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In severe respiratory virus infections, including influenza, an exaggerated host immune response has been linked to the severe disease and death. Control of the overwhelming immune response is thus essential. Efforts with broad-spectrum immunosuppressive agents such as steroids are disappointing. A better understanding of host immune response using animal experimental system is required to avoid undesired outcome of experimental manipulation.Following severe influenza virus infection in influenza hemagglutinin antigen-specific transgenic mouse experimental model, step-wise evolving cells from a pool of naïve hemagglutinin-specific CD4Naïve CD4Origin of regulatory from the effector cells of LAG-3-marked Th1 immunity alleviates lung inflammation without impairment of virus eradication.

Bacterial superinfection aggravates the disease of influenza. Streptococcus pneumoniae is the most common bacterial pathogen. Synergistic virulence has been demonstrated between influenza neuraminidase and pneumococcal NanA and NanB. NanC, the other pneumococcal neuraminidase infrequently present in clinical isolates, is not well characterized. In this study, we report that superinfection with a NanC-negative pneumococcus strain suppresses anti-influenza immunity and impairs viral clearance with higher TGF-β activation in mice. Bacterial load in the lungs also increases as the host immunity is suppressed. NanC-positive isogenic mutant reverses wild type S. pneumoniae–mediated immune suppression and facilitates virus clearance. However, it causes more severe disease as the augmented inflammation causes collateral damage. Both virus-mediated damage and immune response–mediated inflammation are important for pathogenesis of severe influenza. Inflammation may be more critical than virus-mediated damage in influenza with bacterial superinfection.

Bacterial superinfection aggravates the disease of influenza.

Background: Cellular senescence is a state of stable growth arrest triggered by mitogenic and metabolic stressors. Ageing and a high-fat diet (HFD) are proven inducers of senescence in various organs, presenting a challenge for ageing populations worldwide. Our previous study demonstrated that ROS scavenger N-acetylcysteine (NAC) can improve insulin resistance (IR) and chronic inflammation in diet-induced obesity mice, an effect better achieved through early intervention. We, herein, investigate whether NAC can improve cellular senescence in a diet-induced obesity mouse model, and whether a legacy effect is presented with early intervention. Materials and Methods: For a twelve-month treatment course, all C57B/L6 mice were fed a chow diet (CD), high-fat high-sucrose diet (HFD), CD+NAC1-12 (NAC intervention 1st-12th month), HFD+NAC1-12, and HFD+NAC1-6 (NAC intervention 1st-6th month). Staticalanalysis was used to analyze the different markers of cellular senescence and inflammation. Results: Throughout the study, the HFD group exhibited significantly increased body weight (BW) and body fat, markers of senescence, decreased motor activity (MA) and impaired glucose tolerance. Compared to the HFD group, the HFD+NAC1-12 group exhibited increased MA, decreased BW and body fat, improved glucose tolerance, and decreased senescence markers.The HFD+NAC1-6 group showed similar effects to the HFD+NAC1-12 group, despite discontinuing NAC for 6 months. Our study showed that NAC significantly increased MA in both HFD+NAC1-12 and HFD+NAC1-6 groups, and improved HFD-induced mitochondrial and intracellular ROS expression, DNA and protein oxidative damage, and adipose tissue inflammation. Conclusion: Legacy effect was indeed presented in HFD-induced cellular senescence with NAC intervention, with possible mechanisms being persistently increased motor activity and anti-oxidative stress effects.

