Leptin Receptor Deficiency Impairs Lymph Node Development and Adaptive Immune Response.

Activation and clonal expansion of the Ag-specific adaptive immune response in the draining lymph node is essential to clearing influenza A virus infections. Activation sufficient for virus clearance is dependent on the lymph node's architectural organization that is maintained by stromal cells, chiefly fibroblastic reticular cells. During an analysis of influenza A virus clearance in leptin receptor knockout (DB/DB) mice, we observed that the DB/DB mice have markedly reduced numbers of lymph node fibroblastic reticular cells at the steady state. The reduction in lymph node fibroblastic reticular cells resulted in abnormal lymph node organization and diminished numbers of adaptive immune cells in the lymph nodes under homeostatic conditions. As a consequence, the DB/DB mice were impaired in their ability to generate an effective influenza-specific adaptive immune response, which prevented virus clearance. Using leptin receptor mutant mice with point mutations at distinct signaling sites in the leptin receptor, we were able to link the leptin receptor's signaling domain tyrosine 985, which does not contribute to obesity, to lymph node fibroblastic reticular cell development and function. These results demonstrate a novel role for leptin receptor signaling in regulating lymph node development in a manner that is crucial to the generation of Ag-specific adaptive immune responses.

CD4+ T cell help and innate-derived IL-27 induce Blimp-1-dependent IL-10 production by antiviral CTLs.

Interleukin (IL)-10 is an important regulatory cytokine that can modulate excessive immune mediated injury. Several distinct cell types have been demonstrated to produce IL-10, including most recently CD8+ cytotoxic T lymphocytes (CTLs) responding to respiratory virus infection. Here we report that CD4+ T cell help in the form of IL-2 is required for IL-10 production by CTLs, but not for the induction of CTL effector cytokines. We show that IL-2 derived from CD4+ helper T cells cooperates with innate immune cell-derived IL-27 to amplify IL-10 production by CTLs through a Blimp-1-dependent mechanism. These findings reveal a previously unrecognized pathway that coordinates signals derived from innate and helper T cells to control the production of a regulatory cytokine by CTLs during acute viral infection.

Distinct dendritic cell subsets dictate the fate decision between effector and memory CD8(+) T cell differentiation by a CD24-dependent mechanism.

The contribution of different DC subsets to effector and memory CD8(+) T cell generation during infection and the mechanism by which DCs controls these fate decisions is unclear. Here we demonstrated that the CD103(+) and CD11b(hi) migratory respiratory DC (RDC) subsets after influenza virus infection activated naive virus-specific CD8(+) T cells differentially. CD103(+) RDCs supported the generation of CD8(+) T effector (Teff) cells, which migrate from lymph nodes to the infected lungs. In contrast, migrant CD11b(hi) RDCs activated CD8(+) T cells characteristic of central memory CD8(+) T (CD8(+) Tcm) cells including retention within the draining lymph nodes. CD103(+) RDCs expressed CD24 at an elevated level, contributing to the propensity of this DC subpopulation to support CD8(+) Teff cell differentiation. Mechanistically, CD24 was shown to regulate CD8(+) T cell activation through HMGB1-mediated engagement of T cell RAGE. Thus, there is distribution of labor among DC subsets in regulating CD8(+) T cell differentiation.

Bronchoalveolar lavage cytokine patterns in children with severe neutrophilic and paucigranulocytic asthma.

