Fewer CTL, not enhanced NK cells, are sufficient for viral clearance from the lungs of immunocompromised mice

Using the Key Characteristics Framework to Unlock the Mysteries of Aryl Hydrocarbon Receptor-Mediated Effects on the Immune System

Initially discovered for its role mediating the deleterious effects of environmental contaminants, the aryl hydrocarbon receptor (AHR) is now known to be a crucial regulator of the immune system. The expanding list of AHR ligands includes synthetic and naturally derived molecules spanning pollutants, phytochemicals, pharmaceuticals, and substances derived from amino acids and microorganisms. The consequences of engaging AHR vary, depending on factors such as the AHR ligand, cell type, immune challenge, developmental state, dose, and timing of exposure relative to the immune stimulus. This review frames this complexity using the recently identified key characteristics of agents that affect immune system function (altered cell signaling, proliferation, differentiation, effector function, communication, trafficking, death, antigen presentation and processing, and tolerance). The use of these key characteristics provides a scaffold for continued discovery of how AHR and its myriad ligands influence the immune system, which will help harness the power of this enigmatic receptor to prevent or treat disease.

Present and future of cancer nano-immunotherapy: opportunities, obstacles and challenges

Clinically, multimodal therapies are adopted worldwide for the management of cancer, which continues to be a leading cause of death. In recent years, immunotherapy has firmly established itself as a new paradigm in cancer care that activates the body's immune defense to cope with cancer. Immunotherapy has resulted in significant breakthroughs in the treatment of stubborn tumors, dramatically improving the clinical outcome of cancer patients. Multiple forms of cancer immunotherapy, including immune checkpoint inhibitors (ICIs), adoptive cell therapy and cancer vaccines, have become widely available. However, the effectiveness of these immunotherapies is not much satisfying. Many cancer patients do not respond to immunotherapy, and disease recurrence appears to be unavoidable because of the rapidly evolving resistance. Moreover, immunotherapies can give rise to severe off-target immune-related adverse events. Strategies to remove these hindrances mainly focus on the development of combinatorial therapies or the exploitation of novel immunotherapeutic mediations. Nanomaterials carrying anticancer agents to the target site are considered as practical approaches for cancer treatment. Nanomedicine combined with immunotherapies offers the possibility to potentiate systemic antitumor immunity and to facilitate selective cytotoxicity against cancer cells in an effective and safe manner. A myriad of nano-enabled cancer immunotherapies are currently under clinical investigation. Owing to gaps between preclinical and clinical studies, nano-immunotherapy faces multiple challenges, including the biosafety of nanomaterials and clinical trial design. In this review, we provide an overview of cancer immunotherapy and summarize the evidence indicating how nanomedicine-based approaches increase the efficacy of immunotherapies. We also discuss the key challenges that have emerged in the era of nanotechnology-based cancer immunotherapy. Taken together, combination nano-immunotherapy is drawing increasing attention, and it is anticipated that the combined treatment will achieve the desired success in clinical cancer therapy.

Aryl hydrocarbon receptor activation alters immune cell populations in the lung and bone marrow during coronavirus infection

Respiratory viral infections are one of the major causes of illness and death worldwide. Symptoms associated with respiratory infections can range from mild to severe, and there is limited understanding of why there is large variation in severity. Environmental exposures are a potential causative factor. The aryl hydrocarbon receptor (AHR) is an environment-sensing molecule expressed in all immune cells. Although there is considerable evidence that AHR signaling influences immune responses to other immune challenges, including respiratory pathogens, less is known about the impact of AHR signaling on immune responses during coronavirus (CoV) infection. In this study, we report that AHR activation significantly altered immune cells in the lungs and bone marrow of mice infected with a mouse CoV. AHR activation transiently reduced the frequency of multiple cells in the mononuclear phagocyte system, including monocytes, interstitial macrophages, and dendritic cells in the lung. In the bone marrow, AHR activation altered myelopoiesis, as evidenced by a reduction in granulocyte-monocyte progenitor cells and an increased frequency of myeloid-biased progenitor cells. Moreover, AHR activation significantly affected multiple stages of the megakaryocyte lineage. Overall, these findings indicate that AHR activation modulates multiple aspects of the immune response to a CoV infection. Given the significant burden of respiratory viruses on human health, understanding how environmental exposures shape immune responses to infection advances our knowledge of factors that contribute to variability in disease severity and provides insight into novel approaches to prevent or treat disease.NEW & NOTEWORTHY Our study reveals a multifaceted role for aryl hydrocarbon receptor (AHR) signaling in the immune response to coronavirus (CoV) infection. Sustained AHR activation during in vivo mouse CoV infection altered the frequency of mature immune cells in the lung and modulated emergency hematopoiesis, specifically myelopoiesis and megakaryopoiesis, in bone marrow. This provides new insight into immunoregulation by the AHR and extends our understanding of how environmental exposures can impact host responses to respiratory viral infections.

Nanocarriers for cancer nano-immunotherapy

The host immune system possesses an intrinsic ability to target and kill cancer cells in a specific and adaptable manner that can be further enhanced by cancer immunotherapy, which aims to train the immune system to boost the antitumor immune response. Several different categories of cancer immunotherapy have emerged as new standard cancer therapies in the clinic, including cancer vaccines, immune checkpoint inhibitors, adoptive T cell therapy, and oncolytic virus therapy. Despite the remarkable survival benefit for a subset of patients, the low response rate and immunotoxicity remain the major challenges for current cancer immunotherapy. Over the last few decades, nanomedicine has been intensively investigated with great enthusiasm, leading to marked advancements in nanoparticle platforms and nanoengineering technology. Advances in nanomedicine and immunotherapy have also led to the emergence of a nascent research field of nano-immunotherapy, which aims to realize the full therapeutic potential of immunotherapy with the aid of nanomedicine. In particular, nanocarriers present an exciting opportunity in immuno-oncology to boost the activity, increase specificity, decrease toxicity, and sustain the antitumor efficacy of immunological agents by potentiating immunostimulatory activity and favorably modulating pharmacological properties. This review discusses the potential of nanocarriers for cancer immunotherapy and introduces preclinical studies designed to improve clinical cancer immunotherapy modalities using nanocarrier-based engineering approaches. It also discusses the potential of nanocarriers to address the challenges currently faced by immuno-oncology as well as the challenges for their translation to clinical applications.

