Prevalence and prognostic relevance of invasive fungal disease during veno-arterial ECMO: A retrospective single-center study.

PURPOSE: To assess the prevalence and relevance of invasive fungal disease (IFD) during veno-arterial (V-A) extracorporeal membrane oxygenation (ECMO). METHODS: Retrospective analysis from January 2013 to November 2023 of adult V-A ECMO cases at a German University Hospital. Parameters relating to IFD, demographics, length of stay (LoS), days on ECMO and mechanical ventilation, prognostic scores and survival were assessed. Multivariable logistic regression analyses with IFD and death as dependent variables were performed. Outcome was assessed after propensity score matching IFD-patients to non-IFD-controls. RESULTS: 421 patients received V-A ECMO. 392 patients with full electronic datasets were included. The prevalence of IFD, invasive candidiasis and probable invasive pulmonary aspergillosis was 4.6%, 3.8% and 1.0%. Severity of acute disease, pre-existing moderate-to-severe renal disease and continuous kidney replacement therapy were predictive of IFD. In-hospital mortality (94% (17/18) compared to 67% (252/374) in non-IFD patients (p = 0.0156)) was predicted by female sex, SOFA score at admission, SAVE score and IFD (for IFD: OR: 8.31; CI: 1.60-153.18; p: 0.044). There was no difference in outcome after matching IFD-cases to non-IFD-controls. CONCLUSIONS: IFD are detected in about one in 20 patients on V-A ECMO, indicating mortality >90%. However, IFD do not contribute to prognosis in this population.

COVID-19 Is an Independent Risk Factor for Detrimental Invasive Fungal Disease in Patients on Veno-Venous Extracorporeal Membrane Oxygenation: A Retrospective Study.

Invasive fungal disease (IFD) is associated with the mortality of patients on extracorporeal membrane oxygenation (ECMO). Several risk factors for IFD have been identified in patients with or without ECMO. Here, we assessed the relevance of coronavirus disease (COVID-19) for the occurrence of IFD in patients on veno-venous (V-V) ECMO for respiratory failure. In a retrospective analysis of all ECMO cases between January 2013 and December 2022 (2020-2022 for COVID-19 patients), active COVID-19 and the type, timing and duration of IFD were investigated. Demographics, hospital, ICU length of stay (LoS), duration of ECMO, days on invasive mechanical ventilation, prognostic scores (Respiratory ECMO Survival Prediction (RESP) score, Charlson Comorbidity Index (CCI), Therapeutic Intervention Scoring System (TISS)-10, Sequential Organ Failure Assessment (SOFA) score and Simplified Acute Physiology Score (SAPS)-II) and length of survival were assessed. The association of COVID-19 with IFD was investigated using propensity score matching and uni- and multivariable logistic regression analyses. We identified 814 patients supported with ECMO, and 452 patients were included in further analyses. The incidence of IFD was 4.8% and 11.0% in patients without and with COVID-19, respectively. COVID-19 status represented an independent risk factor for IFD (OR 4.30; CI 1.72-10.85; p: 0.002; multivariable regression analysis). In patients with COVID-19, 84.6% of IFD was candidemia and 15.4% represented invasive aspergillosis (IA). All of these patients died. In patients on V-V ECMO, we report that COVID-19 is an independent risk factor for IFD, which is associated with a detrimental prognosis. Further studies are needed to investigate strategies of antifungal therapy or prophylaxis in these patients.

Impact of Invasive Fungal Diseases on Survival under Veno-Venous Extracorporeal Membrane Oxygenation for ARDS.

