receiving vitamin D and free serum 25-hydroxyvitamin D (free-s25OHD) correlated positively with CD38 expression by these cells. At the end of intervention, the change in free-s25OHD was correlated negatively with the change in CD279 (PD-1) expression on MAIT cells. Collectively, these data indicate that vitamin D has robust pleiotropic immunomodulatory effects in CF. Larger studies are needed to explore the immunomodulatory treatment potential of vitamin D in CF in more detail.

Global analysis of glycoproteins identifies markers of endotoxin tolerant monocytes and GPR84 as a modulator of TNFα expression

Exposure of human monocytes to lipopolysaccharide (LPS) induces a temporary insensitivity to subsequent LPS challenges, a cellular state called endotoxin tolerance. In this study, we investigated the LPS-induced global glycoprotein expression changes of tolerant human monocytes and THP-1 cells to identify markers and glycoprotein targets capable to modulate the immunosuppressive state. Using hydrazide chemistry and LC-MS/MS analysis, we analyzed glycoprotein expression changes during a 48 h LPS time course. The cellular snapshots at different time points identified 1491 glycoproteins expressed by monocytes and THP-1 cells. Label-free quantitative analysis revealed transient or long-lasting LPS-induced expression changes of secreted or membrane-anchored glycoproteins derived from intracellular membrane coated organelles or from the plasma membrane. Monocytes and THP-1 cells demonstrated marked differences in glycoproteins differentially expressed in the tolerant state. Among the shared differentially expressed glycoproteins G protein-coupled receptor 84 (GPR84) was identified as being capable of modulating pro-inflammatory TNFα mRNA expression in the tolerant cell state when activated with its ligand Decanoic acid.

sTREM-1 is elevated in cystic fibrosis and correlates with proteases

BACKGROUND

sTREM-1 (soluble triggering receptor expressed on myeloid cells-1) is a novel inflammatory marker that may be of clinical use in cystic fibrosis (CF). Dysregulation of the TREM pathway has been demonstrated in other inflammatory diseases and modulation in animal models has therapeutic benefit. We hypothesised that sTREM-1 could act as a biomarker of disease in cystic fibrosis.

METHODS

Plasma from 17 patients with CF (stable and pre and post pulmonary exacerbation) and eight healthy volunteers was analyzed for sTREM-1 and proteases (matrix metalloproteinase-8 (MMP-8), MMP-9, and human neutrophil elastase HNE).

RESULTS

sTREM-1 Levels were elevated in stable CF subjects compared to controls (148 pg/ml (130-160) [median(IQR)] vs. 87 (55-118) (P < 0.01)) but were not further increased during pulmonary exacerbation nor decreased after antibiotic treatment in CF. Protease levels were increased in CF plasma compared to controls: MMP-8 = 3.1 ng/ml (1.5-7.6) vs. 0.3 (0.18-0.53) (P < 0.01) (Wilcoxon); MMP-9 = 170 ng/ml (124-282) vs. 49 (39-90) (P <  0.01); HNE = 30.2 ng/ml (22.7-30.9) vs. 17.5 (11.2-22.2) (P < 0.05). sTREM-1 correlated positively with protease levels lnMMP-8 r²  = 0.55 (P = 0.08), lnMMP-9 r²  =  0.61(P < 0.05), lnHNE r²  = 0.35 (P < 0.05).

CONCLUSIONS

sTREM-1 is constitutively elevated in CF and positively correlates with protease levels. Modulation of this pathway may be of therapeutic benefit to patients with CF. Pediatr Pulmonol. 2017;52:467-471. © 2017 Wiley Periodicals, Inc.

