Toll-like receptor control of glucocorticoid-induced apoptosis in human plasmacytoid predendritic cells (pDCs)

Preclinical Evidence for the Glucocorticoid-Sparing Potential of a Dual Toll-Like Receptor 7/8 Inhibitor in Autoimmune Diseases

Toll-like receptor 7 (TLR7) and TLR8 are single-stranded RNA-sensing endosomal pattern recognition receptors that evolved to defend against viral infections. However, aberrant TLR7/8 activation by endogenous ligands has been implicated in the pathogenesis of autoimmune diseases including systemic lupus erythematosus. TLR activation and type I interferon (IFN) were shown recently to impart resistance to glucocorticoids (GC), which are part of the standard of care for multiple autoimmune diseases. While GCs are effective, a plethora of undesirable effects limit their use. New treatment approaches that allow for the use of lower and safer doses of GCs would be highly beneficial. Herein, we report that a dual TLR7/8 inhibitor (TLR7/8i) increases the effectiveness of GCs in inflammatory settings. Human peripheral blood mononuclear cell studies revealed increased GC sensitivity in the presence of TLR7/8i for reducing inflammatory cytokine production, a synergistic effect that was most pronounced in myeloid cells, particularly monocytes. Gene expression analysis by NanoString and single-cell RNA sequencing revealed that myeloid cells were substantially impacted by combining low-dose TLR7/8i and GC, as evidenced by the effects on nuclear factor-kappa B-regulated cytokines and GC-response genes, although IFNs were affected to a smaller degree. Low dose of TLR7/8i plus GC was more efficacious then either agent alone in the MRL/lpr mouse model of lupus, with improved proteinuria and survival. Overall, our findings indicate a GC-sparing potential for TLR7/8i compounds, suggesting TLR7/8i may offer a new strategy for the treatment of autoimmune diseases. SIGNIFICANCE STATEMENT: Some features of autoimmune diseases may be resistant to glucocorticoids, mediated at least in part by toll-like receptor (TLR) activation, necessitating higher doses that are associated with considerable toxicities. We demonstrate that TLR7/8 inhibition and glucocorticoids work synergistically to reduce inflammation in a cell-type specific manner and suppress disease in a mouse model of lupus. TLR7/8 inhibition is a promising strategy for the treatment of autoimmune diseases and has glucocorticoid-sparing potential.

The impact of preoperative single low-dose dexamethasone on in-hospital prognosis in geriatric intertrochanteric fracture patients: Analysis of secondary outcomes in a randomized controlled trial

BACKGROUND

Intertrochanteric fracture in the geriatric population is associated with poor prognosis, which may be attributed to consistent stress and the systemic inflammatory response. Dexamethasone is an exogenous glucocorticoid commonly used in clinical practice for broad anti-inflammatory action. The purpose is to investigate whether a single preoperative low-dose dexamethasone can improve the in-hospital prognosis in geriatric intertrochanteric fracture patients undergoing internal fixation surgery.

METHODS

Between June 2020 and October 2022, 219 eligible patients with intertrochanteric fractures were in this study. After meeting the inclusion and exclusion criteria, 160 patients were randomly allocated to the dexamethasone or placebo groups (80 patients who are geriatric with an intertrochanteric fracture in each group). The patients in the dexamethasone group received 10 mg (2 mL) of dexamethasone intravenously, whereas the patients in the placebo group received 2 mL of saline intravenously within 30 minutes before being sent to the operating room. The efficacy-related outcomes (the first bed-chair transfer ability, in-hospital mortality, and length of stay) and safety-related outcomes (infection events and hyperglycemia) were collected for analysis.

RESULTS

There were no significant differences in the baseline characteristics between the 2 groups. The dexamethasone group had a significantly higher rate of the first bed-chair transfer than the placebo group (65.0% [52/80] vs 48.8% [39/80], relative risk = 1.46, 95% confidence interval = 1.02 to 2.11; P = .038). One patient in the dexamethasone group and 7 patients in the placebo group died during hospitalization (1.3% [1/80] vs 8.8% [7/80], relative risk = 0.92, 95% confidence interval = 0.86 to 0.99; P = .07). No differences were found in the length of stay, infections, and hyperglycemia between the 2 groups.

CONCLUSION

A single preoperative low-dose of dexamethasone can improve the in-hospital prognosis (increase the ability of the first bed-chair transfer and potentially decrease the in-hospital mortality) in geriatric intertrochanteric fracture patients after internal fixation surgery.

Type I Interferon Induction and Exhaustion during Viral Infection: Plasmacytoid Dendritic Cells and Emerging COVID-19 Findings

Type I Interferons (IFN-I) are a family of potent antiviral cytokines that act through the direct restriction of viral replication and by enhancing antiviral immunity. However, these powerful cytokines are a caged lion, as excessive and sustained IFN-I production can drive immunopathology during infection, and aberrant IFN-I production is a feature of several types of autoimmunity. As specialized producers of IFN-I plasmacytoid (p), dendritic cells (DCs) can secrete superb quantities and a wide breadth of IFN-I isoforms immediately after infection or stimulation, and are the focus of this review. Notably, a few days after viral infection pDCs tune down their capacity for IFN-I production, producing less cytokines in response to both the ongoing infection and unrelated secondary stimulations. This process, hereby referred to as "pDC exhaustion", favors viral persistence and associates with reduced innate responses and increased susceptibility to secondary opportunistic infections. On the other hand, pDC exhaustion may be a compromise to avoid IFN-I driven immunopathology. In this review we reflect on the mechanisms that initially induce IFN-I and subsequently silence their production by pDCs during a viral infection. While these processes have been long studied across numerous viral infection models, the 2019 coronavirus disease (COVID-19) pandemic has brought their discussion back to the fore, and so we also discuss emerging results related to pDC-IFN-I production in the context of COVID-19.

Effect of dexamethasone on complications or all cause mortality after major non-cardiac surgery: multicentre, double blind, randomised controlled trial

OBJECTIVE

To assess the effect of dexamethasone on complications or all cause mortality after major non-cardiac surgery.

DESIGN

Phase III, randomised, double blind, placebo controlled trial.

SETTING

34 centres in France, December 2017 to March 2019.

