Alveolar Type II Epithelial Cells Present Antigen to CD4+T Cells and Induce Foxp3+Regulatory T Cells

Immune-epithelial cell interactions in lung development, homeostasis and disease

The importance of the crosstalk between lung epithelial and immune cells, which emerges from early development and lasts throughout life, is corroborated by a growing body of scientific evidence. This communication not only has a role in driving lung morphogenesis during development, but it is also required in adulthood for the maintenance of homeostasis and repair following infection or injury. Disruption of the intricate immune-epithelial crosstalk can lead to diseases such as COPD and IPF. In this review we summarise the current knowledge regarding the communication between various immune and epithelial cells in development, homeostasis, regeneration and disease, while identifying the current gaps in our knowledge required to facilitate the development of more effective therapies.

Cytotoxic CD4+ T Cells Are Induced during Infection with Chlamydia trachomatis

Chlamydia trachomatis is the most common cause of bacterial sexually transmitted infection in both men and women. Immunity to C. trachomatis involves many cell types, but CD4+ T cells play a key role in protecting the host during natural infection. Specifically, IFN-γ production by CD4+ T cells is the main effector responsible for bacterial clearance, yet the exact mechanism by which IFN-γ confers protection is poorly defined. In our efforts to define the specific mechanisms for bacterial clearance, we now show that IFN-γ upregulates expression of MHC class II (MHCII) on nonhematopoietic cells during C. trachomatis infection in vivo. We also find that MHCII expression on epithelial cells of the upper genital tract contributes to the efficient clearance of bacteria mediated by pathogen-specific CD4+ Th1 cells. As we further cataloged the protective mechanisms of C. trachomatis-specific CD4+ T cells, we found that the T cells also express granzyme B (GzmB) when coincubated with infected cells. In addition, during C. trachomatis infection of mice, primed activated-naive CD4+ Th1 cells displayed elevated granzyme transcripts (GzmA, GzmB, GzmM, GzmK, GzmC) compared with memory CD4+ T cells in vivo. Finally, using intracellular cytokine staining and a GzmB-/- mouse strain, we show that C. trachomatis-specific CD4+ Th1 cells express GzmB upon Ag stimulation, and that this correlates with Chlamydia clearance in vivo. Together these results have led us to conclude that Chlamydia-specific CD4+ Th1 cells develop cytotoxic capacity through engagement with nonhematopoietic MHCII, and this correlates to C. trachomatis clearance.

Human erythroid progenitors express antigen presentation machinery

Early-life immune exposures can profoundly impact lifelong health. However, functional mechanisms underlying fetal immune development remain incomplete. Erythrocytes are not typically considered active immune mediators, primarily because erythroid precursors discard their organelles as they mature, thus losing the ability to alter gene expression in response to stimuli. Erythroid progenitors and precursors circulate in human fetuses and neonates. Although there is limited evidence that erythroid precursors are immunomodulatory, our understanding of the underlying mechanisms remains inadequate. To define the immunobiological role of fetal and perinatal erythroid progenitors and precursors, we analyzed single cell RNA-sequencing data and found that transcriptomics support erythroid progenitors as putative immune mediators. Unexpectedly, we discovered that human erythroid progenitors constitutively express Major Histocompatibility Complex (MHC) class II antigen processing and presentation machinery, which are hallmarks of specialized antigen presenting immune cells. Furthermore, we demonstrate that erythroid progenitors internalize and cleave foreign proteins into peptide antigens. Unlike conventional antigen presenting cells, erythroid progenitors express atypical costimulatory molecules and immunoregulatory cytokines that direct the development of regulatory T cells, which are critical for establishing maternal-fetal tolerance. Expression of MHC II in definitive erythroid progenitors begins during the second trimester, coinciding with the appearance of mature T cells in the fetus, and is absent in primitive progenitors. Lastly, we demonstrate physical and molecular interaction potential of erythroid progenitors and T cells in the fetal liver. Our findings shed light on a unique orchestrator of fetal immunity and provide insight into the mechanisms by which erythroid cells contribute to host defense.

Epithelial stem cells and niches in lung alveolar regeneration and diseases

Alveoli serve as the functional units of the lungs, responsible for the critical task of blood-gas exchange. Comprising type I (AT1) and type II (AT2) cells, the alveolar epithelium is continuously subject to external aggressors like pathogens and airborne particles. As such, preserving lung function requires both the homeostatic renewal and reparative regeneration of this epithelial layer. Dysfunctions in these processes contribute to various lung diseases. Recent research has pinpointed specific cell subgroups that act as potential stem or progenitor cells for the alveolar epithelium during both homeostasis and regeneration. Additionally, endothelial cells, fibroblasts, and immune cells synergistically establish a nurturing microenvironment-or "niche"-that modulates these epithelial stem cells. This review aims to consolidate the latest findings on the identities of these stem cells and the components of their niche, as well as the molecular mechanisms that govern them. Additionally, this article highlights diseases that arise due to perturbations in stem cell-niche interactions. We also discuss recent technical innovations that have catalyzed these discoveries. Specifically, this review underscores the heterogeneity, plasticity, and dynamic regulation of these stem cell-niche systems. It is our aspiration that a deeper understanding of the fundamental cellular and molecular mechanisms underlying alveolar homeostasis and regeneration will open avenues for identifying novel therapeutic targets for conditions such as chronic obstructive pulmonary disease (COPD), fibrosis, coronavirus disease 2019 (COVID-19), and lung cancer.

The underappreciated role of resident epithelial cell populations in metastatic progression: contributions of the lung alveolar epithelium

Metastatic cancer is difficult to treat and is responsible for the majority of cancer-related deaths. After cancer cells initiate metastasis and successfully seed a distant site, resident cells in the tissue play a key role in determining how metastatic progression develops. The lung is the second most frequent site of metastatic spread, and the primary site of metastasis within the lung is alveoli. The most abundant cell type in the alveolar niche is the epithelium. This review will examine the potential contributions of the alveolar epithelium to metastatic progression. It will also provide insight into other ways in which alveolar epithelial cells, acting as immune sentinels within the lung, may influence metastatic progression through their various interactions with cells in the surrounding microenvironment.

3D tissue-engineered lung models to study immune responses following viral infections of the small airways

Small airway infections caused by respiratory viruses are some of the most prevalent causes of illness and death. With the recent worldwide pandemic due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), there is currently a push in developing models to better understand respiratory diseases. Recent advancements have made it possible to create three-dimensional (3D) tissue-engineered models of different organs. The 3D environment is crucial to study physiological, pathophysiological, and immunomodulatory responses against different respiratory conditions. A 3D human tissue-engineered lung model that exhibits a normal immunological response against infectious agents could elucidate viral and host determinants. To create 3D small airway lung models in vitro, resident epithelial cells at the air-liquid interface are co-cultured with fibroblasts, myeloid cells, and endothelial cells. The air-liquid interface is a key culture condition to develop and differentiate airway epithelial cells in vitro. Primary human epithelial and myeloid cells are considered the best 3D model for studying viral immune responses including migration, differentiation, and the release of cytokines. Future studies may focus on utilizing bioreactors to scale up the production of 3D human tissue-engineered lung models. This review outlines the use of various cell types, scaffolds, and culture conditions for creating 3D human tissue-engineered lung models. Further, several models used to study immune responses against respiratory viruses, such as the respiratory syncytial virus, are analyzed, showing how the microenvironment aids in understanding immune responses elicited after viral infections.