BACKGROUND: Asthma is a complex heterogeneous disease occurring in adults and children that is characterized by distinct inflammatory patterns. While numerous studies have been performed in adults, little is known regarding the heterogeneity of severe asthma in children, particularly inflammatory signatures involving the air spaces. OBJECTIVE: We sought to determine the relationship of bronchoalveolar lavage (BAL) cytokine/chemokine expression patterns in children with severe therapy-resistant asthma stratified according to neutrophilic versus nonneutrophilic BAL inflammatory cell patterns. METHODS: Children with severe asthma with inadequate symptom control despite therapy underwent diagnostic bronchoscopy and BAL. Inflammatory cytokine/chemokine concentrations were determined using a multiplex protein bead assay. RESULTS: Analysis of BAL constituents with an unbiased clustering approach revealed distinct cytokine/chemokine patterns, and these aligned with pathways associated with type 2 innate lymphoid cells, monocytes, neutrophil trafficking, and T effector cells. All cytokines examined (n = 27) with 1 exception (vascular endothelial growth factor) were overexpressed with BAL neutrophilia compared with nonneutrophilic asthma, and this was confirmed in a cross-validation analysis. Cytokines specifically responsible for Th17 (IL-17, IL-6, G-CSF) and Th1 differentiation and expression (IL-12, TNF-α, IFN-γ) were enhanced in the neutrophilic cohorts. Neutrophilic groups were also characterized by higher prevalence of bacterial and viral pathogens; however, cytokine expression patterns manifested independently of pathogen expression. CONCLUSIONS: The results demonstrate that children with refractory asthma and neutrophilic inflammation had a BAL cytokine pattern consistent with a mixed Th17/Th1/Th2 response. In contrast, nonneutrophilic asthma presented independently of cytokine overexpression.

Neutrophil-Derived Tumor Necrosis Factor Drives Fungal Acute Lung Injury in Chronic Granulomatous Disease.

Chronic granulomatous disease (CGD) results from deficiency of nicotinamide adenine dinucleotide phosphate(NADPH) oxidase and impaired reactive oxygen species (ROS) generation. This leads to impaired killing of Aspergillus and, independently, a pathologic hyperinflammatory response to the organism. We hypothesized that neutrophil-derived ROS inhibit the inflammatory response to Aspergillus and that acute lung injury in CGD is due to failure of this regulation. Mice with gp91phox deficiency, the most common CGD mutation, had more severe lung injury, increased neutrophilinfiltration, and increased lung tumor necrosis factor (TNF) after Aspergillus challenge compared with wild-types. Neutrophils were surprisingly the predominant source of TNF in gp91phox-deficient lungs. TNF neutralization inhibited neutrophil recruitment in gp91phox-deficient mice and protected from lung injury. We propose that, in normal hosts, Aspergillus stimulates TNF-dependent neutrophil recruitment to the lungs and neutrophil-derived ROS limit inflammation. In CGD, in contrast, recruited neutrophils are the dominant source of TNF, promoting further neutrophil recruitment in a pathologic positive-feedback cycle, resulting in progressive lung injury.

Alveolar Macrophages Prevent Lethal Influenza Pneumonia By Inhibiting Infection Of Type-1 Alveolar Epithelial Cells.

The Influenza A virus (IAV) is a major human pathogen that produces significant morbidity and mortality. To explore the contribution of alveolar macrophages (AlvMΦs) in regulating the severity of IAV infection we employed a murine model in which the Core Binding Factor Beta gene is conditionally disrupted in myeloid cells. These mice exhibit a selective deficiency in AlvMΦs. Following IAV infection these AlvMΦ deficient mice developed severe diffuse alveolar damage, lethal respiratory compromise, and consequent lethality. Lethal injury in these mice resulted from increased infection of their Type-1 Alveolar Epithelial Cells (T1AECs) and the subsequent elimination of the infected T1AECs by the adaptive immune T cell response. Further analysis indicated AlvMΦ-mediated suppression of the cysteinyl leukotriene (cysLT) pathway genes in T1AECs in vivo and in vitro. Inhibition of the cysLT pathway enzymes in a T1AECs cell line reduced the susceptibility of T1AECs to IAV infection, suggesting that AlvMΦ-mediated suppression of this pathway contributes to the resistance of T1AECs to IAV infection. Furthermore, inhibition of the cysLT pathway enzymes, as well as blockade of the cysteinyl leukotriene receptors in the AlvMΦ deficient mice reduced the susceptibility of their T1AECs to IAV infection and protected these mice from lethal infection. These results suggest that AlvMΦs may utilize a previously unappreciated mechanism to protect T1AECs against IAV infection, and thereby reduce the severity of infection. The findings further suggest that the cysLT pathway and the receptors for cysLT metabolites represent potential therapeutic targets in severe IAV infection.