PARTICIPANTS

1222 adults (>50 years) requiring major non-cardiac surgery with an expected duration of more than 90 minutes. The anticipated time frame for recruitment was 24 months.

INTERVENTIONS

Participants were randomised to receive either dexamethasone (0.2 mg/kg immediately after the surgical procedure, and on day 1) or placebo. Randomisation was stratified on the two prespecified criteria of cancer and thoracic procedure.

MAIN OUTCOMES MEASURES

The primary outcome was a composite of postoperative complications or all cause mortality within 14 days after surgery, assessed in the modified intention-to-treat population (at least one treatment administered).

RESULTS

Of the 1222 participants who underwent randomisation, 1184 (96.9%) were included in the modified intention-to-treat population. 14 days after surgery, 101 of 595 participants (17.0%) in the dexamethasone group and 117 of 589 (19.9%) in the placebo group had complications or died (adjusted odds ratio 0.81, 95% confidence interval 0.60 to 1.08; P=0.15). In the stratum of participants who underwent non-thoracic surgery (n=1038), the primary outcome occurred in 69 of 520 participants (13.3%) in the dexamethasone group and 93 of 518 (18%) in the placebo group (adjusted odds ratio 0.70, 0.50 to 0.99). Adverse events were reported in 288 of 613 participants (47.0%) in the dexamethasone group and 296 of 609 (48.6%) in the placebo group (P=0.46).

CONCLUSIONS

Dexamethasone was not found to significantly reduce the incidence of complications and death in patients 14 days after major non-cardiac surgery. The 95% confidence interval for the main result was, however, wide and suggests the possibility of important clinical effectiveness.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03218553.

Severe T cell hyporeactivity in ventilated COVID-19 patients correlates with prolonged virus persistence and poor outcomes

Coronavirus disease 2019 (COVID-19) can lead to pneumonia and hyperinflammation. Here we show a sensitive method to measure polyclonal T cell activation by downstream effects on responder cells like basophils, plasmacytoid dendritic cells, monocytes and neutrophils in whole blood. We report a clear T cell hyporeactivity in hospitalized COVID-19 patients that is pronounced in ventilated patients, associated with prolonged virus persistence and reversible with clinical recovery. COVID-19-induced T cell hyporeactivity is T cell extrinsic and caused by plasma components, independent of occasional immunosuppressive medication of the patients. Monocytes respond stronger in males than females and IL-2 partially restores T cell activation. Downstream markers of T cell hyporeactivity are also visible in fresh blood samples of ventilated patients. Based on our data we developed a score to predict fatal outcomes and identify patients that may benefit from strategies to overcome T cell hyporeactivity.

Glucocorticoid gene signatures in systemic lupus erythematosus and the effects of type I interferon: a cross-sectional and in-vitro study

BACKGROUND

Glucocorticoids, used as a therapy in systemic lupus erythematosus (SLE), interact with the cytoplasmic glucocorticoid receptor to modulate gene transcription. Minimising the use of glucocorticoids is a goal in SLE; however, pharmacological measures to support clinical guidelines are scarce. We evaluated glucocorticoid-regulated genes for their potential use as biomarkers of glucocorticoid exposure in SLE. We examined interactions between changes in gene expression that are induced by glucocorticoids and type I interferon.

METHODS

Genes regulated by glucocorticoids and type I interferon were analysed in relation to glucocorticoid exposure in adult patients meeting the American College of Rheumatology criteria for SLE from three cross-sectional cohorts: a local cohort from a tertiary hospital in Melbourne, VIC, Australia, and two public datasets (GSE49454, Hospital de la Conception, Marseille, France, and GSE88884, patients enrolled in a large, multicentre clinical trial). RNA sequencing was done using RNA from healthy donor leucocytes treated with the glucocorticoid dexamethasone, or type I interferon, or both.

FINDINGS

Glucocorticoid-regulated genes were analysed in a local SLE cohort (n=18) and public dataset GSE49454 (n=62). Five genes correlated with glucocorticoid dose in both cohorts and were combined to make a glucocorticoid gene signature. Validity of the glucocorticoid gene signature was tested in the public dataset GSE88884 (n=1756). A dose-dependent association was observed with glucocorticoid dose (p<0·0001), and the glucocorticoid gene signature had moderate ability to identify patients taking high-dose glucocorticoid (area under the curve [AUC]=0·77) although was less discriminatory when including all doses (AUC=0·69). We saw no effect of glucocorticoid dose on type I interferon -regulated gene expression. Patients with a high type I interferon gene signature had reduced glucocorticoid gene signature expression compared with patients with a low type I interferon gene signature matched for glucocorticoid dose, suggesting type I interferon inhibits glucocorticoid-stimulated gene expression. In RNA sequencing experiments, type I interferon impaired the expression of glucocorticoid-induced genes, whereas dexamethasone had minimal effect on the expression of type I interferon-stimulated genes. We identified genes regulated by dexamethasone but not affected by type I interferon; combined signatures using these genes also showed moderate ability to distinguish patients taking glucocorticoids.

INTERPRETATION

A gene signature for glucocorticoid exposure was identified, but the substantial effect of type I interferon on glucocorticoid-induced genes might limit its application in SLE. These data confirm the insensitivity of type I interferon-regulated genes to glucocorticoids, and together support the concept that type I interferon has a role in glucocorticoid resistance in SLE.

FUNDING

Lupus Research Alliance and Australian National Health and Medical Research Council.

SARS-CoV-2 induces human plasmacytoid predendritic cell diversification via UNC93B and IRAK4

Several studies have analyzed antiviral immune pathways in late-stage severe COVID-19. However, the initial steps of SARS-CoV-2 antiviral immunity are poorly understood. Here we have isolated primary SARS-CoV-2 viral strains and studied their interaction with human plasmacytoid predendritic cells (pDCs), a key player in antiviral immunity. We show that pDCs are not productively infected by SARS-CoV-2. However, they efficiently diversified into activated P1-, P2-, and P3-pDC effector subsets in response to viral stimulation. They expressed CD80, CD86, CCR7, and OX40 ligand at levels similar to influenza virus-induced activation. They rapidly produced high levels of interferon-α, interferon-λ1, IL-6, IP-10, and IL-8. All major aspects of SARS-CoV-2-induced pDC activation were inhibited by hydroxychloroquine. Mechanistically, SARS-CoV-2-induced pDC activation critically depended on IRAK4 and UNC93B1, as established using pDC from genetically deficient patients. Overall, our data indicate that human pDC are efficiently activated by SARS-CoV-2 particles and may thus contribute to type I IFN-dependent immunity against SARS-CoV-2 infection.