microRNA Expression Profile of Purified Alveolar Epithelial Type II Cells

Alveolar type II (ATII) cells are essential for the maintenance of the alveolar homeostasis. However, knowledge of the expression of the miRNAs and miRNA-regulated networks which control homeostasis and coordinate diverse functions of murine ATII cells is limited. Therefore, we asked how miRNAs expressed in ATII cells might contribute to the regulation of signaling pathways. We purified "untouched by antibodies" ATII cells using a flow cytometric sorting method with a highly autofluorescent population of lung cells. TaqMan® miRNA low-density arrays were performed on sorted cells and intersected with miRNA profiles of ATII cells isolated according to a previously published protocol. Of 293 miRNAs expressed in both ATII preparations, 111 showed equal abundances. The target mRNAs of bona fide ATII miRNAs were used for pathway enrichment analysis. This analysis identified nine signaling pathways with known functions in fibrosis and/or epithelial-to-mesenchymal transition (EMT). In particular, a subset of 19 miRNAs was found to target 21 components of the TGF-β signaling pathway. Three of these miRNAs (miR-16-5p, -17-5p and -30c-5p) were down-modulated by TGF-β1 stimulation in human A549 cells, and concomitant up-regulation of associated mRNA targets (BMPR2, JUN, RUNX2) was observed. These results suggest an important role for miRNAs in maintaining the homeostasis of the TGF-β signaling pathway in ATII cells under physiological conditions.

Antigen Presentation in the Lung

The lungs are constantly exposed to environmental and infectious agents such as dust, viruses, fungi, and bacteria that invade the lungs upon breathing. The lungs are equipped with an immune defense mechanism that involves a wide variety of immunological cells to eliminate these agents. Various types of dendritic cells (DCs) and macrophages (MACs) function as professional antigen-presenting cells (APCs) that engulf pathogens through endocytosis or phagocytosis and degrade proteins derived from them into peptide fragments. During this process, DCs and MACs present the peptides on their major histocompatibility complex class I (MHC-I) or MHC-II protein complex to naïve CD8⁺ or CD4⁺ T cells, respectively. In addition to these cells, recent evidence supports that antigen-specific effector and memory T cells are activated by other lung cells such as endothelial cells, epithelial cells, and monocytes through antigen presentation. In this review, we summarize the molecular mechanisms of antigen presentation by APCs in the lungs and their contribution to immune response.

IL-1β Promotes Expansion of IL-33+ Lung Epithelial Stem Cells Following RSV Infection During Infancy

Respiratory syncytial virus (RSV)-induced immunopathogenesis and disease severity in neonatal mice and human infants have been related to elevated pulmonary IL-33. Thus, targeting IL-33 has been suggested as a potential therapy for respiratory viral infections. Yet, the regulatory mechanisms on IL-33 during early life remain unclear. Here, using a neonatal mouse model of RSV, we demonstrate that IL-1β positively regulates but is not required for RSV-induced expression of pulmonary IL-33 in neonatal mice early after the initial infection. Exogenous IL-1β upregulates RSV-induced IL-33 expression by promoting the proliferation of IL-33pos lung epithelial stem/progenitor cells (EpiSPC). These cells are exclusively detected in RSV-infected neonatal rather than adult mice, partially explaining the IL-1β-independent IL-33 expression in RSV-infected adult mice. Furthermore, IL-1β aggravates IL-33 mediated Th2 biased immunopathogenesis upon reinfection. Collectively, our study demonstrates that IL-1β exacerbates IL-33 mediated RSV immunopathogenesis by promoting the proliferation of IL-33pos EpiSPC in early life.

Niche-specific MHC II and PD-L1 regulate CD4+CD8αα+ intraepithelial lymphocyte differentiation

Conventional CD4⁺ T cells are differentiated into CD4⁺CD8αα⁺ intraepithelial lymphocytes (IELs) in the intestine; however, the roles of intestinal epithelial cells (IECs) are poorly understood. Here, we showed that IECs expressed MHC class II (MHC II) and programmed death–ligand 1 (PD-L1) induced by the microbiota and IFN-γ in the distal part of the small intestine, where CD4⁺ T cells were transformed into CD4⁺CD8αα⁺ IELs. Therefore, IEC-specific deletion of MHC II and PD-L1 hindered the development of CD4⁺CD8αα⁺ IELs. Intracellularly, PD-1 signals supported the acquisition of CD8αα by down-regulating the CD4-lineage transcription factor, T helper–inducing POZ/Krüppel-like factor (ThPOK), via the Src homology 2 domain–containing tyrosine phosphatase (SHP) pathway. Our results demonstrate that noncanonical antigen presentation with cosignals from IECs constitutes niche adaptation signals to develop tissue-resident CD4⁺CD8αα⁺ IELs.

Antigen presentation by lung epithelial cells directs CD4+ TRM cell function and regulates barrier immunity

Barrier tissues are populated by functionally plastic CD4+ resident memory T (TRM) cells. Whether the barrier epithelium regulates CD4+ TRM cell locations, plasticity and activities remains unclear. Here we report that lung epithelial cells, including distinct surfactant protein C (SPC)lowMHChigh epithelial cells, function as anatomically-segregated and temporally-dynamic antigen presenting cells. In vivo ablation of lung epithelial MHC-II results in altered localization of CD4+ TRM cells. Recurrent encounters with cognate antigen in the absence of epithelial MHC-II leads CD4+ TRM cells to co-express several classically antagonistic lineage-defining transcription factors, changes their cytokine profiles, and results in dysregulated barrier immunity. In addition, lung epithelial MHC-II is needed for surface expression of PD-L1, which engages its ligand PD-1 to constrain lung CD4+ TRM cell phenotypes. Thus, we establish epithelial antigen presentation as a critical regulator of CD4+ TRM cell function and identify epithelial-CD4+ TRM cell immune interactions as core elements of barrier immunity.

Type II alveolar cell MHCII improves respiratory viral disease outcomes while exhibiting limited antigen presentation

Type II alveolar cells (AT2s) are critical for basic respiratory homeostasis and tissue repair after lung injury. Prior studies indicate that AT2s also express major histocompatibility complex class II (MHCII) molecules, but how MHCII expression by AT2s is regulated and how it contributes to host defense remain unclear. Here we show that AT2s express high levels of MHCII independent of conventional inflammatory stimuli, and that selective loss of MHCII from AT2s in mice results in modest worsening of respiratory virus disease following influenza and Sendai virus infections. We also find that AT2s exhibit MHCII presentation capacity that is substantially limited compared to professional antigen presenting cells. The combination of constitutive MHCII expression and restrained antigen presentation may position AT2s to contribute to lung adaptive immune responses in a measured fashion, without over-amplifying damaging inflammation.

The receptor for advanced glycation endproducts (RAGE) decreases survival of tumor-bearing mice by enhancing the generation of lung metastasis-associated myeloid-derived suppressor cells

Metastatic cancer has a poor prognosis. Novel pharmacologic targets need to be identified. The receptor for advanced glycation endproducts (RAGE) is a pattern recognition receptor constitutively expressed in the lungs. Absence of overt disease in RAGE null mice suggests that RAGE is unnecessary or redundant in health. We report that RAGE null tumor-bearing mice have reduced lung metastasis and improved survival. Bone marrow chimera studies suggest that hematopoietic cell RAGE is an important contributor to these effects. Deletion of RAGE reduces both the quantity and suppressive activity of tumor-induced MDSC. Protein and mRNA studies suggest that RAGE contributes to the generation and function of MDSC including expression of the alarmins S100A8/A9 and activity of inducible nitric oxide synthase, arginase-1, and NF-κB. These findings demonstrate the important role of RAGE in determining the quantity and function of tumor-associated MDSC and suggest RAGE as a pharmacologic target for patients with metastatic disease.

