SARS-CoV-2 Receptor ACE2 Is an Interferon-Stimulated Gene in Human Airway Epithelial Cells and Is Detected in Specific Cell Subsets across Tissues.

There is pressing urgency to understand the pathogenesis of the severe acute respiratory syndrome coronavirus clade 2 (SARS-CoV-2), which causes the disease COVID-19. SARS-CoV-2 spike (S) protein binds angiotensin-converting enzyme 2 (ACE2), and in concert with host proteases, principally transmembrane serine protease 2 (TMPRSS2), promotes cellular entry. The cell subsets targeted by SARS-CoV-2 in host tissues and the factors that regulate ACE2 expression remain unknown. Here, we leverage human, non-human primate, and mouse single-cell RNA-sequencing (scRNA-seq) datasets across health and disease to uncover putative targets of SARS-CoV-2 among tissue-resident cell subsets. We identify ACE2 and TMPRSS2 co-expressing cells within lung type II pneumocytes, ileal absorptive enterocytes, and nasal goblet secretory cells. Strikingly, we discovered that ACE2 is a human interferon-stimulated gene (ISG) in vitro using airway epithelial cells and extend our findings to in vivo viral infections. Our data suggest that SARS-CoV-2 could exploit species-specific interferon-driven upregulation of ACE2, a tissue-protective mediator during lung injury, to enhance infection.

Cell Culture Differentiation and Proliferation Conditions Influence the In Vitro Regeneration of the Human Airway Epithelium.

The human airway mucociliary epithelium can be recapitulated in vitro using primary cells cultured in an air-liquid interface (ALI), a reliable surrogate to perform pathophysiological studies. As tremendous variations exist among media used for ALI-cultured human airway epithelial cells, the aim of our study was to evaluate the impact of several media (BEGM, PneumaCult, Half & Half, and Clancy) on cell type distribution using single-cell RNA sequencing and imaging. Our work revealed the impact of these media on cell composition, gene expression profile, cell signaling, and epithelial morphology. We found higher proportions of multiciliated cells in PneumaCult-ALI and Half & Half, stronger EGF signaling from basal cells in BEGM-ALI, differential expression of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry factor ACE2, and distinct secretome transcripts depending on the media used. We also established that proliferation in PneumaCult-Ex Plus favored secretory cell fate, showing the key influence of proliferation media on late differentiation epithelial characteristics. Altogether, our data offer a comprehensive repertoire for evaluating the effects of culture conditions on airway epithelial differentiation and will aid in choosing the most relevant medium according to the processes to be investigated, such as cilia, mucus biology, or viral infection. We detail useful parameters that should be explored to document airway epithelial cell fate and morphology.

Airway epithelial type-2 alarmin profiles: Blood eosinophil counts remain in memory.

Epithelial cytokines are involved in the orchestration of T1/T2 inflammatory patterns. We question the persistence of this trait in air-liquid interface (ALI) epithelial cultures and whether this local orientation can be related to systemic patterns (e.g., blood eosinophil counts [BECs]). We investigated alarmin release related to high versus low T2 phenotypes associated with chronic airway diseases. ALIs were reconstituted from 32 control, 40 chronic obstructive pulmonary disease, and 20 asthmatic patients. Interleukin-8 (IL-8; a T1-cytokine), IL-25, IL-33, and thymic stromal lymphopoietin (T2-alarmins) concentrations were assessed in subnatants at steady state and used to explain blood neutrophil and eosinophil counts. IL-25 and IL-8 levels were highest in asthma ALI-subnatants, whereas IL-33 was sparsely detected. Thymic stromal lymphopoietin levels were similar among groups. All asthma cell cultures were T1-high/T2-high, while chronic obstructive pulmonary disease and controls tended to be mixed. BECs were independently explained by both disease and in-culture T2-alarmin levels, irrespective of the T2-alarmin considered. The epithelial ALI-T2 signature was more frequently high in patients with a BEC > 300/mm3 . Despite removal from an in vivo environment for ≥2 months, ALIs release disease-specific cytokine "cocktails" into their subnatants, suggesting continued persistence of alarmin orientation in differentiated cell line environments.

Post viral bronchiolitis obliterans in children: A rare and potentially devastating disease.

