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

Modeling the CD8＋ T cell immune response to influenza infection in adult and aged mice

The CD8＋ T cell response is the main determinant of viral clearance during influenza infection. However, influenza viral dynamics and the respective immune responses are affected by the host's age. To investigate age-related differences in the CD8＋ T cell immune response dynamics, we propose 16 ordinary differential equation models of existing experimental data. These data consist of viral titer and CD8＋ T cell counts collected periodically over a period of 19 days from adult and aged mice infected with influenza A/Puerto Rico/8/34 (H1N1). We use the corrected Akaike Information Criterion to identify the models which best represent the considered data. Our model selection process indicates differences in mechanisms which reduce the CD8＋ T cell response: linear downregulation is favored for adult mice, while baseline exponential decay is favored for aged mice. Parameter fitting of the top ranked models suggests that the aged population has reduced CD8＋ T cell proliferation compared to the adult population. More experimental work is needed to determine the specific immunological features through which age might cause these differences. A better understanding of the immunological mechanisms by which aging leads to discrepant CD8＋ T cell dynamics may inform future treatment strategies.

A novel metric-based approach of scoring early host immune response from oro-nasopharyngeal swabs predicts COVID-19 outcome

Unpredictable fatal outcome of COVID-19 is attributed to dysregulated inflammation. Impaired early adaptive immune response leads to late-stage inflammatory outcome. The purpose of this study was to develop biomarkers for early detection of host immune impairment at first diagnosis from leftover RNA samples, which may in turn identify high risk patients. Leftover RNA samples of COVID-19 patients at first diagnosis were stored. Following prospective follow-up, the samples were shorted and categorized into outcome groups. Impaired adaptive T cell response (severity score) and Impaired IL-10 response (undetectable IL-10 in the presence of high expression of a representative interferon response gene) were determined by RT-PCR based assay. We demonstrate that a T cell response based 'severity score' comprising rational combination of Ct values of a target genes' signature can predict high risk noncomorbid potentially critical COVID-19 patients with a sensitivity of 91% (95% CI 58.7-99.8) and specificity of 92.6% (95% CI 75.7-99) (AUC:0.88). Although inclusion of comorbid patients reduced sensitivity to 77% (95% CI 54.6-92.2), the specificity was still 94% (95% CI 79.8-99.3) (AUC:0.82). The same for 'impaired IL-10 response' were little lower to predict high risk noncomorbid patients 64.2% (95% CI 35.1-87.2) and 82% (95% CI 65.5-93.2) respectively. Inclusion of comorbid patients drastically reduce sensitivity and specificity51.6% (95% CI 33.1-69.8) and 80.5% (95% CI 64.0-91.8) respectively. As best of our knowledge this is the first demonstration of a metric-based approach showing the 'severity score' as an indicator of early adoptive immune response, could be used as predictor of severe COVID-19 outcome at the time of first diagnosis using the same leftover swab RNA. The work flow could reduce expenditure and reporting time of the prognostic test for an earliest clinical decision ensuring possibility of early rational management.

Role of IL-27 in COVID-19: A Thin Line between Protection and Disease Promotion

Cytokine storm is usually described as one of the main reasons behind COVID-associated mortality. Cytokines are essential protein molecules engaged in immune responses; they play a critical role in protection against infections. However, they also contribute to inflammatory reactions and tissue damage, becoming a double-edged sword in the context of COVID-19. Recent studies have suggested various cytokines and chemokines that play a crucial role in the immune response to SARS-CoV-2 infection. One such cytokine is interleukin 27 (IL-27), which has been found to be elevated in the blood plasma of patients with COVID-19. Within this study, we will explore the role of IL-27 in immune responses and analyze both the existing literature and our own prior research findings on this cytokine in the context of COVID-19. It affects a wide variety of immune cells. Regardless of the pathological process it is involved in, IL-27 is critical for upholding the necessary balance between tissue damage and cytotoxicity against infectious agents and/or tumors. In COVID-19, it is involved in multiple processes, including antiviral cytotoxicity via CD8+ cells, IgG subclass switching, and even the activation of Tregs.

An important call: Suggestion of using IL-10 as therapeutic agent for COVID-19 with ARDS and other complications

The global coronavirus disease 2019 (COVID-19) pandemic has a detrimental impact on public health. COVID-19 usually manifests as pneumonia, which can progress into acute respiratory distress syndrome (ARDS) related to uncontrolled TH17 immune reaction. Currently, there is no effective therapeutic agent to manage COVID-19 with complications. The currently available anti-viral drug remdesivir has an effectiveness of 30% in SARS-CoV-2-induced severe complications. Thus, there is a need to identify effective agents to treat COVID-19 and the associated acute lung injury and other complications. The host immunological pathway against this virus typically involves the THαβ immune response. THαβ immunity is triggered by type 1 interferon and interleukin-27 (IL-27), and the main effector cells of the THαβ immune response are IL10-CD4 T cells, CD8 T cells, NK cells, and IgG1-producing B cells. In particular, IL-10 exerts a potent immunomodulatory or anti-inflammatory effect and is an anti-fibrotic agent for pulmonary fibrosis. Concurrently, IL-10 can ameliorate acute lung injury or ARDS, especially those caused by viruses. Owing to its anti-viral activity and anti-pro-inflammatory effects, in this review, IL-10 is suggested as a possible treatment agent for COVID-19.

