Crystal ribcage: a platform for probing real-time lung function at cellular resolution.

Understanding the dynamic pathogenesis and treatment response in pulmonary diseases requires probing the lung at cellular resolution in real time. Despite advances in intravital imaging, optical imaging of the lung during active respiration and circulation has remained challenging. Here, we introduce the crystal ribcage: a transparent ribcage that allows multiscale optical imaging of the functioning lung from whole-organ to single-cell level. It enables the modulation of lung biophysics and immunity through intravascular, intrapulmonary, intraparenchymal and optogenetic interventions, and it preserves the three-dimensional architecture, air-liquid interface, cellular diversity and respiratory-circulatory functions of the lung. Utilizing these capabilities on murine models of pulmonary pathologies we probed remodeling of respiratory-circulatory functions at the single-alveolus and capillary levels during disease progression. The crystal ribcage and its broad applications presented here will facilitate further studies of nearly any pulmonary disease as well as lead to the identification of new targets for treatment strategies.

Integrative Physiology of Pneumonia.

Pneumonia is a type of acute lower respiratory infection that is common and severe. The outcome of lower respiratory infection is determined by the degrees to which immunity is protective and inflammation is damaging. Intercellular and interorgan signaling networks coordinate these actions to fight infection and protect the tissue. Cells residing in the lung initiate and steer these responses, with additional immunity effectors recruited from the bloodstream. Responses of extrapulmonary tissues, including the liver, bone marrow, and others, are essential to resistance and resilience. Responses in the lung and extrapulmonary organs can also be counterproductive and drive acute and chronic comorbidities after respiratory infection. This review discusses cell-specific and organ-specific roles in the integrated physiological response to acute lung infection, and the mechanisms by which intercellular and interorgan signaling contribute to host defense and healthy respiratory physiology or to acute lung injury, chronic pulmonary disease, and adverse extrapulmonary sequelae. Pneumonia should no longer be perceived as simply an acute infection of the lung. Pneumonia susceptibility reflects ongoing and poorly understood chronic conditions, and pneumonia results in diverse and often persistent deleterious consequences for multiple physiological systems.

Diversity of B Cell Populations and Ig Repertoire in Human Lungs.

The human lung carries a unique microbiome adapted to the air-filled, mucous-lined environment, the presence of which requires an immune system capable of recognizing harmful populations while preventing reactions toward commensals. B cells in the lung play a key role in pulmonary immunity, generating Ag-specific Abs, as well as cytokine secretion for immune activation and regulation. In this study, we compared B cell subsets in human lungs versus circulating cells by analyzing patient-paired lung and blood samples. We found a significantly smaller pool of CD19+, CD20+ B cells in the lung relative to the blood. CD27+, IgD-, class-switched memory B cells (Bmems) composed a larger proportion of the pool of pulmonary B cells. The residency marker CD69 was also significantly higher in the lung. We also sequenced the Ig V region genes (IgVRGs) of class-switched Bmems that do, or do not, express CD69. We observed the IgVRGs of pulmonary Bmems to be as heavily mutated from the unmutated common ancestor as those in circulation. Furthermore, we found progenies within a quasi-clone can gain or lose CD69 expression, regardless of whether the parent clone expressed the residency marker. Overall, our results show that despite its vascularized nature, human lungs carry a unique proportion of B cell subsets. The IgVRGs of pulmonary Bmems are as diverse as those in blood, and progenies of Bmems retain the ability to gain or lose residency.

Liver-Dependent Lung Remodeling during Systemic Inflammation Shapes Responses to Secondary Infection.