A mast cell-ILC2-Th9 pathway promotes lung inflammation in cystic fibrosis

T helper 9 (Th9) cells contribute to lung inflammation and allergy as sources of interleukin-9 (IL-9). However, the mechanisms by which IL-9/Th9 mediate immunopathology in the lung are unknown. Here we report an IL-9-driven positive feedback loop that reinforces allergic inflammation. We show that IL-9 increases IL-2 production by mast cells, which leads to expansion of CD25⁺ type 2 innate lymphoid cells (ILC2) and subsequent activation of Th9 cells. Blocking IL-9 or inhibiting CD117 (c-Kit) signalling counteracts the pathogenic effect of the described IL-9-mast cell-IL-2 signalling axis. Overproduction of IL-9 is observed in expectorates from cystic fibrosis (CF) patients, and a sex-specific variant of IL-9 is predictive of allergic reactions in female patients. Our results suggest that blocking IL-9 may be a therapeutic strategy to ameliorate inflammation associated with microbial colonization in the lung, and offers a plausible explanation for gender differences in clinical outcomes of patients with CF.

In patients with cystic fibrosis, IL-9 signalling is increased. The authors describe an inflammatory loop in which IL-9 produced by Th9 cells drives mast cells to produce IL-2, resulting in ILC2 cell activation, and show inhibition of this loop with blocking antibodies to IL-9 in a mouse model of pulmonary infection.

p21 mediates macrophage reprogramming through regulation of p50-p50 NF-κB and IFN-β

M1 and M2 macrophage phenotypes, which mediate proinflammatory and antiinflammatory functions, respectively, represent the extremes of immunoregulatory plasticity in the macrophage population. This plasticity can also result in intermediate macrophage states that support a balance between these opposing functions. In sepsis, M1 macrophages can compensate for hyperinflammation by acquiring an M2-like immunosuppressed status that increases the risk of secondary infection and death. The M1 to M2 macrophage reprogramming that develops during LPS tolerance resembles the pathological antiinflammatory response to sepsis. Here, we determined that p21 regulates macrophage reprogramming by shifting the balance between active p65-p50 and inhibitory p50-p50 NF-κB pathways. p21 deficiency reduced the DNA-binding affinity of the p50-p50 homodimer in LPS-primed and -rechallenged macrophages, impairing their ability to attenuate IFN-β production and acquire an M2-like hyporesponsive status. High p21 levels in sepsis patients correlated with low IFN-β expression, and p21 knockdown in human monocytes corroborated its role in IFN-β regulation. The data demonstrate that p21 adjusts the equilibrium between p65-p50 and p50-p50 NF-κB pathways to mediate macrophage plasticity in LPS tolerance. Identifying p21-related pathways involved in monocyte reprogramming may lead to potential targets for sepsis treatment.

COPD disease severity and innate immune response to pathogen-associated molecular patterns

The airways of COPD patients are often colonized with bacteria leading to increased airway inflammation. This study sought to determine whether systemic cytokine responses to microbial pathogen-associated molecular patterns (PAMPs) are increased among subjects with severe COPD. In an observational cross-sectional study of COPD subjects, PAMP-induced cytokine responses were measured in whole blood ex vivo. We used PAMPs derived from microbial products recognized by toll-like receptors 1, 2, 4, 5, 6, 7, and 8. Patterns of cytokine response to PAMPs were assessed using hierarchical clustering. One-sided Student's t-tests were used to compare PAMP-induced cytokine levels in blood from patients with and without severe COPD, and for subjects with and without chronic bronchitis. Of 28 male patients, 12 had moderate COPD (FEV1 50%-80%) and 16 severe COPD (FEV1 <50%); 27 participants provided data on self-reported chronic bronchitis, of which 15 endorsed chronic bronchitis symptoms and 12 did not. Cytokine responses to PAMPs in severe COPD were generally lower than in subjects with milder COPD. This finding was particularly strong for PAMP-induced interleukin (IL)-10, granulocyte colony stimulating factor, and IL-1β. Subjects with chronic bronchitis showed higher PAMP-induced IL-1RA responses to most of the PAMPs evaluated. COPD patients with more severe disease demonstrated a diminished cytokine response to PAMPs, suggesting that chronic colonization with bacteria may dampen the systemic innate immune response.

