Prior Influenza Infection Mitigates SARS-CoV-2 Disease in Syrian Hamsters.

Seasonal infection rates of individual viruses are influenced by synergistic or inhibitory interactions between coincident viruses. Endemic patterns of SARS-CoV-2 and influenza infection overlap seasonally in the Northern hemisphere and may be similarly influenced. We explored the immunopathologic basis of SARS-CoV-2 and influenza A (H1N1pdm09) interactions in Syrian hamsters. H1N1 given 48 h prior to SARS-CoV-2 profoundly mitigated weight loss and lung pathology compared to SARS-CoV-2 infection alone. This was accompanied by the normalization of granulocyte dynamics and accelerated antigen-presenting populations in bronchoalveolar lavage and blood. Using nasal transcriptomics, we identified a rapid upregulation of innate and antiviral pathways induced by H1N1 by the time of SARS-CoV-2 inoculation in 48 h dual-infected animals. The animals that were infected with both viruses also showed a notable and temporary downregulation of mitochondrial and viral replication pathways. Quantitative RT-PCR confirmed a decrease in the SARS-CoV-2 viral load and lower cytokine levels in the lungs of animals infected with both viruses throughout the course of the disease. Our data confirm that H1N1 infection induces rapid and transient gene expression that is associated with the mitigation of SARS-CoV-2 pulmonary disease. These protective responses are likely to begin in the upper respiratory tract shortly after infection. On a population level, interaction between these two viruses may influence their relative seasonal infection rates.

Recruited monocytes/macrophages drive pulmonary neutrophilic inflammation and irreversible lung tissue remodeling in cystic fibrosis.

Persistent neutrophil-dominated lung inflammation contributes to lung damage in cystic fibrosis (CF). However, the mechanisms that drive persistent lung neutrophilia and tissue deterioration in CF are not well characterized. Starting from the observation that, in patients with CF, c-c motif chemokine receptor 2 (CCR2)+ monocytes/macrophages are abundant in the lungs, we investigate the interplay between monocytes/macrophages and neutrophils in perpetuating lung tissue damage in CF. Here we show that CCR2+ monocytes in murine CF lungs drive pathogenic transforming growth factor ß (TGF-ß) signaling and sustain a pro-inflammatory environment by facilitating neutrophil recruitment. Targeting CCR2 to lower the numbers of monocytes in CF lungs ameliorates neutrophil inflammation and pathogenic TGF-ß signaling and prevents lung tissue damage. This study identifies CCR2+ monocytes as a neglected contributor to the pathogenesis of CF lung disease and as a therapeutic target for patients with CF, for whom lung hyperinflammation and tissue damage remain an issue despite recent advances in CF transmembrane conductance regulator (CFTR)-specific therapeutic agents.

Update on Innate and Adaptive Immunity in Cystic Fibrosis.

Cystic fibrosis (CF) pathophysiology is hallmarked by excessive inflammation and the inability to resolve lung infections, contributing to morbidity and eventually mortality. Paradoxically, despite a robust inflammatory response, CF lungs fail to clear bacteria and are susceptible to chronic infections. Impaired mucociliary transport plays a critical role in chronic infection but the immune mechanisms contributing to the adaptation of bacteria to the lung microenvironment is not clear. CFTR modulator therapy has advanced CF life expectancy opening up the need to understand changes in immunity as CF patients age. Here, we have summarized the current understanding of immune dysregulation in CF.

Human neutrophil development and functionality are enabled in a humanized mouse model.

Mice with a functional human immune system serve as an invaluable tool to study the development and function of the human immune system in vivo. A major technological limitation of all current humanized mouse models is the lack of mature and functional human neutrophils in circulation and tissues. To overcome this, we generated a humanized mouse model named MISTRGGR, in which the mouse granulocyte colony-stimulating factor (G-CSF) was replaced with human G-CSF and the mouse G-CSF receptor gene was deleted in existing MISTRG mice. By targeting the G-CSF cytokine-receptor axis, we dramatically improved the reconstitution of mature circulating and tissue-infiltrating human neutrophils in MISTRGGR mice. Moreover, these functional human neutrophils in MISTRGGR are recruited upon inflammatory and infectious challenges and help reduce bacterial burden. MISTRGGR mice represent a unique mouse model that finally permits the study of human neutrophils in health and disease.

Emerging Concepts in Defective Macrophage Phagocytosis in Cystic Fibrosis.