Systemic duress, such as that elicited by sepsis, burns, or trauma, predisposes patients to secondary pneumonia, demanding better understanding of host pathways influencing this deleterious connection. These pre-existing circumstances are capable of triggering the hepatic acute-phase response (APR), which we previously demonstrated is essential for limiting susceptibility to secondary lung infections. To identify potential mechanisms underlying protection afforded by the lung-liver axis, our studies aimed to evaluate liver-dependent lung reprogramming when a systemic inflammatory challenge precedes pneumonia. Wild-type mice and APR-deficient littermate mice with hepatocyte-specific deletion of STAT3 (hepSTAT3-/-), a transcription factor necessary for full APR initiation, were challenged i.p. with LPS to induce endotoxemia. After 18 h, pneumonia was induced by intratracheal Escherichia coli instillation. Endotoxemia elicited significant transcriptional alterations in the lungs of wild-type and hepSTAT3-/- mice, with nearly 2000 differentially expressed genes between genotypes. The gene signatures revealed exaggerated immune activity in the lungs of hepSTAT3-/- mice, which were compromised in their capacity to launch additional cytokine responses to secondary infection. Proteomics revealed substantial liver-dependent modifications in the airspaces of pneumonic mice, implicating a network of dispatched liver-derived mediators influencing lung homeostasis. These results indicate that after systemic inflammation, liver acute-phase changes dramatically remodel the lungs, resulting in a modified landscape for any stimuli encountered thereafter. Based on the established vulnerability of hepSTAT3-/- mice to secondary lung infections, we believe that intact liver function is critical for maintaining the immunological responsiveness of the lungs.

Update on the Features and Measurements of Experimental Acute Lung Injury in Animals: An Official American Thoracic Society Workshop Report.

Advancements in methods, technology, and our understanding of the pathobiology of lung injury have created the need to update the definition of experimental acute lung injury (ALI). We queried 50 participants with expertise in ALI and acute respiratory distress syndrome using a Delphi method composed of a series of electronic surveys and a virtual workshop. We propose that ALI presents as a "multidimensional entity" characterized by four "domains" that reflect the key pathophysiologic features and underlying biology of human acute respiratory distress syndrome. These domains are 1) histological evidence of tissue injury, 2) alteration of the alveolar-capillary barrier, 3) presence of an inflammatory response, and 4) physiologic dysfunction. For each domain, we present "relevant measurements," defined as those proposed by at least 30% of respondents. We propose that experimental ALI encompasses a continuum of models ranging from those focusing on gaining specific mechanistic insights to those primarily concerned with preclinical testing of novel therapeutics or interventions. We suggest that mechanistic studies may justifiably focus on a single domain of lung injury, but models must document alterations of at least three of the four domains to qualify as "experimental ALI." Finally, we propose that a time criterion defining "acute" in ALI remains relevant, but the actual time may vary based on the specific model and the aspect of injury being modeled. The continuum concept of ALI increases the flexibility and applicability of the definition to multiple models while increasing the likelihood of translating preclinical findings to critically ill patients.

Neutrophil Extracellular Traps as an Exacerbating Factor in Bacterial Pneumonia.

Neutrophils are capable of extruding neutrophil extracellular traps (NETs), a network of granule proteins and chromatin material, upon activation. NETs provide defense against extracellular microbes, but histones in NETs can also induce cytotoxicity and activate inflammatory responses. The relevance of NETs to bacterial pneumonias is beginning to be defined. In the present study, we found that the extracellular concentration of citrullinated histone H3, a component of NETs, was elevated in bronchoalveolar lavage fluid recovered from mice with diverse bacterial pneumonias and correlated with neutrophil infiltration and cell death in the lungs as well as levels of H4. Because the histone H4 component of NETs is sufficient to stimulate inflammation, we tested its effects in the air spaces of the lungs. Recombinant histone H4 in the noninflamed lung produced only modest effects, but in the setting of neutrophilic inflammation, H4 substantially increased pulmonary neutrophils, NETs, necrosis, and edema. However, blockade of histone H4 with a monoclonal antibody during pneumonia did not significantly alter measures of lung damage. Taken together, these results implicate NETs and extracellular histone H4 in exacerbating the lung injury resulting from bacterial pneumonia.