Type I IFN signaling facilitates the development of IL-10-producing effector CD8+ T cells during murine influenza virus infection.

Recent evidence has suggested that IL-10-producing effector CD8+ T cells play an important role in regulating excessive inflammation during acute viral infections. However, the cellular and molecular cues regulating the development of IL-10-producing effector CD8+ T cells are not completely defined. Here, we show that type I interferons (IFNs) are required for the development of IL-10-producing effector CD8+ T cells during influenza virus infection in mice. We find that type I IFNs can enhance IL-27 production by lung APCs, thereby facilitating IL-10-producing CD8+ T-cell development through a CD8+ T-cell-nonautonomous way. Surprisingly, we also demonstrate that direct type I IFN signaling in CD8+ T cells is required for the maximal generation of IL-10-producing CD8+ T cells. Type I IFN signaling in CD8+ T cells, in cooperation with IL-27 and IL-2 signaling, promotes and sustains the expression of IFN regulatory factor 4 (IRF4) and B-lymphocyte-induced maturation protein-1 (Blimp-1), two transcription factors required for the production of IL-10 by effector CD8+ T cells. Our data reveal a critical role of the innate antiviral effector cytokines in regulating the production of a regulatory cytokine by effector CD8+ T cells during respiratory virus infection.

Liver-resident CD103+ dendritic cells prime antiviral CD8+ T cells in situ.

The liver maintains a tolerogenic environment to avoid unwarranted activation of its resident immune cells upon continuous exposure to food and bacterially derived Ags. However, in response to hepatotropic viral infection, the liver's ability to switch from a hyporesponsive to a proinflammatory environment is mediated by select sentinels within the parenchyma. To determine the contribution of hepatic dendritic cells (DCs) in the activation of naive CD8(+) T cells, we first characterized resident DC subsets in the murine liver. Liver DCs exhibit unique properties, including the expression of CD8α (traditionally lymphoid tissue specific), CD11b, and CD103 markers. In both the steady-state and following viral infection, liver CD103(+) DCs express high levels of MHC class II, CD80, and CD86 and contribute to the high number of activated CD8(+) T cells. Importantly, viral infection in the Batf3(-/-) mouse, which lacks CD8α(+) and CD103(+) DCs in the liver, results in a 3-fold reduction in the proliferative response of Ag-specific CD8(+) T cells. Limiting DC migration out of the liver does not significantly alter CD8(+) T cell responsiveness, indicating that CD103(+) DCs initiate the induction of CD8(+) T cell responses in situ. Collectively, these data suggest that liver-resident CD103(+) DCs are highly immunogenic in response to hepatotropic viral infection and serve as a major APC to support the local CD8(+) T cell response. It also implies that CD103(+) DCs present a promising cellular target for vaccination strategies to resolve chronic liver infections.

Late engagement of CD86 after influenza virus clearance promotes recovery in a FoxP3+ regulatory T cell dependent manner.

Influenza A virus (IAV) infection in the respiratory tract triggers robust innate and adaptive immune responses, resulting in both virus clearance and lung inflammation and injury. After virus clearance, resolution of ongoing inflammation and tissue repair occur during a distinct recovery period. B7 family co-stimulatory molecules such as CD80 and CD86 have important roles in modulating T cell activity during the initiation and effector stages of the host response to IAV infection, but their potential role during recovery and resolution of inflammation is unknown. We found that antibody-mediated CD86 blockade in vivo after virus clearance led to a delay in recovery, characterized by increased numbers of lung neutrophils and inflammatory cytokines in airways and lung interstitium, but no change in conventional IAV-specific T cell responses. However, CD86 blockade led to decreased numbers of FoxP3+ regulatory T cells (Tregs), and adoptive transfer of Tregs into αCD86 treated mice rescued the effect of the blockade, supporting a role for Tregs in promoting recovery after virus clearance. Specific depletion of Tregs late after infection mimicked the CD86 blockade phenotype, confirming a role for Tregs during recovery after virus clearance. Furthermore, we identified neutrophils as a target of Treg suppression since neutrophil depletion in Treg-depleted mice reduced excess inflammatory cytokines in the airways. These results demonstrate that Tregs, in a CD86 dependent mechanism, contribute to the resolution of disease after IAV infection, in part by suppressing neutrophil-driven cytokine release into the airways.

