Basal epithelial stem cells cross an alarmin checkpoint for postviral lung disease

IL-33: Friend or foe in transplantation?

Several reports have highlighted the dichotomous nature of the Interleukin-33 (IL-33) system in cardiac and lung disease, where this cytokine can exert both protective effects and drive pro-inflammatory responses in a context-specific manner. This State-of-the-Art review focuses on preclinical mechanistic studies of the IL-33 system in development of allograft rejection in heart and lung transplantation. We address the scope of potential cellular sources of IL-33 and pathways for cellular release that may impact the study of this cytokine system in transplant models. We then highlight soluble IL-33 receptor as a biomarker in cardiac allograft rejection and detail preclinical models that collectively demonstrate a role for this cytokine in driving type-2 immune programs to protect cardiac allografts. We contrast this with investigation of IL-33 in lung transplantation, which has yielded mixed and somewhat conflicting results when comparing human studies with preclinical models, which have implicated the IL-33 system in both allograft tolerance and acceleration of chronic rejection. We summarize and interpret these results in aggregate and provide future directions for study of IL-33 in heart and lung transplantation.

A nasal cell atlas reveals heterogeneity of tuft cells and their role in directing olfactory stem cell proliferation

The olfactory neuroepithelium serves as a sensory organ for odors and forms part of the nasal mucosal barrier. Olfactory sensory neurons are surrounded and supported by epithelial cells. Among them, microvillous cells (MVCs) are strategically positioned at the apical surface, but their specific functions are enigmatic, and their relationship to the other specialized epithelial cells is unclear. Here, we establish that the family of MVCs comprises tuft cells and ionocytes in both mice and humans. Integrating analysis of the respiratory and olfactory epithelia, we define the distinct receptor expression of TRPM5+ tuft-MVCs compared with Gɑ-gustducinhigh respiratory tuft cells and characterize a previously undescribed population of glandular DCLK1+ tuft cells. To establish how allergen sensing by tuft-MVCs might direct olfactory mucosal responses, we used an integrated single-cell transcriptional and protein analysis. Inhalation of Alternaria induced mucosal epithelial effector molecules including Chil4 and a distinct pathway leading to proliferation of the quiescent olfactory horizontal basal stem cell (HBC) pool, both triggered in the absence of olfactory apoptosis. Alternaria- and ATP-elicited HBC proliferation was dependent on TRPM5+ tuft-MVCs, identifying these specialized epithelial cells as regulators of olfactory stem cell responses. Together, our data provide high-resolution characterization of nasal tuft cell heterogeneity and identify a function of TRPM5+ tuft-MVCs in directing the olfactory mucosal response to allergens.

Mitogen-activated protein kinase-guided drug discovery for post-viral and related types of lung disease

Respiratory viral infections are a major public health problem, with much of their morbidity and mortality due to post-viral lung diseases that progress and persist after the active infection is cleared. This paradigm is implicated in the most common forms of chronic lung disease, such as asthma and COPD, as well as other virus-linked diseases including progressive and long-term coronavirus disease 2019. Despite the impact of these diseases, there is a lack of small-molecule drugs available that can precisely modify this type of disease process. Here we will review current progress in understanding the pathogenesis of post-viral and related lung disease with characteristic remodelling phenotypes. We will also develop how this data leads to mitogen-activated protein kinase (MAPK) in general and MAPK13 in particular as key druggable targets in this pathway. We will also explore recent advances and predict the future breakthroughs in structure-based drug design that will provide new MAPK inhibitors as drug candidates for clinical applications. Each of these developments point to a more effective approach to treating the distinct epithelial and immune cell based mechanisms, which better account for the morbidity and mortality of post-viral and related types of lung disease. This progress is vital given the growing prevalence of respiratory viruses and other inhaled agents that trigger stereotyped progression to acute illness and chronic disease.