Epithelial LIF signaling limits apoptosis and lung injury during bacterial pneumonia.

During bacterial pneumonia, alveolar epithelial cells are critical for maintaining gas exchange and providing antimicrobial as well as pro-immune properties. We previously demonstrated that leukemia inhibitory factor (LIF), an IL-6 family cytokine, is produced by type II alveolar epithelial cells (ATII) and is critical for tissue protection during bacterial pneumonia. However, the target cells and mechanisms of LIF-mediated protection remain unknown. Here, we demonstrate that antibody-induced LIF blockade remodels the lung epithelial transcriptome in association with increased apoptosis. Based on these data, we performed pneumonia studies using a novel mouse model in which LIFR (the unique receptor for LIF) is absent in lung epithelium. Although LIFR is expressed on the surface of epithelial cells, its absence only minimally contributed to tissue protection during pneumonia. Single-cell RNA-sequencing (scRNAseq) was conducted to identify adult murine lung cell types most prominently expressing Lifr, revealing endothelial cells, mesenchymal cells, and ATIIs as major sources of Lifr. Sequencing data indicated that ATII cells were significantly impacted by pneumonia, with additional differences observed in response to LIF neutralization, including but not limited to gene programs related to cell death, injury, and inflammation. Overall, our data suggest that LIF signaling on epithelial cells alters responses in this cell type during pneumonia. However, our results also suggest separate and perhaps more prominent roles of LIFR in other cell types, such as endothelial cells or mesenchymal cells, which provide grounds for future investigation.

CPHEN-011: Comprehensive phenotyping of murine lung resident lymphocytes after recovery from pneumococcal pneumonia.

Recovery from pneumococcal (Spn) pneumonia induces development of tissue resident memory CD4+ TRM cells, BRM cells, and antibody secreting plasma cells in experienced lungs. These tissue resident lymphocytes confer protection against subsequent lethal challenge by serotype mismatched Spn (termed as heterotypic immunity). While traditional flow cytometry and gating strategies support premeditated identification of cells using a limited set of markers, discovery of novel tissue resident lymphocytes necessitates stable platforms that can handle larger sets of phenotypic markers and lends itself to unbiased clustering approaches. In this report, we leverage the power of full spectrum flow cytometry (FSFC) to develop a comprehensive panel of phenotypic markers that allows identification of multiple subsets of tissue resident lymphocytes in Spn-experienced murine lungs. Using Phenograph algorithm on this multidimensional data, we identify unforeseen heterogeneity in lung resident adaptive immune landscape which includes unexpected subsets of TRM and BRM cells. Further, using conventional gating strategy informed by our unsupervised clustering data, we confirm their presence exquisitely in Spn-experienced lungs as potentially relevant to heterotypic immunity and define CD73 as a highly expressed marker on TRM cells. Thus, our study emphasizes the utility of FSFC for confirmatory and discovery studies relating to tissue resident adaptive immunity.

Neutrophil-Derived Oncostatin M Triggers Diverse Signaling Pathways during Pneumonia.

Pneumonia is a major public health concern, causing significant morbidity and mortality annually despite the broad use of antimicrobial agents. Underlying many of the severe sequelae of acute lung infections is dysfunction of the immune response, which remains incompletely understood yet is an attractive target of adjunct therapy in pneumonia. Here, we investigate the role of oncostatin M (OSM), a pleiotropic cytokine of the interleukin-6 (IL-6) family, and how its signaling modulates multiple innate immune pathways during pneumonia. Previously, we showed that OSM is necessary for neutrophil recruitment to the lungs during pneumonia by stimulating STAT3-driven CXCL5 expression. In this study, transcriptional profiling of whole-lung pneumonia with OSM neutralization revealed 241 differentially expressed genes following only 6 h of infection. Many downregulated genes are associated with STAT1, STAT3, and interferon signaling, suggesting these pathways are induced by OSM early in pneumonia. Interestingly, STAT1 and STAT3 activation was subsequently upregulated with OSM neutralization by 24 h, suggesting that OSM interruption dysregulates these central signaling pathways. When we investigated the source of OSM in pneumonia, neutrophils and, to a lesser extent, macrophages appear to be primary sources, suggesting a positive feedback loop of OSM production by neutrophils. From these studies, we conclude that OSM produced by recruited neutrophils tunes early innate immune signaling pathways, improving pneumonia outcomes.

