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Loss of epithelial integrity, bronchiolarization, and fibroblast activation are key characteristics of idiopathic pulmonary fibrosis (IPF). Prolonged accumulation of basal-like cells in IPF may impact the fibrotic niche to promote fibrogenesis. To investigate their role in IPF, basal cells were isolated from IPF explant and healthy donor lung tissues. Single Cell RNA sequencing was used to assess differentially expressed genes in basal cells. Basal cell and niche interaction was demonstrated with the sLP-mCherry niche labeling system. Luminex assays were used to assess cytokines secreted by basal cells. The role of basal cells in fibroblast activation was studies. 3D organoid culture assays were used to interrogate basal cell effects on AEC2 renewal capacity. Perturbation was used to investigate WNT7A function in vitro and in a repetitive bleomycin model in vivo. We found that WNT7A is highly and specifically expressed in basal-like cells. Proteins secreted by basal cells can be captured by neighboring fibroblasts and AEC2s. Basal cells or basal cell conditioned media activate fibroblasts through WNT7A. Basal cell-derived WNT7A inhibits AEC2 progenitor cell renewal in 3D organoid cultures. Neutralizing antibodies against WNT7A or a small molecule inhibitor of Frizzled signaling abolished basal cell induced fibroblast activation and attenuated lung fibrosis in mice. In summary, basal cells and basal cell-derived WNT7A are key components of the fibrotic niche, providing a unique non-stem cell function of basal cells in IPF progression and a novel targeting strategy for IPF.

In mid-December 2021, the B.1.1.529 (Omicron) variant of SARS-CoV-2, the virus that causes COVID-19, surpassed the B.1.617.2 (Delta) variant as the predominant strain in California.

Despite the common detection of non-donor specific anti-HLA antibodies (non-DSAs) after lung transplantation, their clinical significance remains unclear. In this retrospective single-center cohort study of 325 lung transplant recipients, we evaluated the association between donor specific HLA antibodies (DSAs) and non-DSAs with subsequent CLAD development. DSAs were detected in 30% of recipients and were associated with increased CLAD risk, with higher HRs for both de novo and high MFI (>5000) DSAs. Non-DSAs were detected in 56% of recipients, and 85% of DSA positive tests had concurrent non-DSAs. In general, non-DSAs did not increase CLAD risk in multivariable models accounting for DSAs. However, non-DSAs in conjunction with high BAL CXCL9 levels were associated with increased CLAD risk. Multivariable proportional hazards models demonstrate the importance of the HLA antibody-CXCL9 interaction: CLAD risk increases when HLA antibodies (both DSAs and non-DSAs) are detected in conjunction with high CXCL9. Conversely, CLAD risk is not increased when HLA antibodies are detected with low CXCL9. This study supports the potential utility of BAL CXCL9 measurement as a biomarker to risk stratify HLA antibodies for future CLAD. The ability to discriminate between high versus low-risk HLA antibodies may improve management by allowing for guided treatment decisions.

BackgroundChronic lung allograft dysfunction (CLAD) phenotype determines prognosis and may have therapeutic implications. Despite the clarity achieved by recent consensus statement definitions, their reliance on radiologic interpretation introduces subjectivity. The Center for Computer Vision and Imaging Biomarkers at the University of California, Los Angeles (UCLA) has established protocols for chest high-resolution computed tomography (HRCT)-based computer-aided quantification of both interstitial disease and air-trapping. We applied quantitative image analysis (QIA) at CLAD onset to demonstrate radiographic phenotypes with clinical implications.MethodsWe studied 47 first bilateral lung transplant recipients at UCLA with chest HRCT performed within 90 d of CLAD onset and 47 no-CLAD control HRCTs. QIA determined the proportion of lung volume affected by interstitial disease and air-trapping in total lung capacity and residual volume images, respectively. We compared QIA scores between no-CLAD and CLAD, and between phenotypes. We also assigned radiographic phenotypes based solely on QIA, and compared their survival outcomes.ResultsCLAD onset HRCTs had more lung affected by the interstitial disease (P = 0.003) than no-CLAD controls. Bronchiolitis obliterans syndrome (BOS) cases had lower scores for interstitial disease as compared with probable restrictive allograft syndrome (RAS) (P < 0.0001) and mixed CLAD (P = 0.02) phenotypes. BOS cases had more air-trapping than probable RAS (P < 0.0001). Among phenotypes assigned by QIA, the relative risk of death was greatest for mixed (relative risk [RR] 11.81), followed by RAS (RR 6.27) and BOS (RR 3.15).ConclusionsChest HRCT QIA at CLAD onset appears promising as a method for precise determination of CLAD phenotypes with survival implications.