Post infectious bronchiolitis obliterans (PIBO) is a rare but severe disease in children. Several respiratory pathogens are incriminated but adenovirus is still the most represented. Risk factors are well described: the male gender, hypoxemia at diagnosis and required mechanical ventilation. No risk factor is linked to the newborn period. The clinical spectrum of PIBO is broad, ranging from asymptomatic patients with fixed airflow obstruction to severe respiratory insufficiency requiring continuous oxygen supplementation. Diagnosis includes a combination of a clinical history, absence of reversible airflow obstructions and ground glass and gas trapping on high resolution computed tomography. PIBO is primarily a neutrophilic pathology of small bronchioles characterized by high levels of pro-inflammatory cytokines leading to tissue remodeling and fibrosis of the small airways. The difficulty is to discriminate between the host's normal response, an exaggerated inflammatory response and the potential iatrogenic consequences of the initial infection treatment, particularly prolonged mechanical ventilation. Damage to the respiratory epithelium with a possible link to viral infections are considered as potential mechanisms of PIBO. No specific management exists. Much remains to be done in this field to clarify the underlying mechanisms, identify biomarkers, and develop clear monitoring pathways and treatment protocols.

Using intracellular SCGB1A1-sorted, formalin-fixed club cells for successful transcriptomic analysis.

As opposed to surface marker staining, certain cell types can only be recognized by intracellular markers. Intracellular staining for use in cell sorting remains challenging. Fixation and permeabilization steps for intracellular staining and the presence of RNases notably affect preservation of high-quality mRNA. We report the work required for the optimization of a successful protocol for microarray analysis of intracellular target-sorted, formalin-fixed human bronchial club cells. Cells obtained from differentiated air-liquid interface cultures were stained with the most characteristic intracellular markers for club cell (SCGB1A1+) sorting. A benchmarked intracellular staining protocol was carried out before flow cytometry. The primary outcome was the extraction of RNA sufficient quality for microarray analysis as assessed by Bioanalyzer System. Fixation with 4% paraformaldehyde coupled with 0.1% Triton/0.1% saponin permeabilization obtained optimal results for SCGB1A1 staining. Addition of RNase inhibitors throughout the protocol and within the appropriate RNA extraction kit (Formalin-Fixed-Paraffin-Embedded) dramatically improved RNA quality, resulting in samples eligible for microarray analysis. The protocol resulted in successful cell sorting according to specific club cell intracellular marker without using cell surface marker. The protocol also preserved RNA of sufficient quality for subsequent microarray transcriptomic analysis, and we were able to generate transcriptomic signature of club cells.

Platelets Purification Is a Crucial Step for Transcriptomic Analysis.

Platelets are small anucleate cells derived from the fragmentation of megakaryocytes and are involved in different biological processes especially hemostasis, thrombosis, and immune response. Despite their lack of nucleus, platelets contain a reservoir of megakaryocyte-derived RNAs and all the machinery useful for mRNA translation. Interestingly, platelet transcriptome was analyzed in health and diseases and led to the identification of disease-specific molecular signatures. Platelet contamination by leukocytes and erythrocytes during platelet purification is a major problem in transcriptomic analysis and the presence of few contaminants in platelet preparation could strongly alter transcriptome results. Since contaminant impacts on platelet transcriptome remains theoretical, we aimed to determine whether low leukocyte and erythrocyte contamination could cause great or only minor changes in platelet transcriptome. Using microarray technique, we compared the transcriptome of platelets from the same donor, purified by common centrifugation method or using magnetic microbeads to eliminate contaminating cells. We found that platelet transcriptome was greatly altered by contaminants, as the relative amount of 8274 transcripts was different between compared samples. We observed an increase of transcripts related to leukocytes and erythrocytes in platelet purified without microbeads, while platelet specific transcripts were falsely reduced. In conclusion, serious precautions should be taken during platelet purification process for transcriptomic analysis, in order to avoid platelets contamination and result alteration.

Will the asthma revolution fostered by biologics also benefit adult ICU patients?