OBJECTIVE: To assess the incidence and significance of invasive fungal diseases (IFD) during veno-venous (VV) ECMO support for acute respiratory distress syndrome (ARDS). METHODS: Retrospective analysis from January 2013 to April 2021 of all ECMO cases for ARDS at a German University Hospital. In patients with IFD (IFD patients), type of IFD, time of IFD, choice of antifungal agent, duration, and success of therapy were investigated. For comparison, patients without IFD (non-IFD patients) were selected by propensity score matching using treatment-independent variables (age, gender, height, weight, and the Sequential Organ Failure Assessment (SOFA) score at ICU admission). Demographics, hospital and ICU length of stay, duration of ECMO therapy, days on mechanical ventilation, prognostic scores (Charlson Comorbidity Index (CCI), Therapeutic Intervention Scoring System (TISS), and length of survival were assessed. RESULTS: A total of 646 patients received ECMO, 368 patients received VV ECMO. The incidence of IFD on VV ECMO was 5.98%, with 5.43% for Candida bloodstream infections (CBSI) and 0.54% for invasive aspergillosis (IA). In IFD patients, in-hospital mortality was 81.8% versus 40.9% in non-IFD patients. The hazard ratio for death was 2.5 (CI 1.1-5.4; p: 0.023) with IFD. CONCLUSIONS: In patients on VV ECMO for ARDS, about one in 17 contracts an IFD, with a detrimental impact on prognosis. Further studies are needed to address challenges in the diagnosis and treatment of IFD in this population.

The value of real-time ultrasound-guidance for definite placement of a right supraclavicular subclavian central venous catheter.

Central venous catheters (CVC) are widely used in critically ill patients and in those undergoing major surgery. Significant adverse events, such as pneumothorax and hemothorax, can be caused by needle insertion during CVC insertion. CVC misplacement is less often described, yet equally important, as it can lead to deleterious complications.Here, we describe a case in which misplacement of a guidewire following infraclavicular puncture of the right axillary vein was detected by continuous ultrasound employing the right supraclavicular fossa view. Utilizing this ultrasound view, the insertion approach to the vessel was changed and correct CVC placement could be achieved.While ultrasound guidance is widely accepted for vessel puncture, this case demonstrates the value of continuous ultrasound guidance for the entire process of CVC insertion: vessel puncture, correct guidewire advancement, catheter placement, and exclusion of complications such as pneumothorax. It also shows that there should be a high index of suspicion for guidewire misplacement, even after successful venipuncture.In conclusion, ultrasound protocols covering the complete CVC insertion process should be implemented into current clinical practice.

Endothelial cell PHD2-HIF1α-PFKFB3 contributes to right ventricle vascular adaptation in pulmonary hypertension.

Humans and animals with pulmonary hypertension (PH) show right ventricular (RV) capillary growth, which positively correlates with overall RV hypertrophy. However, molecular drivers of RV vascular augmentation in PH are unknown. Prolyl hydroxylase (PHD2) is a regulator of hypoxia-inducible factors (HIFs), which transcriptionally activates several proangiogenic genes, including the glycolytic enzyme 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3). We hypothesized that a signaling axis of PHD2-HIF1α-PFKFB3 contributes to adaptive coupling between the RV vasculature and tissue volume to maintain appropriate vascular density in PH. We used design-based stereology to analyze endothelial cell (EC) proliferation and the absolute length of the vascular network in the RV free wall, relative to the tissue volume in mice challenged with hypoxic PH. We observed increased RV EC proliferation starting after 6 h of hypoxia challenge. Using parabiotic mice, we found no evidence for a contribution of circulating EC precursors to the RV vascular network. Mice with transgenic deletion or pharmacological inhibition of PHD2, HIF1α, or PFKFB3 all had evidence of impaired RV vascular adaptation following hypoxia PH challenge. PHD2-HIF1α-PFKFB3 contributes to structural coupling between the RV vascular length and tissue volume in hypoxic mice, consistent with homeostatic mechanisms that maintain appropriate vascular density. Activating this pathway could help augment the RV vasculature and preserve RV substrate delivery in PH, as an approach to promote RV function.

Cytosolic d-type CpG-oligonucleotides induce a type I interferon response by activating the cGAS-STING signaling pathway.