Type I IFN Signaling Protects Mice from Lethal SARS-CoV-2 Neuroinvasion

Multiple organ damage is common in patients with severe COVID-19, even though the underlying pathogenic mechanisms remain unclear. Acute viral infection typically activates type I IFN (IFN-I) signaling. The antiviral role of IFN-I is well characterized in vitro. However, our understanding of how IFN-I regulates host immune response to SARS-CoV-2 infection in vivo is incomplete. Using a human ACE2-transgenic mouse model, we show in the present study that IFN-I receptor signaling is essential for protection against the acute lethality of SARS-CoV-2 in mice. Interestingly, although IFN-I signaling limits viral replication in the lung, the primary infection site, it is dispensable for efficient viral clearance at the adaptive phase of SARS-CoV-2 infection. Conversely, we found that in the absence of IFN-I receptor signaling, the extreme animal lethality is consistent with heightened infectious virus and prominent pathological manifestations in the brain. Taken together, our results in this study demonstrate that IFN-I receptor signaling is required for restricting virus neuroinvasion, thereby mitigating COVID-19 severity.

Evaluation of the immunomodulatory effects of interleukin-10 on peripheral blood immune cells of COVID-19 patients: Implication for COVID-19 therapy

Objective

Several therapies with immune-modulatory functions have been proposed to reduce the overwhelmed inflammation associated with COVID-19. Here we investigated the impact of IL-10 in COVID-19, through the ex-vivo assessment of the effects of exogenous IL-10 on SARS-CoV-2-specific-response using a whole-blood platform.

Methods

Two cohorts were evaluated: in “study population A”, plasma levels of 27 immune factors were measured by a multiplex (Luminex) assay in 39 hospitalized “COVID-19 patients” and 29 “NO COVID-19 controls” all unvaccinated. In “study population B”, 29 COVID-19 patients and 30 NO COVID-19-Vaccinated Controls (NO COVID-19-VCs) were prospectively enrolled for the IL-10 study. Whole-blood was stimulated overnight with SARS-COV-2 antigens and then treated with IL-10. Plasma was collected and used for ELISA and multiplex assay. In parallel, whole-blood was stimulated and used for flow cytometry analysis.

Results

Baseline levels of several immune factors, including IL-10, were significantly elevated in COVID-19 patients compared with NO COVID-19 subjects in “study population A”. Among them, IL-2, FGF, IFN-γ, and MCP-1 reached their highest levels within the second week of infection and then decreased. To note that, MCP-1 levels remained significantly elevated compared with controls. IL-10, GM-CSF, and IL-6 increased later and showed an increasing trend over time. Moreover, exogenous addition of IL-10 significantly downregulated IFN-γ response and several other immune factors in both COVID-19 patients and NO COVID-19-VCs evaluated by ELISA and a multiplex analysis (Luminex) in “study population B”. Importantly, IL-10 did not affect cell survival, but decreased the frequencies of T-cells producing IFN-γ, TNF-α, and IL-2 (p<0.05) and down-modulated HLA-DR expression on CD8⁺ and NK cells.

Conclusion

This study provides important insights into immune modulating effects of IL-10 in COVID-19 and may provide valuable information regarding the further in vivo investigations.

Echinococcus granulosus: The establishment of the metacestode in the liver is associated with control of the CD4+ T-cell-mediated immune response in patients with cystic echinococcosis and a mouse model

The larval stage of the tapeworm Echinococcus granulosus sensu lato (E. granulosus s.l.) caused a chronic infection, known as cystic echinococcosis (CE), which is a worldwide public health problem. The human secondary CE is caused by the dissemination of protoscoleces (PSCs) when fertile cysts are accidentally ruptured, followed by development of PSCs into new metacestodes. The local immune mechanisms responsible for the establishment and established phases after infection with E. granulosus s.l. are not clear. Here, we showed that T cells were involved in the formation of the immune environment in the liver in CE patients and Echinococcus granulosus sensu strict (E. granulosus s.s.)-infected mice, with CD4⁺ T cells being the dominant immune cells; this process was closely associated with cyst viability and establishment. Local T2-type responses in the liver were permissive for early infection establishment by E. granulosus s.s. between 4 and 6 weeks in the experimental model. CD4⁺ T-cell deficiency promoted PSC development into cysts in the liver in E. granulosus s.s.-infected mice. In addition, CD4⁺ T-cell-mediated cellular immune responses and IL-10-producing CD8⁺ T cells play a critical role in the establishment phase of secondary E. granulosus s.s. PSC infection. These data contribute to the understanding of local immune responses to CE and the design of new therapies by restoring effective immune responses and blocking evasion mechanisms during the establishment phase of infection.