PURPOSE: Asthma exacerbations are inflammatory events that rarely result in full hospitalization following an ER visit. Unfortunately, certain patients require prolonged support, including occasional external lung support through ECMO or ECCOR (with subsequent further exposure to other life-threatening issues), and some die. In parallel, biologics are revolutionizing severe asthma management, mostly in T2 high patients. METHODS: We extensively reviewed the current unmet needs surrounding ICU-admitted asthma exacerbations, with a focus on currently available drugs and the underlying biological processes involved. We explored whether currently available T2-targeting drugs can reasonably be seen as potential players not only for relapse prevention but also as candidate drugs for a faster resolution of such episodes. The patient's perspective was also sought. RESULTS: About 30% of asthma exacerbations admitted to the ICU do not resolve within five days. Persistent severe airway obstruction despite massive doses of corticosteroids and maximal pharmacologically induced bronchodilation is the main cause of treatment failure. Previous ICU admission is the main risk factor for such episodes and may eventually be considered as a T2 surrogate marker. Fatal asthma cases are hallmarked by poorly steroid-sensitive T2-inflammation associated with severe mucus plugging. New, fast-acting T2-targeting biologics (already used for preventing asthma exacerbations) have the potential to circumvent steroid sensitivity pathways and decrease mucus plugging. This unmet need was confirmed by patients who reported highly negative, traumatizing experiences. CONCLUSIONS: There is room for improvement in the management of ICU-admitted severe asthma episodes. Clinical trials assessing how biologics might improve ICU outcomes are direly needed.

Bronchial Epithelial Calcium Metabolism Impairment in Smokers and Chronic Obstructive Pulmonary Disease. Decreased ORAI3 Signaling.

The airway epithelium represents a fragile environmental interface potentially disturbed by cigarette smoke (CS), the major risk factor for developing chronic obstructive pulmonary disease (COPD). CS leads to bronchial epithelial damage on ciliated, goblet, and club cells, which could involve calcium (Ca2+) signaling. Ca2+ is a key messenger involved in virtually all fundamental physiological functions, including mucus and cytokine secretion, cilia beating, and epithelial repair. In this study, we analyzed Ca2+ signaling in air-liquid interface-reconstituted bronchial epithelium from control subjects and smokers (with and without COPD). We further aimed to determine how smoking impaired Ca2+ signaling. First, we showed that the endoplasmic reticulum (ER) depletion of Ca2+ stores was decreased in patients with COPD and that the Ca2+ influx was decreased in epithelial cells from smokers (regardless of COPD status). In addition, acute CS exposure led to a decrease in ER Ca2+ release, significant in smoker subjects, and to a decrease in Ca2+ influx only in control subjects. Furthermore, the differential expression of 55 genes involved in Ca2+ signaling highlighted that only ORAI3 expression was significantly altered in smokers (regardless of COPD status). Finally, we incubated epithelial cells with an ORAI antagonist (GSK-7975A). GSK-7975A altered Ca2+ influx and ciliary beating, but not mucus and cytokine secretion or epithelial repair, in control subjects. Our data suggest that Ca2+ signaling is impaired in smoker epithelia (regardless of COPD status) and involves ORAI3. Moreover, ORAI3 is additionally involved in ciliary beating.

Goblet cell hyperplasia as a feature of neutrophilic asthma.

BACKGROUND: Goblet cell hyperplasia (GCH) is a pathological finding classically reported across asthma severity levels and usually associated with smoking. Multiple biological mechanisms may contribute to excessive mucus production. OBJECTIVE: We aimed to decipher the clinical meanings and biological pathways related to GCH in non-smokers with asthma. METHODS: Cough and sputum assessment questionnaire (CASA-Q) responses at entry and 1 year later were compared to clinical and functional outcomes in 59 asthmatic patients. GCH was assessed through periodic-acid shift (PAS) staining on endobronchial biopsies obtained at entry in a subset of 32 patients. RESULTS: Periodic-acid shift-staining analysis revealed a double wave distribution discriminating patients with (>10% of the epithelial area) or without GCH. CASA-Q scores were mostly driven by overall asthma severity (P < 0.0001). CASA-Q scores remained stable at 1 year and were independently associated with BAL eosinophil content irrespective of the presence of GCH. GCH was unrelated to the presence of bronchiectasis at CT, GERD or chronic rhinosinusitis, but correlated well with neutrophilic inflammatory patterns observed upon BAL cellular analysis (P = 0.002 at multivariate analysis). BALF bacterial loads were unrelated to GCH or to CASA-Q. CONCLUSIONS AND CLINICAL RELEVANCE: Goblet cell hyperplasia is disconnected from chronic cough and sputum when assessed by a specific questionnaire. GCH is related to neutrophilic asthma whereas symptoms are related to airway eosinophilia. The clinical counterpart of GCH is unlikely assessed by the CASA-Q.