SARS-CoV-2 induces human plasmacytoid pre-dendritic cell diversification via UNC93B and IRAK4

Several studies have analyzed antiviral immune pathways in late-stage severe COVID-19. However, the initial steps of SARS-CoV-2 antiviral immunity are poorly understood. Here, we have isolated primary SARS-CoV-2 viral strains, and studied their interaction with human plasmacytoid pre-dendritic cells (pDC), a key player in antiviral immunity. We show that pDC are not productively infected by SARS-CoV-2. However, they efficiently diversified into activated P1-, P2-, and P3-pDC effector subsets in response to viral stimulation. They expressed CD80, CD86, CCR7, and OX40 ligand at levels similar to influenza virus-induced activation. They rapidly produced high levels of interferon-α, interferon-λ1, IL-6, IP-10, and IL-8. All major aspects of SARS-CoV-2-induced pDC activation were inhibited by hydroxychloroquine. Mechanistically, SARS-CoV-2-induced pDC activation critically depended on IRAK4 and UNC93B1, as established using pDC from genetically deficient patients. Overall, our data indicate that human pDC are efficiently activated by SARS-CoV-2 particles and may thus contribute to type I IFN-dependent immunity against SARS-CoV-2 infection.

Infection and cancer suppress pDC derived IFN-I

Plasmacytoid dendritic cells (pDCs) are specialized producers of Type I interferon (IFN-I) that promote anti-viral and anti-tumor immunity. However, chronic infections and cancer inhibit pDC-derived IFN-I. While the mechanisms of this inhibition are multifarious they can be classified broadly into two categories: i) reduction or ablation of pDC IFN-I-production capacity (functional exhaustion) and/or ii) decrease in pDC numbers (altered population dynamics). Recent work has identified many processes that contribute to suppression of pDC-derived IFN-I during chronic infections and cancer, including sustained stimulation through Toll Like Receptors (TLRs), inhibitory microenvironments, inhibitory receptor ligation, and reduced development from bone marrow progenitors and apoptosis. Emerging success leveraging pDCs in treatment of disease through TLR activation illustrates the therapeutic potential of targeting pDCs. Deeper understanding of the systems that limit pDC-derived IFN-I has the potential to improve these emerging therapies as well as help devising new approaches that harness the outstanding IFN-I-production capacity of pDCs.

Glucocorticoid receptor modulates dendritic cell function in ulcerative colitis

Ulcerative colitis (UC) is a serious form of inflammatory bowel disease (IBD) occurring worldwide. Although anti-TNF therapy is found to be effective in over 70% of patients with UC, nearly one-third are still deprived of effective treatment. Because glucocorticoids (GC) can effectively inhibit granulocyte-recruitment into the mucosa, cytokine secretion and T cell activation, they are used widely in the treatment of UC. However, remission is observed in only 55% of the patients after one year of steroid use due to a condition known as steroid response. Additionally, it has been noted that 20%-40% of the patients with UC do not respond to GC treatment. Researchers have revealed that the number of dendritic cells (DCs) in patients with UC tends to increase in the colonic mucosa. Many studies have determined that the removal of peripheral DCs through the adsorption and separation of granulocytes and monocytes could improve tolerance of the intestine to its symbiotic flora. Based on these results, further insights regarding the beneficial effects of Adacolumn apheresis in patients subjected to this treatment could be revealed. GC can effectively inhibit the activation of DCs by reducing the levels of major histocompatibility complex class II (MHC II) molecules, which is critical for controlling the recruitment of granulocytes. Therefore, alternative biological and new individualized therapies based on these approaches need to be evaluated to counter UC. In this review, progress in research associated with the regulatory effect of glucocorticoid receptors on DCs under conditions of UC is discussed, thus providing insights and identifying potential targets which could be employed in the treatment strategies against UC.

Harnessing cancer immunotherapy during the unexploited immediate perioperative period

The immediate perioperative period (days before and after surgery) is hypothesized to be crucial in determining long-term cancer outcomes: during this short period, numerous factors, including excess stress and inflammatory responses, tumour-cell shedding and pro-angiogenic and/or growth factors, might facilitate the progression of pre-existing micrometastases and the initiation of new metastases, while simultaneously jeopardizing immune control over residual malignant cells. Thus, application of anticancer immunotherapy during this critical time frame could potentially improve patient outcomes. Nevertheless, this strategy has rarely been implemented to date. In this Perspective, we discuss apparent contraindications for the perioperative use of cancer immunotherapy, suggest safe immunotherapeutic and other anti-metastatic approaches during this important time frame and specify desired characteristics of such interventions. These characteristics include a rapid onset of immune activation, avoidance of tumour-promoting effects, no or minimal increase in surgical risk, resilience to stress-related factors and minimal induction of stress responses. Pharmacological control of excess perioperative stress-inflammatory responses has been shown to be clinically feasible and could potentially be combined with immune stimulation to overcome the direct pro-metastatic effects of surgery, prevent immune suppression and enhance immunostimulatory responses. Accordingly, we believe that certain types of immunotherapy, together with interventions to abrogate stress-inflammatory responses, should be evaluated in conjunction with surgery and, for maximal effectiveness, could be initiated before administration of adjuvant therapies. Such strategies might improve the overall success of cancer treatment.

HTLV-1 infection of myeloid cells: from transmission to immune alterations

Human T cell leukemia virus type 1 (HTLV-1), the etiological agent of adult T-cell leukemia/lymphoma (ATLL) and the demyelinating neuroinflammatory disease known as HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP), was the first human retrovirus to be discovered. T-cells, which represent the main reservoir for HTLV-1, have been the main focus of studies aimed at understanding viral transmission and disease progression. However, other cell types such as myeloid cells are also target of HTLV-1 infection and display functional alterations as a consequence. In this work, we review the current investigations that shed light on infection, transmission and functional alterations subsequent to HTLV-1 infection of the different myeloid cells types, and we highlight the lack of knowledge in this regard.