Cathepsin L-selective inhibitors: A potentially promising treatment for COVID-19 patients

The widespread coronavirus SARS-CoV-2 has already infected over 4 million people worldwide, with a death toll over 280,000. Current treatment of COVID-19 patients relies mainly on antiviral drugs lopinavir/ritonavir, arbidol, and remdesivir, the anti-malarial drugs hydroxychloroquine and chloroquine, and traditional Chinese medicine. There are over 2,118 on-going clinical trials underway, but to date none of these drugs have consistently proven effective. Cathepsin L (CatL) is an endosomal cysteine protease. It mediates the cleavage of the S1 subunit of the coronavirus surface spike glycoprotein. This cleavage is necessary for coronavirus entry into human host cells, virus and host cell endosome membrane fusion, and viral RNA release for next round of replication. Here we summarize data regarding seven CatL-selective inhibitors that block coronavirus entry into cultured host cells and provide a mechanism to block SARS-CoV-2 infection in humans. Given the rapid growth of the SARS-CoV-2-positive population worldwide, ready-to-use CatL inhibitors should be explored as a treatment option. We identify ten US FDA-approved drugs that have CatL inhibitory activity. We provide evidence that supports the combined use of serine protease and CatL inhibitors as a possibly safer and more effective therapy than other available therapeutics to block coronavirus host cell entry and intracellular replication, without compromising the immune system.

IL-23 costimulates antigen-specific MAIT cell activation and enables vaccination against bacterial infection

Mucosal-associated invariant T (MAIT) cells are activated in a TCR-dependent manner by antigens derived from the riboflavin synthesis pathway, including 5-(2-oxopropylideneamino)-6-d-ribitylaminouracil (5-OP-RU), bound to MHC-related protein-1 (MR1). However, MAIT cell activation in vivo has not been studied in detail. Here, we have found and characterized additional molecular signals required for optimal activation and expansion of MAIT cells after pulmonary Legionella or Salmonella infection in mice. We show that either bone marrow-derived APCs or non-bone marrow-derived cells can activate MAIT cells in vivo, depending on the pathogen. Optimal MAIT cell activation in vivo requires signaling through the inducible T cell costimulator (ICOS), which is highly expressed on MAIT cells. Subsequent expansion and maintenance of MAIT-17/1-type responses are dependent on IL-23. Vaccination with IL-23 plus 5-OP-RU augments MAIT cell-mediated control of pulmonary Legionella infection. These findings reveal cellular and molecular targets for manipulating MAIT cell function under physiological conditions.

Lung adenocarcinoma-related TNF-α-dependent inflammation upregulates MHC-II on alveolar type II cells through CXCR-2 to contribute to Treg expansion

MHC-II on alveolar type-II (AT-II) cells is associated with immune tolerance in an inflammatory microenvironment. Recently, we found TNF-α upregulated MHC-II in AT-II in vitro. In this study, we explored whether TNF-α-mediated inflammation upregulates MHC-II on AT-II cells to trigger Treg expansion in inflammation-driven lung adenocarcinoma (IDLA). Using urethane-induced mice IDLA model, we found that IDLA cells mainly arise from AT-II cells, which are the major source of MHC-II. Blocking urethane-induced inflammation by TNF-α neutralization inhibited tumorigenesis and reversed MHC-II upregulation on tumor cells of AT-II cellular origin in IDLA. MHC-II-dependent AT-II cells were isolated from IDLA-induced Treg expansion. In human LA samples, we found high expression of MHC-II in tumor cells of AT-II cellular origin, which was correlated with increased Foxp3⁺ T cells infiltration as well as CXCR-2 expression. CXCR-2 and MHC-II colocalization was observed in inflamed lung tissue and IDLA cells of AT-II cellular origin. Furthermore, at the pro-IDLA inflammatory stage, TNF-α-neutralization or CXCR-2 deficiency inhibited the upregulation of MHC-II on AT-II cells in inflamed lung tissue. Thus, tumor cells of AT-II cellular origin contribute to Treg expansion in an MHC-II-dependent manner in TNF-α-mediated IDLA. At the pro-tumor inflammatory stage, TNF-α-dependent lung inflammation plays an important role in MHC-II upregulation on AT-II cells.

The primacy of gastrointestinal tract antigen-presenting cells in lethal graft-versus-host disease

Allogeneic stem cell transplantation is a cornerstone of curative therapy for high-risk and/or advanced hematological malignancies but remains limited by graft-versus-host disease (GVHD). GVHD is initiated by the interaction between recipient antigen-presenting cells (APCs) and donor T cells, culminating in T-cell differentiation along pathogenic type-1 and type-17 paradigms at the expense of tolerogenic regulatory T-cell patterns. Type-1 and type-17 T cells secrete cytokines (eg, granulocyte-macrophage colony-stimulating factor and interferon-γ) critical to the cytokine storm that amplifies expansion of donor APCs and their alloantigen presentation. It has become increasingly clear that pathogenic donor T-cell differentiation is initiated by both professional recipient APCs (eg, dendritic cells [DCs]) and nonprofessional APCs (eg, epithelial and mesenchymal cells), particularly within the gastrointestinal (GI) tract. In the immediate peritransplantation period, these APCs are profoundly modified by pathogen-associated molecular pattern (PAMP)/damage-associated molecular pattern (DAMP) signals derived from conditioning and intestinal microbiota. Subsequently, donor DCs in the GI tract are activated by DAMP/PAMP signals in the colon that gain access to the lamina propria once the mucosal barrier mucosa is compromised by GVHD. This results in donor DC expansion and alloantigen presentation in the colon and subsequent migration into the mesenteric lymph nodes. Here, new donor T cells are primed, expanded, differentiated, and imprinted with gut-homing integrins permissive of migration into the damaged GI tract, resulting in the lethal feed-forward cascade of GVHD. These new insights into our understanding of the cellular and molecular factors initiating GVHD, both spatially and temporally, give rise to a number of logical therapeutic targets, focusing on the inhibition of APC function in the GI tract.

Schizandrin attenuates inflammation induced by avian pathogenic Escherichia coli in chicken type II pneumocytes

Avian pathogenic Escherichia coli (APEC) is a kind of highly pathogenic parenteral bacteria, which adheres to chicken type II pneumocytes through pili, causing inflammatory damage of chicken type II pneumocytes. Without affecting the growth of bacteria, anti-adhesion to achieve anti-inflammatory effect is considered to be a new method for the treatment of multi-drug-resistant bacterial infections. In this study, the anti-APEC activity of schizandrin was studied in vitro. By establishing the model of chicken type II pneumocytes infected with APEC-O78, the adhesion number, the expression of virulence genes, the release of lactate dehydrogenase (LDH), levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8 and activation of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways were detected. The results showed that schizandrin reduced the release of LDH and the adherence of APEC on chicken type II pneumocytes. Moreover, schizandrin markedly decreased the levels of IL-1β, IL-8, IL-6, and TNF-α, the mechanism responsible for these effects was attributed to the inhibitory effect of schizandrin on NF-κB and MAPK signaling activation. In conclusion, our findings revealed that schizandrin could reduce the inflammatory injury of chicken type II pneumocytes by reducing the adhesion of APEC-O78 to chicken type II pneumocytes. The results indicate that schizandrin can be a potential agent to treat inflammation caused by avian colibacillosis.