Aims: Obesity-induced excessive visceral fat (VF) accumulation is associated with insulin resistance (IR), systemic oxidative stress, and chronic inflammation. As toll-like receptor 4 (TLR4) plays an important role in innate immunity, we herein investigate the effect of TLR4 knockout (T4KO) in a high-fat high-sucrose diet (HFD)-induced obesity mouse model. Results: C57BL6 wild-type (WT) and T4KO mice were fed with either control diet (CD) or HFD for 12 months, rendering four experimental groups: WT+CD, WT+HFD, T4KO+CD, and T4KO+HFD. Compared with WT+CD, WT+HFD demonstrated significant increase in VF accumulation, oxidative damage, M1/M2 macrophage ratio, chronic inflammation, and development of IR. Compared with WT+HFD, T4KO+HFD presented increased BW and body fat with higher subcutaneous fat (SF)/VF ratio, but lower body temperature, as well as decreased oxidative damage, M1/M2 macrophage ratio, chronic inflammation, and IR. Unlike WT+HFD, T4KO+HFD exhibited an increase in mitochondrial electron transport chain activity but a decrease of uncoupling protein 2 (UCP2) level. While T4KO hindered HFD-induced increasing mitochondrial oxygen consumption rate, a shift toward a higher extracellular acidification rate in VF was observed. Notably, T4KO inhibits HFD-induced mitochondrial translocation of nuclear factor of activated T cells 2 (NFATC2), which contributed to mitochondrial metabolic reprogramming. Both fat distribution shifting from VF to SF and mitochondrial metabolic reprogramming may alleviate systemic oxidative stress and chronic inflammation. Innovation and Conclusion: Abrogation of TLR4 contributes to reduction of oxidative stress through metabolic reprogramming of mitochondria in VF, mitigating obesity-induced IR. The study provides critical insight into associating innate immunity-mitochondria interplay with prevention of diabetes.

Influenza hemagglutinin (HA)-specific T-Cell-Receptor (TCR) transgenic mice sustain the influenza virus infection of an inoculum size which is fatal in wild type mice. There is a prominent IL-17 response of the HA-specific TCR transgenic CD4+ T cells in late phase of infection in the transgenic mice. We have demonstrated that the late phase IL-17 response is a de novo response of naïve T cells under guidance of the Th1 cells with influenza viral neuraminidase-activated TGF-β. There is also a late phase up-regulation of epidermal growth factor receptor (EGFR) on the transgenic CD4+ T cells in the lungs. EGFR inhibition with Gefitinib resulted in impaired sustainability of the infection of the transgenic mice. They suffered from profound body weight loss and severe disease with significant mortality. IL-17-induced EGFR-mediated signaling cascade has been documented in skin stem cells that are involved in wound healing. We will further dissect the role of this cascade in alleviation of lung inflammation and recovery from the disease during the late phase of acute influenza virus infection.

The 6.5 CD4+ T cell receptor (TCR) transgenic mice have a monotonous CD4+ TCR which responds to the hemagglutinin (HA) antigen of PR8 influenza virus. Naive 6.5 CD4+ T cells adoptively transferred into wild type mice were activated by PR8 influenza virus with Th1 response. With PR8 influenza virus infection, all CD4+ T cells in 6.5 mice were activated and they were predominantly Th1 in phenotype at the early phase of infection and Th17 at the late phase. Th1 effector responses made infected mice sick and even succumb to death. The 6.5 mice were sicker at the early phase but recovered with better survival at last. IL-17KO 6.5 mice cannot display Th17 responses and lost the survival benefit as well. IL-17 supplement at the late phase of infection enhanced survival of wild type mice with PR8 influenza virus infection. With consecutive two adoptive transfers of naive 6.5 CD4+ T cells, 6.5 CD4+ T cells of the first transfer evolved into Th1 cells but 6.5 CD4+ T cells of the second transfer demonstrated a de novoTh17 response. Thymectomy or aging in 6.5 mice limited the thymic output of naive 6.5 CD4+ T cells and diminished the Th17 response. Viral neuraminidase activated TGF-β in the Th1 6.5 CD4+ T cells at the early phase. T-bet dominance was altered with excessive ROR-γt activation in the following responding 6.5 CD4+ T cells. They have substantial IL-17 with restrained IFN-γ production. We demonstrated a Th1 guided evolution of protective Th17 response in severe influenza.

Bacterial superinfection aggravates the disease of influenza virus infection. Streptococcus pneumoniae is a frequently encountered bacterial pathogen. Superinfection with neuraminidase (Nan) C deficient wild type pneumococcus, which expresses NanA and NanB only, suppressed antigen-specific anti-influenza immunity, with impaired viral clearance. There was augmented TGF-β activation in the lung-infiltrating influenza hemagglutinin (HA)-specific CD4+ T cells. Mice suffered from exacerbated disease and died with higher virus loads in the lung. We modified this wild type strain with NanC insertion. This modified strain expresses all neuraminidases A, B and C. Superinfection with this NanC inserted pneumococcus reverted the immune-suppressive effect of the wild type pneumococcus with NanA and NanB only. There were augmented inflammatory cytokines IFN-γ and TNF-α production and suppressed TGF-β activation in the lung-infiltrating influenza HA-specific CD4+ T cells. The pro-inflammatory response enhanced viral clearance. Even the virus eradication is enhanced, the mice actually suffered from even more severe disease. Our results demonstrated the important role of NanC-mediated inflammation in the disease of severe influenza with pneumococcal superinfection.