Cytosolic DNA receptor cyclic GMP-AMP (cGAMP) synthase (cGAS) has been shown to be critically involved in the detection of cytosolic, self- and non-self-DNA, initiating a type I IFN response through the adaptor protein Stimulator of Interferon Genes (STING) and interferon regulatory factor 3 (IRF3). Current studies propose that canonical binding of dsDNA by cGAS depends on DNA length, but not on base sequence. In contrast, activation of TLR9 is sequence dependent. It requires unmethylated CpG dinucleotides in microbial DNA, which is mimicked by synthetic oligodeoxynucleotides (ODN). Here, we provide evidence that d-type ODN (D-ODN), but not K-type ODN (K-ODN), bind to human cGAS and activate downstream signaling. Transfection of D-ODN into a TLR9-deficient, human monocytic cell line (THP-1) induced phosphorylation of IRF3 and secretion of IFN. This response was absent in cells with CRISPR/Cas9-mediated cGAS- or STING-deficiency. Utilizing a protein pulldown approach, we further demonstrate direct binding of D-ODN to cGAS. Induction of a type I IFN response by D-ODN was confirmed in human primary monocytes and monocyte-derived macrophages. These results are relevant to our understanding of self-nonself-discrimination by cGAS and to the pharmacologic effects of ODN, which currently are investigated in clinical studies.

Suppression of HIF2 signalling attenuates the initiation of hypoxia-induced pulmonary hypertension.

Most published studies addressing the role of hypoxia inducible factors (HIFs) in hypoxia-induced pulmonary hypertension development employ models that may not recapitulate the clinical setting, including the use of animals with pre-existing lung/vascular defects secondary to embryonic HIF ablation or activation. Furthermore, critical questions including how and when HIF signalling contributes to hypoxia-induced pulmonary hypertension remain unanswered.Normal adult rodents in which global HIF1 or HIF2 was inhibited by inducible gene deletion or pharmacological inhibition (antisense oligonucleotides (ASO) and small molecule inhibitors) were exposed to short-term (4 days) or chronic (4-5 weeks) hypoxia. Haemodynamic studies were performed, the animals euthanised, and lungs and hearts obtained for pathological and transcriptomic analysis. Cell-type-specific HIF signals for pulmonary hypertension initiation were determined in normal pulmonary vascular cells in vitro and in mice (using cell-type-specific HIF deletion).Global Hif1a deletion in mice did not prevent hypoxia-induced pulmonary hypertension at 5 weeks. Mice with global Hif2a deletion did not survive long-term hypoxia. Partial Hif2a deletion or Hif2-ASO (but not Hif1-ASO) reduced vessel muscularisation, increases in pulmonary arterial pressures and right ventricular hypertrophy in mice exposed to 4-5 weeks of hypoxia. A small molecule HIF2 inhibitor (PT2567) significantly attenuated early events (monocyte recruitment and vascular cell proliferation) in rats exposed to 4 days of hypoxia, as well as vessel muscularisation, tenascin C accumulation and pulmonary hypertension development in rats exposed to 5 weeks of hypoxia. In vitro, HIF2 induced a distinct set of genes in normal human pulmonary vascular endothelial cells, mediating inflammation and proliferation of endothelial cells and smooth muscle cells. Endothelial Hif2a knockout prevented hypoxia-induced pulmonary hypertension in mice.Inhibition of HIF2 (but not HIF1) can provide a therapeutic approach to prevent the development of hypoxia-induced pulmonary hypertension. Future studies are needed to investigate the role of HIFs in pulmonary hypertension progression and reversal.

The role of inflammation in hypoxic pulmonary hypertension: from cellular mechanisms to clinical phenotypes.