Type I IFN Signaling Is Essential for Preventing IFN-γ Hyperproduction and Subsequent Deterioration of Antibacterial Immunity during Postinfluenza Pneumococcal Infection

Postinfluenza bacterial pneumonia is a significant cause of hospitalization and death in humans. The mechanisms underlying this viral and bacterial synergy remain incompletely understood. Recent evidence indicates that influenza-induced IFNs, particularly type I IFN (IFN-I) and IFN-γ, suppress antibacterial defenses. In this study, we have investigated the relative importance and interplay of IFN-I and IFN-γ pathways in influenza-induced susceptibility to Streptococcus pneumoniae infection. Using gene-deficient mouse models, as well as in vivo blocking Abs, we show that both IFN-I and IFN-γ signaling pathways contribute to the initial suppression of antibacterial immunity; however, IFN-γ plays a dominant role in the disease deterioration, in association with increased TNF-α production and alveolar macrophage (AM) depletion. We have previously shown that IFN-γ impairs AM antibacterial function and thereby acute bacterial clearance. The findings in this study indicate that IFN-γ signaling also impairs AM viability and αβ T cell recruitment during the progression of influenza/S. pneumoniae coinfection. Macrophages insensitive to IFN-γ mice express a dominant-negative mutant IFN-γR in mononuclear phagocytes. Interestingly, macrophages insensitive to IFN-γ mice exhibited significantly improved recovery and survival from coinfection, despite delayed bacterial clearance. Importantly, we demonstrate that IFN-I receptor signaling is essential for preventing IFN-γ hyperproduction and animal death during the progression of postinfluenza pneumococcal pneumonia.

Antiviral Activities of Interleukin-27: A Partner for Interferons?

Emergence of new, pandemic-level viral threats has brought to the forefront the importance of viral immunology and continued improvement of antiviral therapies. Interleukin-27 (IL-27) is a pleiotropic cytokine that regulates both innate and adaptive immune responses. Accumulating evidence has revealed potent antiviral activities of IL-27 against numerous viruses, including HIV, influenza, HBV and more. IL-27 contributes to the immune response against viruses indirectly by increasing production of interferons (IFNs) which have various antiviral effects. Additionally, IL-27 can directly interfere with viral infection both by acting similarly to an IFN itself and by modulating the differentiation and function of various immune cells. This review discusses the IFN-dependent and IFN-independent antiviral mechanisms of IL-27 and highlights the potential of IL-27 as a therapeutic cytokine for viral infection.

Evolutionary conservation and positive selection of Influenza A Nucleoprotein CTL epitopes for universal vaccination: a proof-of-concept

Influenza (flu) infection is a leading cause of respiratory disease and death worldwide. While seasonal flu vaccines are effective at reducing morbidity and mortality, such effects rely on the odds of successful prediction of the upcoming viral strains. Additional threats from emerging flu viruses that we cannot predict and avian flu viruses that can be directly transmitted to humans, urge the strategic development of universal vaccinations that can protect against flu viruses of different subtypes and across species. Annual flu vaccines elicit mainly humoral responses. Under circumstances when antibodies induced by vaccination fail to recognize and neutralize the emerging virus adequately, virus-specific cytotoxic T lymphocytes (CTLs) are the major contributors to the control of viral replication and elimination of infected cells. Our studies exploited the evolutionary conservation of influenza A nucleoprotein (NP) and the fact that NP-specific CTL responses pose a constant selecting pressure on functional CTL epitopes, to screen for NP epitopes that are highly conserved among heterosubtypes but are subjected to positive selection historically. We identified a region on NP that is evolutionarily conserved and historically positively selected (NP_137-182 ) and validated that it contains an epitope that is functional in eliciting NP-specific CTL responses and immunity that can partially protect immunized mice against lethal dose infection of a heterosubtypic influenza A virus. Our proof-of-concept study supports the hypothesis that evolutionary conservation and positive selection of influenza nucleoprotein can be exploited to identify functional CTL epitope to elicit cross protection against different heterosubtypes, therefore, to help develop strategies to modify flu vaccine formula for a broader and more durable protective immunity. This article is protected by copyright. All rights reserved.