COVID-19 and influenza infections mediate distinct pulmonary cellular and transcriptomic changes

SARS-CoV-2 infection can cause persistent respiratory sequelae. However, the underlying mechanisms remain unclear. Here we report that sub-lethally infected K18-human ACE2 mice show patchy pneumonia associated with histiocytic inflammation and collagen deposition at 21 and 45 days post infection (DPI). Transcriptomic analyses revealed that compared to influenza-infected mice, SARS-CoV-2-infected mice had reduced interferon-gamma/alpha responses at 4 DPI and failed to induce keratin 5 (Krt5) at 6 DPI in lung, a marker of nascent pulmonary progenitor cells. Histologically, influenza- but not SARS-CoV-2-infected mice showed extensive Krt5+ "pods" structure co-stained with stem cell markers Trp63/NGFR proliferated in the pulmonary consolidation area at both 7 and 14 DPI, with regression at 21 DPI. These Krt5+ "pods" structures were not observed in the lungs of SARS-CoV-2-infected humans or nonhuman primates. These results suggest that SARS-CoV-2 infection fails to induce nascent Krt5+ cell proliferation in consolidated regions, leading to incomplete repair of the injured lung.

A potent MAPK13-14 inhibitor prevents airway inflammation and mucus production

Common respiratory diseases continue to represent a major public health problem, and much of the morbidity and mortality is due to airway inflammation and mucus production. Previous studies indicated a role for mitogen-activated protein kinase 14 (MAPK14) in this type of disease, but clinical trials are unsuccessful to date. Our previous work identified a related but distinct kinase known as MAPK13 that is activated in respiratory airway diseases and is required for mucus production in human cell-culture models. Support for MAPK13 function in these models came from effectiveness of MAPK13 versus MAPK14 gene-knockdown and from first-generation MAPK13-14 inhibitors. However, these first-generation inhibitors were incompletely optimized for blocking activity and were untested in vivo. Here we report the next generation and selection of a potent MAPK13-14 inhibitor (designated NuP-3) that more effectively downregulates type-2 cytokine-stimulated mucus production in air-liquid interface and organoid cultures of human airway epithelial cells. We also show that NuP-3 treatment prevents respiratory airway inflammation and mucus production in new minipig models of airway disease triggered by type-2 cytokine challenge or respiratory viral infection. The results thereby provide the next advance in developing a small-molecule kinase inhibitor to address key features of respiratory disease.NEW & NOTEWORTHY This study describes the discovery of a potent mitogen-activated protein kinase 13-14 (MAPK13-14) inhibitor and its effectiveness in models of respiratory airway disease. The findings thereby provide a scheme for pathogenesis and therapy of lung diseases [e.g., asthma, chronic obstructive pulmonary disease (COPD), Covid-19, postviral, and allergic respiratory disease] and related conditions that implicate MAPK13-14 function. The findings also refine a hypothesis for epithelial and immune cell functions in respiratory disease that features MAPK13 as a possible component of this disease process.

"MrgprA3 neurons selectively control myeloid-derived cytokines for IL-17 dependent cutaneous immunity"

Skin employs interdependent cellular networks to facilitate barrier integrity and host immunity through ill-defined mechanisms. This study demonstrates that manipulation of itch-sensing neurons bearing the Mas-related G protein-coupled receptor A3 (MrgprA3) drives IL-17+ γδ T cell expansion, epidermal thickening, and resistance to the human pathogen Schistosoma mansoni through mechanisms that require myeloid antigen presenting cells (APC). Activated MrgprA3 neurons instruct myeloid APCs to downregulate interleukin 33 (IL-33) and up-regulate TNFα partially through the neuropeptide calcitonin gene related peptide (CGRP). Strikingly, cell-intrinsic deletion of IL-33 in myeloid APC basally alters chromatin accessibility at inflammatory cytokine loci and promotes IL-17/23-dependent epidermal thickening, keratinocyte hyperplasia, and resistance to helminth infection. Our findings reveal a previously undescribed mechanism of intercellular cross-talk wherein "itch" neuron activation reshapes myeloid cytokine expression patterns to alter skin composition for cutaneous immunity against invasive pathogens.