Identifying Clinical Research Priorities in Adult Pulmonary and Critical Care. NHLBI Working Group Report.

Preventing, treating, and promoting recovery from critical illness due to pulmonary disease are foundational goals of the critical care community and the NHLBI. Decades of clinical research in acute respiratory distress syndrome, acute respiratory failure, pneumonia, and sepsis have yielded improvements in supportive care, which have translated into improved patient outcomes. Novel therapeutics have largely failed to translate from promising preclinical findings into improved patient outcomes in late-phase clinical trials. Recent advances in personalized medicine, "big data," causal inference using observational data, novel clinical trial designs, preclinical disease modeling, and understanding of recovery from acute illness promise to transform the methods of pulmonary and critical care clinical research. To assess the current state of, research priorities for, and future directions in adult pulmonary and critical care research, the NHLBI assembled a multidisciplinary working group of investigators. This working group identified recommendations for future research, including 1) focusing on understanding the clinical, physiological, and biological underpinnings of heterogeneity in syndromes, diseases, and treatment response with the goal of developing targeted, personalized interventions; 2) optimizing preclinical models by incorporating comorbidities, cointerventions, and organ support; 3) developing and applying novel clinical trial designs; and 4) advancing mechanistic understanding of injury and recovery to develop and test interventions targeted at achieving long-term improvements in the lives of patients and families. Specific areas of research are highlighted as especially promising for making advances in pneumonia, acute hypoxemic respiratory failure, and acute respiratory distress syndrome.

NF-κB RelA Is Required for Hepatoprotection during Pneumonia and Sepsis.

Pneumonia and sepsis are distinct but integrally linked public health concerns. The hepatic acute-phase response (APR), which is largely dependent on transcription factors NF-κB RelA and STAT3, is a hallmark of these pathologies and other injurious conditions. Inactivation of the APR can promote liver injury, a frequently observed organ dysfunction during sepsis. However, whether or how the acute-phase changes promote liver tissue resilience during infections is unclear. To determine the hepatoprotective role of the hepatic APR, we utilized mice bearing hepatocyte-specific deletions of either RelA or STAT3. Mice were challenged intratracheally (i.t.), intravenously (i.v.), or intraperitoneally (i.p.) with Escherichia coli, Klebsiella pneumoniae, Streptococcus pneumoniae, lipopolysaccharide (LPS), or alpha-galactosylceramide (αGalCer) to induce pneumonia, sepsis, or NKT cell activation. Liver injury was observed in RelA-null (hepRelAΔ/Δ) mice but not STAT3-null (hepSTAT3Δ/Δ) mice during pneumonia. The absence of RelA resulted in hepatotoxicity across several models of pneumonia, sepsis, and NKT cell activation. Injury was associated with increased levels of activated caspase-3 and -8 and substantial alteration of the hepatic transcriptome. Hepatotoxicity in the absence of RelA could be reversed by neutralization of tumor necrosis factor alpha (TNF-α). These results indicate the requirement of RelA-dependent inducible hepatoprotection during pneumonia and sepsis. Further, the results demonstrate that RelA-dependent gene programs are critical for maintaining liver homeostasis against TNF-α-driven immunotoxicity.

3' Uridylation controls mature microRNA turnover during CD4 T-cell activation.