PACMAN trial protocol, Perioperative Administration of Corticotherapy on Morbidity and mortality After Non-cardiac major surgery: a randomised, multicentre, double-blind, superiority study

INTRODUCTION

Postoperative complications are major healthcare problems and are associated with a reduced short-term and long-term survival after surgery. An excessive postoperative inflammatory response participates to the development of postoperative infection and mortality. The aim of the Perioperative Administration of Corticotherapy on Morbidity and mortality After Non-cardiac surgery (PACMAN) study is to assess the effectiveness of perioperative administration of corticosteroid to reduce postoperative morbidity and mortality in patients undergoing major non-cardiac surgery.

METHODS AND ANALYSIS

The PACMAN is a multicentre, randomised, controlled, double-blind, superiority, two-arm trial of 1222 high-risk patients aged 50 years or older undergoing major non-cardiac surgery at 32 acute care hospital in France. Patients are randomly assigned to dexamethasone (0.2 mg/kg at the end of the surgical procedure and at day +1, n=611) or to placebo (n=611). The primary outcome is a composite of predefined 14-day major pulmonary complications and mortality. Secondary outcomes are surgical complications, infections, organ failures, critical care-free days, length of hospital stay and all-cause mortality at 28 days.

ETHICS AND DISSEMINATION

The PACMAN trial protocol has been approved by the ethics committee of Sud Mediterranée V, and will be carried out according to the Good Clinical Practice guidelines and the principles of the Declaration of Helsinki. The PACMAN trial is a randomised controlled trial powered to investigate whether perioperative administration of corticosteroids in patients undergoing non-cardiac major surgery reduces postoperative complications. The results of this study will be disseminated through presentation at scientific conferences and publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT03218553; Pre-results.

Sensing of cell-associated HTLV by plasmacytoid dendritic cells is regulated by dense β-galactoside glycosylation

Human T Lymphotropic virus (HTLV) infection can persist in individuals resulting, at least in part, from viral escape of the innate immunity, including inhibition of type I interferon response in infected T-cells. Plasmacytoid dendritic cells (pDCs) are known to bypass viral escape by their robust type I interferon production. Here, we demonstrated that pDCs produce type I interferons upon physical cell contact with HTLV-infected cells, yet pDC activation inversely correlates with the ability of the HTLV-producing cells to transmit infection. We show that pDCs sense surface associated-HTLV present with glycan-rich structure referred to as biofilm-like structure, which thus represents a newly described viral structure triggering the antiviral response by pDCs. Consistently, heparan sulfate proteoglycans and especially the cell surface pattern of terminal β-galactoside glycosylation, modulate the transmission of the immunostimulatory RNA to pDCs. Altogether, our results uncover a function of virus-containing cell surface-associated glycosylated structures in the activation of innate immunity.

Hormone Therapy in Trauma Patients

Low-dose hydrocortisone reduces the dose of vasopressors and hospital length of stay; it may also decrease the rate of hospital-acquired pneumonia and time on ventilator. No major side effect was reported, but glycemia and natremia should be monitored. Progesterone did not enhance outcome of trauma patients. A meta-analysis suggested that oxandrolone was associated with shorter length of stay and reduced weight loss. Erythropoietin did not enhance neurologic outcome of traumatic brain-injured patients; such treatment, however, could reduce the mortality in subgroups of patients. This review focuses mainly on glucocorticoids, which are the most extensively investigated treatments in hormone therapy.

Interferon-λs and Plasmacytoid Dendritic Cells: A Close Relationship

Interferon lambdas (IFNλs) are recently discovered cytokines acting not only at the first line of defense against viral infections but also at the mucosal barriers. In fact, a peculiar feature of the IFNλ system is the restricted expression of the functional IFNλR, which is known to be limited to epithelial cells and discrete leukocyte subsets, including the plasmacytoid dendritic cells (pDCs). In the latter case, current data, discussed in this minireview, indicate that IFNλs positively regulate various pDC functions, including pDC expression of interferon-dependent gene (ISG) mRNAs, production of cytokines, survival, and phenotype. Although the knowledge of the effects on pDCs by IFNλs is still incomplete, we speculate that the peculiar pDC responsiveness to IFNλs provide unique advantages for these innate immune cells, not only for viral infections but also during autoimmune disorders and/or tumors, in which pDC involvement and activation variably contribute to their pathogenesis.

Endothelial Response to Glucocorticoids in Inflammatory Diseases

The endothelium plays a crucial role in inflammation. A balanced control of inflammation requires the action of glucocorticoids (GCs), steroidal hormones with potent cell-specific anti-inflammatory properties. Besides the classic anti-inflammatory effects of GCs on leukocytes, recent studies confirm that endothelial cells also represent an important target for GCs. GCs regulate different aspects of endothelial physiology including expression of adhesion molecules, production of pro-inflammatory cytokines and chemokines, and maintenance of endothelial barrier integrity. However, the regulation of endothelial GC sensitivity remains incompletely understood. In this review, we specifically examine the endothelial response to GCs in various inflammatory diseases ranging from multiple sclerosis, stroke, sepsis, and vasculitis to atherosclerosis. Shedding more light on the cross talk between GCs and endothelium will help to improve existing therapeutic strategies and develop new therapies better tailored to the needs of patients.

GR-independent down-modulation on GM-CSF bone marrow-derived dendritic cells by the selective glucocorticoid receptor modulator Compound A

Dendritic cells (DC) initiate the adaptive immune response. Glucocorticoids (GCs) down-modulate the function of DC. Compound A (CpdA, (2-(4-acetoxyphenyl)-2-chloro-N-methyl-ethylammonium chloride) is a plant-derived GR-ligand with marked dissociative properties. We investigated the effects of CpdA on in vitro generated GM-CSF-conditioned bone marrow-derived DC (BMDC). CpdA-exposed BMDC exhibited low expression of cell-surface molecules and diminution of the release of proinflammatory cytokines upon LPS stimulation; processes associated with BMDC maturation and activation. CpdA-treated BMDC were inefficient at Ag capture via mannose receptor-mediated endocytosis and displayed reduced T-cell priming. CpdA prevented the LPS-induced rise in pErk1/2 and pP38, kinases involved in TLR4 signaling. CpdA fully inhibited LPS-induced pAkt_Ser473, a marker associated with the generation of tolerogenic DC. We used pharmacological blockade and selective genetic loss-of-function tools and demonstrated GR-independent inhibitory effects of CpdA in BMDC. Mechanistically, CpdA-mediated inactivation of the NF-κB intracellular signaling pathway was associated with a short-circuiting of pErk1/2 and pP38 upstream signaling. Assessment of the in vivo function of CpdA-treated BMDC pulsed with the hapten trinitrobenzenesulfonic acid showed impaired cell-mediated contact hypersensitivity. Collectively, we provide evidence that CpdA is an effective BMDC modulator that might have a benefit for immune disorders, even when GR is not directly targeted.