The emerging role of regulatory T cells following lung transplantation

Regulatory T cells (Treg) have proven to be a powerful immunologic force in nearly every organ system and hold therapeutic potential for a wide range of diseases. Insights gained from non-transplant pathologies, such as infection, cancer, and autoimmunity, are now being translated to the field of solid organ transplantation, particularly for livers and kidneys. Recent insights from animal models of lung transplantation have established that Tregs play a vital role in suppressing rejection and facilitating tolerance of lung allografts, and such discoveries are being validated in human studies and preclinical trials. Given that long-term outcomes following lung transplantation remain profoundly limited by chronic rejection, Treg therapy holds the potential to significantly improve patient outcomes and should be aggressively investigated.

RNA-seq profiles of chicken type II pneumocyte in response to Escherichia coli infection

Avian pathogenic Escherichia coli (APEC) causes great economic loss to the poultry industry worldwide. Chicken type II pneumocytes (CP II cells) secrete surfactants and modulate lung immunity to decrease the infection of the invading pathogen. Nevertheless, the pathogenesis of CP II cells to APEC infection remains poorly understood. Therefore, we conducted global gene expression profiling of CP II cells after APEC-O78 infection to explore the host-pathogen interaction. The differentially expressed genes of CP II cells to APEC infection were characterized by RNA-seq with EB-seq algorithm. In consequence, the mRNA of 18996 genes was identified, and CP II cells responded to APEC infection with marked changes in the expression of 1390 genes. Among them, there are 803 down-regulated mRNAs and 587 up-regulated mRNAs. The KEGG prediction and Gene Ontology terms analysis revealed that the major enriched pathways were related to NF-κB signaling pathway, apoptosis pathway, tight junction, and cytokine-cytokine receptor interaction and other pathways. We adopted qRT-PCR to verify the validity of the selected gene expression. The fold induction of qPCR was similar to the RNA-seq results. These results provide a better understanding of the pathogenesis of APEC, especially apoptosis pathway involved in APEC infection.

Corneal Epithelial Cells Exhibit Myeloid Characteristics and Present Antigen via MHC Class II

Purpose

To explore the impact of ocular surface insults on the immunomodulatory capacity and phenotype of corneal epithelial cells (CECs) with a focus on epithelial-mesenchymal transition (EMT).

Methods

Corneas were harvested from mice 6 days following scratch injury, ragweed pollen-induced allergy, or herpes simplex virus type 1 (HSV-1) infection and compared to healthy tissue controls. Corneas were enzymatically digested and CECs phenotypically characterized using flow cytometry. CECs were defined as epithelial cell adhesion molecule (EpCAM)-positive CD45-negative cells. CECs were assessed by PCR to evaluate EMT-associated transcripts. Recombinant HSV-1 and transgenic mice were utilized to investigate the role of vascular endothelial growth factor A (VEGFA) on the phenotype observed. The immunomodulatory potential of CECs was assessed in coculture assays with ovalbumin-specific CD4 T cells.

Results

Ectopic expression of classic "myeloid" antigens Ly6G, CCR2, and CX3CR1 was identified in CEC subsets from all groups with evidence supporting an underlying partial EMT event resulting from loss of cell-cell contacts. Corneal HSV-1 infection induced Ly6C expression and major histocompatibility complex (MHC)-II upregulation in CECs through a VEGFA-linked mechanism. These Ly6C+ MHC-II+ CECs were found to function as amateur antigen-presenting cells and induced CD4 T cell proliferation in vitro.

Conclusions

This study characterizes a novel immunomodulatory CEC phenotype with possible implications for immune privilege, chronic inflammation, and tissue fibrosis. Moreover, the identification of CECs masquerading with multiple "myeloid" antigens warrants careful evaluation of flow cytometry data involving corneal digests.

Expression and regulation of immune-modulatory enzyme indoleamine 2,3-dioxygenase (IDO) by human airway epithelial cells and its effect on T cell activation

Indoleamine 2,3-dioxygenase (IDO) catalyzes the degradation of tryptophan, which plays a critical role in immune suppression through regulating the production of a series of metabolites that are generally referred to as kynurenines. It has become increasingly clear that epithelial cells (ECs) play an active role in maintaining lung homeostasis by modulating the function of immune cells via producing cytokines, chemokines, and anti-microbial mediators. In this study we assessed the regulation of IDO activity and expression in human primary ECs and EC lines under steady state conditions and in response to bacterial and allergenic stimuli. We also investigated the potential immune modulatory functions of IDO expression in human airway ECs. Our data clearly show that airway ECs produce IDO, which is down-regulated in response to allergens and TLR ligands while up-regulated in response to IFN-γ. Using gene silencing, we further demonstrate that IDO plays a key role in the EC-mediated suppression of antigen-specific and polyclonal proliferation of T cells. Interestingly, our data also show that ECs lose their inhibitory effect on T cell activation in response to different TLR agonists mimicking bacterial or viral infections. In conclusion, our work provides an understanding of how IDO is regulated in ECs as well as demonstrates that “resting” ECs can suppress T cell activation in an IDO dependent manner. These data provide new insight into how ECs, through the production of IDO, can influence downstream innate and adaptive responses as part of their function in maintaining immune homeostasis in the airways.

Inhibition of T Cell Alloreactivity by Bronchial Epithelium Is Impaired in Lung Transplant Recipients, Through Pathways Involving TGF-β, IL-10 and HLA-G

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) after lung transplantation (LTx) results from bronchial epithelial cell (BECs) damages, thought to be orchestrated by T cells primed by antigen-presenting cell presenting alloantigens. In this cell cross-talk, BECs are also suspected to play a pivotal immunosuppressive role in T cell alloreactivity. We studied the immunomodulating role of BECs in a human ex vivo model of allogeneic T cell response, both in healthy subjects and LTx recipients.

METHODS

BECs from 35 LTx recipients (n = 22 stable, n = 13 BOS) and healthy controls (n = 25) were cultured as primary cell cultures. Their inhibitory capacities through the involvement of tolerogenic molecules (HLA-G, TGF-β, and IL-10) were tested on a mixed lymphocyte reaction between antigen-presenting cells and recipient T cells.

RESULTS

Control BECs inhibited T cell alloproliferation by a mean of 53 ± 7%. This inhibitory effect of BECs was significantly reduced in the stable LTx group (24 ± 8%, P = 0.009), but not in the BOS TxP group (53 ± 10%, P = 0.97). Neutralization of HLA-G, TGF-β, and IL-10 partially restored T cell alloproliferation, arguing for their involvement in the immunosuppressive effect of BECs. BECs culture supernatant from stable LTx patients with impaired BEC properties showed a skewed Th2-type secretion profile (high IL-4/IFN-γ ratio).

CONCLUSIONS

The inhibitory properties of BECs are dysregulated in stable LTx recipients, which could suggest their instrumental role in the initiation of BOS process and potential targeted therapies.