A potent MAPK13-14 inhibitor prevents airway inflammation and mucus production

Common respiratory diseases continue to represent a major public health problem, and much of the morbidity and mortality is due to airway inflammation and mucus production. Previous studies indicated a role for mitogen-activated protein kinase 14 (MAPK14) in this type of disease, but clinical trials are unsuccessful to date. Our previous work identified a related but distinct kinase known as MAPK13 that is activated in respiratory airway diseases and is required for mucus production in human cell-culture models. Support for MAPK13 function in these models came from effectiveness of MAPK13 versus MAPK14 gene-knockdown and from first-generation MAPK13-14 inhibitors. However, these first-generation inhibitors were incompletely optimized for blocking activity and were untested in vivo. Here we report the next generation and selection of a potent MAPK13-14 inhibitor (designated NuP-3) that more effectively down-regulates type-2 cytokine-stimulated mucus production in air-liquid interface and organoid cultures of human airway epithelial cells. We also show that NuP-3 treatment prevents respiratory airway inflammation and mucus production in new minipig models of airway disease triggered by type-2 cytokine challenge or respiratory viral infection. The results thereby provide the next advance in developing a small-molecule kinase inhibitor to address key features of respiratory disease.

Human embryonic stem cell-derived mesenchymal stem cell secretome reverts silica-induced airway epithelial cell injury by regulating Bmi1 signaling

Silicosis is an irreversible chronic pulmonary disease caused by long-term inhalation and deposition of silica particles, which is currently incurable. The exhaustion of airway epithelial stem cells plays a pathogenetic role in silicosis. In present study, we investigated therapeutic effects and potential mechanism of human embryonic stem cell (hESC)-derived MSC-likes immune and matrix regulatory cells (IMRCs) (hESC-MSC-IMRCs), a type of manufacturable MSCs for clinical application in silicosis mice. Our results showed that the transplantation of hESC-MSC-IMRCs led the alleviation of silica-induced silicosis in mice, accompanied by inhibiting epithelia-mesenchymal transition (EMT), activating B-cell-specific Moloney murine leukemia virus integration site 1 (Bmi1) signaling and airway epithelial cell regeneration. In consistence, the secretome of hESC-MSC-IMRC exhibited abilities to restore the potency and plasticity of primary human bronchial epithelial cells (HBECs) proliferation and differentiation following the SiO2 -induced HBECs injury. Mechanistically, the secretome resolved the SiO2 -induced HBECs injury through the activation of BMI1 signaling and restoration of airway basal cell proliferation and differentiation. Moreover, the activation of BMI1 significantly enhanced the capacity of HBEC proliferation and differentiation to multiple airway epithelial cell types in organoids. Cytokine array revealed that DKK1, VEGF, uPAR, IL-8, Serpin E1, MCP-1 and Tsp-1 were the main factors in the hESC-MSC-IMRC secretome. These results demonstrated a potential therapeutic effect of hESC-MSC-IMRCs and their secretome for silicosis, in part through a mechanism by activating Bmi1 signaling to revert the exhaustion of airway epithelial stem cells, subsequentially enhance the potency and plasticity of lung epithelial stem cells.

Lung Science Conference highlights 2023: Post-viral lung diseases - from basic immunology to clinical phenotypes and therapy

This article provides an overview of some of the highlights of the Lung Science Conference 2023 https://bit.ly/46oWCEX.

A Deep View of the Biological Property of Interleukin-33 and Its Dysfunction in the Gut

Intestinal diseases have always posed a serious threat to human health, with inflammatory bowel disease (IBD) being one of them. IBD is an autoimmune disease characterized by chronic inflammation, including ulcerative colitis (UC) and Crohn's disease (CD). The "alarm" cytokine IL-33, which is intimately associated with Th2 immunity, is a highly potent inflammatory factor that is considered to have dual functions-operating as both a pro-inflammatory cytokine and a transcriptional regulator. IL-33 has been shown to play a crucial role in both the onset and development of IBD. Therefore, this review focuses on the pathogenesis of IBD, the major receptor cell types, and the activities of IL-33 in innate and adaptive immunity, as well as its underlying mechanisms and conflicting conclusions in IBD. We have also summarized different medicines targeted to IL-33-associated diseases. Furthermore, we have emphasized the role of IL-33 in gastrointestinal cancer and parasitic infections, giving novel prospective therapeutic utility in the future application of IL-33.