Unexpected cellular players in Rett syndrome pathology

Rett syndrome is a devastating neurodevelopmental disorder, primarily caused by mutations of methyl CpG-binding protein 2 (MeCP2). Although the genetic cause of disease was identified over a decade ago, a significant gap still remains in both our clinical and scientific understanding of its pathogenesis. Neurons are known to be primary players in pathology, with their dysfunction being the key in Rett syndrome. While studies in mice have demonstrated a clear causative - and potential therapeutic - role for neurons in Rett syndrome, recent work has suggested that other tissues also contribute significantly to progression of the disease. Indeed, Rett syndrome is known to present with several common peripheral pathologies, such as osteopenia, scoliosis, gastrointestinal problems including nutritional defects, and general growth deficit. Mouse models assessing the potential role of non-neuronal cell types have confirmed both roles in disease and potential therapeutic targets. A new picture is emerging in which neurons both initiate and drive pathology, while dysfunction of other cell types and peripheral tissues exacerbate disease, possibly amplifying further neurologic problems, and ultimately result in a positive feedback loop of progressively worsening symptoms. Here, we review what is known about neuronal and non-neuronal cell types, and discuss how this new, integrative understanding of the disease may allow for additional clinical and scientific pathways for treating and understanding Rett syndrome.

Breakdown of Immune Tolerance in Systemic Lupus Erythematosus by Dendritic Cells

Dendritic cells (DC) play an important role in the pathogenesis of systemic lupus erythematosus (SLE), an autoimmune disease with multiple tissue manifestations. In this review, we summarize recent studies on the roles of conventional DC and plasmacytoid DC in the development of both murine lupus and human SLE. In the past decade, studies using selective DC depletions have demonstrated critical roles of DC in lupus progression. Comprehensive in vitro and in vivo studies suggest activation of DC by self-antigens in lupus pathogenesis, followed by breakdown of immune tolerance to self. Potential treatment strategies targeting DC have been developed. However, many questions remain regarding the mechanisms by which DC modulate lupus pathogenesis that require further investigations.

A CD2 high-expressing stress-resistant human plasmacytoid dendritic-cell subset

Human plasmacytoid dendritic cells (pDCs) were considered to be a phenotypically and functionally homogeneous cell population; however, recent analyses indicate potential heterogeneity. This is of major interest, given their importance in the induction of anti-viral responses and their role in creating immunologically permissive environments for human malignancies. For this reason, we investigated the possible presence of human pDC subsets in blood and bone marrow, using unbiased cell phenotype clustering and functional studies. This defined two major functionally distinct human pDC subsets, distinguished by differential expression of CD2. The CD2(hi) and CD2(lo) pDCs represent discontinuous subsets, each with hallmark pDC functionality, including interferon-alpha production. The rarer CD2(hi) pDC subset demonstrated a significant survival advantage over CD2(lo) pDC during stress and upon exposure to glucocorticoids (GCs), which was associated with higher expression of the anti-apoptotic molecule BCL2. The differential sensitivity of these two human pDC subsets to GCs is demonstrated in vivo by a relative increase in CD2(hi) pDC in multiple myeloma patients treated with GCs. Hence, the selective apoptosis of CD2(lo) pDC during stress represents a novel mechanism for the control of innate responses.

Prednisolone does not affect direct-acting antivirals against hepatitis C, but inhibits interferon-alpha production by plasmacytoid dendritic cells

BACKGROUND

Chronic hepatitis C virus (HCV) infection compromises long-term outcomes of liver transplantation. Although glucocorticosteroid-based immunosuppression is commonly used, discussion is ongoing on the effect of prednisolone (Pred) on HCV recurrence and response to antiviral therapy post transplantation. Recently, new drugs (direct-acting antivirals) have been approved for the treatment of HCV, however, it remains unknown whether their antiviral activity is affected by Pred. The aim of this study was to investigate the effects of Pred on the antiviral activity of asunaprevir (Asu), daclatasvir (Dac), ribavirin (RBV), and interferon-alpha (IFN-α), and on plasmacytoid dendritic cells (PDCs), the main IFN-α-producing immune cells.

METHODS

The effects of Pred and antiviral compounds were tested in both a subgenomic and infectious HCV replication model. Furthermore, effects were tested on human PDCs stimulated with a Toll-like receptor-7 ligand.

RESULT

Pred did not directly affect HCV replication and did not inhibit the antiviral action of Asu, Dac, RBV, or IFN-α. Stimulated PDCs potently suppressed HCV replication. This suppression was reversed by treating PDCs with Pred. Pred significantly decreased IFN-α production by PDCs without affecting cell viability. When Asu and Dac were combined with PDCs, a significant cooperative antiviral effect was observed.

CONCLUSION

This study shows that Pred acts on the antiviral function of PDCs. Pred does not affect the antiviral action of Asu, Dac, RBV, or IFN-α. This implies that there is no contraindication to combine antiviral therapies with Pred in the post-transplantation management of HCV recurrence.