Bronchial Epithelial IgA Secretion Is Impaired in Asthma. Role of IL-4/IL-13.

RATIONALE: Asthma is associated with increased lung IgE production, but whether the secretory IgA system is affected in this disease remains unknown. OBJECTIVES: We explored mucosal IgA transport in human asthma and its potential regulation by T-helper cell type 2 inflammation. METHODS: Bronchial biopsies from asthma and control subjects were assayed for bronchial epithelial polymeric immunoglobulin receptor (pIgR) expression and correlated to T-helper cell type 2 biomarkers. Bronchial epithelium reconstituted in vitro from these subjects, on culture in air-liquid interface, was assayed for pIgR expression and regulation by IL-4/IL-13. MEASUREMENTS AND MAIN RESULTS: Downregulation of pIgR protein was observed in the bronchial epithelium from patients with asthma (P = 0.0002 vs. control subjects). This epithelial defect was not observed ex vivo in the cultured epithelium from patients with asthma. Exogenous IL-13 and IL-4 could inhibit pIgR expression and IgA transcytosis. Mechanistic experiments showed that autocrine transforming growth factor-ß mediates the IL-4/IL-13 effect on the pIgR, with a partial contribution of upregulated transforming growth factor-α/epidermal growth factor receptor. CONCLUSIONS: This study shows impaired bronchial epithelial pIgR expression in asthma, presumably affecting secretory IgA-mediated frontline defense as a result of type 2 immune activation of the transforming growth factor pathway.

Human bronchial epithelium orchestrates dendritic cell activation in severe asthma.

The innate immune response is impaired in asthma, with increased epithelial release of C-X-C motif chemokine ligand (CXCL)8, interleukin (IL)-33 and thymic stromal lymphopoietin (TSLP). We hypothesised that dendritic cells might modulate the hyperresponsive epithelium in severe asthma.For this purpose, we investigated epithelial-dendritic crosstalk in normal and diseased conditions, and because ultrafine particulate matter may affect asthmatic airways, we investigated its impact on this crosstalk. Air-liquid interface cultures of human bronchial epithelial cells (HBEC) of control subjects (cHBEC) or severe asthma patients (saHBEC) were co-cultured with monocyte-derived dendritic cells (moDC).Increased release of CXCL8, TSLP and IL-33 from saHBEC contrasted with cHBEC producing CXCL10 and CCL2. Regarding moDC activation, saHBEC co-cultures induced only upregulation of CD86 expression, while cHBEC yielded full moDC maturation with HLA-DR, CD80, CD86 and CD40 upregulation. Particulate matter stimulation of HBEC had no effect on cHBEC but stimulated CXCL8 and IL-33 release in saHBEC. Particulate matter impaired epithelium signalling (TSLP, IL-33 and CXCL8) in saHBEC co-cultures despite C-C chemokine ligand 2 induction.Crosstalk between HBEC and moDC can be established in vitro, driving a T1-type response with cHBEC and a T2-type response with saHBEC. Normal or asthmatic status of HBEC differentially shapes the epithelial-dendritic responses. We conclude that control moDC cannot rescue the hyperresponsive airway epithelium of severe asthmatics.

Epithelial ciliated beating cells essential for ex vivo ALI culture growth.

BACKGROUND: Bronchial epithelium plays a key role in orchestrating innate and adaptive immunity. The fate of ex vivo airway epithelial cultures growing at the air liquid interface (ALI) derived from human endobronchial biopsies or brushings is not easy to predict. Calibrating and differentiating these cells is a long and expensive process requiring rigorous expertise. Pinpointing factors associated with ALI culture success would help researchers gain further insight into epithelial progenitor behavior. METHODS: A successful ALI culture was defined as one in which a pseudostratified epithelium has formed after 28 days in the presence of all differentiated epithelial cell types. A 4-year prospective bi-center study was conducted with adult subjects enrolled in different approved research protocols. RESULTS: 463 consecutive endobronchial biopsies were obtained from normal healthy volunteers, healthy smokers, asthmatic patients and smokers with COPD. All demographic variables, the different fiber optic centers and culture operators, numbers of endo-bronchial biopsies and the presence of ciliated cells were carefully recorded. Univariate and multivariate models were developed. A stepwise procedure was used to select the final logistic regression model. ALI culture success was independently associated with the presence of living ciliated cells within the initial biopsy (OR = 2.18 [1.50-3.16], p < 0.001). CONCLUSION: This finding highlights the properties of the cells derived from the epithelium dedifferentiation process. The preferential selection of samples with ciliated beating cells would probably save time and money. It is still unknown whether successful ALI culture is related to indicators of general cell viability or a purported stem cell state specifically associated with ciliated beating cells.