The Aryl Hydrocarbon Receptor as a Modulator of Anti-viral Immunity

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, which interacts with a wide range of organic molecules of endogenous and exogenous origin, including environmental pollutants, tryptophan metabolites, and microbial metabolites. The activation of AHR by these agonists drives its translocation into the nucleus where it controls the expression of a large number of target genes that include the AHR repressor (AHRR), detoxifying monooxygenases (CYP1A1 and CYP1B1), and cytokines. Recent advances reveal that AHR signaling modulates aspects of the intrinsic, innate and adaptive immune response to diverse microorganisms. This review will focus on the increasing evidence supporting a role for AHR as a modulator of the host response to viral infection.

Environmental exposures are hidden modifiers of anti-viral immunity

Significant advances have been made recent years elucidating antiviral immune mechanisms that protect the host from viral infection. Similarly, our understanding of how viruses bind, enter, and replicate within host cells has continued to grow. Yet, viruses continue to take a toll on human health. The influence of chemicals in the environment is among key factors that influence outcomes of viral infection. There is a growing appreciation of the effects that exogenous environmental chemical exposures have on the immune system and antiviral immunity. Epidemiological studies have linked a variety of chemical exposures to poorer health, increased incidence of infection, and worsened vaccine responses. However, the mechanisms that govern these associations are not well understood, limiting our ability to predict or mitigate the effects of environmental exposures on public health. This brief review focuses on recent advances in the field, highlighting novel in vitro and in vivo findings informed by past foundational studies. Furthermore, current information suggests avenues of investigation that have yet to be explored, but which will significantly impact on our understanding about how environmental exposures impact viral defenses, vaccine efficacy, and the spread of contemporary and emerging viral pathogens.

On the Role of CD8+ T Cells in Determining Recovery Time from Influenza Virus Infection

Myriad experiments have identified an important role for CD8⁺ T cell response mechanisms in determining recovery from influenza A virus infection. Animal models of influenza infection further implicate multiple elements of the immune response in defining the dynamical characteristics of viral infection. To date, influenza virus models, while capturing particular aspects of the natural infection history, have been unable to reproduce the full gamut of observed viral kinetic behavior in a single coherent framework. Here, we introduce a mathematical model of influenza viral dynamics incorporating innate, humoral, and cellular immune components and explore its properties with a particular emphasis on the role of cellular immunity. Calibrated against a range of murine data, our model is capable of recapitulating observed viral kinetics from a multitude of experiments. Importantly, the model predicts a robust exponential relationship between the level of effector CD8⁺ T cells and recovery time, whereby recovery time rapidly decreases to a fixed minimum recovery time with an increasing level of effector CD8⁺ T cells. We find support for this relationship in recent clinical data from influenza A (H7N9) hospitalized patients. The exponential relationship implies that people with a lower level of naive CD8⁺ T cells may receive significantly more benefit from induction of additional effector CD8⁺ T cells arising from immunological memory, itself established through either previous viral infection or T cell-based vaccines.

Consecutive oral administration of Bifidobacterium longum MM-2 improves the defense system against influenza virus infection by enhancing natural killer cell activity in a murine model

Bifidobacterium, one of the major components of intestinal microflora, shows anti-influenza virus (IFV) potential as a probiotic, partly through enhancement of innate immunity by modulation of the intestinal immune system. Bifidobacterium longum MM-2 (MM-2), a very safe bacterium in humans, was isolated from healthy humans and its protective effect against IFV infection in a murine model shown. In mice that were intranasally inoculated with IFV, oral administration of MM-2 for 17 consecutive days improved clinical symptoms, reduced mortality, suppressed inflammation in the lower respiratory tract, and decreased virus titers, cell death, and pro-inflammatory cytokines such as IL-6 and TNF-α in bronchoalveolar lavage fluid. The anti-IFV mechanism of MM-2 involves innate immunity through significant increases in NK cell activities in the lungs and spleen and a significant increase in pulmonary gene expression of NK cell activators such as IFN-γ, IL-2, IL-12 and IL-18. Even in non-infected mice, MM-2 administration also induced significant enhancement of both IFN-γ production by Peyer's patch cells (PPs) and splenetic NK cell activity. Oral administration of MM-2 for 17 days activates systemic immunoreactivity in PPs, which contributes to innate immunity, including NK cell activation, resulting in an anti-IFV effect. MM-2 as a probiotic may function as a prophylactic agent in the management of an IFV epidemic.

The inflammatory response to influenza A virus (H1N1): An experimental and mathematical study

Mortality from influenza infections continues as a global public health issue, with the host inflammatory response contributing to fatalities related to the primary infection. Based on Ordinary Differential Equation (ODE) formalism, a computational model was developed for the in-host response to influenza A virus, merging inflammatory, innate, adaptive and humoral responses to virus and linking severity of infection, the inflammatory response, and mortality. The model was calibrated using dense cytokine and cell data from adult BALB/c mice infected with the H1N1 influenza strain A/PR/8/34 in sublethal and lethal doses. Uncertainty in model parameters and disease mechanisms was quantified using Bayesian inference and ensemble model methodology that generates probabilistic predictions of survival, defined as viral clearance and recovery of the respiratory epithelium. The ensemble recovers the expected relationship between magnitude of viral exposure and the duration of survival, and suggests mechanisms primarily responsible for survival, which could guide the development of immuno-modulatory interventions as adjuncts to current anti-viral treatments. The model is employed to extrapolate from available data survival curves for the population and their dependence on initial viral aliquot. In addition, the model allows us to illustrate the positive effect of controlled inflammation on influenza survival.