Single-cell multi-omics reveals dyssynchrony of the innate and adaptive immune system in progressive COVID-19

Dysregulated immune responses against the SARS-CoV-2 virus are instrumental in severe COVID-19. However, the immune signatures associated with immunopathology are poorly understood. Here we use multi-omics single-cell analysis to probe the dynamic immune responses in hospitalized patients with stable or progressive course of COVID-19, explore V(D)J repertoires, and assess the cellular effects of tocilizumab. Coordinated profiling of gene expression and cell lineage protein markers shows that S100Ahi/HLA-DRlo classical monocytes and activated LAG-3hi T cells are hallmarks of progressive disease and highlights the abnormal MHC-II/LAG-3 interaction on myeloid and T cells, respectively. We also find skewed T cell receptor repertories in expanded effector CD8+ clones, unmutated IGHG+ B cell clones, and mutated B cell clones with stable somatic hypermutation frequency over time. In conclusion, our in-depth immune profiling reveals dyssynchrony of the innate and adaptive immune interaction in progressive COVID-19.

The Immune Response to Respiratory Viruses: From Start to Memory

Biomedical research has long strived to improve our understanding of the immune response to respiratory viral infections, an effort that has become all the more important as we live through the consequences of a pandemic. The disease course of these infections is shaped in large part by the actions of various cells of the innate and adaptive immune systems. While these cells are crucial in clearing viral pathogens and establishing long-term immunity, their effector mechanisms may also escalate into excessive, tissue-destructive inflammation detrimental to the host. In this review, we describe the breadth of the immune response to infection with respiratory viruses such as influenza and respiratory syncytial virus. Throughout, we focus on the host rather than the pathogen and try to describe shared patterns in the host response to different viruses. We start with the local cells of the airways, onto the recruitment and activation of innate and adaptive immune cells, followed by the establishment of local and systemic memory cells key in protection against reinfection. We end by exploring how respiratory viral infections can predispose to bacterial superinfection.

Simultaneous or prior activation of intrahepatic type I interferon signaling leads to hepatitis B virus persistence in a mouse model

It remains controversial how interferon (IFN) response contributes to hepatitis B virus (HBV) control and pathogenesis. A previous study identified that hydrodynamic injection (HI) of type I IFN (IFN-I) inducer polyinosinic-polycytidylic acid (poly(I:C)) leads to HBV clearance in a chronic HBV mouse model. However, recent studies have suggested that premature IFN-I activation in the liver may facilitate HBV persistence. In the present study, we investigated how the early IFN-I response induces an immunosuppressive signaling cascade and thus causes HBV persistence. We performed HI of the plasmid adeno-associated virus (pAAV)/HBV 1.2 into adult BALB/c mice to establish an adult acute HBV replication model. Activation of the IFN-I signaling pathway following poly(I:C) stimulation or murine cytomegalovirus (MCMV) infection resulted in subsequent HBV persistence. HI of poly(I:C) with the pAAV/HBV 1.2 plasmid resulted in not only the production of IFN-I and the anti-inflammatory cytokine interleukin (IL)-10 but also the expansion of intrahepatic regulatory T cells (Tregs), Kupffer cells (KCs) and myeloid-derived suppressor cells (MDSCs), all of which impaired the T cell response. However, when poly(I:C) was injected at day 14 after the HBV plasmid injection, it significantly enhanced HBV specific T cell responses. In addition, interferon-alpha/beta receptor (IFNAR) blockade rescued T cell response by downregulating of IL-10 expression and decreasing Treg and KC expansion. Consistently, Treg depletion or IL-10 blockade also controlled HBV replication. Importance: IFN-I plays a double-edged sword role during chronic HBV infection. Here, we identified that application of IFN-I at different time points causes contrast outcome. Activation of the IFN-I pathway before HBV replication induces an immunosuppressive signaling cascade in the liver, and consequently caused HBV persistence while IFN-I activation post HBV infection enhances HBV-specific T cell responses and thus promote HBV clearance. This result provided an important clue to the mechanism of HBV persistence in adult individuals.

NMP4 regulates the innate immune response to influenza A virus infection

Severe influenza A virus infection typically triggers excessive and detrimental lung inflammation with massive cell infiltration and hyper-production of cytokines and chemokines. We identified a novel function for nuclear matrix protein 4 (NMP4), a zinc-finger-containing transcription factor playing roles in bone formation and spermatogenesis, in regulating antiviral immune response and immunopathology. Nmp4-deficient mice are protected from H1N1 influenza infection, losing only 5% body weight compared to a 20% weight loss in wild type mice. While having no effects on viral clearance or CD8/CD4 T cell or humoral responses, deficiency of Nmp4 in either lung structural cells or hematopoietic cells significantly reduces the recruitment of monocytes and neutrophils to the lungs. Consistent with fewer innate cells in the airways, influenza-infected Nmp4-deficient mice have significantly decreased expression of chemokine genes Ccl2, Ccl7 and Cxcl1 as well as pro-inflammatory cytokine genes Il1b and Il6. Furthermore, NMP4 binds to the promoters and/or conserved non-coding sequences of the chemokine genes and regulates their expression in mouse lung epithelial cells and macrophages. Our data suggest that NMP4 functions to promote monocyte- and neutrophil-attracting chemokine expression upon influenza A infection, resulting in exaggerated innate inflammation and lung tissue damage.