Rationale: Idiopathic pulmonary fibrosis (IPF) is an insidious and fatal interstitial lung disease associated with declining pulmonary function. Accelerated aging, loss of epithelial progenitor cell function and/or numbers, and cellular senescence are implicated in the pathogenies of IPF.Objectives: We sought to investigate the role of alveolar type 2 (AT2) cellular senescence in initiation and/or progression of pulmonary fibrosis and therapeutic potential of targeting senescence-related pathways and senescent cells.Methods: Epithelial cells of 9 control donor proximal and distal lung tissues and 11 IPF fibrotic lung tissues were profiled by single-cell RNA sequencing to assesses the contribution of epithelial cells to the senescent cell fraction for IPF. A novel mouse model of conditional AT2 cell senescence was generated to study the role of cellular senescence in pulmonary fibrosis.Measurements and Main Results: We show that AT2 cells isolated from IPF lung tissue exhibit characteristic transcriptomic features of cellular senescence. We used conditional loss of Sin3a in adult mouse AT2 cells to initiate a program of p53-dependent cellular senescence, AT2 cell depletion, and spontaneous, progressive pulmonary fibrosis. We establish that senescence rather than loss of AT2 cells promotes progressive fibrosis and show that either genetic or pharmacologic interventions targeting p53 activation or senescence block fibrogenesis.Conclusions: Senescence of AT2 cells is sufficient to drive progressive pulmonary fibrosis. Early attenuation of senescence-related pathways and elimination of senescent cells are promising therapeutic approaches to prevent pulmonary fibrosis.

Rationale: Declining lung function in patients with interstitial lung disease is accompanied by epithelial remodeling and progressive scarring of the gas-exchange region. There is a need to better understand the contribution of basal cell hyperplasia and associated mucosecretory dysfunction to the development of idiopathic pulmonary fibrosis (IPF). Objectives: We sought to decipher the transcriptome of freshly isolated epithelial cells from normal and IPF lungs to discern disease-dependent changes within basal stem cells. Methods: Single-cell RNA sequencing was used to map epithelial cell types of the normal and IPF human airways. Organoid and air–liquid interface cultures were used to investigate functional properties of basal cell subtypes. Measurements and Main Results: We found that basal cells included multipotent and secretory primed subsets in control adult lung tissue. Secretory primed basal cells include an overlapping molecular signature with basal cells obtained from the distal lung tissue of IPF lungs. We confirmed that NOTCH2 maintains undifferentiated basal cells and restricts basal-to-ciliated differentiation, and we present evidence that NOTCH3 functions to restrain secretory differentiation. Conclusions: Basal cells are dynamically regulated in disease and are specifically biased toward the expansion of the secretory primed basal cell subset in IPF. Modulation of basal cell plasticity may represent a relevant target for therapeutic intervention in IPF.

Progressive tissue fibrosis, including idiopathic pulmonary fibrosis (IPF), is characterized by excessive recruitment of fibroblasts to sites of tissue injury and unremitting extracellular matrix deposition associated with severe morbidity and mortality. However, the molecular mechanisms that control progressive IPF have yet to be fully determined. Previous studies suggested that invasive fibroblasts drive disease progression in IPF. Here, we report profiling of invasive and noninvasive fibroblasts from IPF patients and healthy donors. Pathway analysis revealed that the activated signatures of the invasive fibroblasts, the top of which was ERBB2 (HER2), showed great similarities to those of metastatic lung adenocarcinoma cancer cells. Activation of HER2 in normal lung fibroblasts led to a more invasive genetic program and worsened fibroblast invasion and lung fibrosis, while antagonizing HER2 signaling blunted fibroblast invasion and ameliorated lung fibrosis. These findings suggest that HER2 signaling may be a key driver of fibroblast invasion and serve as an attractive target for therapeutic intervention in IPF.

