Lung resident memory B cells are a common and functionally significant component of lung adaptive immunity

Resident memory B cells (BRM) in influenza-recovered mouse lungs were recently described, but whether other types of infections elicit these cells is unknown. The relevance of BRM in human lungs and to lung immune defenses also remains unexplored. Using flow cytometry and immunofluorescence, we found that respiratory pneumococcal exposures in mice elicited lung BRM without concurrent tertiary lymphoid structure formation. Additionally, flow cytometry analysis of normal human lung tissue showed that human lungs are enriched compared to human blood for B cells bearing a resident memory phenotype. These findings indicate that lung BRM are a common feature of antigen-experienced lungs. Multiple mouse models were used to address the contributions of B cell immunity to anti-pneumococcal lung defenses. Mice exposed to a low virulence pneumococcal strain 4 weeks previously were well-protected from a serotype-mismatched pneumococcal challenge. When previously exposed mice were depleted of circulating B cells (but not lung B cells) with anti-CD20 treatment before the challenge infection, there was no effect on the acquired lung immunity. However, a genetically engineered mouse strain allowed effective depletion of lung B cells bearing PD-L2 (a mouse memory B cell marker) from previously exposed mice, and doing so before the virulent pneumococcal challenge resulted in substantial defects in bacterial clearance compared to mice with lung B cells intact. These results provide the first direct evidence of a role for lung BRM in anti-bacterial lung immunity. Notably, this defense was pneumococcal serotype-independent, distinguishing it from the serotype-specific immunity elicited by current pneumococcal vaccines.

Double Deletion of C5aR1 and C5aR2 during Streptococcal Pneumonia

The complement system is essential for the clearance of encapsulated bacteria such as Streptococcus pneumoniae (Spn), recognized as a major pathogen of pneumonia. Yet, it is not entirely clear whether C5 and its activation product C5a have beneficial or detrimental effects on the outcome of Spn infection. C5a binds to its two homologous C5a receptors (C5aR1 and C5aR2). The extent of functional overlap and role distribution between C5aR1 and C5aR2 remains enigmatic. A critical barrier to allow studies on the role distributions of C5aRs has been the absence of a mouse strain with dual deletion of both receptors - which are encoded as adjacent, linked genes on mouse chromosome 7.

CRISPR/Cas9 guided gene editing was combined with zygote/pronucleus microinjections in C57BL/6J mice to generate a C5aR1/C5aR2 double-knockout strain (C5aR1/2−/−). PCR-based screening and Sanger sequencing confirmed a 12.6 kB deletion of the coding regions of C5aR1 and C5aR2 of the new mouse strain, C57BL/6J-Del( 7C5ar2-C5ar1)1Bosm. Phenotyping of C5aR1/2−/− mice was followed by functional studies including intra-tracheal injections of recombinant mouse C5a or intranasal injections of Spn TIGR4. The airway influx of Ly6G+SiglecF- neutrophils by C5a was abrogated in C5aR1/2−/− mice. Surprisingly, the dual genetic absence of C5a receptors was associated with a higher build-up of neutrophil numbers in alveolar spaces after Spn TIGR4 infection. In a transcriptome-wide screen, FACS-sorted myeloid cells from infected lungs of double and single knockout mice were subjected to RNA-sequencing. Identifying novel differentially expressed genes in the C5aR1/2−/− mice during Spn infection will help to uncover potential synergisms and redundancies of C5aR1 and C5aR2.

The influence of the lung virome on pulmonary B cells

The human microbiome is a complex and diverse environment that is implicated in human health and disease. Major locations that host a microbiome include the gut, respiratory system, and the urogenital tracts. While there have been steady advances of the effect of our commensal flora in regions such as the gut, the impact of the pulmonary microbiome, specifically the viral arm of the microbiome (virome), remains under-researched. Studies that have addressed this field provided insight into a complex interplay between viruses and the immune system. On one hand, there are reports of viruses inducing protection from other microorganisms, while on the other, they are correlated with increased risk towards other diseases. Despite this growing body of work on how the lung virome influences human health through the immune system, the immunological mechanisms that underlie this interaction remains unclear.