Dynamic Natural Killer Cell and T Cell Responses to Influenza Infection

Influenza viruses have perplexed scientists for over a hundred years. Yearly vaccines limit their spread, but they do not prevent all infections. Therapeutic treatments for those experiencing severe infection are limited; further advances are held back by insufficient understanding of the fundamental immune mechanisms responsible for immunopathology. NK cells and T cells are essential in host responses to influenza infection. They produce immunomodulatory cytokines and mediate the cytotoxic response to infection. An imbalance in NK and T cell responses can lead to two outcomes: excessive inflammation and tissue damage or insufficient anti-viral functions and uncontrolled infection. The main cause of death in influenza patients is the former, mediated by hyperinflammatory responses termed “cytokine storm.” NK cells and T cells contribute to cytokine storm, but they are also required for viral clearance. Many studies have attempted to distinguish protective and pathogenic components of the NK cell and T cell influenza response, but it has become clear that they are dynamic and integrated processes. This review will analyze how NK cell and T cell effector functions during influenza infection affect the host response and correlate with morbidity and mortality outcomes.

Silent Infection of B and CD8+ T Lymphocytes by Influenza A Virus in Children with Tonsillar Hypertrophy

Influenza A viruses (IAVs) cause more than 2 million annual episodes of seasonal acute respiratory infections (ARI) and approximately 500,000 deaths worldwide. Depending on virus strain and host immune status, acute infections by IAV may reach sites other than the respiratory tract. In the present study, IAV RNA and antigens were searched for in tissues of palatine tonsils and adenoids removed from patients without ARI symptoms. A real-time reverse transcriptase PCR (RT-PCR) screening revealed that 8 tissue samples from 7 patients out of 103 were positive for IAV. Positive samples were subjected to next-generation sequencing (NGS) and 3 of 8 tissues yielded complete IAV pH1N1 genomes, whereas in 5 samples, the PB1 gene was not fully assembled. Phylogenetic analysis placed tonsil-derived IAV in clusters clearly segregated from contemporaneous Brazilian viruses. Flow cytometry of dispersed tissue fragments and serial immunohistochemistry of paraffin-embedded sections of naturally infected biopsies indicated that CD20⁺ B lymphocytes, CD8⁺ T lymphocytes, and CD11c⁺ cells are susceptible to IAV infection. We sought to investigate whether these lymphoid tissues could be sites of viral replication and sources of viable virus particles. MDCK cells were inoculated with tissue lysates, enabling recovery of one IAV isolate confirmed by immunofluorescence, reverse transcriptase quantitative PCR (RT-qPCR), and NGS. The data indicate that lymphoid tissues not only harbor expression of IAV proteins but also contain infectious virus. Asymptomatic long-term infection raises the possibility of IAV shedding from tonsils, which may have an impact on host-to-host transmission.IMPORTANCE Influenza A virus (IAV) infections are important threats to human health worldwide. Although extensively studied, some aspects of virus pathogenesis and tissue tropism remain unclear. Here, by different strategies, we describe the asymptomatic infection of human lymphoid organs by IAV in children. Our results indicate that IAV was not only detected and isolated from human tonsils but displayed unique genetic features in comparison with those of contemporaneous IAVs circulating in Brazil and detected in swabs and nasal washes. Inside the tissue microenvironment, immune cells were shown to be carrying IAV antigens, especially B and T CD8⁺ lymphocytes. Taken together, these results suggest that human lymphoid tissues can be sites of silent IAV infections with possible impact on virus shedding to the population.

Macrophage PPAR-γ suppresses long-term lung fibrotic sequelae following acute influenza infection