Activation of T lymphocytes requires a tight regulation of microRNA (miRNA) expression. Terminal uridyltransferases (TUTases) catalyze 3' nontemplated nucleotide addition (3'NTA) to miRNAs, which may influence miRNA stability and function. Here, we investigated 3'NTA to mature miRNA in CD4 T lymphocytes by deep sequencing. Upon T-cell activation, miRNA sequences bearing terminal uridines are specifically decreased, concomitantly with down-regulation of TUT4 and TUT7 enzymes. Analyzing TUT4-deficient T lymphocytes, we proved that this terminal uridyltransferase is essential for the maintenance of miRNA uridylation in the steady state of T lymphocytes. Analysis of synthetic uridylated miRNAs shows that 3' addition of uridine promotes degradation of these uridylated miRNAs after T-cell activation. Our data underline post-transcriptional uridylation as a mechanism to fine-tune miRNA levels during T-cell activation.

Future Research Directions in Pneumonia. NHLBI Working Group Report.

Pneumonia is a complex pulmonary disease in need of new clinical approaches. Although triggered by a pathogen, pneumonia often results from dysregulations of host defense that likely precede infection. The coordinated activities of immune resistance and tissue resilience then dictate whether and how pneumonia progresses or resolves. Inadequate or inappropriate host responses lead to more severe outcomes such as acute respiratory distress syndrome and to organ dysfunction beyond the lungs and over extended time frames after pathogen clearance, some of which increase the risk for subsequent pneumonia. Improved understanding of such host responses will guide the development of novel approaches for preventing and curing pneumonia and for mitigating the subsequent pulmonary and extrapulmonary complications of pneumonia. The NHLBI assembled a working group of extramural investigators to prioritize avenues of host-directed pneumonia research that should yield novel approaches for interrupting the cycle of unhealthy decline caused by pneumonia. This report summarizes the working group's specific recommendations in the areas of pneumonia susceptibility, host response, and consequences. Overarching goals include the development of more host-focused clinical approaches for preventing and treating pneumonia, the generation of predictive tools (for pneumonia occurrence, severity, and outcome), and the elucidation of mechanisms mediating immune resistance and tissue resilience in the lung. Specific areas of research are highlighted as especially promising for making advances against pneumonia.

Dynamics of lung defense in pneumonia: resistance, resilience, and remodeling.

Pneumonia is initiated by microbes in the lung, but physiological processes integrating responses across diverse cell types and organ systems dictate the outcome of respiratory infection. Resistance, or actions of the host to eradicate living microbes, in the lungs involves a combination of innate and adaptive immune responses triggered by air-space infection. Resilience, or the ability of the host tissues to withstand the physiologically damaging effects of microbial and immune activities, is equally complex, precisely regulated, and determinative. Both immune resistance and tissue resilience are dynamic and change throughout the lifetime, but we are only beginning to understand such remodeling and how it contributes to the incidence of severe pneumonias, which diminishes as childhood progresses and then increases again among the elderly. Here, we review the concepts of resistance, resilience, and remodeling as they apply to pneumonia, highlighting recent advances and current significant knowledge gaps.

Riboflavin Metabolism Variation among Clinical Isolates of Streptococcus pneumoniae Results in Differential Activation of Mucosal-associated Invariant T Cells.

Streptococcus pneumoniae is an important bacterial pathogen that causes a range of noninvasive and invasive diseases. The mechanisms underlying variability in the ability of S. pneumoniae to transition from nasopharyngeal colonization to disease-causing pathogen are not well defined. Mucosal-associated invariant T (MAIT) cells are prevalent in mucosal tissues such as the airways and are believed to play an important role in the early response to infection with bacterial pathogens. The ability of MAIT cells to recognize and contain infection with S. pneumoniae is not known. In the present study, we analyzed MAIT-cell responses to infection with clinical isolates of S. pneumoniae serotype 19A, a serotype linked to invasive pneumococcal disease. We found that although MAIT cells were capable of responding to human dendritic and airway epithelial cells infected with S. pneumoniae, the magnitude of response to different serotype 19A isolates was determined by genetic differences in the expression of the riboflavin biosynthesis pathway. MAIT-cell release of cytokines correlated with differences in the ability of MAIT cells to respond to and control S. pneumoniae in vitro and in vivo in a mouse challenge model. Together, these results demonstrate first that there are genetic differences in riboflavin metabolism among clinical isolates of the same serotype and second that these likely determine MAIT-cell function in response to infection with S. pneumoniae. These differences are critical when considering the role that MAIT cells play in early responses to pneumococcal infection and determining whether invasive disease will develop.