Hypoxic pulmonary hypertension (PH) comprises a heterogeneous group of diseases sharing the common feature of chronic hypoxia-induced pulmonary vascular remodeling. The disease is usually characterized by mild to moderate pulmonary vascular remodeling that is largely thought to be reversible compared with the progressive irreversible disease seen in World Health Organization (WHO) group I disease. However, in these patients, the presence of PH significantly worsens morbidity and mortality. In addition, a small subset of patients with hypoxic PH develop "out-of-proportion" severe pulmonary hypertension characterized by pulmonary vascular remodeling that is irreversible and similar to that in WHO group I disease. In all cases of hypoxia-related vascular remodeling and PH, inflammation, particularly persistent inflammation, is thought to play a role. This review focuses on the effects of hypoxia on pulmonary vascular cells and the signaling pathways involved in the initiation and perpetuation of vascular inflammation, especially as they relate to vascular remodeling and transition to chronic irreversible PH. We hypothesize that the combination of hypoxia and local tissue factors/cytokines ("second hit") antagonizes tissue homeostatic cellular interactions between mesenchymal cells (fibroblasts and/or smooth muscle cells) and macrophages and arrests these cells in an epigenetically locked and permanently activated proremodeling and proinflammatory phenotype. This aberrant cellular cross-talk between mesenchymal cells and macrophages promotes transition to chronic nonresolving inflammation and vascular remodeling, perpetuating PH. A better understanding of these signaling pathways may lead to the development of specific therapeutic targets, as none are currently available for WHO group III disease.

Ultrasonography for haemodynamic monitoring.

Echocardiography has become an indispensable tool in the evaluation of medical and surgical patients. As ultrasound (US) machines have become more widely available and significantly more compact, there has been an exponential growth in the use of transthoracic echocardiography (TTE), transoesophageal echocardiography (TOE) and other devices in the perioperative setting. Here, we review recent findings relevant to the use of perioperative US, with a special focus on the haemodynamic management of the surgical patient.

Hypoxia-induced deoxycytidine kinase contributes to epithelial proliferation in pulmonary fibrosis.

RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a deadly lung disease with few therapeutic options. Apoptosis of alveolar epithelial cells, followed by abnormal tissue repair characterized by hyperplastic epithelial cell formation, is a pathogenic process that contributes to the progression of pulmonary fibrosis. However, the signaling pathways responsible for increased proliferation of epithelial cells remain poorly understood. OBJECTIVES: To investigate the role of deoxycytidine kinase (DCK), an important enzyme for the salvage of deoxynucleotides, in the progression of pulmonary fibrosis. METHODS: DCK expression was examined in the lungs of patients with IPF and mice exposed to bleomycin. The regulation of DCK expression by hypoxia was studied in vitro and the importance of DCK in experimental pulmonary fibrosis was examined using a DCK inhibitor and alveolar epithelial cell-specific knockout mice. MEASUREMENTS AND MAIN RESULTS: DCK was elevated in hyperplastic alveolar epithelial cells of patients with IPF and in mice exposed to bleomycin. Increased DCK was localized to cells associated with hypoxia, and hypoxia directly induced DCK in alveolar epithelial cells in vitro. Hypoxia-induced DCK expression was abolished by silencing hypoxia-inducible factor 1α and treatment of bleomycin-exposed mice with a DCK inhibitor attenuated pulmonary fibrosis in association with decreased epithelial cell proliferation. Furthermore, DCK expression, and proliferation of epithelial cells and pulmonary fibrosis was attenuated in mice with conditional deletion of hypoxia-inducible factor 1α in the alveolar epithelium. CONCLUSIONS: Our findings suggest that the induction of DCK after hypoxia plays a role in the progression of pulmonary fibrosis by contributing to alveolar epithelial cell proliferation.

Adventitial fibroblasts induce a distinct proinflammatory/profibrotic macrophage phenotype in pulmonary hypertension.