An alternative mechanism for skeletal muscle dysfunction in long-term post-viral lung disease

Chronic lung disease is often accompanied by disabling extrapulmonary symptoms, notably skeletal muscle dysfunction and atrophy. Moreover, the severity of respiratory symptoms correlates with decreased muscle mass and in turn lowered physical activity and survival rates. Previous models of muscle atrophy in chronic lung disease often modeled chronic obstructive pulmonary disease (COPD) and relied on cigarette smoke exposure and LPS stimulation, but these conditions independently affect skeletal muscle even without accompanying lung disease. Moreover, there is an emerging and pressing need to understand the extrapulmonary manifestations of long-term post-viral lung disease (PVLD) as found in COVID-19. Here, we examine the development of skeletal muscle dysfunction in the setting of chronic pulmonary disease caused by infection due to the natural pathogen Sendai virus using a mouse model of PVLD. We identify a significant decrease in myofiber size when PVLD is maximal at 49 days after infection. We find no change in the relative types of myofibers, but the greatest decrease in fiber size is localized to fast-twitch-type IIB myofibers based on myosin heavy chain immunostaining. Remarkably, all biomarkers of myocyte protein synthesis and degradation (total RNA, ribosomal abundance, and ubiquitin-proteasome expression) were stable throughout the acute infectious illness and chronic post-viral disease process. Together, the results demonstrate a distinct pattern of skeletal muscle dysfunction in a mouse model of long-term PVLD. The findings thereby provide new insights into prolonged limitations in exercise capacity in patients with chronic lung disease after viral infections and perhaps other types of lung injury.NEW & NOTEWORTHY Our study used a mouse model of post-viral lung disease to study the impact of chronic lung disease on skeletal muscle. The model reveals a decrease in myofiber size that is selective for specific types of myofibers and an alternative mechanism for muscle atrophy that might be independent of the usual markers of protein synthesis and degradation. The findings provide a basis for new therapeutic strategies to correct skeletal muscle dysfunction in chronic respiratory disease.

Lung Remodeling Regions in Long-Term Coronavirus Disease 2019 Feature Basal Epithelial Cell Reprogramming

Respiratory viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can trigger chronic lung disease that persists and even progresses after expected clearance of infectious virus. To gain an understanding of this process, we examined a series of consecutive fatal cases of coronavirus disease 2019 (COVID-19) that came to autopsy at 27 to 51 days after hospital admission. In each patient, we identify a stereotyped bronchiolar-alveolar pattern of lung remodeling with basal epithelial cell hyperplasia, immune activation, and mucinous differentiation. Remodeling regions also feature macrophage infiltration and apoptosis and a marked depletion of alveolar type 1 and 2 epithelial cells. This entire pattern closely resembles findings from an experimental model of post-viral lung disease that requires basal-epithelial stem cell growth, immune activation, and differentiation. Together, the results provide evidence of basal epithelial cell reprogramming in long-term COVID-19 and thereby yield a pathway for explaining and correcting lung dysfunction in this type of disease.

Full-length IL-33 augments pulmonary fibrosis in an ST2- and Th2-independent, non-transcriptomic fashion

Mature IL-33 (MIL33) acting through its receptor, ST2, is known to regulate fibrosis. The precursor, full-length IL-33 (FLIL33), may function differently from MIL33 and independently of ST2. Here we report that genetic deletion of either IL-33 or ST2 attenuates pulmonary fibrosis in the bleomycin model, as does Cre-induced IL-33 deficiency in response to either acute or chronic bleomycin challenge. However, adenovirus-mediated gene delivery of FLIL33, but not MIL33, to the lungs of either wild-type or ST2-deficient mice potentiates the profibrotic effect of bleomycin without inducing a Th2 phenotype. In cultured mouse lung cells, FLIL33 overexpression induces moderate and distinct transcriptomic changes compared with a robust response induced by MIL33, whereas ST2 deletion abrogates the effects of both IL-33 forms. Thus, FLIL33 may contribute to fibrosis in an ST2-independent, Th2-independent, non-transcriptomic fashion, suggesting that pharmacological targeting of both FLIL33 and MIL33 may prove efficacious in patients with pulmonary fibrosis.