The effector T cell response to influenza infection.

Influenza virus infection induces a potent initial innate immune response, which serves to limit the extent of viral replication and virus spread. However, efficient (and eventual) viral clearance within the respiratory tract requires the subsequent activation, rapid proliferation, recruitment, and expression of effector activities by the adaptive immune system, consisting of antibody producing B cells and influenza-specific T lymphocytes with diverse functions. The ensuing effector activities of these T lymphocytes ultimately determine (along with antibodies) the capacity of the host to eliminate the viruses and the extent of tissue damage. In this review, we describe this effector T cell response to influenza virus infection. Based on information largely obtained in experimental settings (i.e., murine models), we will illustrate the factors regulating the induction of adaptive immune T cell responses to influenza, the effector activities displayed by these activated T cells, the mechanisms underlying the expression of these effector mechanisms, and the control of the activation/differentiation of these T cells, in situ, in the infected lungs.

Group 2 innate lymphoid cell production of IL-5 is regulated by NKT cells during influenza virus infection.

Respiratory virus infections, such as influenza, typically induce a robust type I (pro-inflammatory cytokine) immune response, however, the production of type 2 cytokines has been observed. Type 2 cytokine production during respiratory virus infection is linked to asthma exacerbation; however, type 2 cytokines may also be tissue protective. Interleukin (IL)-5 is a prototypical type 2 cytokine that is essential for eosinophil maturation and egress out of the bone marrow. However, little is known about the cellular source and underlying cellular and molecular basis for the regulation of IL-5 production during respiratory virus infection. Using a mouse model of influenza virus infection, we found a robust transient release of IL-5 into infected airways along with a significant and progressive accumulation of eosinophils into the lungs, particularly during the recovery phase of infection, i.e. following virus clearance. The cellular source of the IL-5 was group 2 innate lymphoid cells (ILC2) infiltrating the infected lungs. Interestingly, the progressive accumulation of eosinophils following virus clearance is reflected in the rapid expansion of c-kit⁺ IL-5 producing ILC2. We further demonstrate that the enhanced capacity for IL-5 production by ILC2 during recovery is concomitant with the enhanced expression of the IL-33 receptor subunit, ST2, by ILC2. Lastly, we show that NKT cells, as well as alveolar macrophages (AM), are endogenous sources of IL-33 that enhance IL-5 production from ILC2. Collectively, these results reveal that c-kit⁺ ILC2 interaction with IL-33 producing NKT and AM leads to abundant production of IL-5 by ILC2 and accounts for the accumulation of eosinophils observed during the recovery phase of influenza infection.

Liver-primed CD8+ T cells suppress antiviral adaptive immunity through galectin-9-independent T-cell immunoglobulin and mucin 3 engagement of high-mobility group box 1 in mice.