TGF-β1 Upregulates the Expression of Triggering Receptor Expressed on Myeloid Cells 1 in Murine Lungs

Triggering receptor expressed on myeloid cells 1 (TREM-1) increases the expression of TGF-β family genes, which are known as profibrogenic cytokines in the pathogenesis of pulmonary fibrosis. In this study, we determined whether TGF-β1 regulated the expression of TREM-1 in a mouse model of pulmonary fibrosis. The expression of TGF-β1 and TREM-1 was increased on day 7, 14, and 21 after single intratracheal injection of bleomycin (BLM). And there was positive correlation between the expression of TGF-β1 and TREM-1. TGF-β1 increased expression of TREM-1 mRNA and protein in a time- and dose-dependent manner in mouse macrophages. The expression of the activator protein 1 (AP-1) was increased in lung tissues from mouse after BLM injection and in mouse macrophages after TGF-β1 treatment, respectively. TGF-β1 significantly increased the relative activity of luciferase in the cells transfected with plasmid contenting wild type-promoter of TREM-1. But TGF-β1 had no effect on the activity of luciferase in the cells transfected with a mutant-TREM1 plasmid carrying mutations in the AP-1 promoter binding site. In conclusion, we found the expression of TREM-1 was increased in lung tissues from mice with pulmonary fibrosis. TGF-β1 increased the expression of TREM-1 in mouse macrophages partly via the transcription factor AP-1.

MiR-146b Mediates Endotoxin Tolerance in Human Phagocytes

A proper regulation of the innate immune response is fundamental to keep the immune system in check and avoid a chronic status of inflammation. As they act as negative modulators of TLR signaling pathways, miRNAs have been recently involved in the control of the inflammatory response. However, their role in the context of endotoxin tolerance is just beginning to be explored. We here show that miR-146b is upregulated in human monocytes tolerized by LPS, IL-10, or TGFβ priming and demonstrate that its transcription is driven by STAT3 and RUNX3, key factors downstream of IL-10 and TGFβ signaling. Our study also found that IFNγ, known to revert LPS tolerant state, inhibits miR-146b expression. Finally, we provide evidence that miR-146b levels have a profound effect on the tolerant state, thus candidating miR-146b as a molecular mediator of endotoxin tolerance.

Galactomannan Downregulates the Inflammation Responses in Human Macrophages via NFκB2/p100

We show that galactomannan, a polysaccharide consisting of a mannose backbone with galactose side groups present on the cell wall of several fungi, induces a reprogramming of the inflammatory response in human macrophages through dectin-1 receptor. The nuclear factor kappa-light-chain-enhancer of activated B cells 2 (NFκB2)/p100 was overexpressed after galactomannan challenge. Knocking down NFκB2/p100 using small interfering RNA (siRNA) indicated that NFκB2/p100 expression is a crucial factor in the progression of the galactomannan-induced refractoriness. The data presented in this study could be used as a modulator of inflammatory response in clinical situations where refractory state is required.

In vivo attenuation and genetic evolution of a ST247-SCCmecI MRSA clone after 13 years of pathogenic bronchopulmonary colonization in a patient with cystic fibrosis: implications of the innate immune response

Methicillin-resistant Staphylococcus aureus (MRSA) causes chronic pulmonary infections in patients with cystic fibrosis (CF). This study tracks the 13-year evolution (1996-2009) of a single MRSA clone in a male patient with CF, evaluating both the host immunogenic response and the microbial variations. Whole-genome sequencing was performed for the initial (CF-96) and evolved (CF-09) isolates. The immunogenicity of CF-96 and CF-09 was evaluated by incubation with innate immune cells from healthy volunteers. We also studied the patient's innate immune response profile, cytokine production, expression of triggering receptor expressed on myeloid cells-1 (TREM-1), and phagocytosis. A total of 30 MRSA ST247-SCCmecI-pvl(-) isolates were collected, which evidenced a genome size reduction from the CF-96 ancestor to the evolved CF-09 strain. Up to six changes in the spa-type were observed over the course of the 13-year evolution. Cytokine production, TREM-1 expression, and phagocytosis were significantly lower for the healthy volunteer monocytes exposed to CF-09, compared with those exposed to CF-96. Patient monocytes exhibited a reduced inflammatory response when challenged with CF-09. Genetic changes in MRSA, leading to reduced immunogenicity and entry into the refractory state, may contribute to the attenuation of virulence and efficient persistence of the bacteria in the CF lung.