CpG-ODN Facilitates Effective Intratracheal Immunization and Recall of Memory against Neoantigen-Expressing Alveolar Cells

Intrapulmonary immune reactions are impaired by the tolerogenic environment of the lung. This is manifested by the absence of effective endogenous T cell responses upon neoantigen expression. This tolerance is considered to contribute to lung cancer and inefficient immune therapeutic interventions. To investigate the mechanisms contributing to lung tolerance and to overcome these restrictions, we developed a transgenic mouse model with induction of a neoantigen (OVA) exclusively in alveolar type II epithelial cells. This model is characterized by the absence of functional endogenous T cell responses upon OVA neoantigen induction. Standard DNA and protein vaccination protocols resulted in the accumulation of high numbers of antigen-specific CD8 T cells in the lung. However, clearance of antigen-expressing cells was not achieved. To overcome this tolerance, we induced inflammatory conditions by coapplication of the TLR ligands LPS and CpG-ODN during intrapulmonary vaccinations. Both ligands induced high numbers of neoantigen-specific T cells in the lung. However, only coapplication of CpG-ODN was sufficient to establish functional cytotoxic responses resulting in the elimination of neoantigen presenting target cells. Remarkably, CpG-ODN was also crucial for functional memory responses upon re-induction of the neoantigen. The results highlight the need of TLR9 co-stimulation for overcoming tolerization, which might be a key factor for therapeutic interventions.

Quantitative Analysis of Proteome Modulations in Alveolar Epithelial Type II Cells in Response to Pulmonary Aspergillus fumigatus Infection

The ubiquitous mold Aspergillus fumigatus threatens immunosuppressed patients as inducer of lethal invasive aspergillosis. A. fumigatus conidia are airborne and reach the alveoli, where they encounter alveolar epithelial cells (AEC). Previous studies reported the importance of the surfactant-producing AEC II during A. fumigatus infection via in vitro experiments using cell lines. We established a negative isolation protocol yielding untouched primary murine AEC II with a purity >90%, allowing ex vivo analyses of the cells, which encountered the mold in vivo By label-free proteome analysis of AEC II isolated from mice 24h after A. fumigatus or mock infection we quantified 2256 proteins and found 154 proteins to be significantly differentially abundant between both groups (ANOVA p value ≤ 0.01, ratio of means ≥1.5 or ≤0.67, quantified with ≥2 peptides). Most of these proteins were higher abundant in the infected condition and reflected a comprehensive activation of AEC II on interaction with A. fumigatus This was especially represented by proteins related to oxidative phosphorylation, hence energy production. However, the most strongly induced protein was the l-amino acid oxidase (LAAO) Interleukin 4 induced 1 (IL4I1) with a 42.9 fold higher abundance (ANOVA p value 2.91^-10). IL4I1 has previously been found in B cells, macrophages, dendritic cells and rare neurons. Increased IL4I1 abundance in AEC II was confirmed by qPCR, Western blot and immunohistology. Furthermore, A. fumigatus infected lungs showed high levels of IL4I1 metabolic products. Importantly, higher IL4I1 abundance was also confirmed in lung tissue from human aspergilloma. Because LAAO are key enzymes for bactericidal product generation, AEC II might actively participate in pathogen defense. We provide insights into proteome changes of primary AEC II thereby opening new avenues to analyze the molecular changes of this central lung cell on infectious threats. Data are available via ProteomeXchange with identifier PXD005834.

Modeling DNA damage-induced pneumopathy in mice: insight from danger signaling cascades

Radiation-induced pneumonitis and fibrosis represent severe and dose-limiting side effects in the radiotherapy of thorax-associated neoplasms leading to decreased quality of life or - as a consequence of treatment with suboptimal radiation doses - to fatal outcomes by local recurrence or metastatic disease. It is assumed that the initial radiation-induced damage to the resident cells triggers a multifaceted damage-signalling cascade in irradiated normal tissues including a multifactorial secretory program. The resulting pro-inflammatory and pro-angiogenic microenvironment triggers a cascade of events that can lead within weeks to a pronounced lung inflammation (pneumonitis) or after months to excessive deposition of extracellular matrix molecules and tissue scarring (pulmonary fibrosis).The use of preclinical in vivo models of DNA damage-induced pneumopathy in genetically modified mice has helped to substantially advance our understanding of molecular mechanisms and signalling molecules that participate in the pathogenesis of radiation-induced adverse late effects in the lung. Herein, murine models of whole thorax irradiation or hemithorax irradiation nicely reproduce the pathogenesis of the human disease with respect to the time course and the clinical symptoms. Alternatively, treatment with the radiomimetic DNA damaging chemotherapeutic drug Bleomycin (BLM) has frequently been used as a surrogate model of radiation-induced lung disease. The advantage of the BLM model is that the symptoms of pneumonitis and fibrosis develop within 1 month.Here we summarize and discuss published data about the role of danger signalling in the response of the lung tissue to DNA damage and its cross-talk with the innate and adaptive immune systems obtained in preclinical studies using immune-deficient inbred mouse strains and genetically modified mice. Interestingly we observed differences in the role of molecules involved in damage sensing (TOLL-like receptors), damage signalling (MyD88) and immune regulation (cytokines, CD73, lymphocytes) for the pathogenesis and progression of DNA damage-induced pneumopathy between the models of pneumopathy induced by whole thorax irradiation or treatment with the radiomimetic drug BLM. These findings underline the importance to pursue studies in the radiation model(s) if we are to unravel the mechanisms driving radiation-induced adverse late effects.A better understanding of the cross-talk of danger perception and signalling with immune activation and repair mechanisms may allow a modulation of these processes to prevent or treat radiation-induced adverse effects. Vice-versa an improved knowledge of the normal tissue response to injury is also particularly important in view of the increasing interest in combining radiotherapy with immune checkpoint blockade or immunotherapies to avoid exacerbation of radiation-induced normal tissue toxicity.

MicroRNAs in mucosal inflammation

Of the total human body's surface, the majority is internal surface, belonging to the lungs (100 m²) and intestinal tract (400 m²). In comparison, the external surface area, belonging to the skin, comprises less than 1% (2 m²). Continuous exposure of the mucosal surface to external factors (e.g., pathogens, food particles) requires tight regulation to maintain homeostasis. MicroRNAs (miRNAs) have gained noticeable attention as playing important roles in maintaining the steady-state of tissues by modulating immune functions and inflammatory responses. Accordingly, associations have been found between miRNA expression levels and human health conditions and diseases. These findings have important implications in inflammatory diseases involving pulmonary and intestinal mucosa, such as acute lung injury or inflammatory bowel disease. In this review, we highlight the known biology of miRNAs and discuss the role of miRNAs in modulating mucosal defense and homeostasis. Additionally, we discuss miRNAs serving as potential therapeutic targets to treat immunological conditions, particularly mucosal inflammation.

Chronic lung inflammation primes humoral immunity and augments antipneumococcal resistance

Airway epithelial cells (AECs) display remarkable plasticity in response to infectious stimuli and their functional adaptations are critical for antimicrobial immunity. However, the roles of AECs and humoral mediators to host defense in non-communicable lung inflammation remain elusive. We dissected pulmonary defense against Streptococcus pneumoniae in hosts with pre-existing inflammatory conditions (SPC-HAxTCR-HA mice). Lung tissue transcriptomics and bronchoalveolar lavage fluid (BALF) proteomics revealed an induction of humoral defense mechanisms in inflamed lungs. Accordingly, besides antibacterial proteins and complement components being overrepresented in inflamed lungs, elevated polymeric immunoglobulin receptor (pIgR)-expression in AECs correlated with increased secretory immunoglobulin (SIg) transport. Consequently, opsonization assays revealed augmented pneumococcal coverage by SIgs present in the BALF of SPC-HAxTCR-HA mice, which was associated with enhanced antipneumococcal resistance. These findings emphasize the immunologic potential of AECs as well as their central role in providing antibacterial protection and put forward pIgR as potential target for therapeutic manipulation in infection-prone individuals.