Naïve CD4+ T cells respond in influenza with T-bet expression, a transcription factor up-regulated with Th1 commitment. We report concomitant LAG-3 expression on these Th1 committed cells with evolution into regulatory T cells. LAG-3 expression increases with activation as revealed by CFSE cell division study. Cells with moderate LAG-3 expression produce IFN-γ and contribute to inflammation and disease. They no longer produce IFN-γ with higher LAG-3 expression upon further activation. High LAG-3 cells suppress and decouple effector function from the preserved proliferation of CD8+ T cells. They restrain inflammation with facilitated viral clearance and ameliorate the disease of severe influenza. Foxp-3+CD4+ T cells suppress both effector and proliferative responses with impaired viral clearance and they are less potent in disease amelioration. Principal component analysis of genome-wide expression further confirmed the stepwise evolution from effector to regulatory T cells. Regulatory genes are up-regulated progressively from LAG-3Neg to LAG-3Med and to LAG-3High cells.

Reactive oxygen species (ROS) plays a crucial role in pathogenesis of insulin resistance (IR) and type 2 diabetes. In the United Kingdom, Prospective Diabetes Study and its 10-year post-trial monitoring, a beneficial effect of early optimisation of blood glucose control is clearly demonstrated. In this study, we investigated whether ROS scavenger N-acetylcysteine (NAC) and the time point of intervention can affect IR in a diet-induced obesity mouse model. Male C57B/L6 mice were fed chow diet (CD), high-fat high-sucrose diet (HFD), CD + NAC1-6 (NAC intervention 1st to 6th month), HFD + NAC1-6, and HFD + NAC3-6 (NAC intervention 3rd to 6th month) for a 6-month treatment course. HFD group showed significantly increased body weight (BW) and body fat, decreased motor activity (MA), impaired intraperitoneal glucose tolerance test (IPGTT), and insulin tolerance test (IPITT) throughout the study. HFD + NAC1-6, as compared with HFD group, had increased MA, improved IPGTT and IPITT since first month, followed by decreased BW and body fat. HFD + NAC3-6 group, although showed improved IPGTT and IPITT than HFD group, still had higher BW, decreased MA, and impaired IPGTT and IPITT as compared with HFD + NAC1-6 at the end of the study. NAC significantly increased MA, and ameliorated the HFD-induced mitochondrial and intracellular ROS expression, DNA and protein oxidative damage, and adipose tissue inflammation. We concluded that ROS scavenger can improve IR and chronic inflammation in diet-induced obesity mice. This action is likely better expressed through early intervention. The mechanism is probably through a virtuous circle of suppressed oxidative stress, and increased motor activity, which helps to reduce body fat.

Background: Millions of people are infected by the influenza virus worldwide every year. Current selections of anti-influenza agents are limited and their effectiveness and drug resistance are still of concern. Purpose: Investigation on in vitro and in vivo effect of aloin from Aloe vera leaves against influenza virus infection. Methods: In vitro antiviral property of aloin was measured by plaque reduction assay in which MDCK cells were infected with oseltamivir-sensitive A(H1N1)pdm09, oseltamivir-resistant A(H1N1)pdm09, H1N1 or H3N2 influenza A or with influenza B viruses in the presence of aloin. In vivo activity was tested in H1N1 influenza virus infected mice. Aloin-mediated inhibition of influenza neuraminidase activity was tested by MUNANA assay. Aloin treatment-mediated modulation of anti-influenza immunity was tested by the study of hemagglutinin-specific T cells in vivo. Results: Aloin significantly reduced in vitro infection by all the tested strains of influenza viruses, including oseltamivir-resistant A(H1N1)pdm09 influenza viruses, with an average IC50 value 91.83 ± 18.97 μM. In H1N1 influenza virus infected mice, aloin treatment (intraperitoneal, once daily for 5 days) reduced virus load in the lungs and attenuated body weight loss and mortality. Adjuvant aloin treatment also improved the outcome with delayed oseltamivir treatment. Aloin inhibited viral neuraminidase and impeded neuraminidase-mediated TGF-β activation. Viral neuraminidase mediated immune suppression with TGF-β was constrained and influenza hemagglutinin-specific T cell immunity was increased. There was more infiltration of hemagglutinin-specific CD4+ and CD8+ T cells in the lungs and their production of effector cytokines IFN-γ and TNF-α was boosted. Conclusion: Aloin from Aloe vera leaves is a potent anti-influenza compound that inhibits viral neuraminidase activity, even of the oseltamivir-resistant influenza virus. With suppression of this virus machinery, aloin boosts host immunity with augmented hemagglutinin-specific T cell response to the infection. In addition, in the context of compromised benefit with delayed oseltamivir treatment, adjuvant aloin treatment ameliorates the disease and improves survival. Taken together, aloin has the potential to be further evaluated for clinical applications in human influenza.

