Two New Neutrophil Subsets Define a Discriminating Sepsis Signature.

Rationale: Sepsis is the leading cause of death in adult ICUs. At present, sepsis diagnosis relies on nonspecific clinical features. It could transform clinical care to have immune-cell biomarkers that could predict sepsis diagnosis and guide treatment. For decades, neutrophil phenotypes have been studied in sepsis, but a diagnostic cell subset has yet to be identified. Objectives: To identify an early, specific immune signature of sepsis severity that does not overlap with other inflammatory biomarkers and that distinguishes patients with sepsis from those with noninfectious inflammatory syndrome. Methods: Mass cytometry combined with computational high-dimensional data analysis was used to measure 42 markers on whole-blood immune cells from patients with sepsis and control subjects and to automatically and comprehensively characterize circulating immune cells, which enables identification of novel, disease-specific cellular signatures. Measurements and Main Results: Unsupervised analysis of high-dimensional mass cytometry data characterized previously unappreciated heterogeneity within the CD64+ immature neutrophils and revealed two new subsets distinguished by CD123 and PD-L1 (programmed death ligand 1) expression. These immature neutrophils exhibited diminished activation and phagocytosis functions. The proportion of CD123-expressing neutrophils correlated with clinical severity. Conclusions: This study showed that these two new neutrophil subsets were specific to sepsis and detectable through routine flow cytometry by using seven markers. The demonstration here that a simple blood test distinguishes sepsis from other inflammatory conditions represents a key biological milestone that can be immediately translated into improvements in patient care.

Clinical and histopathologic predictors of therapeutic response to bronchial thermoplasty in severe refractory asthma.

BACKGROUND: Phenotypes and endotypes predicting optimal response to bronchial thermoplasty (BT) in patients with severe asthma remain elusive. OBJECTIVE: Our aim was to compare the clinical characteristics and hallmarks of airway inflammation and remodeling before and after BT in responder and partial responder patients with severe asthma refractory to oral steroids and to omalizumab. METHODS: In all, 23 patients with severe refractory asthma were divided into BT responders (n = 15) and BT partial responders (n = 8), according to the decrease in asthma exacerbations at 12 months after BT. Clinical parameters were compared at baseline and 12 months after BT, and hallmarks of airway inflammation and remodeling were analyzed by immunohistochemistry in bronchial biopsy specimens before and 3 months after BT. RESULTS: At baseline, the BT responders were around 8 years younger than the BT partial responders (P = .02) and they had a greater incidence of atopy, higher numbers of blood eosinophils (both P = .03) and IgE levels, higher epithelial IFN-α expression, and higher numbers of mucosal eosinophils and IL-33-positive cells (P ≤ .05). A reduction in blood eosinophil count, serum IgE level, type 2 airway inflammation, and numbers of mucosal IL-33-positive cells and mast cells associated with augmented epithelial MUC5AC and IFN-α/ß immunostaining was noted after BT in responders, whereas the numbers of mucosal IL-33-positive cells were augmented in BT partial responders. Most of these changes were correlated with clinical parameters. Subepithelial membrane thickening and airway smooth muscle area were similar in the 2 patient groups at baseline and after BT. CONCLUSION: By reducing allergic type 2 inflammation and increasing epithelial MUC5AC and anti-viral IFN-α/ß expression, BT may enhance host immune responses and thus attenuate exacerbations and symptoms in BT responders. Instead, targeting IL-33 may provide a clinical benefit in BT partial responders.

IL-1R1-MyD88 axis elicits papain-induced lung inflammation.