Polarized Airway Epithelial Models for Immunological Co-Culture Studies

Epithelial cells line all cavities and surfaces throughout the body and play a substantial role in maintaining tissue homeostasis. Asthma and other atopic diseases are increasing worldwide and allergic disorders are hypothesized to be a consequence of a combination of dysregulation of the epithelial response towards environmental antigens and genetic susceptibility, resulting in inflammation and T cell-derived immune responses. In vivo animal models have long been used to study immune homeostasis of the airways but are limited by species restriction and lack of exposure to a natural environment of both potential allergens and microflora. Limitations of these models prompt a need to develop new human cell-based in vitro models. A variety of co-culture systems for modelling the respiratory epithelium exist and are available to the scientific community. The models have become increasingly sophisticated and specific care needs to be taken with regard to cell types, culture medium and culture models, depending on the aim of the study. Although great strides have been made, there is still a need for further optimization, and optimally also for standardization, in order for in vitro co-culture models to become powerful tools in the discovery of key molecules dictating immunity and/or tolerance, and for understanding the complex interplay that takes place between mucosa, airway epithelium and resident or infiltrating immune cells. This review focuses on current knowledge and the advantages and limitations of the different cell types and culture methods used in co-culture models of the human airways.

Alveolar Type II Epithelial Cells Contribute to the Anti-Influenza A Virus Response in the Lung by Integrating Pathogen- and Microenvironment-Derived Signals

Influenza A virus (IAV) periodically causes substantial morbidity and mortality in the human population. In the lower lung, the primary targets for IAV replication are type II alveolar epithelial cells (AECII), which are increasingly recognized for their immunological potential. So far, little is known about their reaction to IAV and their contribution to respiratory antiviral immunity in vivo. Therefore, we characterized the AECII response during early IAV infection by analyzing transcriptional regulation in cells sorted from the lungs of infected mice. We detected rapid and extensive regulation of gene expression in AECII following in vivo IAV infection. The comparison to transcriptional regulation in lung tissue revealed a strong contribution of AECII to the respiratory response. IAV infection triggered the expression of a plethora of antiviral factors and immune mediators in AECII with a high prevalence for interferon-stimulated genes. Functional pathway analyses revealed high activity in pathogen recognition, immune cell recruitment, and antigen presentation. Ultimately, our analyses of transcriptional regulation in AECII and lung tissue as well as interferon I/III levels and cell recruitment indicated AECII to integrate signals provided by direct pathogen recognition and surrounding cells. Ex vivo analysis of AECII proved a powerful tool to increase our understanding of their role in respiratory immune responses, and our results clearly show that AECII need to be considered a part of the surveillance and effector system of the lower respiratory tract.

In order to confront the health hazard posed by IAV, we need to complete our understanding of its pathogenesis. AECII are primary targets for IAV replication in the lung, and while we are beginning to understand their importance for respiratory immunity, the in vivo AECII response during IAV infection has not been analyzed. In contrast to studies addressing the response of AECII infected with IAV ex vivo, we have performed detailed gene transcriptional profiling of AECII isolated from the lungs of infected mice. Thereby, we have identified an exceptionally rapid and versatile response to IAV infection that is shaped by pathogen-derived as well as microenvironment-derived signals and aims at the induction of antiviral measures and the recruitment and activation of immune cells. In conclusion, our study presents AECII as active players in antiviral defense in vivo that need to be considered part of the sentinel and effector immune system of the lung.

Effects of Lung Cotransplantation on Cardiac Allograft Tolerance Across a Full Major Histocompatibility Complex Barrier in Miniature Swine

A 12-day course of high-dose tacrolimus induces tolerance of major histocompatibility complex-mismatched lung allografts in miniature swine but does not induce tolerance of heart allografts unless a kidney is cotransplanted. To determine whether lungs share with kidneys the ability to induce cardiac allograft tolerance, we investigated heart-lung cotransplantation using the same induction protocol. Hearts (n = 3), heart-kidneys (n = 3), lungs (n = 6), and hearts-lungs (n = 3) were transplanted into fully major histocompatibility complex-mismatched recipients treated with high-dose tacrolimus for 12 days. Serial biopsy samples were used to evaluate rejection, and in vitro assays were used to detect donor responsiveness. All heart-kidney recipients and five of six lung recipients demonstrated long-term graft survival for longer than 272 days, while all heart recipients rejected their allografts within 35 days. Tolerant recipients remained free of alloantibody and showed persistent donor-specific unresponsiveness by cell-mediated lympholysis/mixed-lymphocyte reaction. In contrast, heart-lung recipients demonstrated rejection of both allografts (days 47, 55, and 202) and antidonor responsiveness in vitro. In contrast to kidneys, lung cotransplantation leads to rejection of both heart and lung allografts, indicating that lungs do not have the same tolerogenic capacity as kidneys. We conclude that cells or cell products present in kidney, but not heart or lung allografts, have a unique capacity to confer unresponsiveness on cotransplanted organs, most likely by amplifying host regulatory mechanisms.

Morphological and Functional Alterations of Alveolar Macrophages in a Murine Model of Chronic Inflammatory Lung Disease

Purpose

Chronic lung inflammation commonly induces a multitude of structural and functional adaptations within the lung tissue and airspaces. Yet the impact of a persistent inflammatory environment on alveolar macrophages is still incompletely understood. Here, we examined morphology and function of alveolar macrophages in a transgenic mouse model of chronic lung disease.

Methods

Imaging flow cytometry, flow cytometry, and microscopic evaluation of alveolar macrophages isolated from healthy and inflamed lungs were performed. Gene expression of polarization markers was compared by quantitative real-time RT-PCR. The pro-inflammatory immune response of alveolar macrophages toward bacterial ligands was assessed in in vivo clodronate-liposome depletion studies.

Results

Chronic lung inflammation is associated with a substantially altered, activated alveolar macrophage morphology, and blunted TNF-α response by these cells following stimulation with ligands derived from the respiratory pathogen Streptococcus pneumoniae.

Conclusions

These results demonstrate pleiotropic effects of pulmonary inflammation on alveolar macrophage phenotype and function and suggest a functional impairment of these cells during infection with airborne pathogens.

Enhanced phenotypic alterations of alveolar type II cells in response to Aflatoxin G1 -induced lung inflammation

Recently, we discovered that Aflatoxin G1 (AFG1 ) induces chronic lung inflammatory responses, which may contribute to lung tumorigenesis in Balb/C mice. The cancer cells originate from alveolar type II cells (AT-II cells). The activated AT-II cells express high levels of MHC-II and COX-2, may exhibit altered phenotypes, and likely inhibit antitumor immunity by triggering regulatory T cells (Tregs). However, the mechanism underlying phenotypic alterations of AT-II cells caused by AFG1 -induced inflammation remains unknown. In this study, increased MHC-II expression in alveolar epithelium was observed and associated with enhanced Treg infiltration in mouse lung tissues with AFG1 -induced inflammation. This provides a link between phenotypically altered AT-II cells and Treg activity in the AFG1 -induced inflammatory microenvironment. AFG1 -activated AT-II cells underwent phenotypic maturation since AFG1 upregulated MHC-II expression on A549 cells and primary human AT-II cells in vitro. However, mature AT-II cells may exhibit insufficient antigen presentation, which is necessary to activate effector T cells, due to the absence of CD80 and CD86. Furthermore, we treated A549 cells with AFG1 and TNF-α together to mimic an AFG1 -induced inflammatory response in vitro, and we found that TNF-α and AFG1 coordinately enhanced MHC-II, CD54, COX-2, IL-10, and TGF-β expression levels in A549 cells compared to AFG1 alone. The phenotypic alterations of A549 cells in response to the combination of TNF-α and AFG1 were mainly regulated by TNF-α-mediated induction of the NF-κB pathway. Thus, enhanced phenotypic alterations of AT-II cells were induced in response to AFG1 -induced inflammation. Thus, AT-II cells are likely to suppress anti-tumor immunity by triggering Treg activity.