Cystic fibrosis (CF) is caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Chronic inflammation and decline in lung function are major reasons for morbidity in CF. Mutant CFTR expressed in phagocytic cells such as macrophages contributes to persistent infection, inflammation, and lung disease in CF. Macrophages play a central role in innate immunity by eliminating pathogenic microbes by a process called phagocytosis. Phagocytosis is required for tissue homeostasis, balancing inflammation, and crosstalk with the adaptive immune system for antigen presentation. This review focused on (1) current understandings of the signaling underlying phagocytic mechanisms; (2) existing evidence for phagocytic dysregulation in CF; and (3) the emerging role of CFTR modulators in influencing CF phagocytic function. Alterations in CF macrophages from receptor initiation to phagosome formation are linked to disease progression in CF. A deeper understanding of macrophages in the context of CFTR and phagocytosis proteins at each step of phagosome formation might contribute to the new therapeutic development of dysregulated innate immunity in CF. Therefore, the review also indicates future areas of research in the context of CFTR and macrophages.

Recruitment of monocytes primed to express heme oxygenase-1 ameliorates pathological lung inflammation in cystic fibrosis.

Overwhelming neutrophilic inflammation is a leading cause of lung damage in many pulmonary diseases, including cystic fibrosis (CF). The heme oxygenase-1 (HO-1)/carbon monoxide (CO) pathway mediates the resolution of inflammation and is defective in CF-affected macrophages (MΦs). Here, we provide evidence that systemic administration of PP-007, a CO releasing/O2 transfer agent, induces the expression of HO-1 in a myeloid differentiation factor 88 (MyD88) and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)-dependent manner. It also rescues the reduced HO-1 levels in CF-affected cells induced in response to lipopolysaccharides (LPS) or Pseudomonas aeruginosa (PA). Treatment of CF and muco-obstructive lung disease mouse models with a single clinically relevant dose of PP-007 leads to effective resolution of lung neutrophilia and to decreased levels of proinflammatory cytokines in response to LPS. Using HO-1 conditional knockout mice, we show that the beneficial effect of PP-007 is due to the priming of circulating monocytes trafficking to the lungs in response to infection to express high levels of HO-1. Finally, we show that PP-007 does not compromise the clearance of PA in the setting of chronic airway infection. Overall, we reveal the mechanism of action of PP-007 responsible for the immunomodulatory function observed in clinical trials for a wide range of diseases and demonstrate the potential use of PP-007 in controlling neutrophilic pulmonary inflammation by promoting the expression of HO-1 in monocytes/macrophages.

Combined liver-cytokine humanization comes to the rescue of circulating human red blood cells.

In vivo models that recapitulate human erythropoiesis with persistence of circulating red blood cells (RBCs) have remained elusive. We report an immunodeficient murine model in which combined human liver and cytokine humanization confer enhanced human erythropoiesis and RBC survival in the circulation. We deleted the fumarylacetoacetate hydrolase (Fah) gene in MISTRG mice expressing several human cytokines in place of their murine counterparts. Liver humanization by intrasplenic injection of human hepatocytes (huHep) eliminated murine complement C3 and reduced murine Kupffer cell density. Engraftment of human sickle cell disease (SCD)-derived hematopoietic stem cells in huHepMISTRGFah -/- mice resulted in vaso-occlusion that replicated acute SCD pathology. Combined liver-cytokine-humanized mice will facilitate the study of diseases afflicting RBCs, including bone marrow failure, hemoglobinopathies, and malaria, and also preclinical testing of therapies.

Targeting the Heme Oxygenase 1/Carbon Monoxide Pathway to Resolve Lung Hyper-Inflammation and Restore a Regulated Immune Response in Cystic Fibrosis.

In individuals with cystic fibrosis (CF), lung hyper-inflammation starts early in life and is perpetuated by mucus obstruction and persistent bacterial infections. The continuous tissue damage and scarring caused by non-resolving inflammation leads to bronchiectasis and, ultimately, respiratory failure. Macrophages (MΦs) are key regulators of immune response and host defense. We and others have shown that, in CF, MΦs are hyper-inflammatory and exhibit reduced bactericidal activity. Thus, MΦs contribute to the inability of CF lung tissues to control the inflammatory response or restore tissue homeostasis. The non-resolving hyper-inflammation in CF lungs is attributed to an impairment of several signaling pathways associated with resolution of the inflammatory response, including the heme oxygenase-1/carbon monoxide (HO-1/CO) pathway. HO-1 is an enzyme that degrades heme groups, leading to the production of potent antioxidant, anti-inflammatory, and bactericidal mediators, such as biliverdin, bilirubin, and CO. This pathway is fundamental to re-establishing cellular homeostasis in response to various insults, such as oxidative stress and infection. Monocytes/MΦs rely on abundant induction of the HO-1/CO pathway for a controlled immune response and for potent bactericidal activity. Here, we discuss studies showing that blunted HO-1 activation in CF-affected cells contributes to hyper-inflammation and defective host defense against bacteria. We dissect potential cellular mechanisms that may lead to decreased HO-1 induction in CF cells. We review literature suggesting that induction of HO-1 may be beneficial for the treatment of CF lung disease. Finally, we discuss recent studies highlighting how endogenous HO-1 can be induced by administration of controlled doses of CO to reduce lung hyper-inflammation, oxidative stress, bacterial infection, and dysfunctional ion transport, which are all hallmarks of CF lung disease.