Interstitial lung diseases (ILDs) represent a major challenge to public health and the medical research community. The pathogenic mechanisms underlying many of the ILDs have been challenging to unravel, thus halting the development of therapies. Recent research in both basic science and clinical settings suggests that regional stem cells in the lung participate in tissue repair and disease pathogenesis. Understanding the roles that stem cells play in basic lung biology and in the pathogenesis of interstitial lung diseases could identify novel targets and facilitate the development of effective therapeutics for these diseases.

IntroductionIdiopathic pulmonary fibrosis (IPF) is a progressive and often fatal interstitial lung disease (ILD); other ILDs have a progressive, fibrotic phenotype (PF-ILD). Antifibrotic agents can slow but not stop disease progression in patients with IPF or PF-ILD. c-Jun N-terminal kinases (JNKs) are stress-activated protein kinases implicated in the underlying mechanisms of fibrosis, including epithelial cell death, inflammation and polarisation of profibrotic macrophages, fibroblast activation and collagen production. CC-90001, an orally administered (PO), one time per day, JNK inhibitor, is being evaluated in IPF and PF-ILD.Methods and analysisThis is a phase 2, randomised, double-blind, placebo-controlled study evaluating efficacy and safety of CC-90001 in patients with IPF (main study) and patients with PF-ILD (substudy). Both include an 8-week screening period, a 24-week treatment period, up to an 80-week active-treatment extension and a 4-week post-treatment follow-up. Patients with IPF (n=165) will be randomised 1:1:1 to receive 200 mg or 400 mg CC-90001 or placebo administered PO one time per day; up to 25 patients/arm will be permitted concomitant pirfenidone use. Forty-five patients in the PF-ILD substudy will be randomised 2:1 to receive 400 mg CC-90001 or placebo. The primary endpoint is change in per cent predicted forced vital capacity from baseline to Week 24 in patients with IPF.Ethics and disseminationThis study will be conducted in accordance with Good Clinical Practice guidelines, Declaration of Helsinki principles and local ethical and legal requirements. Results will be reported in a peer-reviewed publication.Trial registration numberNCT03142191.

Mesenchymal vesicular GHR supports alveolar epithelial progenitor cell renewal and limits lung fibrosis., Recent studies have identified impaired type 2 alveolar epithelial cell (ATII) renewal in idiopathic pulmonary fibrosis (IPF) human organoids and severe fibrosis when ATII is defective in mice. ATIIs function as progenitor cells and require supportive signals from the surrounding mesenchymal cells. The mechanisms by which mesenchymal cells promote ATII progenitor functions in lung fibrosis are incompletely understood. We identified growth hormone receptor (GHR) is mainly expressed in mesenchymal cells, and its expression is substantially decreased in IPF lungs. Higher levels of GHR expression correlated with better lung function in patients with IPF. Profibrotic mesenchymal cells retarded ATII growth and were associated with suppressed vesicular GHR expression. Vesicles enriched with Ghr promote ATII proliferation and diminished pulmonary fibrosis in mesenchymal Ghr-deficient mice. Our findings demonstrate a previously unidentified mesenchymal paracrine signaling coordinated by GHR that is capable of supporting ATII progenitor cell renewal and limiting the severity of lung fibrosis.