Capacity of Pneumococci to Activate Macrophage Nuclear Factor κB: Influence on Necroptosis and Pneumonia Severity.

During pneumococcal pneumonia, antibacterial defense requires the orchestrated expression of innate immunity mediators, initiated by alveolar macrophages and dependent on transcription driven by nuclear factor κB (NF-κB). Such immune pressure may select for pneumococci, which avoid or subvert macrophage NF-κB activation. Analyzing pneumococci collected from children in Massachusetts, we found that the activation of macrophage NF-κB by Streptococcus pneumoniae is highly diverse, with a preponderance of low NF-κB activators that associate particularly with complicated pneumonia. Low NF-κB activators cause more severe lung infections in mice, and they drive macrophages toward an alternate and detrimental cell fate of necroptosis. Both outcomes can be reversed by activation of macrophages with pneumococci that are high NF-κB activators. These results suggest that low NF-κB activation is a virulence property of pneumococci and that the appropriate activation of macrophages, including NF-κB, may hold promise as an adjunct therapeutic avenue for pneumococcal pneumonia.

Myeloid-epithelial cross talk coordinates synthesis of the tissue-protective cytokine leukemia inhibitory factor during pneumonia.

In bacterial pneumonia, lung damage resulting from epithelial cell injury is a major contributor to the severity of disease and, in some cases, can lead to long-term sequelae, especially in the setting of severe lung injury or acute respiratory distress syndrome. Leukemia inhibitory factor (LIF), a member of the IL-6 cytokine family, is a critical determinant of lung tissue protection during pneumonia, but the cellular sources of LIF and the signaling pathways leading to its production in the infected lung are not known. Here, we demonstrate that lung epithelium, specifically alveolar type II cells, is the predominant site of LIF transcript induction in pneumonic mouse lungs. Epithelial cell cultures were induced to express LIF by bacteria and by sterile bronchoalveolar lavage fluid from pneumonic mice. Reciprocal bone marrow chimera studies demonstrated that LIF deficiency in the nonhematopoietic compartment, but not LIF deficiency in hematopoietic cells, eliminated LIF induction during pneumonia. Although NF-κB RelA (p65) is essential for the expression of many cytokines during pneumonia, its targeted mutation in the lung epithelium was inconsequential for pneumonia-driven LIF induction. However, maximal expression of this epithelial-derived cytokine was dependent on NF-κB RelA in myeloid cells. Overall, our data suggest a signaling axis whereby activation of NF-κB RelA in myeloid cells promotes epithelial LIF induction during lung infections, representing a means through which these two cell types collaborate to improve tissue resilience during pneumonia.

Pathogenesis of severe pneumonia: advances and knowledge gaps.

PURPOSE OF REVIEW: Pneumonia is a common disease that becomes severe in a subset of patients, dependent on host biology including mechanisms of immune resistance and tissue resilience. This review emphasizes discoveries in pneumonia biology from 2016, highlighting questions and directions that are especially pressing or newly emerging. RECENT FINDINGS: Novel cell-cell interactions mediating innate immune responses against microbes in the lung have been elucidated, between distinct leukocyte subtypes as well as between leukocytes and the structural cells of the lung. Adaptive immunity has received growing attention for determining the outcome of pneumonia, particularly the lung resident memory cells that arise from repeated prior respiratory infections and direct heterotypic recall responses. New tissue resilience components have been identified that contribute to anti-inflammatory, proresolution, tissue-protective, and reparative regeneration pathways in the infected lung. SUMMARY: Recent findings will direct research into fundamental mechanisms of lung protection. Over the longer term, manipulating these pathways has implications for clinical practice, as strategies to bolster resistance and resilience have potential to ameliorate severe pneumonia.