New insights into the role of the aryl hydrocarbon receptor in the function of CD11c⁺ cells during respiratory viral infection

The aryl hydrocarbon receptor (AHR) has garnered considerable attention as a modulator of CD4(+) cell lineage development and function. It also regulates antiviral CD8(+) T-cell responses, but via indirect mechanisms that have yet to be determined. Here, we show that during acute influenza virus infection, AHR activation skews dendritic-cell (DC) subsets in the lung-draining lymph nodes, such that there are fewer conventional CD103(+) DCs and CD11b(+) DCs. Sorting DC subsets reveals AHR activation reduces immunostimulatory function of CD103(+) DCs in the mediastinal lymph nodes, and decreases their frequency in the lung. DNA-binding domain Ahr mutants demonstrate that alterations in DC subsets require the ligand-activated AHR to contain its inherent DNA-binding domain. To evaluate the intrinsic role of AHR in DCs, conditional knockouts were created using Cre-LoxP technology, which revealed that AHR in CD11c(+) cells plays a key role in controlling the acquisition of effector CD8(+) T cells in the infected lung. However, AHR within other leukocyte lineages contributes to diminished naïve CD8(+) T-cell activation in the draining lymphoid nodes. These findings indicate DCs are among the direct targets of AHR ligands in vivo, and AHR signaling modifies host responses to a common respiratory pathogen by affecting the complex interplay of multiple cell types.

Effects of aging on influenza virus infection dynamics

The consequences of influenza virus infection are generally more severe in individuals over 65 years of age (the elderly). Immunosenescence enhances the susceptibility to viral infections and renders vaccination less effective. Understanding age-related changes in the immune system is crucial in order to design prophylactic and immunomodulatory strategies to reduce morbidity and mortality in the elderly. Here, we propose different mathematical models to provide a quantitative understanding of the immune strategies in the course of influenza virus infection using experimental data from young and aged mice. Simulation results suggested a central role of CD8(+) T cells for adequate viral clearance kinetics in young and aged mice. Adding the removal of infected cells by natural killer cells did not improve the model fit in either young or aged animals. We separately examined the infection-resistant state of cells promoted by the cytokines alpha/beta interferon (IFN-α/β), IFN-γ, and tumor necrosis factor alpha (TNF-α). The combination of activated CD8(+) T cells with any of the cytokines provided the best fits in young and aged animals. During the first 3 days after infection, the basic reproductive number for aged mice was 1.5-fold lower than that for young mice (P < 0.05).

IMPORTANCE

The fits of our models to the experimental data suggest that the increased levels of IFN-α/β, IFN-γ, and TNF-α (the "inflammaging" state) promote slower viral growth in aged mice, which consequently limits the stimulation of immune cells and contributes to the reported impaired responses in the elderly. A quantitative understanding of influenza virus pathogenesis and its shift in the elderly is the key contribution of this work.

New insights into the aryl hydrocarbon receptor as a modulator of host responses to infection

The host response to infection is known to be influenced by many factors, including genetics, nutritional status, age, as well as drug and chemical exposures. Recent advances reveal that the aryl hydrocarbon receptor (AhR) modulates aspects of the innate and adaptive immune response to viral, bacterial, and parasitic organisms. Although many of these observations were made using the high affinity but poorly metabolized AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), not all of the effects are detrimental to the host. Sometimes AhR activation, even with TCDD, was beneficial and improved host resistance and survival. A similar dichotomy is observed in infected AhR-deficient mice, wherein absence of functional AhR sometimes, but not always, alters host resistance. When examined in their totality, current data indicate that AhR controls multiple regulatory pathways that converge with infection-associated signals and depending on the context (e.g., type of pathogen, site of infection), lead to distinct outcomes. This creates numerous exciting opportunities to harness the immunomodulatory action of AhR to transform host responses to infection. Moreover, since many of the mechanisms cued in response to infectious agents are pivotal in the context of other diseases, there is much to be learned about AhR's cellular targets and molecular mechanisms of action.

Neonatal hyperoxia alters the host response to influenza A virus infection in adult mice through multiple pathways

Exposing preterm infants or newborn mice to high concentrations of oxygen disrupts lung development and alters the response to respiratory viral infections later in life. Superoxide dismutase (SOD) has been separately shown to mitigate hyperoxia-mediated changes in lung development and attenuate virus-mediated lung inflammation. However, its potential to protect adult mice exposed to hyperoxia as neonates against viral infection is not known. Here, transgenic mice overexpressing extracellular (EC)-SOD in alveolar type II epithelial cells are used to test whether SOD can alleviate the deviant pulmonary response to influenza virus infection in adult mice exposed to hyperoxia as neonates. Fibrotic lung disease, observed following infection in wild-type (WT) mice exposed to hyperoxia as neonates, was prevented by overexpression of EC-SOD. However, leukocyte recruitment remained excessive, and levels of monocyte chemoattractant protein (MCP)-1 remained modestly elevated following infection in EC-SOD Tg mice exposed to hyperoxia as neonates. Because MCP-1 is often associated with pulmonary inflammation and fibrosis, the host response to infection was concurrently evaluated in adult Mcp-1 WT and Mcp-1 knockout mice exposed to neonatal hyperoxia. In contrast to EC-SOD, excessive leukocyte recruitment, but not lung fibrosis, was dependent upon MCP-1. Our findings demonstrate that neonatal hyperoxia alters the inflammatory and fibrotic responses to influenza A virus infection through different pathways. Therefore, these data suggest that multiple therapeutic strategies may be needed to provide complete protection against diseases attributed to prematurity and early life exposure to oxygen.

Assessing mathematical models of influenza infections using features of the immune response

The role of the host immune response in determining the severity and duration of an influenza infection is still unclear. In order to identify severity factors and more accurately predict the course of an influenza infection within a human host, an understanding of the impact of host factors on the infection process is required. Despite the lack of sufficiently diverse experimental data describing the time course of the various immune response components, published mathematical models were constructed from limited human or animal data using various strategies and simplifying assumptions. To assess the validity of these models, we assemble previously published experimental data of the dynamics and role of cytotoxic T lymphocytes, antibodies, and interferon and determined qualitative key features of their effect that should be captured by mathematical models. We test these existing models by confronting them with experimental data and find that no single model agrees completely with the variety of influenza viral kinetics responses observed experimentally when various immune response components are suppressed. Our analysis highlights the strong and weak points of each mathematical model and highlights areas where additional experimental data could elucidate specific mechanisms, constrain model design, and complete our understanding of the immune response to influenza.