We hypothesize that constant exposure to pulmonary virus will generate a unique B cell repertoire distinct from peripheral B cells that is adapted specifically to pulmonary viruses. To address this hypothesis, we compared memory B cells from patent-paired lung and blood samples by flow cytometry as well as their secreted antibody affinity towards viral epitopes. Our results show B cell population distributions unique in the lung relative to blood. Secreted antibodies collected from cultured B cells have also shown specificity towards human viral pathogens. We believe our results will provide insight into the influence of a unique and chronic viral presence on pulmonary immunity.

Unique Roles for Streptococcus pneumoniae Phosphodiesterase 2 in Cyclic di-AMP Catabolism and Macrophage Responses

Cyclic di-AMP (c-di-AMP) is an important signaling molecule for pneumococci, and as a uniquely prokaryotic product it can be recognized by mammalian cells as a danger signal that triggers innate immunity. Roles of c-di-AMP in directing host responses during pneumococcal infection are only beginning to be defined. We hypothesized that pneumococci with defective c-di-AMP catabolism due to phosphodiesterase deletions could illuminate roles of c-di-AMP in mediating host responses to pneumococcal infection. Pneumococci deficient in phosphodiesterase 2 (Pde2) stimulated a rapid induction of interferon β (IFNβ) expression that was exaggerated in comparison to that induced by wild type (WT) bacteria or bacteria deficient in phosphodiesterase 1. This IFNβ burst was elicited in mouse and human macrophage-like cell lines as well as in primary alveolar macrophages collected from mice with pneumococcal pneumonia. Macrophage hyperactivation by Pde2-deficient pneumococci led to rapid cell death. STING and cGAS were essential for the excessive IFNβ induction, which also required phagocytosis of bacteria and triggered the phosphorylation of IRF3 and IRF7 transcription factors. The select effects of Pde2 deletion were products of a unique role of this enzyme in c-di-AMP catabolism when pneumococci were grown on solid substrate conditions designed to enhance virulence. Because pneumococci with elevated c-di-AMP drive aberrant innate immune responses from macrophages involving hyperactivation of STING, excessive IFNβ expression, and rapid cytotoxicity, we surmise that c-di-AMP is pivotal for directing innate immunity and host-pathogen interactions during pneumococcal pneumonia.

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 National Heart, Lung, and Blood Institute. 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 pre-clinical 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, pre-clinical disease modeling, and understanding recovery from acute illness promise to transform the methods of pulmonary and critical care clinical research. To assess the current state, research priorities, and future directions for 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 pre-clinical models by incorporating comorbidities, co-interventions, and organ support; (3) developing and applying novel clinical trial designs; and (4) advancing mechanistic understanding of injury and recovery in order 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.

Lung CD4+ resident memory T cells remodel epithelial responses to accelerate neutrophil recruitment during pneumonia

Previous pneumococcal experience establishes lung-resident IL-17A-producing CD4⁺ memory T_RM cells that accelerate neutrophil recruitment against heterotypic pneumococci. Herein, we unravel a novel crosstalk between CD4⁺ T_RM cells and lung epithelial cells underlying this protective immunity. Depletion of CD4⁺ cells in pneumococcus-experienced mice diminished CXCL5 (but not CXCL1 or CXCL2) and downstream neutrophil accumulation in the lungs. Epithelial cells from experienced lungs exhibited elevated mRNA for CXCL5 but not other epithelial products such as GM-CSF or CCL20, suggesting a skewing by CD4⁺ T_RM cells. Genome-wide expression analyses revealed a significant remodeling of the epithelial transcriptome of infected lungs due to infection history, ~80% of which was CD4⁺ cell-dependent. The CD4⁺ T_RM cell product IL-17A stabilized CXCL5 but not GM-CSF or CCL20 mRNA in cultured lung epithelial cells, implicating posttranscriptional regulation as a mechanism for altered epithelial responses. These results suggest that epithelial cells in experienced lungs are effectively different, owing to their communication with T_RM cells. Our study highlights the role of tissue-resident adaptive immune cells in fine-tuning epithelial functions to hasten innate immune responses and optimize defense in experienced lungs, a concept that may apply broadly to mucosal immunology.