Influenza virus causes a heterogeneous respiratory infectious disease ranging from self-limiting symptoms to non-resolving pathology in the lungs. Worldwide, seasonal influenza infections claim ~500,000 lives annually. Recent reports describe pathologic pulmonary sequelae that result in remodeling the architecture of lung parenchyma following respiratory infections. These dysfunctional recovery processes that disproportionately impact the elderly have been understudied. Macrophages are involved in tissue remodeling and are critical for survival of severe influenza infection. Here, we found intrinsic deficiency of the nuclear receptor PPAR-γ in myeloid cells delayed the resolution of pulmonary inflammation following influenza infection. Mice with myeloid cell-specific PPAR-γ deficiency subsequently presented with increased influenza-induced deposition of pulmonary collagen compared to control mice. This dysfunctional lung remodeling was progressive and sustained for at least 3 months following infection of mice with myeloid PPAR-γ deficiency. These progressive changes were accompanied by a pro-fibrotic gene signature from lung macrophages and preceded by deficiencies in activation of genes involved with damage repair. Importantly similar aberrant gene expression patterns were also found in a secondary analysis of a study where macrophages were isolated from patients with fibrotic interstitial lung disease. Quite unexpectedly, mice with PPAR-γ deficient macrophages were more resistant to bleomycin-induced weight loss whereas extracellular matrix deposition was unaffected compared to controls. Therefore PPAR-γ expression in macrophages may be a pathogen-specific limiter of organ recovery rather than a ubiquitous effector pathway in response to generic damage.

Blocking IL-10 receptor signaling ameliorates Mycobacterium tuberculosis infection during influenza-induced exacerbation

Epidemiological findings indicate that coinfection with influenza viruses is associated with an increased risk of death in patients suffering from tuberculosis, but the underlying pathomechanisms are not well understood. In this study, we demonstrate that influenza A virus (IAV) coinfection rapidly impairs control of Mycobacterium tuberculosis (Mtb) in C57BL/6 mice. IAV coinfection was associated with significantly increased bacterial loads, reduced survival, and a substantial modulation of innate and adaptive immune defenses including an impaired onset and development of Mtb-specific CD4⁺ T cell responses and the accumulation of macrophages with increased arginase-1 production in the lungs. Our findings strongly indicate that IAV coinfection compromises the host’s ability to control Mtb infection via the production of IL-10, which was rapidly induced upon viral infection. The blockade of IL-10 receptor signaling reduced the bacterial load in coinfected mice to a level comparable to that in Mtb-only-infected animals. Taken together, our data suggest that IL-10 signaling constitutes a major pathway that enhances susceptibility to Mtb during concurrent IAV infection.

IL-10R signaling constitutes a major pathway that impairs control of Mycobacterium tuberculosis during influenza co-infection.

Regulatory cytokine function in the respiratory tract

The respiratory tract is an important site of immune regulation; required to allow protective immunity against pathogens, while minimizing tissue damage and avoiding aberrant inflammatory responses to inhaled allergens. Several cell types work in concert to control pulmonary immune responses and maintain tolerance in the respiratory tract, including regulatory and effector T cells, airway and interstitial macrophages, dendritic cells and the airway epithelium. The cytokines transforming growth factor β, interleukin (IL-) 10, IL-27, and IL-35 are key coordinators of immune regulation in tissues such as the lung. Here, we discuss the role of these cytokines during respiratory infection and allergic airway disease, highlighting the critical importance of cellular source and immunological context for the effects of these cytokines in vivo.

Eomesodermin driven IL-10 production in effector CD8+ T cells promotes a memory phenotype

CD8⁺ T cell differentiation is controlled by the transcription factors T-bet and Eomesodermin, in concert with the cytokines IL-2, IL-10 and IL-12. Among these pathways, the mechanisms by which T-box proteins and IL-10 interact to promote a memory T cell fate remain poorly understood. Here, we show that Eomes and IL-10 drive a central memory phenotype in murine CD8⁺ T cells. Eomes expression led to increased IL-10 expression by the effector CD8⁺ T cells themselves as well as an increase in the level of the lymph node homing selectin CD62L. Furthermore, exposure of effector CD8⁺ T cells to IL-10 maintained CD62L expression levels in culture. Thus, Eomes promotes a step-wise transition of effector T cells towards a memory phenotype, synergizing with IL-10 to enhance the expression of CD62L. The early augmentation of lymph node homing markers by Eomes may facilitate the retention of effector T cells in the relatively low inflammatory milieu of the secondary lymphoid organs that promotes central memory development.

Beyond Type 1 Regulatory T Cells: Co-expression of LAG3 and CD49b in IL-10-Producing T Cell Lineages

Type 1 regulatory CD4⁺ T (Tr1) cells express high levels of the immunosuppressive cytokine IL-10 but not the master transcription factor Foxp3, and can suppress inflammation and promote immune tolerance. In order to identify and obtain viable Tr1 cells for research and clinical applications, co-expression of CD49b and LAG3 has been proposed as a unique surface signature for both human and mouse Tr1 cells. However, recent studies have revealed that this pattern of co-expression is dependent on the stimulating conditions and the differentiation stage of the CD4⁺ T cells. Here, using an IL-10^GFP/Foxp3^RFP dual reporter transgenic murine model, we demonstrate that co-expression of CD49b and LAG3 is not restricted to the Foxp3⁻ Tr1 cells, but is also observed in Foxp3⁺ T regulatory (Treg) cells and CD8⁺ T cells that produce IL-10. Our data indicate that IL-10-producing Tr1 cells, Treg cells and CD8⁺ T cells are all capable of co-expressing LAG3 and CD49b in vitro following differentiation under IL-10-inducing conditions, and in vivo following pathogenic insult or infection in the pulmonary mucosa. Our findings urge caution in the use of LAG3/CD49b co-expression as sole markers to identify Tr1 cells, since it may mark IL-10-producing T cell lineages more broadly, including the Foxp3⁻ Tr1 cells, Foxp3⁺ Treg cells, and CD8⁺ T cells.