Idiopathic pulmonary fibrosis (IPF) is characterized by aberrant repair that diminishes lung function via mechanisms that remain poorly understood. CC chemokine receptor (CCR10) and its ligand CCL28 were both elevated in IPF compared with normal donors. CCR10 was highly expressed by various cells from IPF lungs, most notably stage-specific embryonic antigen-4-positive mesenchymal progenitor cells (MPCs). In vitro, CCL28 promoted the proliferation of CCR10+ MPCs while CRISPR/Cas9-mediated targeting of CCR10 resulted in the death of MPCs. Following the intravenous injection of various cells from IPF lungs into immunodeficient (NOD/SCID-γ, NSG) mice, human CCR10+ cells initiated and maintained fibrosis in NSG mice. Eph receptor A3 (EphA3) was among the highest expressed receptor tyrosine kinases detected on IPF CCR10+ cells. Ifabotuzumab-targeted killing of EphA3+ cells significantly reduced the numbers of CCR10+ cells and ameliorated pulmonary fibrosis in humanized NSG mice. Thus, human CCR10+ cells promote pulmonary fibrosis, and EphA3 mAb-directed elimination of these cells inhibits lung fibrosis.

Summary Pulmonary mesenchymal cells are critical players in both the mouse and human during lung development and disease states. They are increasingly recognized as highly heterogeneous, but there is no consensus on subpopulations or discriminative markers for each subtype. We completed scRNA-seq analysis of mesenchymal cells from the embryonic, postnatal, adult and aged fibrotic lungs of mice and humans. We consistently identified and delineated the transcriptome of lipofibroblasts, myofibroblasts, smooth muscle cells, pericytes, mesothelial cells, and a novel population characterized by Ebf1 expression. Subtype selective transcription factors and putative divergence of the clusters during development were described. Comparative analysis revealed orthologous subpopulations with conserved transcriptomic signatures in murine and human lung mesenchymal cells. All mesenchymal subpopulations contributed to matrix gene expression in fibrosis. This analysis would enhance our understanding of mesenchymal cell heterogeneity in lung development, homeostasis and fibrotic disease conditions., Graphical abstract, Highlights • Comprehensively profiling of lung mesenchymal subtypes in development and fibrosis. • Identification of novel lung mesenchymal cell subtypes in development and fibrosis. • Delineation of novel discriminative and consistent mesenchymal subtype markers. • Redefinition of the cell contributors of ECM in pulmonary fibrosis., Cell biology; Organizational aspects of cell biology; Pathophysiology

Data from controlled clinical studies in patients with more advanced idiopathic pulmonary fibrosis (IPF) could inform clinical practice, but they are limited, since this sub-population is usually excluded from clinical trials. These exploratory post-hoc analyses of the open-label, long-term extension study RECAP (NCT00662038) aimed to assess the efficacy and safety of pirfenidone in patients with more advanced IPF. Patients were categorised according to the extent of lung function impairment at baseline: more advanced (percent predicted FVC

Background Exuberant tissue repair and extracellular matrix (ECM) deposition by pulmonary mesenchymal cells, notably fibroblasts, is believed to be central to the pathogenesis of fibrotic lung diseases like idiopathic pulmonary fibrosis (IPF). Few studies to date have utilised advanced omic technologies, like single cell RNA sequencing (scRNA-seq), to solely investigate these diverse and poorly described cell types. Aims and Objectives As there is no consensus on the mesenchymal subtypes present in the lung we performed a comprehensive analysis of pulmonary mesenchymal cells to identify all molecularly distinct subtypes, validate the efficacy of commonly used markers, identify new ones, and address longstanding controversies in the literature. Methods We undertook scRNA-seq and associated analyses on mesenchymal cells from healthy (n=34) donors and IPF (n=33) patients’ lungs with comparative analyses in the murine lung (embryonic, post-natal, adult, aged, healthy vs. fibrotic). Results We identified, and resolved the transcriptome of; lipofibroblasts, myofibroblasts, smooth muscle cells, pericytes, mesothelial cells, a novel population delineated by Early B-cell Factor 1 expression and an “intermediate” subtype. Commonly reported markers, like ACTA2 or PLIN2, were found to be suboptimal. We identified conserved, novel, markers and transcription factors for all subtypes. These data suggest all mesenchymal subtypes contribute to ECM deposition in the IPF lung. We found no evidence of transdifferentiation between subtypes, nor an increase in myofibroblasts in the fibrotic lung. Conclusions This study provides a basis for interrogating each mesenchymal subype and enhances our understanding of the contribution of these cell types to lung development, lung repair, and pulmonary fibrosis.