UNLABELLED: The liver is a tolerogenic environment exploited by persistent infections, such as hepatitis B (HBV) and C (HCV) viruses. In a murine model of intravenous hepatotropic adenovirus infection, liver-primed antiviral CD8(+) T cells fail to produce proinflammatory cytokines and do not display cytolytic activity characteristic of effector CD8(+) T cells generated by infection at an extrahepatic, that is, subcutaneous, site. Importantly, liver-generated CD8(+) T cells also appear to have a T-regulatory (Treg) cell function exemplified by their ability to limit proliferation of antigen-specific T-effector (Teff ) cells in vitro and in vivo via T-cell immunoglobulin and mucin 3 (Tim-3) expressed by the CD8(+) Treg cells. Regulatory activity did not require recognition of the canonical Tim-3 ligand, galectin-9, but was dependent on CD8(+) Treg cell-surface Tim-3 binding to the alarmin, high-mobility group box 1 (HMGB-1). CONCLUSION: Virus-specific Tim-3(+) CD8(+) T cells operating through HMGB-1 recognition in the setting of acute and chronic viral infections of the liver may act to dampen hepatic T-cell responses in the liver microenvironment and, as a consequence, limit immune-mediated tissue injury or promote the establishment of persistent infections.

Cytokine-dependent induction of CD4+ T cells with cytotoxic potential during influenza virus infection.

Recent evidence has identified the role of granzyme B- and perforin-expressing CD4(+) T cells with cytotoxic potential in antiviral immunity. However, the in vivo cytokine cues and downstream pathways governing the differentiation of these cells are unclear. Here, we have identified that CD4(+) T cells with cytotoxic potential are specifically induced at the site of infection during influenza virus infection. The development of CD4(+) T cells with cytotoxic potential in vivo was dependent on the cooperation of the STAT2-dependent type I interferon signaling and the interleukin-2/interleukin-2 receptor alpha pathway for the induction of the transcription factors T-bet and Blimp-1. We showed that Blimp-1 promoted the binding of T-bet to the promoters of cytolytic genes in CD4(+) T cells and was required for the cytolytic function of the in vitro- and in vivo-generated CD4(+) T cells with cytotoxic potential. Thus, our data define the molecular basis of regulation of the in vivo development of this functionally cytotoxic Th subset during acute respiratory virus infection. The potential implications for the functions of these cells are discussed.

The adaptive immune response to respiratory syncytial virus.

Respiratory syncytial virus (RSV) causes severe respiratory disease in children, the elderly and immunocompromised individuals. The combined actions of CD4 and CD8 T cells play a critical role in terminating an acute RSV infection whereas antibodies can provide protection from re-infection. Despite eliciting an immune response that mediates clearance of the virus, immunity to the virus appears to wane over time and individuals remain susceptible to reinfection with RSV throughout their lifetime. The ineffectiveness of the natural infection to induce long-term immunity has hampered vaccine efforts and there is currently no licensed RSV vaccine. In this review, we summarize our current understanding of the adaptive immune response to RSV and its contribution to disease.

T cell responses during influenza infection: getting and keeping control.

The 2009 influenza pandemic highlighted the threat that type A influenza poses to human health. Thus, there is an urgency to understand the pathobiology of influenza infection and the contribution of the host immune response to virus elimination and the development of lung injury. This review focuses on the T cell arm of the adaptive host immune response to influenza. We assess recent developments in the understanding of how primary influenza virus-specific T cell responses are induced by antigen-presenting cells, the interaction of activated effector T cells with antigen-bearing cells in the infected lungs. Also examined is the contribution of influenza-specific effector T cells to the development and control of lung injury and inflammation during infection.

Viral infection of the lung: host response and sequelae.

Because of its essential role in gas exchange and oxygen delivery, the lung has evolved a variety of strategies to control inflammation and maintain homeostasis. Invasion of the lung by pathogens (and in some instances exposure to certain noninfectious particulates) disrupts this equilibrium and triggers a cascade of events aimed at preventing or limiting colonization (and more importantly infection) by pathogenic microorganisms. In this review we focus on viral infection of the lung and summarize recent advances in our understanding of the triggering of innate and adaptive immune responses to viral respiratory tract infection, mechanisms of viral clearance, and the well-recognized consequences of acute viral infection complicating underlying lung diseases, such as asthma.

Mitigating reactive oxygen species production and increasing gel porosity improves lymphocyte motility and fibroblast spreading in photocrosslinked gelatin-thiol hydrogels.