Murine γ-Herpesvirus 68 Induces Severe Lung Inflammation in IL-27-Deficient Mice with Liver Dysfunction Preventable by Oral Neomycin

IL-27 is an immunoregulatory cytokine consisting of p28 and EBI3. Its receptor also has two subunits, WSX1 and gp130. Although IL-27 promotes Th1 differentiation in naive T cells, it also induces IL-10 expression in effector Th1 cells to curtail excessive immune responses. By using p28-deficient mice and WSX1-deficient mice (collectively called IL-27-deficient mice), we examined the role of IL-27 in primary infection by murine γ-herpesvirus 68 (MHV68), a murine model of EBV. Upon airway infection with MHV68, IL-27-deficient mice had more aggravated lung inflammation than wild-type mice, although MHV68 infection per se was better controlled in IL-27-deficient mice. Although epithelial cells and alveolar macrophages were primarily infected by MHV68, interstitial macrophages and dendritic cells were the major producers of IL-27. The lung inflammation of IL-27-deficient mice was characterized by more IFN-γ-producing CD8⁺ T cells and fewer IL-10-producing CD8⁺ T cells than that of wild-type mice. An infectious mononucleosis-like disease was also aggravated in IL-27-deficient mice, with prominent splenomegaly and severe hepatitis. Infiltration of IFN-γ-producing effector cells and upregulation of the CXCR3 ligand chemokines CXCL9, CXCL10, and CXCL11 were noted in the liver of MHV68-infected mice. Oral neomycin effectively ameliorated hepatitis, with decreased production of these chemokines in the liver, suggesting that the intestinal microbiota plays a role in liver inflammation through upregulation of these chemokines. Collectively, IL-27 is essential for the generation of IL-10-producing effector cells in primary infection by MHV68. Our findings may also provide new insight into the mechanism of hepatitis associated with infectious mononucleosis.

Breaking self-tolerance during autoimmunity and cancer immunity: Myeloid cells and type I IFN response regulation

The generation and regulation of innate immune signals are key determinants of autoimmune pathogenesis. Emerging evidence suggests that parallel processes operating in the setting of solid tumors can similarly determine the balance between tolerance and immunity and ultimately the effectiveness of the antitumor immune response. In both contexts, self-specific responses start with innate immune cell activation that leads to the initial break in self-tolerance, which can be followed by immune response amplification and maturation through innate-adaptive crosstalk, and finally immune-mediated tissue/tumor destruction that can further potentiate inflammation. Of particular importance for these processes is type I IFN, which is induced in response to endogenous ligands, such as self-nucleic acids, and acts on myeloid cells to promote the expansion of autoreactive or tumor-specific T cells and their influx into the target tissue. Evidence from the study of human disease pathophysiology and genetics and mouse models of disease has revealed an extensive and complex network of negative regulatory pathways that has evolved to restrain type I IFN production and activity. Here, we review the overlapping features of self- and tumor-specific immune responses, including the central role that regulators of the type I IFN response and innate immune cell activation play in maintaining tolerance, and discuss how a better understanding of the pathophysiology of autoimmunity can help to identify new approaches to promote immune-mediated tumor destruction.

Pandemic 2009 H1N1 Influenza Venus reporter virus reveals broad diversity of MHC class II-positive antigen-bearing cells following infection in vivo

Although it is well established that Influenza A virus infection is initiated in the respiratory tract, the sequence of events and the cell types that become infected or access viral antigens remains incompletely understood. In this report, we used a novel Influenza A/California/04/09 (H1N1) reporter virus that stably expresses the Venus fluorescent protein to identify antigen-bearing cells over time in a mouse model of infection using flow cytometry. These studies revealed that many hematopoietic cells, including subsets of monocytes, macrophages, dendritic cells, neutrophils and eosinophils acquire influenza antigen in the lungs early post-infection. Surface staining of the viral HA revealed that most cell populations become infected, most prominently CD45^neg cells, alveolar macrophages and neutrophils. Finally, differences in infection status, cell lineage and MHC class II expression by antigen-bearing cells correlated with differences in their ability to re-stimulate influenza-specific CD4 T cells ex vivo. Collectively, these studies have revealed the cellular heterogeneity and complexity of antigen-bearing cells within the lung and their potential as targets of antigen recognition by CD4 T cells.