SUMMARY Idiopathic pulmonary fibrosis (IPF) is a fatal form of interstitial lung disease and aging has been identified as a risk factor to the disease. Alveolar type II cells (AEC2s) function as progenitor cells in the lung. Growing evidences indicate that IPF results from repeating AEC2 injury and inadequate epithelial repair. We previously reported that there was a significant loss of alveolar progenitors in the lungs of patients with IPF. In our current study, we performed single cell RNA-seq of epithelial cells from lungs of patients with IPF and healthy donors as well as epithelial cells from old and young mouse lungs with bleomycin injury. We identified a defect of zinc metabolism of AEC2s from IPF lungs and bleomycin-injured old mouse lungs. We further discovered that a specific zinc transporter ZIP8 was down regulated in IPF AEC2s and AEC2s from aged mice. Loss of ZIP8 expression is associated with impaired AEC2 renewal through sirtuin signaling in aging and IPF. Targeted deletion of Zip8 in murine AEC2 compartment led to reduced AEC2 renewal capacity, impaired AEC2 recovery, and worsened lung fibrosis after bleomycin injury. In summary, we have identified novel metabolic defects of AEC2s during aging and in IPF which contribute to the pathogenesis of lung fibrosis. Therapeutic strategies to restore critical components of these metabolic programs could improve AEC2 progenitor activity and mitigate ongoing fibrogenesis. In Brief Liang et al. performed single cell RNA-seq (scRNA-seq) of epithelial cells in IPF and in mice and discovered a zinc metabolic defect of alveolar progenitor cells (AEC2) in IPF and injured old mice characterized by down-regulation of a specific zinc transporter ZIP8. Manipulation of ZIP8 and zinc in 3D organoid culture of AEC2 in vitro and targeted deletion of Zip8 in AEC2s in vivo demonsrated a role of ZIP8 in promoting AEC2 progenitor function. Highlights ScRNA-seq revealed dysregulation of zinc metabolism in AEC2s and decreased stem cell signaling in IPF Reduced SLC39A8 and related gene expression of IPF AEC2s and aged mouse AEC2s ZIP8-dependent zinc metabolism is required for AEC2 renewal Targeted deletion of Slc39a8 impaired AEC2 renewal and promoted lung fibrosis

Aging is a critical risk factor in progressive lung fibrotic diseases such as idiopathic pulmonary fibrosis (IPF). Loss of integrity of type 2 alveolar epithelial cells (AEC2s) is the main causal event in the pathogenesis of IPF. To systematically examine the genomic program changes of AEC2s with aging and lung injury, we performed unbiased single cell RNA-seq analyses of lung epithelial cells from either uninjured or bleomycin-injured young and old mice. Major lung epithelial cell types were readily identified with canonical cell markers in our dataset. Heterogenecity of AEC2s was apparent, and AEC2s were then classified into three subsets according to their gene signatures. Genes related to lipid metabolism and glycolysis were significantly altered within these three clusters of AEC2s, and also affected by aging and lung injury. Importantly, IPF AEC2s showed similar genomic programming and metabolic changes as that of AEC2s from bleomycin injured old mouse lungs relative to controls. Furthermore, perturbation of both lipid metabolism and glycolysis significantly changed progenitor renewal capacity in 3-Demensional organoid culture of AEC2s. Taken togather, this work identified metabolic defects of AEC2s in aging and during lung injury. Strategies to rectify these altered programs would promote AEC2 renewal which in turn improves lung repair.One sentence summaryMetabolic defects of alveolar progenitors in aging and during lung injury impair their renewal.