On-chip 3D culture systems that incorporate immune cells such as lymphocytes and stromal cells are needed to model immune organs in engineered systems such as organs-on-chip. Photocrosslinking is a useful tool for creating such immune-competent hydrogel cultures with spatial cell organization. However, loss of viability and motility in photocrosslinked gels can limit its utility, especially when working with fragile primary cells. We hypothesized that optimizing photoexposure-induced ROS production, hydrogel porosity or a combination of both factors was necessary to sustain cell viability and motility during culture in photocrosslinked gelatin-thiol (GelSH) hydrogels. Jurkat T cells, primary human CD4+ T cells and human lymphatic fibroblasts were selected as representative lymphoid immune cells to test this hypothesis. Direct exposure of these cells to 385 nm light and LAP photoinitiator dramatically increased ROS levels. Pretreatment with an antioxidant, ascorbic acid (AA), protected the cells from light + LAP-induced ROS and was non-toxic at optimized doses. Furthermore, scanning electron microscopy showed that native GelSH hydrogels had limited porosity, and that adding collagen to GelSH precursor before crosslinking markedly increased gel porosity. Next, we tested the impact of AA pretreatment and increasing gel porosity, alone or in combination, on cell viability and function in 3D GelSH hydrogel cultures. Increasing gel porosity, rather than AA pretreatment, was more critical for rescuing viability of Jurkat T cells and spreading of human lymphatic fibroblasts in GelSH-based gels, but both factors improved the motility of primary human CD4+ T cells. Increased porosity enabled formation of spatially organized co-cultures of primary human CD4+ T cells and human lymphatic fibroblasts in photo-crosslinked gels in a multi-lane microfluidic chip, towards modeling the lymphoid organ microenvironment. Some optimization is still needed to improve homogeneity between regions on the chip. These findings will enable researchers utilizing photocrosslinking methods to develop immunocompetent 3D culture models that support viability and function of sensitive lymphoid cells.

Autocrine regulation of pulmonary inflammation by effector T-cell derived IL-10 during infection with respiratory syncytial virus.

Respiratory syncytial virus (RSV) infection is the leading viral cause of severe lower respiratory tract illness in young infants. Clinical studies have documented that certain polymorphisms in the gene encoding the regulatory cytokine IL-10 are associated with the development of severe bronchiolitis in RSV infected infants. Here, we examined the role of IL-10 in a murine model of primary RSV infection and found that high levels of IL-10 are produced in the respiratory tract by anti-viral effector T cells at the onset of the adaptive immune response. We demonstrated that the function of the effector T cell -derived IL-10 in vivo is to limit the excess pulmonary inflammation and thereby to maintain critical lung function. We further identify a novel mechanism by which effector T cell-derived IL-10 controls excess inflammation by feedback inhibition through engagement of the IL-10 receptor on the antiviral effector T cells. Our findings suggest a potentially critical role of effector T cell-derived IL-10 in controlling disease severity in clinical RSV infection.

Single cell RNA sequencing unravels mechanisms underlying senescence-like phenotypes of alveolar macrophages.

Alveolar macrophages (AMs) are resident innate immune cells that play vital roles in maintaining lung physiological functions. However, the effects of aging on their dynamics, heterogeneity, and transcriptional profiles remain to be fully elucidated. Through single cell RNA sequencing (scRNA-seq), we identified CBFß as an indispensable transcription factor that ensures AM self-renewal. Intriguingly, despite transcriptome similarities of proliferating cells, AMs from aged mice exhibited reduced embryonic stem cell-like features. Aged AMs also displayed compromised DNA repair abilities, potentially leading to obstructed cell cycle progression and an elevation of senescence markers. Consistently, AMs from aged mice exhibited impaired self-renewal ability and reduced sensitivity to GM-CSF. Decreased CBFß was observed in the cytosol of AMs from aged mice. Similar senescence-like phenotypes were also found in human AMs. Taken together, these findings suggest that AMs in aged hosts demonstrate senescence-like phenotypes, potentially facilitated by the abrogated CBF ß activity.