Macrophage accumulation is not only a characteristic hallmark but is also a critical component of pulmonary artery remodeling associated with pulmonary hypertension (PH). However, the cellular and molecular mechanisms that drive vascular macrophage activation and their functional phenotype remain poorly defined. Using multiple levels of in vivo (bovine and rat models of hypoxia-induced PH, together with human tissue samples) and in vitro (primary mouse, rat, and bovine macrophages, human monocytes, and primary human and bovine fibroblasts) approaches, we observed that adventitial fibroblasts derived from hypertensive pulmonary arteries (bovine and human) regulate macrophage activation. These fibroblasts activate macrophages through paracrine IL-6 and STAT3, HIF1, and C/EBPß signaling to drive expression of genes previously implicated in chronic inflammation, tissue remodeling, and PH. This distinct fibroblast-activated macrophage phenotype was independent of IL-4/IL-13-STAT6 and TLR-MyD88 signaling. We found that genetic STAT3 haplodeficiency in macrophages attenuated macrophage activation, complete STAT3 deficiency increased macrophage activation through compensatory upregulation of STAT1 signaling, and deficiency in C/EBPß or HIF1 attenuated fibroblast-driven macrophage activation. These findings challenge the current paradigm of IL-4/IL-13-STAT6-mediated alternative macrophage activation as the sole driver of vascular remodeling in PH, and uncover a cross-talk between adventitial fibroblasts and macrophages in which paracrine IL-6-activated STAT3, HIF1α, and C/EBPß signaling are critical for macrophage activation and polarization. Thus, targeting IL-6 signaling in macrophages by completely inhibiting C/EBPß or HIF1α or by partially inhibiting STAT3 may hold therapeutic value for treatment of PH and other inflammatory conditions characterized by increased IL-6 and absent IL-4/IL-13 signaling.

Anti-atherogenic effects of statins: Impact on angiopoietin-2 release from endothelial cells.

Beyond lipid lowering, statins are supposed to exert pleiotropic effects positively influencing the progression of atherosclerotic lesions. The development of such lesions is associated with increased release of angiopoietin-2 (Ang-2), an endothelial cell-specific protein growth factor stored in Weibel-Palade bodies (WPBs). The aim of our study was to examine whether statin pretreatment influences the release of Ang-2 from endothelial cells. Stimulation of HUVECs and HMVECs with PMA, thrombin or histamine resulted in significant release of Ang-2, as evidenced by ELISA. Pretreatment with simvastatin and mevastatin suppressed this release to basal level, while pravastatin had no effect. Simvastatin itself increased nitric oxide (NO, EC number 1.14.13.39) synthesis, measured by Griess reaction. Combining the statin pretreatment with the eNOS inhibitor L-NNA as well as bypassing the HMG-CoA reductase (EC number: 1.1.1.34) by adding mevalonic acid or geranyl pyrophosphate restored the exocytotic effect of PMA. Immunofluorescence microscopy showed that depletion of WPBs upon PMA stimulation ceased after pretreatment with simvastatin. This study demonstrates a potent suppressive effect of statins on the release of Ang-2 from endothelial cells. Regarding its harmful effects in the development of atherosclerotic lesions, our data provide further insight into the mechanisms of the anti-atherogenic potential of statins.

Beta2-adrenoceptor stimulation suppresses TLR9-dependent IFNA1 secretion in human peripheral blood mononuclear cells.