Cellular FLIP Inhibits Myeloid Cell Activation by Suppressing Selective Innate Signaling

Cellular FLIP (c-FLIP) specifically inhibits caspase-8 and suppresses death receptor-induced apoptosis. c-FLIP has also been reported to transmit activation signals. In this study, we report a novel function of c-FLIP involving inhibition of myeloid cell activation through antagonizing the selective innate signaling pathway. We found that conditional knockout of c-FLIP in dendritic cells (DCs) led to neutrophilia and splenomegaly. Peripheral DC populations, including CD11b(+) conventional DCs (cDCs), CD8(+) cDCs, and plasmacytoid DCs, were not affected by c-FLIP deficiency. We also found that c-FLIP knockout cDCs, plasmacytoid DCs, and bone marrow-derived DCs (BMDCs) displayed enhanced production of TNF-α, IL-2, or G-CSF in response to stimulation of TLR4, TLR2, and dectin-1. Consistent with the ability of c-FLIP to inhibit the activation of p38 MAPK, the enhanced activation of c-FLIP-deficient BMDCs could be partly linked to an elevated activation of p38 MAPK after engagement of innate receptors. Increased activation was also found in c-FLIP(+/-) macrophages. Additionally, the increased activation in c-FLIP-deficient DCs was independent of caspase-8. Our results reveal a novel inhibitory role of c-FLIP in myeloid cell activation and demonstrate the unexpected anti-inflammatory activity of c-FLIP. Additionally, our observations suggest that cancer therapy targeting c-FLIP downregulation may facilitate DC activation and increase T cell immunity.

The multifaceted biology of plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are a unique DC subset that specializes in the production of type I interferons (IFNs). pDCs promote antiviral immune responses and have been implicated in the pathogenesis of autoimmune diseases that are characterized by a type I IFN signature. However, pDCs can also induce tolerogenic immune responses. In this Review, we summarize recent progress in the field of pDC biology, focusing on the molecular mechanisms that regulate the development and functions of pDCs, the pathways involved in their sensing of pathogens and endogenous nucleic acids, their functions at mucosal sites, and their roles in infection, autoimmunity and cancer.

Recognition of Aspergillus fumigatus hyphae by human plasmacytoid dendritic cells is mediated by dectin-2 and results in formation of extracellular traps

Plasmacytoid dendritic cells (pDCs) were initially considered as critical for innate immunity to viruses. However, our group has shown that pDCs bind to and inhibit the growth of Aspergillus fumigatus hyphae and that depletion of pDCs renders mice hypersusceptible to experimental aspergillosis. In this study, we examined pDC receptors contributing to hyphal recognition and downstream events in pDCs stimulated by A. fumigatus hyphae. Our data show that Dectin-2, but not Dectin-1, participates in A. fumigatus hyphal recognition, TNF-α and IFN-α release, and antifungal activity. Moreover, Dectin-2 acts in cooperation with the FcRγ chain to trigger signaling responses. In addition, using confocal and electron microscopy we demonstrated that the interaction between pDCs and A. fumigatus induced the formation of pDC extracellular traps (pETs) containing DNA and citrullinated histone H3. These structures closely resembled those of neutrophil extracellular traps (NETs). The microarray analysis of the pDC transcriptome upon A. fumigatus infection also demonstrated up-regulated expression of genes associated with apoptosis as well as type I interferon-induced genes. Thus, human pDCs directly recognize A. fumigatus hyphae via Dectin-2; this interaction results in cytokine release and antifungal activity. Moreover, hyphal stimulation of pDCs triggers a distinct pattern of pDC gene expression and leads to pET formation.

Lymphotoxin-LIGHT pathway regulates the interferon signature in rheumatoid arthritis

A subset of patients with autoimmune diseases including rheumatoid arthritis (RA) and lupus appear to be exposed continually to interferon (IFN) as evidenced by elevated expression of IFN induced genes in blood cells. In lupus, detection of endogenous chromatin complexes by the innate sensing machinery is the suspected driver for the IFN, but the actual mechanisms remain unknown in all of these diseases. We investigated in two randomized clinical trials the effects on RA patients of baminercept, a lymphotoxin-beta receptor-immunoglobulin fusion protein that blocks the lymphotoxin-αβ/LIGHT axis. Administration of baminercept led to a reduced RNA IFN signature in the blood of patients with elevated baseline signatures. Both RA and SLE patients with a high IFN signature were lymphopenic and lymphocyte counts increased following baminercept treatment of RA patients. These data demonstrate a coupling between the lymphotoxin-LIGHT system and IFN production in rheumatoid arthritis. IFN induced retention of lymphocytes within lymphoid tissues is a likely component of the lymphopenia observed in many autoimmune diseases.

ClinicalTrials.gov NCT00664716.

Cell-intrinsic regulation of murine dendritic cell function and survival by prereceptor amplification of glucocorticoid

Although the inhibitory effects of therapeutic glucocorticoids (GCs) on dendritic cells (DCs) are well established, the roles of endogenous GCs in DC homeostasis are less clear. A critical element regulating endogenous GC concentrations involves local conversion of inactive substrates to active 11-hydroxyglucocorticoids, a reduction reaction catalyzed within the endoplasmic reticulum by an enzyme complex containing 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and hexose-6-phosphate dehydrogenase (H6PDH). In this study, we found that this GC amplification pathway operates both constitutively and maximally in steady state murine DC populations and is unaffected by additional inflammatory stimuli. Under physiologic conditions, 11βHSD1-H6PDH increases the sensitivity of plasmacytoid DCs (pDCs) to GC-induced apoptosis and restricts the survival of this population through a cell-intrinsic mechanism. Upon CpG activation, the effects of enzyme activity are overridden, with pDCs becoming resistant to GCs and fully competent to release type I interferon. CD8α(+) DCs are also highly proficient in amplifying GC levels, leading to impaired maturation following toll-like receptor-mediated signaling. Indeed, pharmacologic inhibition of 11βHSD1 synergized with CpG to enhance specific T-cell responses following vaccination targeted to CD8α(+) DCs. In conclusion, amplification of endogenous GCs is a critical cell-autonomous mechanism for regulating the survival and functions of DCs in vivo.