The heterogeneity of fibroblasts in the murine and human lung during homeostasis and disease is increasingly recognized. It remains unclear if the different phenotypes identified to date are characteristic of unique subpopulations with unique progenitors or whether they arise by a process of differentiation from common precursors. Our understanding of this ubiquitous cell type is limited by an absence of well validated, specific, markers with which to identify each cell type and a clear consensus on the distinct populations present in the lung. Here we describe single cell RNA sequencing (scRNA-seq) analysis on mesenchymal cells from the murine lung throughout embryonic (E) development (E9.5 – 17.5), at post-natal day (P1 – 15), as well as in the adult and the aged murine lungs before and after bleomycin-induced fibrosis. We carried out complementary scRNA-seq on human lung tissue from a P1 lung, a month 21 lung and lung tissue from healthy donors and patients with idiopathic pulmonary fibrosis (IPF). The murine and human data were supplemented with publicly available scRNA-seq datasets. We consistently identified lipofibroblasts, myofibroblasts, pericytes, mesothelial cells and smooth muscle cells. In addition, we identified a novel population delineated by Ebf1 (early B-cell factor 1) expression and an intermediate subtype. Comparative analysis with human mesenchymal cells revealed homologous mesenchymal subpopulations with remarkably conserved transcriptomic signatures. Comparative analysis of changes in gene expression in the fibroblast subpopulations from age matched non-fibrotic and fibrotic lungs in the mouse and human demonstrates that many of these subsets contribute to matrix gene expression in fibrotic conditions. Subtype selective transcription factors were identified and putative divergence of the clusters during development were delineated. Prospective isolation of these fibroblast subpopulations, localization of signature gene markers, and lineage-tracing each cluster are under way in the laboratory. This analysis will enhance our understanding of fibroblast heterogeneity in homeostasis and fibrotic disease conditions.

RationaleDeclining lung function in patients with interstitial lung disease is accompanied by epithelial remodeling and progressive scarring of the gas-exchange region. There is a need to better understand the contribution of basal cell hyperplasia and associated mucosecretory dysfunction to the development of idiopathic pulmonary fibrosis (IPF).ObjectivesWe sought to decipher the transcriptome of freshly isolated epithelial cells from normal and IPF lung to discern disease-dependent changes within basal stem cells.MethodsSingle cell RNA sequencing was used to map epithelial cell types of the normal and IPF human airway. Organoid and ALI cultures were used to investigate functional properties of basal cell subtypes.Measurements and Main ResultsWe found that basal cells included multipotent and secretory primed subsets in control adult lung tissue. Secretory primed basal cells include an overlapping molecular signature with basal cells obtained from distal lung tissue of IPF lungs. We confirmed that NOTCH2 maintains undifferentiated basal cells and restrict basal-to-ciliated differentiation, and present evidence that NOTCH3 functions to restrain secretory differentiation.ConclusionsBasal cells are dynamically regulated in disease and are specifically biased towards expansion of the secretory primed basal cell subset in idiopathic pulmonary fibrosis. Modulation of basal cell plasticity may represent a relevant target for therapeutic intervention in IPF.

BackgroundCertain individuals, when infected by SARS-CoV-2, tend to develop the more severe forms of Covid-19 illness for reasons that remain unclear.MethodsWe studied N=442 patients who presented with laboratory confirmed Covid-19 illness to our U.S. metropolitan healthcare system. We curated data from the electronic health record, and used multivariable logistic regression to examine the association of pre-existing traits with a Covid-19 illness severity defined by level of required care: need for hospital admission, need for intensive care, and need for intubation.ResultsOf all patients studied, 48% required hospitalization, 17% required intensive care, and 12% required intubation. In multivariable-adjusted analyses, patients requiring a higher levels of care were more likely to be older (OR 1.5 per 10 years, PinteractionConclusionsIn our healthcare system, greater Covid-19 illness severity is seen in patients who are older, male, African American, obese, with diabetes, and with greater overall comorbidity burden. Certain comorbidities paradoxically augment risk to a greater extent in younger patients. In hospitalized patients, male sex is the main determinant of needing more intensive care. Further investigation is needed to understand the mechanisms underlying these findings.