Novel cellular targets of AhR underlie alterations in neutrophilic inflammation and inducible nitric oxide synthase expression during influenza virus infection

The underlying reasons for variable clinical outcomes from respiratory viral infections remain uncertain. Several studies suggest that environmental factors contribute to this variation, but limited knowledge of cellular and molecular targets of these agents hampers our ability to quantify or modify their contribution to disease and improve public health. The aryl hydrocarbon receptor (AhR) is an environment-sensing transcription factor that binds many anthropogenic and natural chemicals. The immunomodulatory properties of AhR ligands are best characterized with extensive studies of changes in CD4(+) T cell responses. Yet, AhR modulates other aspects of immune function. We previously showed that during influenza virus infection, AhR activation modulates neutrophil accumulation in the lung, and this contributes to increased mortality in mice. Enhanced levels of inducible NO synthase (iNOS) in infected lungs are observed during the same time frame as AhR-mediated increased pulmonary neutrophilia. In this study, we evaluated whether these two consequences of AhR activation are causally linked. Reciprocal inhibition of AhR-mediated elevations in iNOS and pulmonary neutrophilia reveal that although they are contemporaneous, they are not causally related. We show using Cre/loxP technology that elevated iNOS levels and neutrophil number in the infected lung result from separate, AhR-dependent signaling in endothelial and respiratory epithelial cells, respectively. Studies using mutant mice further reveal that AhR-mediated alterations in these innate responses to infection require a functional nuclear localization signal and DNA binding domain. Thus, gene targets of AhR in non-hematopoietic cells are important new considerations for understanding AhR-mediated changes in innate anti-viral immunity.

Differential effects of stimulatory factors on natural killer cell activities of young and aged mice

Age-associated influences on natural killer (NK) cell functions following cytokine stimulation were examined in splenocytes from C57BL/6 mice. NK cells of both young and aged mice exhibited significantly increased: interferon-γ production after interleukin (IL)-12 or IL-15 alone or any combination of IL-12, IL-18, and IL-2; cytotoxicity after IL-2 or IL-15; and granzyme B expression after IL-15. The only significant age-associated differences were observed in interferon-γ production after IL-15 or IL-12 + 18 + 2 and in granzyme B expression following IL-2 or IL-15. Perforin expression did not increase following stimulation; however, NK cells from aged mice expressed significantly higher levels than young mice. These results underscore the complexity of the cytokine-induced functional activities of NK cells and illustrate the differential response of NK cells from young and aged mice to cytokine stimulation.

Consequences of TCDD treatment on intra-hepatic lymphocytes during liver regeneration

Increasing evidence demonstrates a physiological role for the aryl hydrocarbon receptor (AhR) in regulating hepatocyte cell cycle progression. Previous studies have used a murine model of liver regeneration to show that exposure to the potent exogenous AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), suppresses hepatocyte proliferation in vivo. Based on recent reports that natural killer (NK) cells negatively regulate liver regeneration, coupled with the well-established immunomodulatory effects of TCDD, it was hypothesized that alterations in lymphocyte activation contribute to the suppression of liver regeneration in TCDD-treated mice. To test this, mice were treated with TCDD (20 μg/kg) 1 day prior to 70% partial hepatectomy (PH), in which two-thirds of the liver was surgically resected. Lymphocytes were collected from the remnant liver and analyzed by flow cytometry. Whereas exposure to TCDD did not alter the number of NK cells or CD3(+) T-cells recovered from the regenerating liver, it reduced the percentage and number of intra-hepatic NKT cells 42 h after PH. With regard to lymphocyte activation, TCDD treatment transiently increased CD69 expression on NK and NKT cells 12 h after PH, but had no effect on intracellular levels of IFNγ in NK, NKT, or CD3(+) T-cells. To determine the relevance of NK cells to the suppression of liver regeneration by TCDD, mice were treated with anti-Asialo GM-1 (ASGM-1) antibody to deplete NK cells prior to TCDD treatment and PH, and hepatocyte proliferation was measured using bromodeoxyuridine incorporation. Exposure to TCDD was found to inhibit hepatocyte proliferation in the regenerating liver of NK cell-depleted mice and control mice to the same extent. Hence, it is unlikely that enhanced numbers or increased activation of NK cells contribute to the suppression of liver regeneration in TCDD-treated mice.

Lung development and the host response to influenza A virus are altered by different doses of neonatal oxygen in mice

Oxygen exposure in preterm infants has been associated with altered lung development and increased risk for respiratory viral infections later in life. Although the dose of oxygen sufficient to exert these changes in humans remains unknown, adult mice exposed to 100% oxygen between postnatal days 1-4 exhibit alveolar simplification and increased sensitivity to influenza virus infection. Additionally, two nonlinear thresholds of neonatal oxygen exposures were previously identified that promote modest (between 40% and 60% oxygen) and severe (between 80% and 100% oxygen) changes in lung development. Here, we investigate whether these two thresholds correlate with the severity of lung disease following respiratory viral infection. Adult mice exposed to 100% oxygen at birth, and to a lesser extent 80% oxygen, demonstrated enhanced body weight loss, persistent inflammation, and fibrosis following infection compared with infected siblings exposed to room air at birth. In contrast, the host response to infection was indistinguishable between mice exposed to room air and 40% or 60% oxygen. Interestingly, levels of monocyte chemoattractant protein (MCP)-1 were equivalently elevated in infected mice that had been exposed to 80% or 100% oxygen as neonates. However, reducing levels of MCP-1 using heterozygous Mcp-1 mice did not affect oxygen-dependent changes in the response to infection. Thus lung development and the host response to respiratory viral infection are disrupted by different doses of oxygen. Our findings suggest that measuring lung function alone may not be sufficient to identify individuals born prematurely who have increased risk for respiratory viral infection.