Pneumonia recovery reprograms the alveolar macrophage pool

Community-acquired pneumonia is a widespread disease with significant morbidity and mortality. Alveolar macrophages are tissue-resident lung cells that play a crucial role in innate immunity against bacteria that cause pneumonia. We hypothesized that alveolar macrophages display adaptive characteristics after resolution of bacterial pneumonia. We studied mice 1 to 6 months after self-limiting lung infections with Streptococcus pneumoniae, the most common cause of bacterial pneumonia. Alveolar macrophages, but not other myeloid cells, recovered from the lung showed long-term modifications of their surface marker phenotype. The remodeling of alveolar macrophages was (a) long-lasting (still observed 6 months after infection), (b) regionally localized (observed only in the affected lobe after lobar pneumonia), and (c) associated with macrophage-dependent enhanced protection against another pneumococcal serotype. Metabolomic and transcriptomic profiling revealed that alveolar macrophages of mice that recovered from pneumonia had new baseline activities and altered responses to infection that better resembled those of adult humans. The enhanced lung protection after mild and self-limiting bacterial respiratory infections includes a profound remodeling of the alveolar macrophage pool that is long-lasting; compartmentalized; and manifest across surface receptors, metabolites, and both resting and stimulated transcriptomes.

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.

Roles of interleukin-11 during acute bacterial pneumonia

Interleukin-11 (IL-11) is an interleukin-6 (IL-6) family cytokine shown to play a protective role in acute inflammatory settings including systemic infection. In this study we addressed the role of IL-11 in acute bacterial pneumonia using a mouse model of E. coli pneumonia. Compared with other related cytokines, IL-11 protein was maintained at high levels in the lung at baseline, with only mild alterations in whole lung and BALF levels during acute infection. The primary source of IL-11 in the lung was the epithelium, but steady state production was not dependent on the inflammatory transcription factor nuclear factor kappa B in cells of either myeloid or epithelial lineage. Blockade of IL-11 with neutralizing antibodies resulted in a mild but significant decrease in neutrophil recruitment and increase in pulmonary edema during pneumonia, without detectable alterations in bacterial clearance. Exogenous IL-11 administration, however, had no effect at baseline or during infection. Overall, we conclude that maintenance of lung IL-11 concentrations may influence acute pulmonary inflammation during infection, albeit modestly.

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.

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.

The Influence of The Lung Virome on Pulmonary B cells

The human microbiome is a complex and diverse environment that is implicated in human health and disease. Major locations that host a microbiome include the gut, respiratory system, and the urogenital tracts. While there have been steady advances of the effect of our commensal flora in regions such as the gut microbiome, the impact of the pulmonary microbiome, specifically the viral arm of the microbiome (virome), remains unclear and under-researched. Recent studies have shown that pulmonary viruses can influence disease susceptibility to the benefit, or detriment, to the host. Despite increasing evidence that the lung virome influences human health through the immune system, the direct effects on the host immune system remain unclear. We hypothesize that the chronic presence of the lung virome influences the pulmonary B cell repertoire. The constant exposure to pulmonary virus can generate a unique B cell repertoire independent of peripheral B cells that is tailored specifically towards pulmonary viruses. To address this hypothesis, we have utilized a single-cell B cell culture system to amplify human lung-derived memory B cells (MBCs) from limited human donor samples. By analyzing these MBCs at the genetic level by RNA sequencing and protein level by antigen affinity from secreted antibodies, we can begin to understand the impact of the lung virome on the pulmonary B cell repertoire.