Airway lipoxin A4/formyl peptide receptor 2-lipoxin receptor levels in pediatric patients with severe asthma.

BACKGROUND: Lipoxins are biologically active eicosanoids with anti-inflammatory properties. Lipoxin A4 (LXA4) signaling blocks asthmatic responses in human and experimental model systems. There is evidence that patients with respiratory diseases, including severe asthma (SA), display defective generation of lipoxin signals despite glucocorticoid therapy. OBJECTIVE: We investigated airway levels of formyl peptide receptor 2-lipoxin receptor (FPR2/ALXR), LXA4, and its counterregulatory compound, leukotriene B4 (LTB4), in patients with childhood asthma. We addressed the potential interplay of the LXA4-FPR2/ALXR axis and glucocorticoids in the resolution of inflammation. METHODS: We examined LXA4 and LTB4 concentrations in induced sputum supernatants from children with intermittent asthma (IA), children with SA, and healthy control (HC) children. In addition, we investigated FPR2/ALXR expression in induced sputum cells obtained from the study groups. Finally, we evaluated in vitro the molecular interaction between LXA4 and glucocorticoid receptor-based mechanisms. RESULTS: We found that children with SA have decreased LXA4 concentrations in induced sputum supernatants in comparison with children with IA. In contrast to decreases in LXA4 concentrations, LTB4 concentrations were increased in children with asthma independent of severity. LXA4 concentrations negatively correlated with LTB4 concentrations and with exacerbation numbers in children with SA. FPR2/ALXR expression was reduced in induced sputum cells of children with SA compared with that seen in HC subjects and children with IA. Finally, we describe in vitro the existence of crosstalk between LXA4 and glucocorticoid receptor at the cytosolic level mediated by G protein-coupled FPR2/ALXR in peripheral blood granulocytes isolated from HC subjects, children with IA, and children with SA. CONCLUSION: Our findings provide evidence for defective LXA4 generation and FPR2/ALXR expression that, associated with increased LTB4, might be involved in a reduction in the ability of inhaled corticosteroids to impair control of airway inflammation in children with SA.

Poly-L-Lysine compacts DNA, kills bacteria, and improves protease inhibition in cystic fibrosis sputum.

RATIONALE: Neutrophil serine proteases in cystic fibrosis (CF) lung secretions partially resist inhibition by natural and exogenous inhibitors, mostly because DNA impairs their control. Cationic polypeptides display the property of condensing DNA and retain antimicrobial properties. We hypothesized that DNA condensation by cationic polypeptides in CF sputum would result in a better control of CF inflammation and infection. OBJECTIVES: We examined whether poly-L-lysine would compact DNA in CF lung secretions and liquefy CF sputum, improve the control of extracellular proteases by exogenous inhibitors, and whether it displays antibacterial properties toward CF-associated bacteria. METHODS: We used fluorogenic methods to measure proteolytic activities and inhibition by protease inhibitors in whole sputum homogenates from patients with CF before and after treatment with poly-L-lysine. Antibacterial properties of poly-L-lysine were measured in bacterial cultures and in whole CF sputum. Poly-L-lysine toxicity was evaluated after aerosolization by histologic analysis, flow cytometry, and quantification of proinflammatory cytokines. MEASUREMENTS AND MAIN RESULTS: Poly-L-lysine compacts CF sputum DNA, generating a liquid phase that improves ciliary beating frequency at the lung epithelial surface, and allows the control of neutrophil elastase and cathepsin G by their natural inhibitors. It retains antimicrobial properties against Pseudomonas aeruginosa and Staphylococcus aureus at doses that induce no inflammation in the mouse lung after aerosol administration. CONCLUSIONS: Poly-L-lysine may be an alternative to dornase-α to liquefy sputum with added benefits because it helps natural inhibitors to better control the deleterious effects of extracellularly released neutrophil serine proteases and has the ability to kill bacteria in CF sputum.

An ex vivo model of severe asthma using reconstituted human bronchial epithelium.