Distinct phenotype of unrestricted cytotoxic T lymphocytes from human immunodeficiency virus-infected individuals

INTRODUCTION

Human immunodeficiency virus (HIV)-infected individuals have CD8(+) cytotoxic T lymphocytes (CTL) that kill activated uninfected T lymphocytes. These CTL are independent of class Ia human histocompatibility-linked leukocyte antigens (HLA-Ia).

METHODS

To further characterize these CTL, we investigated their possible restriction to non-classical class Ib HLA-E molecules and their expression of natural killer cell receptors (NKR) that are often affected in HIV infection.

RESULTS

We found no role for HLA-E in CTL-mediated killing of activated uninfected T lymphocytes. The non-HLA-restricted CTL did not express NKG2A, an inhibitory NKR that binds HLA-E, nor CD56, a prominent marker on previously described non-HLA-restricted CTL.

DISCUSSION

This NKG2A(-)CD56(-) phenotype of HLA-unrestricted CTL that kill uninfected activated T lymphocytes matches generalized changes on CD8(+) T lymphocytes that occur in progressive HIV infection, suggesting these phenotypic changes may reflect pathogenic evolution of the CD8(+) T cell repertoire. These CTL represent a unique phenotypic and functional subset with potential relevance to HIV pathogenesis.

Neonatal exposure to low-dose 2,3,7,8-tetrachlorodibenzo-p-dioxin causes autoimmunity due to the disruption of T cell tolerance

Although 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been shown to influence immune responses, the effects of low-dose TCDD on the development of autoimmunity are unclear. In this study, using NFS/sld mice as a model for human Sjögren's syndrome, in which the lesions are induced by the thymectomy on day 3 after birth, the autoimmune lesions in the salivary glands, and in later phase, inflammatory cell infiltrations in the other organs were developed by neonatal exposure to nonapoptotic dosage of TCDD without thymectomy on day 3 after birth. We found disruption of thymic selection, but not thymic atrophy, in TCDD-administered mice. The endogenous expression of aryl hydrocarbon receptor in the neonatal thymus was significantly higher than that in the adult thymus, suggesting that the neonatal thymus may be much more sensitive to TCDD compared with the adult thymus. In addition, the production of T(H)1 cytokines such as IL-2 and IFN-gamma from splenic CD4(+) T cells and the autoantibodies relevant for Sjögren's syndrome in the sera from TCDD-exposed mice were significantly increased compared with those in control mice. These results suggest that TCDD/aryl hydrocarbon receptor signaling in the neonatal thymus plays an important role in the early thymic differentiation related to autoimmunity.

P58(IPK): a novel "CIHD" member of the host innate defense response against pathogenic virus infection

To support their replication, viruses take advantage of numerous cellular factors and processes. Recent large-scale screens have identified hundreds of such factors, yet little is known about how viruses exploit any of these. Influenza virus infection post-translationally activates P58(IPK), a cellular inhibitor of the interferon-induced, dsRNA-activated eIF2alpha kinase, PKR. Here, we report that infection of P58(IPK) knockout mice with influenza virus resulted in increased lung pathology, immune cell apoptosis, PKR activation, and mortality. Analysis of lung transcriptional profiles, including those induced by the reconstructed 1918 pandemic virus, revealed increased expression of genes associated with the cell death, immune, and inflammatory responses. These experiments represent the first use of a mammalian infection model to demonstrate the role of P58(IPK) in the antiviral response. Our results suggest that P58(IPK) represents a new class of molecule, a cellular inhibitor of the host defense (CIHD), as P58(IPK) is activated during virus infection to inhibit virus-induced apoptosis and inflammation to prolong host survival, even while prolonging viral replication.

The aryl hydrocarbon receptor is a modulator of anti-viral immunity

Although immune modulation by AhR ligands has been studied for many years, the impact of AhR activation on host defenses against viral infection has not, until recently, garnered much attention. The development of novel reagents and model systems, new information regarding anti-viral immunity, and a growing appreciation for the global health threat posed by viruses have invigorated interest in understanding how environmental signals affect susceptibility to and pathological consequences of viral infection. Using influenza A virus as a model of respiratory viral infection, recent studies show that AhR activation cues signaling events in both leukocytes and non-immune cells. Functional alterations include suppressed lymphocyte responses and increased inflammation in the infected lung. AhR-mediated events within and extrinsic to hematopoietic cells has been investigated using bone marrow chimeras, which show that AhR alters different elements of the immune response by affecting different tissue targets. In particular, suppressed CD8(+) T cell responses are due to deregulated events within leukocytes themselves, whereas increased neutrophil recruitment to and IFN-gamma levels in the lung result from AhR-regulated events extrinsic to bone marrow-derived cells. This latter discovery suggests that epithelial and endothelial cells are overlooked targets of AhR-mediated changes in immune function. Further support that AhR influences host cell responses to viral infection are provided by several studies demonstrating that AhR interacts directly with viral proteins and affects viral latency. While AhR clearly modulates host responses to viral infection, we still have much to understand about the complex interactions between immune cells, viruses, and the host environment.

AHR-mediated immunomodulation: the role of altered gene transcription

The immune system is a sensitive target for aryl hydrocarbon receptor (AHR)-mediated transcriptional regulation. Most of the cells that participate in immune responses express AHR protein, and many genes involved in their responses contain multiple DRE sequences in their promoters. However, the potential involvement of many of these candidate genes in AHR-mediated immunomodulation has never been investigated. Many obstacles to understanding the transcriptional effects of AHR activation exist, owing to the complexities of pathogen-driven inflammatory and adaptive immune responses, and to the fact that activation of AHR often influences the expression of genes that are already being regulated by other transcriptional events in responding cells. Studies with TCDD as the most potent, non-metabolized AHR ligand indicate that AHR activation alters many inflammatory signals that shape the adaptive immune response, contributing to altered differentiation of antigen-specific CD4(+) T helper (TH) cells and altered adaptive immune responses. With TCDD, most adaptive immune responses are highly suppressed, which has been recently linked to the AHR-dependent induction of CD4(+)CD25(+) regulatory T cells. However activation of AHR by certain non-TCDD ligands may result in other immune outcomes, as a result of metabolism of the ligand to active metabolites or to unknown ligand-specific effects on AHR-mediated gene transcription. Based on studies using AHR(-/-) mice, evidence for a role of endogenous AHR ligands in regulation of the immune response is growing, with bilirubin and lipoxinA4 representing two promising candidates.