Allergic asthma is characterized by a strong Th2 response with inflammatory cell recruitment and structural changes in the lung. Papain is a protease allergen disrupting the airway epithelium triggering a rapid inflammation with eosinophilia mediated by innate lymphoid cell activation (ILC2) and leading to a Th2 immune response. In this study, we focused on inflammatory responses to a single exposure to papain and showed that intranasal administration of papain results in the recruitment of inflammatory cells, including neutrophils and eosinophils with a rapid production of IL-1α, IL-1ß, and IL-33. The inflammatory response is abrogated in the absence of IL-1R1 and MyD88. To decipher the cell type(s) involved in MyD88-dependent IL-1R1/MyD88 signaling, we used new cell-specific MyD88-deficient mice and found that the deletion of MyD88 signaling in single cell types such as T cells, epithelial cells, CD11c-positive or myeloid cells leads to only a partial inhibition compared to complete absence of MyD88, suggesting that several cell types contribute to the response. Importantly, the inflammatory response is largely ST2 and IL-36R independent. In conclusion, IL-1R1 signaling via MyD88 is critical for the first step of inflammatory response to papain.

Airway smooth muscle enlargement is associated with protease-activated receptor 2/ligand overexpression in patients with difficult-to-control severe asthma.

BACKGROUND: Asthma is a complex disease with heterogeneous features of airway inflammation and remodeling. The increase in airway smooth muscle (ASM) mass is an essential component of airway remodeling in patients with severe asthma, yet the pathobiological mechanisms and clinical outcomes associated with ASM enlargement remain elusive. OBJECTIVE: We sought to compare ASM area in control subjects and patients with mild-to-moderate or severe asthma and to identify specific clinical and pathobiological characteristics associated with ASM enlargement. METHODS: Bronchial biopsy specimens from 12 control subjects, 24 patients with mild-to-moderate asthma, and 105 patients with severe asthma were analyzed for ASM area, basement membrane thickness, vessels, eosinophils, neutrophils, T lymphocytes, mast cells, and protease-activated receptor 2 (PAR-2). In parallel, the levels of several ASM mitogenic factors, including the PAR-2 ligands, mast cell tryptase, trypsin, tissue factor, and kallikrein (KLK) 5 and KLK14, were assessed in bronchoalveolar lavage fluid. Data were correlated with asthma severity and control both at inclusion and after 12 to 18 months of optimal management and therapy. RESULTS: Analyses across ASM quartiles in patients with severe asthma demonstrated that patients with the highest ASM quartile (median value of ASM area, 26.3%) were younger (42.5 vs ≥50 years old in the other groups, P ≤ .04) and had lower asthma control after 1 year of optimal management (P ≤ .006). ASM enlargement occurred independently of features of airway inflammation and remodeling, whereas it was associated with PAR-2 overexpression and higher alveolar tryptase (P ≤ .02) and KLK14 (P ≤ .03) levels. CONCLUSION: Increase in ASM mass, possibly involving aberrant expression and activation of PAR-2-mediated pathways, characterizes younger patients with severe asthma with poor asthma control.

Visualizing the spatial organization of monocytes, interstitial macrophages, and tissue-specific macrophages in situ.

Tissue-resident mononuclear phagocytes (MPs) are an abundant cell population whose localization in situ reflects their identity. To enable assessment of their heterogeneity, we developed the red/green/blue (RGB)-Mac mouse based upon combinations of Cx3cr1 and Csf1r reporter transgenes, providing a complete visualization of their spatial organization in situ. 3D-multi-photon imaging for spatial mapping and spectral cytometry employing the three markers in combination distinguished tissue-associated monocytes, tissue-specific macrophages, and three subsets of connective-tissue-associated MPs, including CCR2+ monocyte-derived cell, CX3CR1+, and FOLR2+ interstitial subsets, associated with distinct sub-anatomic territories. These populations were selectively reduced by blockade of CSF1, CSF2, CCR2, and CX3CR1 and efficiently reconstitute their spatial distribution after transient myelo-ablation, suggesting an autonomous regulatory environment. Our findings emphasize the organization of the MP compartment at the sub-anatomic level under steady-state conditions, thereby providing a holistic understanding of their relative heterogeneity across different tissues.

IL-33-activated dendritic cells are critical for allergic airway inflammation.