Prevalence and Mechanisms of Mucus Accumulation in COVID-19 Lung Disease

Rationale: The incidence and sites of mucus accumulation and molecular regulation of mucin gene expression in coronavirus (COVID-19) lung disease have not been reported. Objectives: To characterize the incidence of mucus accumulation and the mechanisms mediating mucin hypersecretion in COVID-19 lung disease. Methods: Airway mucus and mucins were evaluated in COVID-19 autopsy lungs by Alcian blue and periodic acid-Schiff staining, immunohistochemical staining, RNA in situ hybridization, and spatial transcriptional profiling. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected human bronchial epithelial (HBE) cultures were used to investigate mechanisms of SARS-CoV-2-induced mucin expression and synthesis and test candidate countermeasures. Measurements and Main Results: MUC5B and variably MUC5AC RNA concentrations were increased throughout all airway regions of COVID-19 autopsy lungs, notably in the subacute/chronic disease phase after SARS-CoV-2 clearance. In the distal lung, MUC5B-dominated mucus plugging was observed in 90% of subjects with COVID-19 in both morphologically identified bronchioles and microcysts, and MUC5B accumulated in damaged alveolar spaces. SARS-CoV-2-infected HBE cultures exhibited peak titers 3 days after inoculation, whereas induction of MUC5B/MUC5AC peaked 7-14 days after inoculation. SARS-CoV-2 infection of HBE cultures induced expression of epidermal growth factor receptor (EGFR) ligands and inflammatory cytokines (e.g., IL-1α/β) associated with mucin gene regulation. Inhibiting EGFR/IL-1R pathways or administration of dexamethasone reduced SARS-CoV-2-induced mucin expression. Conclusions: SARS-CoV-2 infection is associated with a high prevalence of distal airspace mucus accumulation and increased MUC5B expression in COVID-19 autopsy lungs. HBE culture studies identified roles for EGFR and IL-1R signaling in mucin gene regulation after SARS-CoV-2 infection. These data suggest that time-sensitive mucolytic agents, specific pathway inhibitors, or corticosteroid administration may be therapeutic for COVID-19 lung disease.

Interleukin (IL)-33 immunobiology in asthma and airway inflammatory diseases

OBJECTIVE

Identify key features of IL-33 immunobiology important in allergic and nonallergic airway inflammatory diseases and potential therapeutic strategies to reduce disease burden.

DATA SOURCES

PubMed, clinicaltrials.gov.

STUDY SELECTIONS

A systematic and focused literature search was conducted of PubMed from March 2021 to December 2021 using keywords to either PubMed or BioMed Explorer including IL-33/ST2, genetic polymorphisms, transcription, translation, post-translation modification, nuclear protein, allergy, asthma, and lung disease. Clinical trial information on IL-33 was extracted from clinicaltrials.gov in August 2021.

RESULTS

In total, 72 publications with relevance to IL-33 immunobiology and/or clinical lung disease were identified (allergic airway inflammation/allergic asthma n = 26, non-allergic airway inflammation n = 9, COPD n = 8, lung fibrosis n = 10). IL-33 levels were higher in serum, BALF and/or lungs across inflammatory lung diseases. Eight studies described viral infections and IL-33 and 4 studies related to COVID-19. Mechanistic studies (n = 39) including transcript variants and post-translational modifications related to the immunobiology of IL-33. Single nucleotide polymorphism in IL-33 or ST2 were described in 9 studies (asthma n = 5, inflammatory bowel disease n = 1, mycosis fungoides n = 1, ankylosing spondylitis n = 1, coronary artery disease n = 1). Clinicaltrials.gov search yielded 84 studies of which 17 were related to therapeutic or biomarker relevance in lung disease.