De novo T-lymphocyte responses against baculovirus-derived recombinant influenzavirus hemagglutinin generated by a naive umbilical cord blood model of dendritic cell vaccination

Cancer patients and recipients of hematopoietic stem cell transplantation exhibit a negligible response to influenza vaccine. Toward the goal of addressing this issue, we developed an in vitro model of dendritic cell (DC) immunotherapy utilizing DCs generated from naïve umbilical cord blood (UCB). UCB DCs were loaded with purified rHA protein and used to stimulate autologous T-lymphocytes. Upon recall with HA-loaded autologous DC, a 4-10-fold increase in the number of IFN-gamma producing T-lymphocytes was observed in comparison to T-cells stimulated with control DCs. Antigen-specific T-cell functionality was determined by (51)Cr lytic assay. Using a peptide library of predicted HA binding epitopes, we mapped an HA-specific, DR15-restricted CD4 T-cell epitope and observed tetramer positive cells. This model demonstrates that HA-specific immune responses might possibly be generated in a de novo fashion and suggests that dendritic cell immunotherapy for the prevention of influenza in populations of immunosuppressed individuals could be feasible.

Aryl hydrocarbon receptor targets pathways extrinsic to bone marrow cells to enhance neutrophil recruitment during influenza virus infection

There is growing evidence that neutrophils influence host resistance during influenza virus infection; however, factors that regulate neutrophil migration to the lung during viral infection are unclear. Activation of the aryl hydrocarbon receptor (AhR) by the pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin) results in an increased number of neutrophils in the lung after influenza virus infection. The mechanism of AhR-mediated neutrophilia does not involve elevated levels of soluble neutrophil chemoattractants, upregulated adhesion molecules on pulmonary neutrophils, delayed neutrophil apoptosis, or increased vascular damage. In this study, we determined whether AhR activation increases neutrophil numbers systemically or only in the infected lung, and whether AhR-regulated events within the hematopoietic system underlie the dioxin-induced increase in pulmonary neutrophils observed during influenza virus infection. We report here that AhR activation does not increase neutrophil numbers systemically or increase neutrophil production in hematopoietic tissue, suggesting that the elevated number of neutrophils is restricted to the site of antigen challenge. The generation of CD45.2AhR-/--->CD45.1AhR+/+ bone marrow chimeric mice demonstrates that even when hematopoietic cells lack the AhR, TCDD treatment still results in twice as many pulmonary neutrophils compared with control-treated, infected CD45.2AhR-/--->CD45.1AhR+/+ chimeric mice. This finding reveals that AhR-mediated events extrinsic to bone marrow-derived cells affect the directional migration of neutrophils to the infected lung. These results suggest that the lung contains important and heretofore overlooked targets of AhR regulation, unveiling a novel mechanism for controlling neutrophil recruitment to the infected lung.

Neonatal hyperoxia enhances the inflammatory response in adult mice infected with influenza A virus

RATIONALE

Lungs of adult mice exposed to hyperoxia as newborns are simplified and exhibit reduced function much like that observed in people who had bronchopulmonary dysplasia (BPD) as infants. Because survivors of BPD also show increased risk for symptomatic respiratory infections, we investigated how neonatal hyperoxia affected the response of adult mice infected with influenza A virus infection.

OBJECTIVES

To determine whether neonatal hyperoxia increased the severity of influenza A virus infection in adult mice.

METHODS

Adult female mice exposed to room air or hyperoxia between Postnatal Days 1 and 4 were infected with a sublethal dose of influenza A virus.

MEASUREMENTS AND MAIN RESULTS

The number of macrophages, neutrophils, and lymphocytes observed in airways of infected mice that had been exposed to hyperoxia as neonates was significantly greater than in infected siblings that had been exposed to room air. Enhanced inflammation correlated with increased levels of monocyte chemotactic protein-1 (CCL2) in lavage fluid, whereas infection-associated changes in IFN-gamma, IL-1beta, IL-6, tumor necrosis factor-alpha, KC, granulocyte-macrophage colony-stimulating factor, and macrophage inflammatory protein-1alpha, and production of virus-specific antibodies, were largely unaffected. Increased mortality of mice exposed to neonatal hyperoxia occurred by Day 14 of infection, and was associated with persistent inflammation and fibrosis.

CONCLUSIONS

These data suggest that the disruptive effect of hyperoxia on neonatal lung development also reprograms key innate immunoregulatory pathways in the lung, which may contribute to exacerbated pathology and poorer resistance to respiratory viral infections typically seen in people who had BPD.

Environmental toxins as modulators of antiviral immune responses

Exposure to environmental contaminants has a profound effect on immune function, yet mechanistic understanding of how pollutants deregulate immune responses has, for many chemicals, remained elusive. Available data suggest that certain pollutants alter host immune responses and increase susceptibility to viral infection. In particular, data from a combination of epidemiological and animal studies show that exposure to dioxins, cigarette smoke, diesel exhaust and other air pollutants increase pathology associated with infection. Mechanistically, some of these chemicals disrupt the kinetics and efficacy of innate and adaptive responses to infection, whereas others influence viral latency. While there remain considerable gaps in our knowledge of the complex interactions between viruses, immune cells, and the host environment, these observations indicate that pollutants are important but overlooked contributors to susceptibility and pathogenesis of viral infections.