Granulocyte-macrophage colony stimulatory factor enhances the pro-inflammatory response of interferon-γ-treated macrophages to Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is an opportunistic pathogen that can cause severe infections at compromised epithelial surfaces, such those found in burns, wounds, and in lungs damaged by mechanical ventilation or recurrent infections, particularly in cystic fibrosis (CF) patients. CF patients have been proposed to have a Th2 and Th17-biased immune response suggesting that the lack of Th1 and/or over exuberant Th17 responses could contribute to the establishment of chronic P. aeruginosa infection and deterioration of lung function. Accordingly, we have observed that interferon (IFN)-γ production by peripheral blood mononuclear cells from CF patients positively correlated with lung function, particularly in patients chronically infected with P. aeruginosa. In contrast, IL-17A levels tended to correlate negatively with lung function with this trend becoming significant in patients chronically infected with P. aeruginosa. These results are in agreement with IFN-γ and IL-17A playing protective and detrimental roles, respectively, in CF. In order to explore the protective effect of IFN-γ in CF, the effect of IFN-γ alone or in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF), on the ability of human macrophages to control P. aeruginosa growth, resist the cytotoxicity induced by this bacterium or promote inflammation was investigated. Treatment of macrophages with IFN-γ, in the presence and absence of GM-CSF, failed to alter bacterial growth or macrophage survival upon P. aeruginosa infection, but changed the inflammatory potential of macrophages. IFN-γ caused up-regulation of monocyte chemoattractant protein-1 (MCP-1) and TNF-α and down-regulation of IL-10 expression by infected macrophages. GM-CSF in combination with IFN-γ promoted IL-6 production and further reduction of IL-10 synthesis. Comparison of TNF-α vs. IL-10 and IL-6 vs. IL-10 ratios revealed the following hierarchy in regard to the pro-inflammatory potential of human macrophages infected with P. aeruginosa: untreated < treated with GM-CSF < treated with IFN-γ < treated with GM-CSF and IFN-γ.

NFκB2/p100 is a key factor for endotoxin tolerance in human monocytes: a demonstration using primary human monocytes from patients with sepsis

Endotoxin tolerance (ET) is a state of reduced responsiveness to endotoxin stimulation after a primary bacterial insult. This phenomenon has been described in several pathologies, including sepsis, in which an endotoxin challenge results in reduced cytokine production. In this study, we show that the NFκ L chain enhancer of activated B cells 2 (NFκB2)/p100 was overexpressed and accumulated in a well-established in vitro human monocyte model of ET. The p100 accumulation in these cells inversely correlated with the inflammatory response after LPS stimulation. Knocking down NFκB2/p100 using small interfering RNA in human monocytes further indicated that p100 expression is a crucial factor in the progression of ET. The monocytes derived from patients with sepsis had high levels of p100, and a downregulation of NFκB2/p100 in these septic monocytes reversed their ET status.

Mitochondrial DAMPs induce endotoxin tolerance in human monocytes: an observation in patients with myocardial infarction

Monocyte exposure to mitochondrial Danger Associated Molecular Patterns (DAMPs), including mitochondrial DNA (mtDNA), induces a transient state in which these cells are refractory to further endotoxin stimulation. In this context, IRAK-M up-regulation and impaired p65 activity were observed. This phenomenon, termed endotoxin tolerance (ET), is characterized by decreased production of cytokines in response to the pro-inflammatory stimulus. We also show that monocytes isolated from patients with myocardial infarction (MI) exhibited high levels of circulating mtDNA, which correlated with ET status. Moreover, a significant incidence of infection was observed in those patients with a strong tolerant phenotype. The present data extend our current understanding of the implications of endotoxin tolerance. Furthermore, our data suggest that the levels of mitochondrial antigens in plasma, such as plasma mtDNA, should be useful as a marker of increased risk of susceptibility to nosocomial infections in MI and in other pathologies involving tissue damage.