Atypical MHC class II-expressing antigen-presenting cells: can anything replace a dendritic cell?

Dendritic cells, macrophages and B cells are regarded as the classical antigen-presenting cells of the immune system. However, in recent years, there has been a rapid increase in the number of cell types that are suggested to present antigens on MHC class II molecules to CD4(+) T cells. In this Review, we describe the key characteristics that define an antigen-presenting cell by examining the functions of dendritic cells. We then examine the functions of the haematopoietic cells and non-haematopoietic cells that can express MHC class II molecules and that have been suggested to represent 'atypical' antigen-presenting cells. We consider whether any of these cell populations can prime naive CD4(+) T cells and, if not, question the effects that they do have on the development of immune responses.

Cyclooxygenase inhibition abrogates aeroallergen-induced immune tolerance by suppressing prostaglandin I2 receptor signaling

BACKGROUND

The prevalence of allergic diseases has doubled in developed countries in the past several decades. Cyclooxygenase (COX)-inhibiting drugs augmented allergic diseases in mice by increasing allergic sensitization and memory immune responses. However, whether COX inhibition can promote allergic airway diseases by inhibiting immune tolerance is not known.

OBJECTIVE

To determine the role of the COX pathway and prostaglandin I2 (PGI2) signaling through the PGI2 receptor (IP) in aeroallergen-induced immune tolerance.

METHODS

Wild-type (WT) BALB/c mice and IP knockout mice were aerosolized with ovalbumin (OVA) to induce immune tolerance prior to immune sensitization with an intraperitoneal injection of OVA/alum. The COX inhibitor indomethacin or vehicle was administered in drinking water to inhibit enzyme activity during the sensitization phase. Two weeks after sensitization, the mice were challenged with OVA aerosols. Mouse bronchoalveolar lavage fluid was harvested for cell counts and TH2 cytokine measurements.

RESULTS

WT mice treated with indomethacin had greater numbers of total cells, eosinophils, and lymphocytes, and increased IL-5 and IL-13 protein expression in BAL fluid compared to vehicle-treated mice. Similarly, IP knockout mice had augmented inflammation and TH2 cytokine responses compared to WT mice. In contrast, the PGI2 analog cicaprost attenuated the anti-tolerance effect of COX inhibition.

CONCLUSION

COX inhibition abrogated immune tolerance by suppressing PGI2 IP signaling, suggesting that PGI2 signaling promotes immune tolerance and that clinical use of COX-inhibiting drugs may increase the risk of developing allergic diseases.

Gene expression profiles reveal distinct immunological responses of cobalt and cerium dioxide nanoparticles in two in vitro lung epithelial cell models

Fragmentary knowledge exists on cellular signaling responses underlying possible adverse health effects of CoO- and CeO2-nanoparticles (NP)s after inhalation. We aimed to perform a time kinetic study of gene expression profiles induced by these NPs in alveolar A549 and bronchial BEAS-2B epithelial cells, and investigated possible immune system modulation. The kinetics of the cell responses induced by the NPs were different between the lung epithelial models. Both CoO- and CeO2-NP exposure induced mainly downregulation of gene transcription. BEAS-2B cells were found to be more sensitive, as they showed a higher number of differentially expressed transcripts (DET) at a 10-fold lower NP-concentration than A549 cells. Hierarchical clustering of all DET indicated that the transcriptional responses were heterogeneous among the two cell types and two NPs. Between 1% and 14% DET encoding markers involved in immune processes were observed. The transcriptional impact of the metal oxide NPs appeared to be cell-dependent, both at the general and immune response level, whereas each lung epithelial cell model responded differently to the two NP types. Thus, the study provides gene expression markers and immune processes involved in CoO- and CeO2-NP-induced toxicity, and demonstrates the usefulness of comprehensive-omics studies to differentiate between NP responses.

Mycobacterium bovis BCG triggered MyD88 induces miR-124 feedback negatively regulates immune response in alveolar epithelial cells

The emerging roles of microRNAs (miRNAs) and pulmonary epithelial cells in regulating the immune response against microbial invasion has attracted increasing attention in recent years, however, the immunoregulatory roles of miRNAs in the pulmonary epithelial cells in response to mycobacterial infection has not been fully demonstrated. In this study, we show that miR-124 expression is induced upon Mycobacterium bovis Bacillus Calmette-Guerin (BCG) infection in A549 alveolar epithelial cells and murine lungs. miR-124 is able to modulate Toll-like receptor (TLR) signaling in A459 cells. In this regard, multiple components, including TLR6, myeloid differentiation factor 88 (MyD88), TNFR-associated factor 6 and tumor necrosis factor-α of the TLR signaling cascade are directly regulated by miR-124 in response to BCG stimulation. In addition, miR-124 expression was induced upon MyD88 overexpression and/or BCG stimulation, while silencing MyD88 expression by small interfering RNA dramatically down-regulated miR-124 transcription in A549 cells. These results indicate an underlying negative feedback mechanism between miR-124 and MyD88 in alveolar epithelial cells to prevent an excessive inflammatory response during mycobacterial infection. These observations suggest that miR-124 is a potential target for preventive and therapeutic intervention against the pulmonary tuberculosis, an infectious disease caused by Mycobacterium tuberculosis infection.

The Yin-Yang arms of vaccines: disease-fighting power versus tissue-destructive inflammation

The disease-fighting power of vaccines has defeated many pathogens and has been credited with global reduction of mortality and morbidity. However, most vaccine developments focus on the enhancement of effector responses with systemic inflammation and the consequences overlooked. Recent evidence shows that systemic inflammatory phenotypes, acute or chronic, are both detrimental and should be avoided if possible. Since noninvasive vaccination by painless delivery of nasal vaccines and skin patch vaccines could elicit potent protective immunity without inducing systemic inflammation, it can be predicted that vaccinology will increasingly see the abandonment of the 'needle-injection' paradigm for vaccine development. The findings that specific viral particles could rapidly remodel the tissue environment postinfection in favor of some pathogens with the capacity to suppress others illustrate the pressing need for a deeper understanding of the underlying mechanisms in order to unlock the full potential of immunological intervention.

Vitamin D, the immune system and asthma

The effects of vitamin D on bone metabolism and calcium homeostasis have long been recognized. Emerging evidence has implicated vitamin D as a critical regulator of immunity, playing a role in both the innate and cell-mediated immune systems. Vitamin D deficiency has been found to be associated with several immune-mediated diseases, susceptibility to infection and cancer. Recently, there has been increasing interest in the possible link between vitamin D and asthma. Further elucidation of the role of vitamin D in lung development and immune system function may hold profound implications for the prevention and treatment of asthma.

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.