Timing of valproic acid in acute lung injury: prevention is the best therapy?

BACKGROUND: Acute lung injury and respiratory distress syndrome is characterized by uncontrolled inflammation of the lungs after a severe inflammatory stimulus. We have previously demonstrated an ameliorated syndrome and improved survival in mice with early administration of valproic acid (VPA), a broad-spectrum histone deacetylase inhibitor, while studies in humans have shown no benefit when anti-inflammatories are administered late. The current study tested the hypothesis that early treatment would improve outcomes in our gram-negative pneumonia-induced acute lung injury. MATERIALS AND METHODS: Mice (C57BL/6) had 50 × 106 Escherichia coli (strain 19,138) instilled endotracheally and VPA (250 mg/kg) administered intraperitoneally 3, 4, 6, and 9 h (n = 12/group) later. Six hours after VPA administration, the animals were sacrificed, and bronchoalveolar lavage (BAL) fluid interleukin-6 (IL-6), tumor necrosis factor, neutrophils and macrophages as well as the E coli colony-forming units were quantified. Plasma IL-6 was also measured. A separate group of mice (n = 12/group) were followed prospectively for 7 days to assess survival. RESULTS: BAL IL-6 and tumor necrosis factor as well as plasma IL-6 were significantly lower in the animals administered VPA within 3 h (P < 0.05) but not when administered later (4, 6, 9 h). There was no difference in the BAL E coli colony-forming units, macrophage, or neutrophil numbers at any time point. Survival improved only when VPA was administered within 3 h. CONCLUSIONS: A narrow therapeutic window exists in this murine model of gram-negative pneumonia-induced acute lung injury and likely explains the lack of response in studies with late administration of anti-inflammatory therapies in clinical studies.

Epithelial Cell-Derived Secreted and Transmembrane 1a Signals to Activated Neutrophils during Pneumococcal Pneumonia.

Airway epithelial cell responses are critical to the outcome of lung infection. In this study, we aimed to identify unique contributions of epithelial cells during lung infection. To differentiate genes induced selectively in epithelial cells during pneumonia, we compared genome-wide expression profiles from three sorted cell populations: epithelial cells from uninfected mouse lungs, epithelial cells from mouse lungs with pneumococcal pneumonia, and nonepithelial cells from those same infected lungs. Of 1,166 transcripts that were more abundant in epithelial cells from infected lungs compared with nonepithelial cells from the same lungs or from epithelial cells of uninfected lungs, 32 genes were identified as highly expressed secreted products. Especially strong signals included two related secreted and transmembrane (Sectm) 1 genes, Sectm1a and Sectm1b. Refinement of sorting strategies suggested that both Sectm1 products were induced predominantly in conducting airway epithelial cells. Sectm1 was induced during the early stages of pneumococcal pneumonia, and mutation of NF-κB RelA in epithelial cells did not diminish its expression. Instead, type I IFN signaling was necessary and sufficient for Sectm1 induction in lung epithelial cells, mediated by signal transducer and activator of transcription 1. For target cells, Sectm1a bound to myeloid cells preferentially, in particular Ly6G(bright)CD11b(bright) neutrophils in the infected lung. In contrast, Sectm1a did not bind to neutrophils from uninfected lungs. Sectm1a increased expression of the neutrophil-attracting chemokine CXCL2 by neutrophils from the infected lung. We propose that Sectm1a is an epithelial product that sustains a positive feedback loop amplifying neutrophilic inflammation during pneumococcal pneumonia.