CONCLUSION

An integral role of IL-33 in the pathogenesis of allergic and nonallergic airway inflammatory disease is evident with several emerging clinical trials investigating therapeutic approaches. Current data support a critical role of IL-33 in damage signaling, repair and regeneration of lungs.

Immunotherapy: State-of-the-art review of therapies and theratypes

Through its disease-modifying potential, immunotherapy is the keystone to curing allergic diseases. Allergen immunotherapy, applied for more than a century, is currently supported by novel modalities such as mAb-based therapies or small molecules targeting the key nodes of the allergic inflammation network. In this review, a summary of the most significant advances in immunotherapy is presented, addressing not only novel approaches to stratifying patients but also major controlled clinical trials and real-world evidence that strengthen the role of immunotherapy in the treatment of allergies.

An alternative mechanism for skeletal muscle dysfunction in long-term post-viral lung disease

Chronic lung disease is often accompanied by disabling extrapulmonary symptoms, notably skeletal muscle dysfunction and atrophy. Moreover, the severity of respiratory symptoms correlates with decreased muscle mass and in turn lowered physical activity and survival rates. Previous models of muscle atrophy in chronic lung disease often modeled COPD and relied on cigarette smoke exposure and LPS-stimulation, but these conditions independently affect skeletal muscle even without accompanying lung disease. Moreover, there is an emerging and pressing need to understand the extrapulmonary manifestations of long-term post-viral lung disease (PVLD) as found in Covid-19. Here, we examine the development of skeletal muscle dysfunction in the setting of chronic pulmonary disease using a mouse model of PVLD caused by infection due to the natural pathogen Sendai virus. We identify a significant decrease in myofiber size when PVLD is maximal at 49 d after infection. We find no change in the relative types of myofibers, but the greatest decrease in fiber size is localized to fast-twitch type IIB myofibers based on myosin heavy chain immunostaining. Remarkably, all biomarkers of myocyte protein synthesis and degradation (total RNA, ribosomal abundance, and ubiquitin-proteasome expression) were stable throughout the acute infectious illness and chronic post-viral disease process. Together, the results demonstrate a distinct pattern of skeletal muscle dysfunction in a mouse model of long-term PVLD. The findings thereby provide new insight into prolonged limitations in exercise capacity in patients with chronic lung disease after viral infections and perhaps other types of lung injury.

Lung remodeling regions in long-term Covid-19 feature basal epithelial cell reprogramming

Respiratory viruses, including SARS-CoV-2, can trigger chronic lung disease that persists and even progresses after expected clearance of infectious virus. To gain an understanding of this process, we examined a series of consecutive fatal cases of Covid-19 that came to autopsy at 27-51 d after hospital admission. In each patient, we identify a stereotyped bronchiolar-alveolar pattern of lung remodeling with basal epithelial cell hyperplasia and mucinous differentiation. Remodeling regions also feature macrophage infiltration and apoptosis and a marked depletion of alveolar type 1 and 2 epithelial cells. This entire pattern closely resembles findings from an experimental model of post-viral lung disease that requires basal-epithelial stem cell growth, immune activation, and differentiation. The present results thereby provide evidence of possible basal epithelial cell reprogramming in long-term Covid-19 as well and thereby a pathway for explaining and correcting lung dysfunction in this type of disease.