Single-Cell Transcriptional Archetypes of Airway Inflammation in Cystic Fibrosis.

Rationale: Cystic fibrosis (CF) is a life-shortening, multisystem hereditary disease caused by abnormal chloride transport. CF lung disease is driven by innate immune dysfunction and exaggerated inflammatory responses that contribute to tissue injury. To define the transcriptional profile of this airway immune dysfunction, we performed the first single-cell transcriptome characterization of CF sputum.Objectives: To define the transcriptional profile of sputum cells and its implication in the pathogenesis of immune function and the development of CF lung disease.Methods: We performed single-cell RNA sequencing of sputum cells from nine subjects with CF and five healthy control subjects. We applied novel computational approaches to define expression-based cell function and maturity profiles, herein called transcriptional archetypes.Measurements and Main Results: The airway immune cell repertoire shifted from alveolar macrophages in healthy control subjects to a predominance of recruited monocytes and neutrophils in CF. Recruited lung mononuclear phagocytes were abundant in CF and were separated into the following three archetypes: activated monocytes, monocyte-derived macrophages, and heat shock-activated monocytes. Neutrophils were the most prevalent in CF, with a dominant immature proinflammatory archetype. Although CF monocytes exhibited proinflammatory features, both monocytes and neutrophils showed transcriptional evidence of abnormal phagocytic and cell-survival programs.Conclusions: Our findings offer an opportunity to understand subject-specific immune dysfunction and its contribution to divergent clinical courses in CF. As we progress toward personalized applications of therapeutic and genomic developments, we hope this inflammation-profiling approach will enable further discoveries that change the natural history of CF lung disease.

A highly efficient and faithful MDS patient-derived xenotransplantation model for pre-clinical studies.

Comprehensive preclinical studies of Myelodysplastic Syndromes (MDS) have been elusive due to limited ability of MDS stem cells to engraft current immunodeficient murine hosts. Here we report a MDS patient-derived xenotransplantation model in cytokine-humanized immunodeficient "MISTRG" mice that provides efficient and faithful disease representation across all MDS subtypes. MISTRG MDS patient-derived xenografts (PDX) reproduce patients' dysplastic morphology with multi-lineage representation, including erythro- and megakaryopoiesis. MISTRG MDS-PDX replicate the original sample's genetic complexity and can be propagated via serial transplantation. MISTRG MDS-PDX demonstrate the cytotoxic and differentiation potential of targeted therapeutics providing superior readouts of drug mechanism of action and therapeutic efficacy. Physiologic humanization of the hematopoietic stem cell niche proves critical to MDS stem cell propagation and function in vivo. The MISTRG MDS-PDX model opens novel avenues of research and long-awaited opportunities in MDS research.

Surfactant protein C dampens inflammation by decreasing JAK/STAT activation during lung repair.

Surfactant protein C (SPC), a key component of pulmonary surfactant, also plays a role in regulating inflammation. SPC deficiency in patients and mouse models is associated with increased inflammation and delayed repair, but the key drivers of SPC-regulated inflammation in response to injury are largely unknown. This study focuses on a new mechanism of SPC as an anti-inflammatory molecule using SPC-TK/SPC-KO (surfactant protein C-thymidine kinase/surfactant protein C knockout) mice, which represent a novel sterile injury model that mimics clinical acute respiratory distress syndrome (ARDS). SPC-TK mice express the inducible suicide gene thymidine kinase from by the SPC promoter, which targets alveolar type 2 (AT2) cells for depletion in response to ganciclovir (GCV). We compared GCV-induced injury and repair in SPC-TK mice that have normal endogenous SPC expression with SPC-TK/SPC-KO mice lacking SPC expression. In contrast to SPC-TK mice, SPC-TK/SPC-KO mice treated with GCV exhibited more severe inflammation, resulting in over 90% mortality; there was only 8% mortality of SPC-TK animals. SPC-TK/SPC-KO mice had highly elevated inflammatory cytokines and granulocyte infiltration in the bronchoalveolar lavage (BAL) fluid. Consistent with a proinflammatory phenotype, immunofluorescence revealed increased phosphorylated signal transduction and activation of transcription 3 (pSTAT3), suggesting enhanced Janus kinase (JAK)/STAT activation in inflammatory and AT2 cells of SPC-TK/SPC-KO mice. The level of suppressor of cytokine signaling 3, an anti-inflammatory mediator that decreases pSTAT3 signaling, was significantly decreased in the BAL fluid of SPC-TK/SPC-KO mice. Hyperactivation of pSTAT3 and inflammation were rescued by AZD1480, a JAK1/2 inhibitor. Our findings showing a novel role for SPC in regulating inflammation via JAK/STAT may have clinical applications.