Emerging roles for triggering receptor expressed on myeloid cells receptor family signaling in inflammatory diseases

Innate immune receptors represent important therapeutic targets for inflammatory disorders. In particular, the Toll-like receptor (TLR) family has emerged as a promoter of chronic inflammation that contributes to obesity, insulin resistance and atherosclerosis. Importantly, triggering receptor expressed on myeloid cells-1 (TREM-1) has been characterized as an 'amplifier' of TLR2 and TLR4 signaling. TREM-1- and TREM-2-dependent signaling, as opposed to TREM-like transcript-1 (TLT-1 or TREML1), are mediated through association with the transmembrane adaptor DNAX activation protein of 12 kDa (DAP12). Recessive inheritance of rare mutations in DAP12 or TREM-2 results in a disorder called polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy, and surprisingly these subjects are not immunocompromised. Recent progress into the roles of TREM/DAP12 signaling is critically reviewed here with a focus on metabolic, cardiovascular and inflammatory diseases. The expanding repertoire of putative ligands for TREM receptors is also discussed.

Pathophysiology of endotoxin tolerance: mechanisms and clinical consequences

Endotoxin tolerance was first described in a study that exposed animals to a sublethal dose of bacterial endotoxin. The animals subsequently survived a lethal injection of endotoxin. This refractory state is associated with the innate immune system and, in particular, with monocytes and macrophages, which act as the main participants. Several mechanisms are involved in the control of endotoxin tolerance; however, a full understanding of this phenomenon remains elusive. A number of recent reports indicate that clinical examples of endotoxin tolerance include not only sepsis but also diseases such as cystic fibrosis and acute coronary syndrome. In these pathologies, the risk of new infections correlates with a refractory state. This review integrates the molecular basis and clinical implications of endotoxin tolerance in various pathologies.

Synthetic cationic peptide IDR-1018 modulates human macrophage differentiation

Macrophages play a critical role in the innate immune response. To respond in a rapid and efficient manner to challenges in the micro-environment, macrophages are able to differentiate towards classically (M1) or alternatively (M2) activated phenotypes. Synthetic, innate defense regulators (IDR) peptides, designed based on natural host defence peptides, have enhanced immunomodulatory activities and reduced toxicity leading to protection in infection and inflammation models that is dependent on innate immune cells like monocytes/macrophages. Here we tested the effect of IDR-1018 on macrophage differentiation, a process essential to macrophage function and the immune response. Using transcriptional, protein and systems biology analysis, we observed that differentiation in the presence of IDR-1018 induced a unique signature of immune responses including the production of specific pro and anti-inflammatory mediators, expression of wound healing associated genes, and increased phagocytosis of apoptotic cells. Transcription factor IRF4 appeared to play an important role in promoting this IDR-1018-induced phenotype. The data suggests that IDR-1018 drives macrophage differentiation towards an intermediate M1-M2 state, enhancing anti-inflammatory functions while maintaining certain pro-inflammatory activities important to the resolution of infection. Synthetic peptides like IDR-1018, which act by modulating the immune system, could represent a powerful new class of therapeutics capable of treating the rising number of multidrug resistant infections as well as disorders associated with dysregulated immune responses.