Intermediary Role of Lung Alveolar Type 1 Cells in Epithelial Repair upon Sendai Virus Infection

The lung epithelium forms the first barrier against respiratory pathogens and noxious chemicals; however, little is known about how more than 90% of this barrier, made of AT1 (alveolar type 1) cells, responds to injury. Using the Sendai virus to model natural infection in mice, we find evidence that AT1 cells have an intermediary role by persisting in areas depleted of AT2 cells, upregulating IFN responsive genes, and receding from invading airway cells. Sendai virus infection mobilizes airway cells to form alveolar SOX2⁺ (Sry-box 2⁺) clusters without differentiating into AT1 or AT2 cells. Large AT2 cell-depleted areas remain covered by AT1 cells, which we name "AT2-less regions", and are replaced by SOX2⁺ clusters spreading both basally and luminally. AT2 cell proliferation and differentiation are largely confined to topologically distal regions and form de novo alveolar surface, with limited contribution to in situ repairs of AT2-less regions. Time-course single-cell RNA sequencing profiling and RNAscope validation suggest enhanced immune responses and altered growth signals in AT1 cells. Our comprehensive spatiotemporal and genomewide study highlights the hitherto unappreciated role of AT1 cells in lung injury-repair.

IL-33 biology in cancer: An update and future perspectives

Interleukin-33 (IL-33) is a member of the IL-1 family of cytokines that is constitutively expressed in the nucleus of epithelial, endothelial and fibroblast-like cells. Upon cell stress, damage or necrosis, IL-33 is released into the cytoplasm to exert its prime role as an alarmin by binding to its specific receptor moiety, ST2. IL-33 exhibits pleiotropic function in inflammatory diseases and particularly in cancer. IL-33 may play a dual role as both a pro-tumorigenic and anti-tumorigenic cytokine, dependent on tumor and cellular context, expression levels, bioactivity and the nature of the inflammatory environment. In this review, we discuss the differential contribution of IL-33 to malignant or inflammatory conditions, its multifaceted effects on the tumor microenvironment, while providing possible explanations for the discrepant findings described in the literature. Additionally, we examine the emerging and divergent functions of IL-33 in the nucleus, and aspects of IL-33 biology that are currently under-addressed.

Immune determinants of chronic sequelae after respiratory viral infection

The acute effects of various respiratory viral infections have been well studied, with extensive characterization of the clinical presentation as well as viral pathogenesis and host responses. However, over the course of the recent COVID-19 pandemic, the incidence and prevalence of chronic sequelae after acute viral infections have become increasingly appreciated as a serious health concern. Post-acute sequelae of COVID-19, alternatively described as “long COVID-19,” are characterized by symptoms that persist for longer than 28 days after recovery from acute illness. Although there exists substantial heterogeneity in the nature of the observed sequelae, this phenomenon has also been observed in the context of other respiratory viral infections including influenza virus, respiratory syncytial virus, rhinovirus, severe acute respiratory syndrome coronavirus, and Middle Eastern respiratory syndrome coronavirus. In this Review, we discuss the various sequelae observed following important human respiratory viral pathogens and our current understanding of the immunological mechanisms underlying the failure of restoration of homeostasis in the lung.

Chloride channel accessory 1 gene deficiency causes selective loss of mucus production in a new pig model

Morbidity and mortality of respiratory diseases are linked to airway obstruction by mucus but there are still no specific, safe, and effective drugs to correct this phenotype. The need for better treatment requires a new understanding of the basis for mucus production. In that regard, studies of human airway epithelial cells in primary culture show that a mucin granule constituent known as chloride channel accessory 1 (CLCA1) is required for inducible expression of the inflammatory mucin MUC5AC in response to potent type 2 cytokines. However, it remained uncertain whether CLCLA1 is necessary for mucus production in vivo. Conventional approaches to functional biology using targeted gene knockout were difficult due to the functional redundancy of additional Clca genes in mice not found in humans. We reasoned that CLCA1 function might be better addressed in pigs that maintain the same four-member CLCA gene locus and the corresponding mucosal and submucosal populations of mucous cells found in humans. Here we develop to our knowledge the first CLCA1-gene-deficient (CLCA1-/-) pig and show that these animals exhibit loss of MUC5AC+ mucous cells throughout the airway mucosa of the lung without affecting comparable cells in the tracheal mucosa or MUC5B+ mucous cells in submucosal glands. Similarly, CLCA1-/- pigs exhibit loss of MUC5AC+ mucous cells in the intestinal mucosa without affecting MUC2+ mucous cells. These data establish CLCA1 function for controlling MUC5AC expression as a marker of mucus production and provide a new animal model to study mucus production at respiratory and intestinal sites.