The role of dendritic cells in autoimmunity

Dendritic cells (DCs) initiate and shape both the innate and adaptive immune responses. Accordingly, recent evidence from clinical studies and experimental models implicates DCs in the pathogenesis of most autoimmune diseases. However, fundamental questions remain unanswered concerning the actual roles of DCs in autoimmunity, both in general and, in particular, in specific diseases. In this Review, we discuss the proposed roles of DCs in immunological tolerance, the effect of the gain or loss of DCs on autoimmunity and DC-intrinsic molecular regulators that help to prevent the development of autoimmunity. We also review the emerging roles of DCs in several autoimmune diseases, including autoimmune myocarditis, multiple sclerosis, psoriasis, type 1 diabetes and systemic lupus erythematosus.

miR-29b and miR-29c are involved in Toll-like receptor control of glucocorticoid-induced apoptosis in human plasmacytoid dendritic cells

Glucocorticoids (GCs) are frequently used to treat many of the acute disease manifestations associated with inflammatory and autoimmune disorders. However, Toll-like receptor (TLR) pathway-activated plasmacytoid dendritic cells (pDCs) are resistant to GC-induced apoptosis, which leads to the inefficiency of GCs in the treatment of type I interferon-related autoimmune diseases, such as systemic lupus erythematosus (SLE). Therefore, compounds promoting pDC apoptosis may be helpful for improving the efficacy of GCs. In this study, we performed screening to identify microRNAs (miRNAs) involved in TLR-inhibited GC-induced pDC apoptosis and found an array of miRNAs that may regulate pDC apoptosis. Among those demonstrating altered expression, 6 miRNAs were inhibited in TLR-activated pDCs. Bioinformatics analysis and functional studies indicated that miR-29b and miR-29c were 2 key miRNAs involved in TLR-inhibited GC-induced pDC apoptosis. Furthermore, both of these miRNAs promoted pDC apoptosis by directly targeting Mcl-1 and Bcl-2 in human primary pDCs. Our findings provide new targets that could improve the efficacy of GCs for the treatment of SLE.

Etomidate increases susceptibility to pneumonia in trauma patients

PURPOSE

To investigate the impact of etomidate on the rate of hospital-acquired pneumonia (HAP) in trauma patients and the effects of hydrocortisone in etomidate-treated patients.

METHODS

This was a sub-study of the HYPOLYTE multi-centre, randomized, double-blind, placebo-controlled trial of hydrocortisone in trauma patients (NCT00563303). Inclusion criterion was trauma patient with mechanical ventilation (MV) of ≥48 h. The use of etomidate was prospectively collected. Endpoints were the results of the cosyntropin test and rate of HAP on day 28 of follow-up.

RESULTS

Of the 149 patients enrolled in the study, 95 (64 %) received etomidate within 36 h prior to inclusion. 79 (83 %) of 95 patients receiving etomidate and 34 of the 54 (63 %) not receiving etomidate had corticosteroid insufficiency (p = 0.006). The administration of etomidate did not alter basal cortisolemia (p = 0.73), but it did decrease the delta of cortisolemia at 60 min (p = 0.007). There was a correlation between time from etomidate injection to inclusion in the study and sensitivity to corticotropin (R (2) = 0.19; p = 0.001). Forty-nine (51.6 %) patients with etomidate and 16 (29.6 %) patients without etomidate developed HAP by day 28 (p = 0.009). Etomidate was associated with HAP on day 28 in the multivariate analysis (hazard ratio 2.48; 95 % confidence interval 1.19-5.18; p = 0.016). Duration of MV with or without etomidate was not significantly different (p = 0.278). Among etomidate-exposed patients, 18 (40 %) treated with hydrocortisone developed HAP compared with 31 (62 %) treated with placebo (p = 0.032). Etomidate-exposed patients treated with hydrocortisone had fewer ventilator days (p < 0.001).

CONCLUSIONS

Among the patients enrolled in the study, etomidate did not alter basal cortisolemia, but it did decrease reactivity to corticotropin. We suggest that in trauma patients, etomidate is an independent risk factor for HAP and that the administration of hydrocortisone should be considered after etomidate use.

The transcription factor Spi-B regulates human plasmacytoid dendritic cell survival through direct induction of the antiapoptotic gene BCL2-A1

Plasmacytoid dendritic cells (pDCs) selectively express Toll-like receptor (TLR)-7 and TLR-9, which allow them to rapidly secrete massive amounts of type I interferons after sensing nucleic acids derived from viruses or bacteria. It is not completely understood how development and function of pDCs are controlled at the transcriptional level. One of the main factors driving pDC development is the ETS factor Spi-B, but little is known about its target genes. Here we demonstrate that Spi-B is crucial for the differentiation of hematopoietic progenitor cells into pDCs by controlling survival of pDCs and its progenitors. In search for Spi-B target genes, we identified the antiapoptotic gene Bcl2-A1 as a specific and direct target gene, thereby consolidating the critical role of Spi-B in cell survival.

Circulating plasmacytoid dendritic cells in patients with primary and Helicobacter pylori-associated immune thrombocytopenia

OBJECTIVES

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by the production of autoreactive antibodies against platelet antigens. Although dysfunction of multiple aspects of cellular immunity is considered to be important in the pathogenesis of ITP, it has not been clarified which cell types play a principal role.

METHODS

We enrolled 46 untreated patients with chronic ITP and 47 healthy adult volunteers, and investigated by flow cytometry the percentage and absolute number of cells in their peripheral blood that participate in the regulation of cellular immunity. These included plasmacytoid dendritic cells (pDCs), myeloid dendritic cells (mDCs), natural killer (NK) cells, natural killer T (NKT) cells, regulatory T (Treg) cells, and Th17 cells.

RESULTS

We found a significant reduction in the absolute number of pDCs, but not of mDCs, in patients with ITP when compared with healthy controls (P < 0.001). Reduced numbers of circulating pDCs were observed in both Helicobacter pylori (H. pylori)-positive and Helicobacter pylori (H. pylori)-negative patients with ITP. In contrast, there were no significant differences in the numbers of circulating Treg cells, Th17 cells, NK cells, or NKT cells. Interestingly, we observed increases in the number of pDCs after H. pylori eradication by antibiotics in responders but not in non-responders, while pDCs and mDCs decreased markedly after prednisolone therapy in both responders and non-responders. In patients without treatment, low pDC numbers persisted during the observational period.

CONCLUSIONS

We demonstrated that the number of circulating pDCs is low in patients with primary and H. pylori-associated ITP and that it changes depending on treatment modality. Further investigation is warranted with regard to the role of pDCs in the immunopathogenesis of ITP.

dsRNA sensors and plasmacytoid dendritic cells in host defense and autoimmunity

The innate immune system detects viruses through molecular sensors that trigger the production of type I interferons (IFN-I) and inflammatory cytokines. As viruses vary tremendously in size, structure, genomic composition, and tissue tropism, multiple sensors are required to detect their presence in various cell types and tissues. In this review, we summarize current knowledge of the diversity, specificity, and signaling pathways downstream of viral sensors and ask whether two distinct sensors that recognize the same viral component are complementary, compensatory, or simply redundant. We also discuss why viral sensors are differentially distributed in distinct cell types and whether a particular cell type dominates the IFN-I response during viral infection. Finally, we review evidence suggesting that inappropriate signaling through viral sensors may induce autoimmunity. The picture emerging from these studies is that disparate viral sensors in different cell types form a dynamic and integrated molecular network that can be exploited for improving vaccination and therapeutic strategies for infectious and autoimmune diseases.