Cytosolic, autocrine alpha-1 proteinase inhibitor (A1PI) inhibits caspase-1 and blocks IL-1β dependent cytokine release in monocytes

Rationale

Activation state-dependent secretion of alpha-1 proteinase inhibitor (A1PI) by monocytes and macrophages was first reported in 1985. Since then, monocytes and tissue macrophages have emerged as key sentinels of infection and tissue damage via activation of self-assembling pattern recognition receptors (inflammasomes), which trigger inflammation and cell death in a caspase-1 dependent process. These studies examine the relationship between A1PI expression in primary monocytes and monocytic cell lines, and inflammatory cytokine expression in response to inflammasome directed stimuli.

Methods

IL-1 β expression was examined in lung macrophages expressing wild type A1PI (A1PI-M) or disease-associated Z isoform A1PI (A1PI-Z). Inflammatory cytokine release was evaluated in THP-1 monocytic cells or THP-1 cells lacking the inflammasome adaptor ASC, transfected with expression vectors encoding A1PI-M or A1PI-Z. A1PI-M was localized within monocytes by immunoprecipitation in hypotonic cell fractions. Cell-free titration of A1PI-M was performed against recombinant active caspase-1 in vitro.

Results

IL-1 β expression was elevated in lung macrophages expressing A1PI-Z. Overexpression of A1PI-M in THP-1 monocytes reduced secretion of IL-1β and TNF-α. In contrast, overexpression of A1PI-Z enhanced IL-1β and TNF- α secretion in an ASC dependent manner. A1PI-Z-enhanced cytokine release was inhibited by a small molecule caspase-1 inhibitor but not by high levels of exogenous wtA1PI. Cytosolic localization of A1PI-M in monocytes was not diminished with microtubule-inhibiting agents. A1PI-M co-localized with caspase-1 in gel-filtered cytoplasmic THP-1 preparations, and was co-immunoprecipitated with caspase 1 from nigericin-stimulated THP-1 cell lysate. Plasma-derived A1PI inhibited recombinant caspase-1 mediated conversion of a peptide substrate in a dose dependent manner.

Conclusions

Our results suggest that monocyte/macrophage-expressed A1PI-M antagonizes IL-1β secretion possibly via caspase-1 inhibition, a function which disease-associated A1PI-Z may lack. Therapeutic approaches which limit inflammasome responses in patients with A1PI deficiency, in combination with A1PI augmentation, may provide additional respiratory tissue-sparing benefits.

Innate immunity in cystic fibrosis lung disease

Chronic lung disease determines the morbidity and mortality of cystic fibrosis (CF) patients. The pulmonary immune response in CF is characterized by an early and non-resolving activation of the innate immune system, which is dysregulated at several levels. Here we provide a comprehensive overview of innate immunity in CF lung disease, involving (i) epithelial dysfunction, (ii) pathogen sensing, (iii) leukocyte recruitment, (iv) phagocyte impairment, (v) mechanisms linking innate and adaptive immunity and (iv) the potential clinical relevance. Dissecting the complex network of innate immune regulation and associated pro-inflammatory cascades in CF lung disease may pave the way for novel immune-targeted therapies in CF and other chronic infective lung diseases.

Absence of the cystic fibrosis transmembrane regulator (Cftr) from myeloid-derived cells slows resolution of inflammation and infection

The absence or reduction of CFTR function causes CF and results in a pulmonary milieu characterized by bacterial colonization and unresolved inflammation. The ineffectiveness at controlling infection by species such as Pseudomonas aeruginosa suggests defects in innate immunity. Macrophages, neutrophils, and DCs have all been shown to express CFTR mRNA but at low levels, raising the question of whether CFTR has a functional role in these cells. Bone marrow transplants between CF and non-CF mice suggest that these cells are inherently different; we confirm this observation using conditional inactivation of Cftr in myeloid-derived cells. Mice lacking Cftr in myeloid cells overtly appear indistinguishable from non-CF mice until challenged with bacteria instilled into the lungs and airways, at which point, they display survival and inflammatory profiles intermediate in severity as compared with CF mice. These studies demonstrate that Cftr is involved directly in myeloid cell function and imply that these cells contribute to the pathophysiological phenotype of the CF lung.