INTRODUCTION: IFNA1 (interferon alpha) is a key cytokine regulating the activity of numerous immune cells. Plasmacytoid dendritic cells (pDCs) as natural interferon-producing cells play critical roles as sensors of pathogens and link innate to adaptive immunity. CpG motifs within DNA sequences activating toll-like receptor 9 (TLR9) are the main stimuli eliciting IFNA1 secretion from pDCs. Adrenergic substances are capable of differentially modulating the response from various immune cells. Hence, the aim of this study was to examine how adrenoceptor stimulation influences TLR9-induced IFNA1 secretion from human pDCs. METHODS: PBMCs generated from human whole blood and pDCs enriched from buffy coats were stimulated with LPS and CpG-ODN 2336 in the presence or absence of epinephrine and different adrenoceptor antagonists. Secretion of TNF and IFNA1 was measured by ELISA. Flow cytometry was used to determine efficacy of pDC enrichment and adrenoceptor expression of PBMC subsets. The influence of modified IFNA1 secretion on NK cell activity was evaluated using a colorimetric tumor cell lysis assay. RESULTS: TLR9-induced IFNA1 secretion as well as TLR4-induced TNF secretion from PBMCs was dose-dependently attenuated by coincubation with epinephrine. Combination with different specific adrenoceptor antagonists revealed that this effect was mediated by the adrenoceptor ß2 (ADRB2). Since flow cytometric analysis could exclude the presence of ADRB2 on pDCs, highly enriched pDCs lacked any visible impact of adrenoceptor stimulation on TLR9-induced IFNA1 release. Combination of pDCs with PBMCs restored the effect, even when they were separated by a permeable membrane. Suppression of TLR9-mediated IFNA1 secretion from PBMCs by adrenoceptor stimulation reduced the lytic activity of NK cells on K562 tumor cells. CONCLUSION: We provide insights into the underlying mechanisms of the interrelation between immune responses and pharmacological agents widely used in clinical practice. Our results have implications for the future treatment of human patients, in which the endogenous immune response plays a pivotal role, such as during viral infections, inflammatory diseases and cancers.

CD73+ regulatory T cells contribute to adenosine-mediated resolution of acute lung injury.

Acute lung injury (ALI) is characterized by alveolar injury and uncontrolled inflammation. Since most cases of ALI resolve spontaneously, understanding the endogenous mechanisms that promote ALI resolution is important to developing effective therapies. Previous studies have implicated extracellular adenosine signaling in tissue adaptation and wound healing. Therefore, we hypothesized a functional contribution for the endogenous production of adenosine during ALI resolution. As a model, we administered intratracheal LPS and observed peak lung injury at 3 d, with resolution by d 14. Treatment with pegylated adenosine-deaminase to enhance extracellular adenosine breakdown revealed impaired ALI resolution. Similarly, genetic deletion of cd73, the pacemaker for extracellular adenosine generation, was associated with increased mortality (0% wild-type and 40% in cd73(-/-) mice; P<0.05) and failure to resolve ALI adequately. Studies of inflammatory cell trafficking into the lungs during ALI resolution revealed that regulatory T cells (Tregs) express the highest levels of CD73. While Treg numbers in cd73(-/-) mice were similar to controls, cd73-deficient Tregs had attenuated immunosuppressive functions. Moreover, adoptive transfer of cd73-deficient Tregs into Rag(-/-) mice emulated the observed phenotype in cd73(-/-) mice, while transfer of wild-type Tregs was associated with normal ALI resolution. Together, these studies implicate CD73-dependent adenosine generation in Tregs in promoting ALI resolution.

Transcriptional control of adenosine signaling by hypoxia-inducible transcription factors during ischemic or inflammatory disease.

Inflammatory lesions, ischemic tissues, or solid tumors are characterized by the occurrence of severe tissue hypoxia within the diseased tissue. Subsequent stabilization of hypoxia-inducible transcription factors-particularly of hypoxia-inducible factor 1α (HIF1A)--results in significant alterations of gene expression of resident cells or inflammatory cells that have been recruited into such lesions. Interestingly, studies of hypoxia-induced changes of gene expression identified a transcriptional program that promotes extracellular adenosine signaling. Adenosine is a signaling molecule that functions through the activation of four distinct adenosine receptors--the ADORA1, ADORA2A, ADORA2B, and ADORA3 receptors. Extracellular adenosine is predominantly derived from the phosphohydrolysis of precursor nucleotides, such as adenosine triphosphate or adenosine monophosphate. HIF1A-elicited alterations in gene expression enhance the enzymatic capacity within inflamed tissues to produce extracellular adenosine. Moreover, hypoxia-elicited induction of adenosine receptors--particularly of ADORA2B--results in increased signal transduction. Functional studies in genetic models for HIF1A or adenosine receptors implicate this pathway in an endogenous feedback loop that dampens excessive inflammation and promotes injury resolution, while at the same time enhancing ischemia tolerance. Therefore, pharmacological strategies to enhance HIF-elicited adenosine production or to promote adenosine signaling through adenosine receptors are being investigated for the treatment of acute inflammatory or ischemic diseases characterized by tissue hypoxia.