Ezrin links CFTR to TLR4 signaling to orchestrate anti-bacterial immune response in macrophages.

Macrophages (MΦs) with mutations in cystic fibrosis transmembrane conductance regulator (CFTR) have blunted induction of PI3K/AKT signaling in response to TLR4 activation, leading to hyperinflammation, a hallmark of cystic fibrosis (CF) disease. Here, we show that Ezrin links CFTR and TLR4 signaling, and is necessary for PI3K/AKT signaling induction in response to MΦ activation. Because PI3K/AKT signaling is critical for immune regulation, Ezrin-deficient MΦs are hyperinflammatory and have impaired Pseudomonas aeruginosa phagocytosis, phenocopying CF MΦs. Importantly, we show that activated CF MΦs have reduced protein levels and altered localization of the remaining Ezrin to filopodia that form during activation. In summary, we have described a direct link from CFTR to Ezrin to PI3K/AKT signaling that is disrupted in CF, and thus promotes hyper-inflammation and weakens phagocytosis.

Cellular Innate Immunity: An Old Game with New Players.

Innate immunity is a rapidly evolving field with novel cell types and molecular pathways being discovered and paradigms changing continuously. Innate and adaptive immune responses are traditionally viewed as separate from each other, but emerging evidence suggests that they overlap and mutually interact. Recently discovered cell types, particularly innate lymphoid cells and myeloid-derived suppressor cells, are gaining increasing attention. Here, we summarize and highlight current concepts in the field, focusing on innate immune cells as well as the inflammasome and DNA sensing which appear to be critical for the activation and orchestration of innate immunity, and may provide novel therapeutic opportunities for treating autoimmune, autoinflammatory, and infectious diseases.

Cystic Fibrosis Lung Immunity: The Role of the Macrophage.

Cystic fibrosis (CF) pathophysiology is hallmarked by excessive inflammation and the inability to efficiently resolve lung infections, contributing to major morbidity and eventually the mortality of patients with this disease. Macrophages (MΦs) are major players in lung homeostasis through their diverse contributions to both the innate and adaptive immune networks. The setting of MΦ function and activity in CF is multifaceted, encompassing the response to the unique environmental cues in the CF lung as well as the intrinsic changes resulting from CFTR dysfunction. The complexity is further enhanced with the identification of modifier genes, which modulate the CFTR contribution to disease, resulting in epigenetic and transcriptional shifts in MΦ phenotype. This review focuses on the contribution of MΦ to lung homeostasis, providing an overview of the diverse literature and various perspectives on the role of these immune guardians in CF.

Increased susceptibility of Cftr-/- mice to LPS-induced lung remodeling.

Cystic fibrosis (CF) is caused by homozygous mutations of the CF transmembrane conductance regulator (CFTR) Cl(-) channel, which result in chronic pulmonary infection and inflammation, the major cause of morbidity and mortality. Although these processes are clearly related to each other, each is likely to contribute to the pathology differently. Understanding the contribution of each of these processes to the overall pathology has been difficult, because they are usually so intimately connected. Various CF mouse models have demonstrated abnormal immune responses compared with wild-type (WT) littermates when challenged with live bacteria or bacterial products acutely. However, these studies have not investigated the consequences of persistent inflammation on lung tissue in CF mice, which may better model the lung pathology in patients. We characterized the lung pathology and immune response of Cftr(-/-) (CF) and Cftr(+/+) (WT) mice to chronic administration of Pseudomonas aeruginosa lipopolysaccharide (LPS). We show that, after long-term repeated LPS exposure, CF mice develop an abnormal and persistent immune response, which is associated with more robust structural changes in the lung than those observed in WT mice. Although CF mice and their WT littermates develop lung pathology after chronic exposure to LPS, the inflammation and damage resolve in WT mice. However, CF mice do not recover efficiently, and, as a consequence of their chronic inflammation, CF mice are more susceptible to morphological changes and lung remodeling. This study shows that chronic inflammation alone contributes significantly to aspects of CF lung pathology.