Addressing bioterrorism concerns: options for investigating the mechanism of action of Staphylococcus aureus enterotoxin B

Staphylococcal enterotoxin B (SEB) is of concern to military and civilian populations as a bioterrorism threat agent. It is a highly potent toxin produced by Staphylococcus aureus and is stable in storage and under aerosolisation; it is able to produce prolonged highly incapacitating illness at very low-inhaled doses and death at elevated doses. Concerns regarding SEB are compounded by the lack of effective medical countermeasures for mass treatment of affected populations. This article considers the mechanism of action of SEB, the availability of appropriate experimental models for evaluating the efficacy of candidate medical countermeasures with particular reference to the need to realistically model SEB responses in man and the availability of candidate countermeasures (with an emphasis on commercial off-the-shelf options). The proposed in vitro approaches would be in keeping with Dstl’s commitment to reduction, refinement and replacement of animal models in biomedical research, particularly in relation to identifying valid alternatives to the use of nonhuman primates in experimental studies.

Establishment and evaluation of a stable cattle type II alveolar epithelial cell line

Macrophages and dendritic cells are recognized as key players in the defense against mycobacterial infection. Recent research has confirmed that alveolar epithelial cells (AECs) also play important roles against mycobacterium infections. Thus, establishing a stable cattle AEC line for future endogenous immune research on bacterial invasion is necessary. In the present study, we first purified and immortalized type II AECs (AEC II cells) by transfecting them with a plasmid containing the human telomerase reverse trancriptase gene. We then tested whether or not the immortalized cells retained the basic physiological properties of primary AECs by reverse-transcription polymerase chain reaction and Western blot. Finally, we tested the secretion capacity of immortalized AEC II cells upon stimulation by bacterial invasion. The cattle type II alveolar epithelial cell line (HTERT-AEC II) that we established retained lung epithelial cell characteristics: the cells were positive for surfactants A and B, and they secreted tumor necrosis factor-α and interleukin-6 in response to bacterial invasion. Thus, the cell line we established is a potential tool for research on the relationship between AECs and Mycobacterium tuberculosis.

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.

Immunomodulation of alveolar epithelial cells by Mycobacterium tuberculosis phosphatidylinositol mannosides results in apoptosis

During intracellular residence in macrophages, mycobacterial lipids, namely phosphatidylinositol mannosides (PIM) and lipoarabinomannans, are expelled in the lung milieu to interact with host cells. PIM include a group of essential lipid components of Mycobacterium tuberculosis (M. tb) cell wall. Given that PIM function as mycobacterial adhesins for binding to host cells, the present study explored the consequences of interaction of M. tb PIM with alveolar epithelial cells (AEC). A 24-h PIM exposure at a concentration of 10 μg/mL to AEC conferred cytolysis to AEC via induction of apoptosis, suggesting their potential to alter alveolar epithelium integrity. The results also reflected that type I like AEC are more sensitive to cytolysis than type II AEC. PIM-treated AEC exhibited significant production of reactive oxygen species (ROS) and an immunosuppressive cytokine transforming growth factor-β (TGF-β) in the culture supernatants. Although AEC displayed constitutive mRNA transcripts for toll-like receptors (TLR2 and 4) as well as chemokines (IL-8 and MCP-1), no significant change in their expression was observed upon PIM treatment. Collectively, these results offer insights into PIM potential as M. tb virulence factor that might promote mycobacterial dissemination by causing cytolysis of AEC via increased production of ROS and TGF-β.

Human intrahepatic biliary epithelial cells engulf blebs from their apoptotic peers

The phagocytic clearance of apoptotic cells is critical for tissue homeostasis; a number of non-professional phagocytic cells, including epithelial cells, can both take up and process apoptotic bodies, including the release of anti-inflammatory mediators. These observations are particularly important in the case of human intrahepatic biliary cells (HiBEC), because such cells are themselves a target of destruction in primary biliary cirrhosis, the human autoimmune disease. To address the apoptotic ability of HiBECs, we have focused on their ability to phagocytize apoptotic blebs from autologous HiBECs. In this study we report that HiBEC cells demonstrate phagocytic function from autologous HiBEC peers accompanied by up-regulation of the chemokines CCL2 [monocyte chemotactic protein-1 (MCP-1)] and CXCL8 [interleukin (IL)-8]. In particular, HiBEC cells express the phagocytosis-related receptor phosphatidylserine receptors (PSR), implying that HiBECs function through the 'eat-me' signal phosphatidylserine expressed by apoptotic cells. Indeed, although HiBEC cells acquire antigen-presenting cell (APC) function, they do not change the expression of classic APC function surface markers after engulfment of blebs, both with and without the presence of Toll-like receptor (TLR) stimulation. These results are important not only for understanding of the normal physiological function of HiBECs, but also explain the inflammatory potential and reduced clearance of HiBEC cells following the inflammatory cascade in primary biliary cirrhosis.

COPD is associated with production of autoantibodies to a broad spectrum of self-antigens, correlative with disease phenotype

The role of autoimmune pathology in development and progression of chronic obstructive pulmonary disease (COPD) is becoming increasingly appreciated. In this study, we identified serum autoantibody reactivities associated with chronic bronchitis or emphysema, as well as systemic autoimmunity and associated lung disease. Using autoantigen array analysis, we demonstrated that COPD patients produce autoantibodies reactive to a broad spectrum of self-antigens. Further, the level and reactivities of these antibodies, or autoantibody profile, correlated with disease phenotype. Patients with emphysema produced autoantibodies of higher titer and reactive to an increased number of array antigens. Strikingly, the autoantibody reactivities observed in emphysema were increased over those detected in rheumatoid arthritis patients, and included similar reactivities to those associated with lupus. These findings raise the possibility that autoantibody profiles may be used to determine COPD risk, as well as provide a diagnostic and prognostic tool. They shed light on the heterogeneity of autoantibody reactivities associated with COPD phenotype and could be of use in the personalization of medical treatment, including determining and monitoring therapeutic interventions.

Expression of the atypical chemokine receptor D6 in human alveolar macrophages in COPD

BACKGROUND

D6 is an atypical chemokine receptor involved in chemokine degradation and resolution of acute inflammatory responses in mice. Emerging evidence suggests that D6 might behave differently in human chronic inflammatory conditions. We, therefore, investigated the involvement of D6 in the immune responses in COPD, a chronic inflammatory condition of the lung.

METHODS

D6 expression was quantified by immunohistochemistry in surgical resected lung specimens from 16 patients with COPD (FEV(1), 57% ± 6% predicted) and 18 control subjects with normal lung function (nine smokers and nine nonsmokers). BAL was also obtained and analyzed by flow cytometry, immunofluorescence, and molecular analysis for further assessment of D6 involvement.

RESULTS

D6 expression in the lung was mainly detected in alveolar macrophages (AMs). The percentage of D6(+) AMs was markedly increased in patients with COPD as compared with both smoker and nonsmoker control subjects (P < .0005 for both). D6 expression was detected at both transcript and protein level in AMs but not in monocyte-derived macrophages. Finally, D6 expression was positively correlated with markers of immune activation (CD8(+) T lymphocytes, IL-32, tumor necrosis factor-α, B-cell activating factor of the tumor necrosis factor family, phospho-p38 mitogen-activated protein kinase) and negatively with lung function (FEV(1), FEV(1)/FVC).

CONCLUSIONS

D6 is expressed in AMs from patients with COPD, and its expression correlates with the degree of functional impairment and markers of immune activation. Upregulation of D6 in AMs could indicate that, besides its known scavenger activity in acute inflammation, D6 may have additional roles in chronic inflammatory conditions possibly promoting immune activation.