IL-33, a new member of the IL-1 family cytokine, is involved in Th2-type responses in a wide range of diseases and signals through the ST2 receptor expressed on many immune cells. Since the effects of IL-33 on DCs remain controversial, we investigated the ability of IL-33 to modulate DC functions in vitro and in vivo. Here, we report that IL-33 activates myeloid DCs to produce IL-6, IL-1b, TNF, CCL17 and to express high levels of CD40, CD80 OX40L and CCR7. Importantly, IL-33-activated DCs prime naive lymphocytes to produce the Th2 cytokines IL-5 and IL-13, but not IL-4. In vivo, IL-33 exposure induces DC recruitment and activation in the lung. Using an OVA-induced allergic lung inflammation model, we demonstrate that the reduced airway inflammation in ST2-deficient mice correlates with the failure in DC activation and migration to the draining LN. Finally, we show that adoptive transfer of IL-33-activated DCs exacerbates lung inflammation in a DC-driven model of allergic airway inflammation. These data demonstrate for the first time that IL-33 activates DCs during antigen presentation and thereby drives a Th2-type response in allergic lung inflammation.

CD8+PD-L1+CXCR3+ polyfunctional T cell abundances are associated with survival in critical SARS-CoV-2-infected patients.

The importance of the adaptive T cell response in the control and resolution of viral infection has been well established. However, the nature of T cell-mediated viral control mechanisms in life-threatening stages of COVID-19 has yet to be determined. The aim of the present study was to determine the function and phenotype of T cell populations associated with survival or death of patients with COVID-19 in intensive care as a result of phenotypic and functional profiling by mass cytometry. Increased frequencies of circulating, polyfunctional CD4+CXCR5+HLA-DR+ stem cell memory T cells (Tscms) and decreased proportions of granzyme B-expressing and perforin-expressing effector memory T cells were detected in recovered and deceased patients, respectively. The higher abundance of polyfunctional PD-L1+CXCR3+CD8+ effector T cells (Teffs), CXCR5+HLA-DR+ Tscms, and anti-nucleocapsid (anti-NC) cytokine-producing T cells permitted us to differentiate between recovered and deceased patients. The results from a principal component analysis show an imbalance in the T cell compartment that allowed for the separation of recovered and deceased patients. The paucity of circulating PD-L1+CXCR3+CD8+ Teffs and NC-specific CD8+ T cells accurately forecasts fatal disease outcome. This study provides insight into the nature of the T cell populations involved in the control of COVID-19 and therefore might impact T cell-based vaccine designs for this infectious disease.

LOX-1-Expressing Immature Neutrophils Identify Critically-Ill COVID-19 Patients at Risk of Thrombotic Complications.

Background: Lymphopenia and the neutrophil/lymphocyte ratio may have prognostic value in COVID-19 severity. Objective: We investigated neutrophil subsets and functions in blood and bronchoalveolar lavage (BAL) of COVID-19 patients on the basis of patients' clinical characteristics. Methods: We used a multiparametric cytometry profiling based to mature and immature neutrophil markers in 146 critical or severe COVID-19 patients. Results: The Discovery study (38 patients, first pandemic wave) showed that 80% of Intensive Care Unit (ICU) patients develop strong myelemia with CD10-CD64+ immature neutrophils (ImNs). Cellular profiling revealed three distinct neutrophil subsets expressing either the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), the interleukin-3 receptor alpha (CD123), or programmed death-ligand 1 (PD-L1) overrepresented in ICU patients compared to non-ICU patients. The proportion of LOX-1- or CD123-expressing ImNs is positively correlated with clinical severity, cytokine storm (IL-1ß, IL-6, IL-8, TNFα), acute respiratory distress syndrome (ARDS), and thrombosis. BALs of patients with ARDS were highly enriched in LOX-1-expressing ImN subsets and in antimicrobial neutrophil factors. A validation study (118 patients, second pandemic wave) confirmed and strengthened the association of the proportion of ImN subsets with disease severity, invasive ventilation, and death. Only high proportions of LOX-1-expressing ImNs remained strongly associated with a high risk of severe thrombosis independently of the plasma antimicrobial neutrophil factors, suggesting an independent association of ImN markers with their functions. Conclusion: LOX-1-expressing ImNs may help identifying COVID-19 patients at high risk of severity and thrombosis complications.