Aryl Hydrocarbon Receptor Activation during Influenza Virus Infection Unveils a Novel Pathway of IFN-γ Production by Phagocytic Cells

The contribution of environmental factors is important as we consider reasons that underlie differential susceptibility to influenza virus. Aryl hydrocarbon receptor (AhR) activation by the pollutant dioxin during influenza virus infection decreases survival, which correlates with a 4-fold increase in pulmonary IFN-gamma levels. We report here that the majority of IFN-gamma-producing cells in the lung are neutrophils and macrophages not lymphocytes, and elevated IFN-gamma is associated with increased pulmonary inducible NO synthase (iNOS) levels. Moreover, we show that even in the absence of dioxin, infection with influenza virus elicits IFN-gamma production by B cells, gammadelta T cells, CD11c(+) cells, macrophages and neutrophils, as well as CD3(+) and NK1.1(+) cells in the lung. Bone marrow chimeric mice reveal that AhR-mediated events external to hemopoietic cells direct dioxin-enhanced IFN-gamma production. We also show that AhR-mediated increases in IFN-gamma are dependent upon iNOS, but elevated iNOS in lung epithelial cells is not driven by AhR-dependent signals from bone marrow-derived cells. Thus, the lung contains important targets of AhR regulation, which likely influence a novel iNOS-mediated mechanism that controls IFN-gamma production by phagocytic cells. This suggests that AhR activation changes the response of lung parenchymal cells, such that regulatory pathways in the lung are cued to respond inappropriately during infection. These findings also imply that environmental factors may contribute to differential susceptibility to influenza virus and other respiratory pathogens.

Pneumococcal capsular polysaccharide vaccine-mediated protection against serotype 3 Streptococcus pneumoniae in immunodeficient mice

Pneumococcal capsular polysaccharide (PPS) vaccines are less immunogenic in immunocompromised than immunocompetent individuals. However, neither the efficacy of PPS vaccines in immunocompromised individuals nor the host cellular subsets required for vaccine efficacy against pneumococcal disease have been directly investigated. In this study, we vaccinated CD4-deficient (CD4(-/-)), CD8-deficient (CD8(-/-)), and secretory immunoglobulin M-deficient (sIgM(-/-)) mice and wild-type C57BL/6 (Wt) mice with a conjugate of PPS of serotype 3 and tetanus toxoid (PPS3-TT) and determined the antibody response and efficacy of vaccination against systemic and pulmonary challenge with serotype 3 pneumococcus in immunized and control mice. Our results showed that the isotype and predominant IgG subclass of the PPS3 response differed between immunodeficient mouse strains and between immunodeficient and Wt mice, with CD8(-/-) mice having the most robust response. Vaccination protected Wt, CD4(-/-), and sIgM(-/-) mice from death resulting from both systemic and pulmonary challenge, whereas CD8(-/-) mice were protected only from systemic and not from pulmonary challenge. Passive vaccination with PPS3-TT-induced sera from Wt, CD4(-/-), CD8(-/-), and sIgM(-/-) mice protected naïve Wt mice from death due to pulmonary challenge; however, CD8(-/-) mice were not protected by sera from Wt or CD8(-/-) mice. Our findings suggest that PPS-based vaccines can be effective in the setting of CD4 T-cell deficiency but that CD8 T cells could be required for vaccine-mediated protection against pulmonary challenge with serotype 3 pneumococcus.

Supplementation with active hexose correlated compound increases the innate immune response of young mice to primary influenza infection

The emergence of H5N1 avian influenza and the threat of new or adapted viruses in bioterrorism have created an urgent interest in identifying agents to enhance the immune response to primary virus infection. Active hexose correlated compound (AHCC) is a natural mushroom extract reported to increase natural killer (NK) cell activity, survival, and bacterial clearance in young mice. However, the effects of AHCC on the response to viral infections have not been studied. In this study, young C57BL/6 mice were supplemented with 1 g AHCC/(kg body weight x d) for 1 wk prior to and throughout infection with influenza A (H1N1, PR8). Supplementation increased survival, decreased the severity of infection, and shortened recovery time following intranasal infection with flu, as determined by the recovery of body weight and epithelial integrity in the lungs. AHCC increased NK activity in lungs at d 1 (P < 0.05) and d 4 (P < 0.01) and in the spleen at d 2 postinfection (P < 0.01). Supplementation increased the percentage (P < 0.05) and number (P < 0.01) of NK1.1+ cells in the lung and reduced the infiltration of lymphocytes and macrophages compared with controls (P < 0.01). These data suggest that AHCC supplementation boosts NK activity, improves survival, and reduces the severity of influenza infection in young mice. Bolstering innate immunity with dietary bioactives may be one avenue for improving the immune response to primary flu infection.

Aryl Hydrocarbon Receptor Activation Impairs the Priming but Not the Recall of Influenza Virus-Specific CD8+T Cells in the Lung

The response of CD8+ T cells to influenza virus is very sensitive to modulation by aryl hydrocarbon receptor (AhR) agonists; however, the mechanism underlying AhR-mediated alterations in CD8+ T cell function remains unclear. Moreover, very little is known regarding how AhR activation affects anamnestic CD8+ T cell responses. In this study, we analyzed how AhR activation by the pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters the in vivo distribution and frequency of CD8+ T cells specific for three different influenza A virus epitopes during and after the resolution of a primary infection. We then determined the effects of TCDD on the expansion of virus-specific memory CD8+ T cells during recall challenge. Adoptive transfer of AhR-null CD8+ T cells into congenic AhR(+/+) recipients, and the generation of CD45.2AhR(-/-)-->CD45.1AhR(+/+) chimeric mice demonstrate that AhR-regulated events within hemopoietic cells, but not directly within CD8+ T cells, underlie suppressed expansion of virus-specific CD8+ T cells during primary infection. Using a dual-adoptive transfer approach, we directly compared the responsiveness of virus-specific memory CD8+ T cells created in the presence or absence of TCDD, which revealed that despite profound suppression of the primary response to influenza virus, the recall response of virus-specific CD8+ T cells that form in the presence of TCDD is only mildly impaired. Thus, the delayed kinetics of the recall response in TCDD-treated mice reflects the fact that there are fewer memory cells at the time of reinfection rather than an inherent defect in the responsive capacity of virus-specific memory CD8+ cells.