Repeated respiratory bacterial exposures elicit lung resident memory B cells in the absence of organized tertiary lymphoid tissue

Recent work has shown that resident memory B cells (BRM) are generated in the lung after flu infection. However, it is unclear whether the existence of lung BRM is unique to influenza, which often elicits iBALT, or alternatively if these cells represent a common feature of the lung immune landscape. We aimed to determine whether bacterial lung exposures experienced by nearly all human children might also elicit lung BRM. To model this scenario, we gave young mice repeated respiratory exposures to low virulence pneumococci. After at least 4 weeks, we then analyzed lung B cells using flow cytometry and an intravital CD45 stain to exclude intravascular leukocytes. Pneumococcus-exposed mice had many more extravascular IgD- lung B cells than controls, and these B cells remained in the lung at least 12 weeks after the last exposure. Although unorganized aggregates of B and T cells were observed in previously exposed lungs, no iBALT structures were generated. Most of the IgD-B cells expressed the memory markers PD-L2, CD80, and CD73; a majority of the B cells expressed two or more of these markers, indicating they are poised to become antibody secreting upon rechallenge. Notably, the hallmark lung TRM phenotype (CD11abrightCD69+CD44brightCD62Llow) was also observed on lung B cells; these markers may represent a common resident memory lymphocyte phenotype. Although all lung B cells were CD20+, they were not affected by αCD20 antibody treatment, which requires circulation of bound cells for depletion to occur. BRM appear to be a common feature of the adaptive immune cell repertoire of experienced lungs. These cells do not require iBALT for their maintenance and represent a previously unrecognized pool of B cells resistant to depletion with αCD20 therapy.

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.

Inflammation and Pneumonia: Why Are Some More Susceptible than Others?

Pneumonia is an important cause of morbidity and mortality. However, pneumonia is an unusual outcome of respiratory infection. Most of the time, microbes in the lung can be controlled by a combination of constitutive and recruited defense mechanisms. Inflammation is a key component of recruited defenses. Variations in inflammation that influence pneumonia susceptibility and severity are considered here.

MicroRNA Signature of Cigarette Smoking and Evidence for a Putative Causal Role of MicroRNAs in Smoking-Related Inflammation and Target Organ Damage

BACKGROUND

Cigarette smoking increases risk for multiple diseases. MicroRNAs regulate gene expression and may play a role in smoking-induced target organ damage. We sought to describe a microRNA signature of cigarette smoking and relate it to smoking-associated clinical phenotypes, gene expression, and lung inflammatory signaling.

METHODS AND RESULTS

Expression profiling of 283 microRNAs was conducted on whole blood-derived RNA from 5023 Framingham Heart Study participants (54.0% women; mean age, 55±13 years) using TaqMan assays and high-throughput reverse transcription quantitative polymerase chain reaction. Associations of microRNA expression with smoking status and associations of smoking-related microRNAs with inflammatory biomarkers and pulmonary function were tested with linear mixed effects models. We identified a 6-microRNA signature of smoking. Five of the 6 smoking-related microRNAs were associated with serum levels of C-reactive protein or interleukin-6; miR-1180 was associated with pulmonary function measures at a marginally significant level. Bioinformatic evaluation of smoking-associated genes coexpressed with the microRNA signature of cigarette smoking revealed enrichment for immune-related pathways. Smoking-associated microRNAs altered expression of selected inflammatory mediators in cell culture gain-of-function assays.

CONCLUSIONS

We characterized a novel microRNA signature of cigarette smoking. The top microRNAs were associated with systemic inflammatory markers and reduced pulmonary function, correlated with expression of genes involved in immune function, and were sufficient to modulate inflammatory signaling. Our results highlight smoking-associated microRNAs and are consistent with the hypothesis that smoking-associated microRNAs serve as mediators of smoking-induced inflammation and target organ damage. These findings call for further mechanistic studies to explore the diagnostic and therapeutic use of smoking-related microRNAs.

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.

Expression of Piwi protein MIWI2 defines a distinct population of multiciliated cells