Monocyte-mediated inhibition of TLR9-dependent IFN-α induction in plasmacytoid dendritic cells questions bacterial DNA as the active ingredient of bacterial lysates.

Bacterial DNA contains unmethylated CpG dinucleotides and is a potent ligand for TLR9. Bacterial DNA has been claimed the active ingredient in bacterial lysates used for immunotherapy. Whereas the detection of viral DNA by TLR9 expressed in plasmacytoid dendritic cells (PDCs) with subsequent IFN-α production is well defined, the role of bacterial DNA during microbial infection is less clear. In fact, IFN-α is not a hallmark of antibacterial immune responses. Unlike in mice, TLR9 expression in humans is restricted to PDCs and B cells; thus, conclusions from murine models of infection have limitations. In this study, we demonstrate that lysates of heat-killed Escherichia coli containing bacterial DNA induced IFN-α in isolated PDCs but not in the mixed cell populations of human PBMCs. Depletion of monocytes restored IFN-α secretion by PDCs within PBMCs. We found that monocyte-derived IL-10 and PGs contribute to monocyte-mediated inhibition of IFN-α release in PDCs. We conclude that human PDCs can be stimulated by bacterial DNA via TLR9; however, in the physiological context of mixed-cell populations, PDC activation is blocked by factors released from monocytes stimulated in parallel by other components of bacterial lysates such as LPS. This functional repression of PDCs by concomitantly stimulated monocytes avoids production of antiviral IFN-α during bacterial infection and thus explains how the innate immune system is enabled to distinguish bacterial from viral CpG DNA and thus to elicit the appropriate responses despite the presence of CpG DNA in both types of infection.

Selective and direct activation of human neutrophils but not eosinophils by Toll-like receptor 8.

BACKGROUND: Granulocytes represent the largest fraction of immune cells in peripheral blood and are directly exposed to circulating Toll-like receptor (TLR) ligands. Although highly relevant for TLR-based therapies, because of the technical challenge, activation of the granulocyte subsets of neutrophils and eosinophils by TLR ligands is less well studied than activation of other immune cell subsets. OBJECTIVE: The aim of this work was to study direct versus indirect neutrophil and eosinophil activation by TLR7 and TLR8 ligands. METHODS: We used a new whole-blood assay, single cell-based cytokine detection, and highly purified primary human neutrophils and eosinophils to separate direct and indirect effects on these blood cell subsets. RESULTS: We found indirect but not direct activation of neutrophils but not eosinophils in whole blood by using unmodified immunostimulatory RNA (isRNA; TLR7/8 ligand). In contrast, direct activation and stimulation of the respiratory burst and degranulation was seen with nuclease-stable isRNA and with the small-molecule TLR8 agonist 3M002 but not 3M001 (TLR7). Neutrophils expressed TLR8 but none of the other 2 RNA-detecting TLRs (TLR3 and TLR7). CONCLUSIONS: Together, these results demonstrate that neutrophils are directly and fully activated through TLR8 but not TLR7. Furthermore, the results predict that the clinical utility of small-molecule TLR8 ligands or nuclease-stable RNA ligands for TLR8 might be limited because of neutrophil-mediated toxicity and that no such limitation applies for unmodified isRNA, which is known to induce desired T(H)1 activities in other immune cell subsets.