Sepsis Triggers a Late Expansion of Functionally Impaired Tissue-Vascular Inflammatory Monocytes During Clinical Recovery.

Sepsis is characterized by a systemic inflammation that can cause an immune dysfunction, for which the underlying mechanisms are unclear. We investigated the impact of cecal ligature and puncture (CLP)-mediated polymicrobial sepsis on monocyte (Mo) mobilization and functions. Our results show that CLP led to two consecutive phases of Mo deployment. The first one occurred within the first 3 days after the induction of the peritonitis, while the second phase was of a larger amplitude and extended up to a month after apparent clinical recovery. The latter was associated with the expansion of Mo in the tissue reservoirs (bone marrow and spleen), their release in the blood and their accumulation in the vasculature of peripheral non-lymphoid tissues. It occurred even after antibiotic treatment but relied on inflammatory-dependent pathways and inversely correlated with increased susceptibility and severity to a secondary infection. The intravascular lung Mo displayed limited activation capacity, impaired phagocytic functions and failed to transfer efficient protection against a secondary infection into monocytopenic CCR2-deficient mice. In conclusion, our work unveiled key dysfunctions of intravascular inflammatory Mo during the recovery phase of sepsis and provided new insights to improve patient protection against secondary infections.

CX3CL1 homo-oligomerization drives cell-to-cell adherence.

During inflammatory response, blood leukocytes adhere to the endothelium. This process involves numerous adhesion molecules, including a transmembrane chemokine, CX3CL1, which behaves as a molecular cluster. How this cluster assembles and whether this association has a functional role remain unknown. The analysis of CX3CL1 clusters using native electrophoresis and single molecule fluorescence kinetics shows that CX3CL1 is a homo-oligomer of 3 to 7 monomers. Fluorescence recovery after photobleaching assays reveal that the CX3CL1-transmembrane domain peptide self-associates in both cellular and acellular lipid environments, while its random counterpart (i.e. peptide with the same residues in a different order) does not. This strongly indicates that CX3CL1 oligomerization is driven by its intrinsic properties. According to the molecular modeling, CX3CL1 does not associate in compact bundles but rather with monomers linearly assembled side by side. Finally, the CX3CL1 transmembrane peptide inhibits both the CX3CL1 oligomerization and the adhesive function, while its random counterpart does not. This demonstrates that CX3CL1 oligomerization is mandatory for its adhesive potency. Our results provide a new direction to control CX3CL1-dependent cellular adherence in key immune processes.

Caspase-1 activation by NLRP3 inflammasome dampens IL-33-dependent house dust mite-induced allergic lung inflammation.

The cysteine protease caspase-1 (Casp-1) contributes to innate immunity through the assembly of NLRP3, NLRC4, AIM2, and NLRP6 inflammasomes. Here we ask whether caspase-1 activation plays a regulatory role in house dust mite (HDM)-induced experimental allergic airway inflammation. We report enhanced airway inflammation in caspase-1-deficient mice exposed to HDM with a marked eosinophil recruitment, increased expression of IL-4, IL-5, IL-13, as well as full-length and bioactive IL-33. Furthermore, mice deficient for NLRP3 failed to control eosinophil influx in the airways and displayed augmented Th2 cytokine and chemokine levels, suggesting that the NLPR3 inflammasome complex controls HDM-induced inflammation. IL-33 neutralization by administration of soluble ST2 receptor inhibited the enhanced allergic inflammation, while administration of recombinant IL-33 during challenge phase enhanced allergic inflammation in caspase-1-deficient mice. Therefore, we show that caspase-1, NLRP3, and ASC, but not NLRC4, contribute to the upregulation of allergic lung inflammation. Moreover, we cannot exclude an effect of caspase-11, because caspase-1-deficient mice are deficient for both caspases. Mechanistically, absence of caspase-1 is associated with increased expression of IL-33, uric acid, and spleen tyrosine kinase (Syk) production. This study highlights a critical role of caspase-1 activation and NLPR3/ASC inflammasome complex in the down-modulation of IL-33 in vivo and in vitro, thereby regulating Th2 response in HDM-induced allergic lung inflammation.