P-element-induced wimpy testes (Piwi) proteins are known for suppressing retrotransposon activation in the mammalian germline. However, whether Piwi protein or Piwi-dependent functions occur in the mammalian soma is unclear. Contrary to germline-restricted expression, we observed that Piwi-like Miwi2 mRNA is indeed expressed in epithelial cells of the lung in adult mice and that it is induced during pneumonia. Further investigation revealed that MIWI2 protein localized to the cytoplasm of a discrete population of multiciliated airway epithelial cells. Isolation and next-generation sequencing of MIWI2-positive multiciliated cells revealed that they are phenotypically distinct from neighboring MIWI2-negative multiciliated cells. Mice lacking MIWI2 exhibited an altered balance of airway epithelial cells, demonstrating fewer multiciliated cells and an increase in club cells. During pneumococcal pneumonia, Miwi2-deficient mice exhibited increased expression of inflammatory mediators and increased immune cell recruitment, leading to enhanced bacterial clearance. Taken together, our data delineate MIWI2-dependent functions outside of the germline and demonstrate the presence of distinct subsets of airway multiciliated cells that can be discriminated by MIWI2 expression. By demonstrating roles for MIWI2 in airway cell identity and pulmonary innate immunity, these studies elucidate unanticipated physiological functions for Piwi proteins in somatic tissues.

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.

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.

The RNA uridyltransferase Zcchc6 is expressed in macrophages and impacts innate immune responses

Alveolar macrophages orchestrate pulmonary innate immunity and are essential for early immune surveillance and clearance of microorganisms in the airways. Inflammatory signaling must be sufficiently robust to promote host defense but limited enough to prevent excessive tissue injury. Macrophages in the lungs utilize multiple transcriptional and post-transcriptional mechanisms of inflammatory gene expression to delicately balance the elaboration of immune mediators. RNA terminal uridyltransferases (TUTs), including the closely homologous family members Zcchc6 (TUT7) and Zcchc11 (TUT4), have been implicated in the post-transcriptional regulation of inflammation from studies conducted in vitro. In vivo, we observed that Zcchc6 is expressed in mouse and human primary macrophages. Zcchc6-deficient mice are viable and born in Mendelian ratios and do not exhibit an observable spontaneous phenotype under basal conditions. Following an intratracheal challenge with S. pneumoniae, Zcchc6 deficiency led to a modest but significant increase in the expression of select cytokines including IL-6, CXCL1, and CXCL5. These findings were recapitulated in vitro whereby Zcchc6-deficient macrophages exhibited similar increases in cytokine expression due to bacterial stimulation. Although loss of Zcchc6 also led to increased neutrophil emigration to the airways during pneumonia, these responses were not sufficient to impact host defense against infection.

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.

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.

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.

Role for the Aryl Hydrocarbon Receptor and Diverse Ligands in Oral Squamous Cell Carcinoma Migration and Tumorigenesis

Over 45,000 new cases of oral and pharyngeal cancers are diagnosed and account for over 8,000 deaths a year in the United States. An environmental chemical receptor, the aryl hydrocarbon receptor (AhR), has previously been implicated in oral squamous cell carcinoma (OSCC) initiation as well as in normal tissue-specific stem cell self-renewal. These previous studies inspired the hypothesis that the AhR plays a role in both the acquisition and progression of OSCC, as well as in the formation and maintenance of cancer stem-like cells. To test this hypothesis, AhR activity in two oral squamous cell lines was modulated with AhR prototypic, environmental and bacterial AhR ligands, AhR-specific inhibitors, and phenotypic, genomic and functional characteristics were evaluated. The data demonstrate that: (i) primary OSCC tissue expresses elevated levels of nuclear AhR as compared with normal tissue, (ii) AhR mRNA expression is upregulated in 320 primary OSCCs, (iii) AhR hyperactivation with several ligands, including environmental and bacterial ligands, significantly increases AhR activity, ALDH1 activity, and accelerates cell migration, (iv) AhR inhibition blocks the rapid migration of OSCC cells and reduces cell chemoresistance, (v) AhR knockdown inhibits tumorsphere formation in low adherence conditions, and (vi) AhR knockdown inhibits tumor growth and increases overall survival in vivo These data demonstrate that the AhR plays an important role in development and progression of OSCC, and specifically cancer stem-like cells. Prototypic, environmental, and bacterial AhR ligands may exacerbate OSCC by enhancing expression of these properties.

IMPLICATIONS

This study, for the first time, demonstrates the ability of diverse AhR ligands to regulate AhR activity in oral squamous cell carcinoma cells, as well as regulate several important characteristics of oral cancer stem cells, in vivo and in vitro Mol Cancer Res; 14(8); 696-706. ©2016 AACR.