Innate and Adaptive Immunity in Cystic Fibrosis.

Cystic fibrosis (CF) lung disease is characterized by persistent and unresolved inflammation, with elevated proinflammatory and decreased anti-inflammatory cytokines, and greater numbers of immune cells. Hyperinflammation is recognized as a leading cause of lung tissue destruction in CF. Hyper-inflammation is not solely observed in the lungs of CF patients, since it may contribute to destruction of exocrine pancreas and, likely, to defects in gastrointestinal tract tissue integrity. Paradoxically, despite the robust inflammatory response, and elevated number of immune cells (such as neutrophils and macrophages), CF lungs fail to clear bacteria and are more susceptible to infections. Here, we have summarized the current understanding of immune dysregulation in CF, which may drive hyperinflammation and impaired host defense.

Pharmacological modulation of the AKT/microRNA-199a-5p/CAV1 pathway ameliorates cystic fibrosis lung hyper-inflammation.

In cystic fibrosis (CF) patients, hyper-inflammation is a key factor in lung destruction and disease morbidity. We have previously demonstrated that macrophages drive the lung hyper-inflammatory response to LPS in CF mice, because of reduced levels of the scaffold protein CAV1 with subsequent uncontrolled TLR4 signalling. Here we show that reduced CAV1 and, consequently, increased TLR4 signalling, in human and murine CF macrophages and murine CF lungs, is caused by high microRNA-199a-5p levels, which are PI3K/AKT-dependent. Downregulation of microRNA-199a-5p or increased AKT signalling restores CAV1 expression and reduces hyper-inflammation in CF macrophages. Importantly, the FDA-approved drug celecoxib re-establishes the AKT/miR-199a-5p/CAV1 axis in CF macrophages, and ameliorates lung hyper-inflammation in Cftr-deficient mice. Thus, we identify the AKT/miR-199a-5p/CAV1 pathway as a regulator of innate immunity, which is dysfunctional in CF macrophages contributing to lung hyper-inflammation. In addition, we found that this pathway can be targeted by celecoxib.

SRF is required for neutrophil migration in response to inflammation.

Serum response factor (SRF) is a ubiquitously expressed transcription factor and master regulator of the actin cytoskeleton. We have previously shown that SRF is essential for megakaryocyte maturation and platelet formation and function. Here we elucidate the role of SRF in neutrophils, the primary defense against infections. To study the effect of SRF loss in neutrophils, we crossed Srf(fl/fl) mice with select Cre-expressing mice and studied neutrophil function in vitro and in vivo. Despite normal neutrophil numbers, neutrophil function is severely impaired in Srf knockout (KO) neutrophils. Srf KO neutrophils fail to polymerize globular actin to filamentous actin in response to N-formyl-methionine-leucine-phenylalanine, resulting in significantly disrupted cytoskeletal remodeling. Srf KO neutrophils fail to migrate to sites of inflammation in vivo and along chemokine gradients in vitro. Polarization in response to cytokine stimuli is absent and Srf KO neutrophils show markedly reduced adhesion. Integrins play an essential role in cellular adhesion, and although integrin expression levels are maintained with loss of SRF, integrin activation and trafficking are disrupted. Migration and cellular adhesion are essential for normal cell function, but also for malignant processes such as metastasis, underscoring an essential function for SRF and its pathway in health and disease.

Very small embryonic-like stem cells from the murine bone marrow differentiate into epithelial cells of the lung.

The view that adult stem cells are lineage restricted has been challenged by numerous reports of bone marrow (BM)-derived cells giving rise to epithelial cells. Previously, we demonstrated that nonhematopoietic BM cells are the primary source of BM-derived lung epithelial cells. Here, we tested the hypothesis that very small embryonic like cells (VSELs) are responsible for this engraftment. We directly compared the level of BM-derived epithelial cells after transplantation of VSELs, hematopoietic stem/progenitor cells, or other nonhematopoietic cells. VSELs clearly had the highest rate of forming epithelial cells in the lung. By transplanting VSELs from donor mice expressing H2B-GFP under a type 2 pneumocyte-specific promoter, we demonstrate that this engraftment occurs by differentiation and not fusion. This is the first report of VSELs differentiating into an endodermal lineage in vivo, thereby potentially crossing germ layer lineages. Our data suggest that Oct4+ VSELs in the adult BM exhibit broad differentiation potential.