Introduction and background: Idiopathic pulmonary fibrosis (IPF) is a fatal form of interstitial lung disease that mainly affects the elderly population. One of the hallmarks of IPF pathogenesis is dysfunction of Type 2 alveolar epithelial progenitor cells (AEC2s). We reported that there is a significant loss of AEC2s from IPF lungs. Aims and objective: To determine the metabolic mechanism of AEC2 dysfunction during aging in persistent lung fibrosis. Methods: Single cell RNA-seq of IPF AEC2s as well as murine AEC2s from old and bleomycin-injured mouse lungs. 3D organoid culture of AEC2 was used for assessing AEC2 renewal capacity. Mouse line with AEC2 cell type specific gene deletion was generated to determine the role of Zip8 in lung fibrosis in vivo. Results: Similar to that in IPF lungs, there is a reduction in AEC2 cell number as well as renewal capacity of AEC2s in old mouse lungs. Single cell RNA-seq analysis identified reduction in gene expression of SLC39A8 (ZIP8), the gene encoding a specific zinc transporter for AEC2s, in IPF AEC2s, as well as AEC2s from old and bleomycin injured mouse lungs. Replenishment with exogenous zinc promotes self-renewal and differentiation of AEC2s, and the response to zinc treatment was diminished in aged AEC2s. Zip8 Deletion in murine AEC2s leads to downregulation of Sirt1 expression, reduced number of AEC2s recovered from the lungs, and reduced renewal capacity of AEC2s. Conclusion: We have identified novel metabolic defects of AEC2s during aging and in IPF. Therapeutic strategies to restore critical components of these metabolic programs could improve AEC2 progenitor activity and mitigate ongoing fibrogenesis.

Rationale: Idiopathic pulmonary fibrosis (IPF) is characterized by aberrant lung remodeling, which progressively abolishes lung function in an RTK (receptor tyrosine kinase)–dependent manner. Gas6 ...

Rationale: Current diagnosis of chronic hypersensitivity pneumonitis (cHP) involves considering a combination of clinical, radiological, and pathological information in multidisciplinary team discussions. However, this approach is highly variable with poor agreement between centers. Objectives: We aimed to identify diagnostic criteria for cHP that reach consensus among international experts. Methods: A three-round modified Delphi survey was conducted between April and August 2017. A total of 45 experts in interstitial lung disease from 14 countries participated in the online survey. Diagnostic items included in round 1 were generated using expert interviews and literature review. During rounds 1 and 2, experts rated the importance of each diagnostic item on a 5-point Likert scale. The a priori threshold of consensus was 75% or greater of experts rating a diagnostic item as very important or important. In the third round, experts graded the items that met consensus as important and provided their level of diagnostic confidence for a series of clinical scenarios. Measurements and Main Results: Consensus was achieved on 18 of the 40 diagnostic items. Among these, experts gave the highest level of importance to the identification of a causative antigen, time relation between exposure and disease, mosaic attenuation on chest imaging, and poorly formed nonnecrotizing granulomas on pathology. In clinical scenarios, the diagnostic confidence of experts in cHP was heightened by the presence of these diagnostic items. Conclusions: This consensus-based approach for the diagnosis of cHP represents a first step toward the development of international guidelines for the diagnosis of cHP.

SUMMARY Fibroblast heterogeneity has long been recognized in mouse and human lungs, homeostasis, and disease states. However, there is no common consensus on fibroblast subtypes, lineages, biological properties, signaling, and plasticity, which severely hampers our understanding of the mechanisms of fibrosis. To comprehensively classify fibro-blast populations in the lung using an unbiased approach, single-cell RNA sequencing was performed with mesenchymal preparations from either uninjured or bleomycin-treated mouse lungs. Single-cell transcriptome analyses classified and defined six mesenchymal cell types in normal lung and seven in fibrotic lung. Furthermore, delineation of their differentiation trajectory was achieved by a machine learning method. This collection of single-cell transcriptomes and the distinct classification of fibroblast subsets provide a new resource for understanding the fibroblast landscape and the roles of fibroblasts in fibrotic diseases., In Brief Xie et al. have analyzed mesenchymal cell subpopulations at single-cell resolution and have demonstrated known subtypes and a newly emerging subtype during pulmonary fibrosis in mouse lung.