IRF4 Modulates CD8+ T Cell Sensitivity to IL-2 Family Cytokines

IFN regulatory factor 4 (IRF4) is a key transcription factor that promotes effector CD8+ T cell differentiation and expansion. The roles of IRF4 in regulating the CD8+ T cell response to cytokines have not been explored. In this article, we show that IL-2 and IL-15 signaling and STAT5 activation regulate IRF4 expression in CD8+ T cells. Gene-expression profile analysis has also revealed that IRF4 is required for expression of the receptors of IL-2 family cytokines CD122 and CD127. We found that IRF4 binds directly to CD122 and CD127 gene loci, indicating that it may directly promote CD122 and CD127 gene transcription. As a consequence, IRF4-deficient CD8+ T cells show diminished sensitivity to IL-2, IL-15, and IL-7 treatment in vitro. Furthermore, we found that IRF4-deficient CD8+ T cells had lower expression of CD122 and CD127 in vivo during influenza virus infection. These data suggest that IRF4 regulates the sensitivity of CD8+ T cells to IL-2 family cytokines, which correlates with the diminished effector and memory CD8+ T cell responses in IRF4-deficient CD8+ T cells.

New insights into Blimp-1 in T lymphocytes: a divergent regulator of cell destiny and effector function

B lymphocyte-induced maturation protein-1 (Blimp-1) serves as a master regulator of the development and function of antibody-producing B cells. Given that its function in T lymphocytes has been identified within the past decade, we review recent findings with emphasis on its role in coordinated control of gene expression during the development, differentiation, and function of T cells. Expression of Blimp-1 is mainly confined to activated T cells and is essential for the production of interleukin (IL)-10 by a subset of forkhead box (Fox)p3⁺ regulatory T cells with an effector phenotype. Blimp-1 is also required to induce cell elimination in the thymus and critically modulates peripheral T cell activation and proliferation. In addition, Blimp-1 promotes T helper (Th) 2 lineage commitment and limits Th1, Th17 and follicular helper T cell differentiation. Furthermore, Blimp-1 coordinates with other transcription factors to regulate expression of IL-2, IL-21 and IL-10 in effector T lymphocytes. In CD8⁺ T cells, Blimp-1 expression is distinct in heterogeneous populations at the stages of clonal expansion, differentiation, contraction and memory formation when they encounter antigens. Moreover, Blimp-1 plays a fundamental role in coordinating cytokine receptor signaling networks and transcriptional programs to regulate diverse aspects of the formation and function of effector and memory CD8⁺ T cells and their exhaustion. Blimp-1 also functions as a gatekeeper of T cell activation and suppression to prevent or dampen autoimmune disease, antiviral responses and antitumor immunity. In this review, we discuss the emerging roles of Blimp-1 in the complex regulation of gene networks that regulate the destiny and effector function of T cells and provide a Blimp-1-dominated transcriptional framework for T lymphocyte homeostasis.

Type I Interferons as Regulators of Lung Inflammation

Immune responses to lung infections must be tightly regulated in order to permit pathogen eradication while maintaining organ function. Exuberant or dysregulated inflammation can impair gas exchange and underlies many instances of lung disease. An important driver of inflammation in the lung is the interferon (IFN) response. Type I IFNs are antiviral cytokines that induce a large range of proteins that impair viral replication in infected cells. This cell-intrinsic action plays a crucial role in protecting the lungs from spread of respiratory viruses. However, type I IFNs have also recently been found to be central to the initiation of lung inflammatory responses, by inducing recruitment and activation of immune cells. This helps control virus burden but can cause detrimental immunopathology and contribute to disease severity. Furthermore, there is now increasing evidence that type I IFNs are not only induced after viral infections but also after infection with bacteria and fungi. The pro-inflammatory function of type I IFNs in the lung opens up the possibility of immune modulation directed against this antiviral cytokine family. In this review, the initiation and signaling of type I IFNs as well as their role in driving and maintaining lung inflammation will be discussed.

IL-10: A Multifunctional Cytokine in Viral Infections

The anti-inflammatory master regulator IL-10 is critical to protect the host from tissue damage during acute phases of immune responses. This regulatory mechanism, central to T cell homeostasis, can be hijacked by viruses to evade immunity. IL-10 can be produced by virtually all immune cells, and it can also modulate the function of these cells. Understanding the effects of this multifunctional cytokine is therefore a complex task. In the present review we discuss the factors driving IL-10 production and the cellular sources of the cytokine during antiviral immune responses. We particularly focus on the IL-10 regulatory mechanisms that impact antiviral immune responses and how viruses can use this central regulatory pathway to evade immunity and establish chronic/latent infections.