BACKGROUND: Structural changes to the airways are features of severe asthma. The bronchial epithelium facilitates this remodeling process. Learning about the changes that develop in the airway epithelium could improve our understanding of asthma pathogenesis and lead to new therapeutic approaches. OBJECTIVE: We sought to determine the feasibility and relevance of air-liquid interface cultures of bronchial epithelium derived from endobronchial biopsy specimens of patients with different severities of asthma for studying the airway epithelium. METHODS: Human bronchial epithelial cells derived from endobronchial biopsy specimens of patients with mild and severe asthma were maintained in culture for 21 days in an air-liquid interface to reproduce a fully differentiated airway epithelium. Initially, features of remodeling that included epithelial and subepithelial layers, as well as mucus production, were assessed in paraffin-embedded endobronchial biopsy specimens to evaluate morphologic characteristics of asthmatic patients' epithelia. Ex vivo differentiated epithelia were then analyzed for morphology and function based on ultrastructural analysis, IL-8 release, lipoxin A(4) generation, mucin production, and lipoxygenase gene expression. RESULTS: Morphologic and inflammatory imbalances initially observed in endobronchial biopsy specimens obtained from patients with severe or mild asthma persisted in the air-liquid interface reconstituted epithelium throughout the differentiation process to 21 days. Epithelium from patients with severe asthma produced greater levels of mucin, released more IL-8, and produced lower levels of lipoxin A(4) than that from patients with mild asthma. Expression of 15-lipoxygenase 2 was increased in epithelium from patients with severe asthma, whereas expression levels of MUC5AC, MUC5B, 5-lipoxygenase, and 15-lipoxygeanse 1 were similar to those of patients with mild asthma. CONCLUSION: Ex vivo cultures of fully differentiated bronchial epithelium from endobronchial biopsy specimens maintain inherent phenotypic differences specifically related to the severity of asthma.

Natural killer cells in the lung: potential role in asthma and virus-induced exacerbation?

Asthma is a chronic inflammatory airway disorder whose pathophysiological and immunological mechanisms are not completely understood. Asthma exacerbations are mostly driven by respiratory viral infections and characterised by worsening of symptoms. Despite current therapies, asthma exacerbations can still be life-threatening. Natural killer (NK) cells are innate lymphoid cells well known for their antiviral activity and are present in the lung as circulating and resident cells. However, their functions in asthma and its exacerbations are still unclear. In this review, we will address NK cell activation and functions, which are particularly relevant for asthma and virus-induced asthma exacerbations. Then, the role of NK cells in the lungs at homeostasis in healthy individuals will be described, as well as their functions during pulmonary viral infections, with an emphasis on those associated with asthma exacerbations. Finally, we will discuss the involvement of NK cells in asthma and virus-induced exacerbations and examine the effect of asthma treatments on NK cells.

Mobilisation of HLA-F on the surface of bronchial epithelial cells and platelets in asthmatic patients.

Uncontrolled inflammation of the airways in chronic obstructive lung diseases leads to exacerbation, accelerated lung dysfunction and respiratory insufficiency. Among these diseases, asthma affects 358 million people worldwide. Human bronchial epithelium cells (HBEC) express both anti-inflammatory and activating molecules, and their deregulated expression contribute to immune cell recruitment and activation, especially platelets (PLT) particularly involved in lung tissue inflammation in asthma context. Previous results supported that HLA-G dysregulation in lung tissue is associated with immune cell activation. We investigated here HLA-F expression, reported to be mobilised on immune cell surface upon activation and displaying its highest affinity for the KIR3DS1-activating NK receptor. We explored HLA-F transcriptional expression in HBEC; HLA-F total expression in PBMC and HBEC collected from healthy individuals at rest and upon chemical activation and HLA-F membrane expression in PBMC, HBEC and PLT collected from healthy individuals at rest and upon chemical activation. We compared HLA-F transcriptional expression in HBEC from healthy individuals and asthmatic patients and its surface expression in HBEC and PLT from healthy individuals and asthmatic patients. Our results support that HLA-F is expressed by HBEC and PLT under healthy physiological conditions and is retained in cytoplasm, barely expressed on the surface, as previously reported in immune cells. In both cell types, HLA-F reaches the surface in the inflammatory asthma context whereas no effect is observed at the transcriptional level. Our study suggests that HLA-F surface expression is a ubiquitous post-transcriptional process in activated cells. It may be of therapeutic interest in controlling lung inflammation.