A nonredundant role for plasmacytoid dendritic cells in host defense against the human fungal pathogen Aspergillus fumigatus

While plasmacytoid dendritic cells (pDCs), a natural type I interferon (IFN)-producing cell type, are regarded as critical for innate immunity to viruses, their role in defense against fungal infections remains unknown. We examined the interactions of pDCs with hyphae of the invasive human fungal pathogen Aspergillus fumigatus. Human pDCs spread over hyphae and inhibited their growth. Antifungal activity was retained in pDC lysates, did not require direct fungal contact, and was partially reversed by zinc. Incubation with hyphae resulted in pDC cytotoxicity, partly due to fungal gliotoxin secretion. Following hyphal stimulation, pDCs released proinflammatory cytokines via a TLR9-independent mechanism. Pulmonary challenge of mice with A. fumigatus resulted in a substantial influx of pDCs into lungs, and pDC-depleted mice were hypersusceptible to invasive aspergillosis. These data demonstrate the antifungal activity of pDCs against A. fumigatus and establish their nonredundant role in host defenses against invasive aspergillosis in vivo.

Interactions between glucocorticoid treatment and cis-regulatory polymorphisms contribute to cellular response phenotypes

Glucocorticoids (GCs) mediate physiological responses to environmental stress and are commonly used as pharmaceuticals. GCs act primarily through the GC receptor (GR, a transcription factor). Despite their clear biomedical importance, little is known about the genetic architecture of variation in GC response. Here we provide an initial assessment of variability in the cellular response to GC treatment by profiling gene expression and protein secretion in 114 EBV-transformed B lymphocytes of African and European ancestry. We found that genetic variation affects the response of nearby genes and exhibits distinctive patterns of genotype-treatment interactions, with genotypic effects evident in either only GC-treated or only control-treated conditions. Using a novel statistical framework, we identified interactions that influence the expression of 26 genes known to play central roles in GC-related pathways (e.g. NQO1, AIRE, and SGK1) and that influence the secretion of IL6.

Plasmacytoid dendritic cells: recent progress and open questions

Plasmacytoid dendritic cells (pDCs) are specialized in rapid and massive secretion of type I interferon (IFN-α/β) in response to foreign nucleic acids. Combined with their antigen presentation capacity, this powerful functionality enables pDCs to orchestrate innate and adaptive immune responses. pDCs combine features of both lymphocytes and classical dendritic cells and display unique molecular adaptations to nucleic acid sensing and IFN production. In the decade since the identification of the pDC as a distinct immune cell type, our understanding of its molecular underpinnings and role in immunity has progressed rapidly. Here we review select aspects of pDC biology including cell fate establishment and plasticity, specific molecular mechanisms of pDC function, and the role of pDCs in T cell responses, antiviral immunity, and autoimmune diseases. Important unresolved questions remain in these areas, promising exciting times in pDC research for years to come.

Minireview: Glucocorticoids in autoimmunity: unexpected targets and mechanisms

For decades, natural and synthetic glucocorticoids (GC) have been among the most commonly prescribed classes of immunomodulatory drugs. Their unsurpassed immunosuppressive and antiinflammatory activity along with cost-effectiveness makes these compounds a treatment of choice for the majority of autoimmune and inflammatory diseases, despite serious side effects that frequently accompany GC therapy. The activated GC receptor (GR) that conveys the signaling information of these steroid ligands to the transcriptional machinery engages a number of pathways to ultimately suppress autoimmune responses. Of those, GR-mediated apoptosis of numerous cell types of hematopoietic origin and suppression of proinflammatory cytokine gene expression have been described as the primary mechanisms responsible for the antiinflammatory actions of GC. However, along with the ever-increasing appreciation of the complex functions of the immune system in health and disease, we are beginning to recognize new facets of GR actions in immune cells. Here, we give a brief overview of the extensive literature on the antiinflammatory activities of GC and discuss in greater detail the unexpected pathways, factors, and mechanisms that have recently begun to emerge as novel targets for GC-mediated immunosuppression.

Distinct host cell proteins incorporated by SIV replicating in CD4+ T cells from natural disease resistant versus non-natural disease susceptible hosts

BACKGROUND

Enveloped viruses including the simian immunodeficiency virus (SIV) replicating within host cells acquire host proteins upon egress from the host cells. A number of studies have catalogued such host proteins, and a few have documented the potential positive and negative biological functions of such host proteins. The studies conducted herein utilized proteomic analysis to identify differences in the spectrum of host proteins acquired by a single source of SIV replicating within CD4+ T cells from disease resistant sooty mangabeys and disease susceptible rhesus macaques.

RESULTS

While a total of 202 host derived proteins were present in viral preparations from CD4+ T cells from both species, there were 4 host-derived proteins that consistently and uniquely associated with SIV replicating within CD4+ T cells from rhesus macaques but not sooty mangabeys; and, similarly, 28 host-derived proteins that uniquely associated with SIV replicating within CD4+ T cells from sooty mangabeys, but not rhesus macaques. Of interest was the finding that of the 4 proteins uniquely present in SIV preparations from rhesus macaques was a 26 S protease subunit 7 (MSS1) that was shown to enhance HIV-1 'tat' mediated transactivation. Among the 28 proteins found in SIV preparations from sooty mangabeys included several molecules associated with immune function such as CD2, CD3ε, TLR4, TLR9 and TNFR and a bioactive form of IL-13.

CONCLUSIONS

The finding of 4 host proteins that are uniquely associated with SIV replicating within CD4+ T cells from disease susceptible rhesus macaques and 28 host proteins that are uniquely associated with SIV replicating within CD4+ T cells from disease resistant sooty mangabeys provide the foundation for determining the potential role of each of these unique host-derived proteins in contributing to the polarized clinical outcome in these 2 species of nonhuman primates.