Nasally delivered interferon-λ protects mice against infection by SARS-CoV-2 variants including Omicron

Although vaccines and monoclonal antibody countermeasures have reduced the morbidity and mortality associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, variants with constellations of mutations in the spike gene jeopardize their efficacy. Accordingly, antiviral interventions that are resistant to further virus evolution are needed. The host-derived cytokine interferon lambda (IFN-λ) has been proposed as a possible treatment based on studies in human coronavirus 2019 (COVID-19) patients. Here, we show that IFN-λ protects against SARS-CoV-2 B.1.351 (Beta) and B.1.1.529 (Omicron) variants in three strains of conventional and human ACE2 transgenic mice. Prophylaxis or therapy with nasally delivered IFN-λ2 limits infection of historical or variant SARS-CoV-2 strains in the upper and lower respiratory tracts without causing excessive inflammation. In the lung, IFN-λ is produced preferentially in epithelial cells and acts on radio-resistant cells to protect against SARS-CoV-2 infection. Thus, inhaled IFN-λ may have promise as a treatment for evolving SARS-CoV-2 variants that develop resistance to antibody-based countermeasures.

Clinical, radiological, and pathological findings in patients with persistent lung disease following SARS-CoV-2 infection

Some patients experience pulmonary sequelae after SARS-CoV-2 infection, ranging from self-limited abnormalities to major lung diseases. Morphological analysis of lung tissue may help our understanding of pathogenic mechanisms and help to provide consistent personalised management. The aim of this study was to ascertain morphological and immunomolecular features of lung tissue. Transbronchial lung cryobiopsy was carried out in patients with persistent symptoms and computed tomography suggestive of residual lung disease after recovery from SARS-CoV-2 infection. 164 patients were referred for suspected pulmonary sequelae after COVID-19; 10 patients with >5% parenchymal lung disease underwent lung biopsy. The histological pattern of lung disease was not homogeneous and three different case clusters could be identified, which was mirrored by their clinical and radiological features. Cluster 1 (“chronic fibrosing”) was characterised by post-infection progression of pre-existing interstitial pneumonias. Cluster 2 (“acute/subacute injury”) was characterised by different types and grades of lung injury, ranging from organising pneumonia and fibrosing nonspecific interstitial pneumonia to diffuse alveolar damage. Cluster 3 (“vascular changes”) was characterised by diffuse vascular increase, dilatation and distortion (capillaries and venules) within otherwise normal parenchyma. Clusters 2 and 3 had immunophenotypical changes similar to those observed in early/mild COVID-19 pneumonias (abnormal expression of STAT3 in hyperplastic pneumocytes and PD-L1, IDO and STAT3 in endothelial cells). This is the first study correlating histological/immunohistochemical patterns with clinical and radiological pictures of patients with post-COVID lung disease. Different phenotypes with potentially different underlying pathogenic mechanisms have been identified.

Post-COVID lung disease is not a single entity, but includes different subtypes, each of them potentially requiring separate and different managementhttps://bit.ly/3BJDeUF

Nuclear IL-33 as a growth and survival agent within basal cells

IL-33 is a well-studied cytokine that resides normally within nuclei but can be released by cell damage or stress to then signal via a single receptor widely expressed on immune cells to promote host resistance and type 2 allergic immunity. In this issue of the JCI, Wu et al. used a well-established model of mouse Sendai viral infection to show that IL-33 was induced in distal lung airway epithelium, specifically in cell-cycling basal cells. IL-33 induced cell-cycling basal cells to expand and migrate into the alveolar compartment, presumably to restore barrier function. However, restoring barrier function with airway-derived cells may also result in persistent alveolar metaplasia. Surprisingly, nuclear IL-33 in this system acted cell autonomously, independently of release and conventional ST2 (IL1RL1) receptor signaling. The findings uncover a signaling role for nuclear IL-33 in viral activation of mouse basal cells and add to the well-known "alarmin" function of IL-33.