A dose-response study of the effects of prenatal and lactational exposure to TCDD on the immune response to influenza a virus

The goal of the current study was to evaluate the immune response to a common respiratory pathogen, influenza A virus, in mice exposed to increasing doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during development. Additionally, the treatment paradigm was designed to provide exposure throughout fetal and neonatal development, beginning on d 1 of gestation. To accomplish this, impregnated C57Bl/6 mice were treated with 0.25 microg/kg TCDD on d 0 and 7 of pregnancy, followed by 2 additional doses of 0.25, 1, or 5 microg/kg given on d 14 and postpartum d 2. The adult offspring were infected with influenza virus, and components of the adaptive and innate immune responses were evaluated. Our results show that developmental exposure to TCDD dose-responsively suppressed both the cell-mediated and antibody responses to influenza virus in female but not males. In contrast, TCDD exposure enhanced the innate immune responses in offspring of both sexes; specifically, neutrophilia and interferon (IFN) gamma levels in the lung were increased. These alterations in functional immunity did not result from overt toxicity to the immune organs, as developmental TCDD exposure did not alter the cellular composition of the thymus, spleen, or bone marrow. These findings extend our knowledge of the dose-responsive nature of immunological defects induced by developmental exposure to TCDD and offer insight regarding the dose required to alter the immune response to viral infection. Moreover, we demonstrate a clear dose at which no observable effects on immune function later in life were detected.

Oncolytic virotherapy for cancer treatment: challenges and solutions

Advances in gene modification and viral therapy have led to the development of a variety of vectors in several viral families that are capable of replication specifically in tumor cells. Because of the nature of viral delivery, infection, and replication, this technology, oncolytic virotherapy, may prove valuable for treating cancer patients, especially those with inoperable tumors. Current limitations exist, however, for oncolytic virotherapy. They include the body's B and T cell responses, innate inflammatory reactions, host range, safety risks involved in using modified viruses as treatments, and the requirement that most currently available oncolytic viruses require local administration. Another important constraint is that genetically enhanced vectors may or may not adhere to their replication restrictions in long-term applications. Several solutions and strategies already exist, however, to minimize or circumvent many of these limitations, supporting viral oncolytic therapy as a viable option and powerful tool in the fight against cancer.

Caloric restriction decreases survival of aged mice in response to primary influenza infection

Caloric restriction (CR) extends life span of healthy rodents compared to those fed ad libitum. Previous studies have shown positive effects of CR on the immune response of aged mice after influenza immunization. To extend these studies, a mouse model of CR was used to determine if CR could modulate primary responses of aged mice to influenza. Although CR delayed the age-related decrease in mitogen-induced lymphoproliferation of aged mice, in stark contrast, CR decreased survival, increased virus titers, and reduced natural killer cell activity in lungs of aged mice after primary influenza infection. Thus, CR has differential effects on immunity of aged mice, as general indices of immune response are maintained, but primary responses to influenza infection are impaired. This suggests that, although CR may positively affect many long-term parameters of aging, increased susceptibility after primary exposure of aged mice to virus, such as influenza, may not be correctable by CR.

Increased mortality associated with TCDD exposure in mice infected with influenza A virus is not due to severity of lung injury or alterations in Clara cell protein content

Most studies examining the cause of increased mortality in mice infected with a normally non-lethal dose of influenza A virus after exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have focused on defects in the immune system. This study examined other possible consequences of TCDD exposure, which could alter pulmonary inflammation during infection. We measured bronchoalveolar lavage (BAL) fluid lactate dehydrogenase (LDH) and protein concentrations and lung wet to dry weight ratios to assess lung damage and edema formation. Immunohistochemistry for Cyp1A1 was used to evaluate the responsiveness of the lung to TCDD. Additionally, we characterized the effects of TCDD on Clara cell secretory protein (CCSP), which plays a regulatory role in pulmonary inflammation. There were no differences in BAL fluid LDH and protein levels, lung wet to dry weight ratios, or the amount of CCSP in the lungs from mice treated with TCDD or vehicle control. The amount of Cyp1A1 in endothelial cells, Clara cells, and Type II pneumocytes was greatly induced after TCDD exposure. Although lung tissue was clearly responsive to TCDD as shown by Cyp1A1 induction, the increased mortality in infected mice exposed to TCDD did not correlate with increased damage to the lung or decreased CCSP concentrations.

Activation of the aryl hydrocarbon receptor increases pulmonary neutrophilia and diminishes host resistance to influenza A virus

Unlike their role in bacterial infection, less is known about the role of neutrophils during pulmonary viral infection. Exposure to pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) results in excess neutrophils in the lungs of mice infected with influenza A virus. TCDD is the most potent agonist for the aryl hydrocarbon receptor (AhR), and exposure to AhR ligands has been correlated with exacerbated inflammatory lung diseases. However, knowledge of the effects of AhR agonists on neutrophils is limited. Likewise, the factors regulating neutrophil responses during respiratory viral infections are not well characterized. To address these knowledge gaps, we determined the in vivo levels of KC, MIP-1alpha, MIP-2, LIX, IL-6, and C5a in infected mouse lungs. Our data show that these neutrophil chemoattractants are generally produced transiently in the lung within 12-24 h of infection. We also report that expression of CD11a, CD11b, CD49d, CD31, and CD38 is increased on pulmonary neutrophils in response to influenza virus. Using AhR-deficient mice, we demonstrate that excess neutrophilia in the lung is mediated by activation of the AhR and that this enhanced neutrophilia correlates directly with decreased survival in TCDD-exposed mice. Although AhR activation results in more neutrophils in the lungs, we show that this is not mediated by deregulation in levels of common neutrophil chemoattractants, expression of adhesion molecules on pulmonary neutrophils, or delayed death of neutrophils. Likewise, exposure to TCDD did not enhance pulmonary neutrophil function. This study provides an important first step in elucidating the mechanisms by which AhR agonists exacerbate pulmonary inflammatory responses.