T-bet induced CD4+ T cells are committed to be IFN-γ competent Th1 cells. The Th1 response is essential for virus eradication, but is also a major cause of inflammation and disease aggravation in severe influenza. In our influenza hemagglutinin (HA) Ag-specific mouse experimental system, naïve CD4+ T cells respond to the infection with T-bet expression. However, they suppress cognate CD8+ T cell effector response-mediated inflammation and alleviate the disease. Here we report concomitant LAG-3 expression and IFN-γ competence in Th1 committed CD4+ T cells. LAG-3 expression increases with activation by virus as revealed by CFSE based cell division study. The Th1 committed cells with moderate LAG-3 expression produce IFN-γ and contribute to inflammation and aggravated disease. They can no longer produce IFN-γ with higher LAG-3 expression upon further activation. Th1 committed CD4+ T cells with high LAG-3 expression suppress cognate CD8+ T cells by decoupling their effector function from proliferative response, restrain lung inflammation and facilitate viral clearance. They are better than Foxp-3+HA-specific CD4+ T cells in disease amelioration. The Foxp-3+ cells suppress both effector function and proliferative response of CD8+ T cells. They moderate inflammation but impair viral clearance. Principal component analysis of genome-wide gene expression profiles further confirmed the stepwise evolution. Several regulatory function-associated genes such as Lag3, Pdcd1, Tigit, Ctla2a, Nr4a2, Klrc1, Rgs16, Sytl3, Il21, Il1r2 and Dusp4 are up-regulated graduallly as well from LAG-3Neg to LAG-3Med and LAG-3High cells.

Induced regulatory T cells (iTreg) is an adaptive response in inflammation with disease processes such as infection, autoimmunity or cancer. A small number of iTreg may exert long-lasting regulation. Here we report the LAG-3+ iTreg transfer regulatory activity to the CD4+ T cells they suppress. This infectious propagation of regulatory activity exemplify a dominant immune regulation in vivo. Naïve hemagglutinin (HA) antigen-specific CD4+ T cells are induced to differentiate into IFN-γ competent effector T cells and then LAG-3+ Tregs in HA transgenic mice inherently expressing the cognate HA antigen. The LAG-3+ iTreg suppresses activation of effector function of cognate naïve CD4+ T cells in HA transgenic mice, with silenced IFN-γ machinery including STAT1 phosphorylation and T-bet induction. The LAG-3 iTreg suppressed, IFN-γ disarmed CD4+ T cells still proliferate and acquire LAG-3 expression on their surface in vivo. They become the next generation LAG-3+ iTregs with the ability of suppression of activation of effector function of cognate naïve CD4+ T cells in HA transgenic mice, with the same mechanism of silenced IFN-γ machinery. LAG-3+ iTreg exercises regulation in vivo by suppression of effector function decoupled from reserved proliferative response. The effector function suppressed CD4+ T cells still proliferate upon activation and acquire LAG-3+ iTreg phenotype, a reminiscence of the infectious tolerance proposed in 1970.

Cytokine storm has been postulated as one of the major causes of mortality in patients with severe respiratory viral infections such as influenza. With the help of an influenza Ag- specific mouse experimental system, we report that CD4+ T cells contribute effector cytokines leading to lung inflammation in acute influenza. Although virus can no longer be detected from tissues 14 d postinfection, virus-derived Ag continues to drive a CD4+ T cell response after viral clearance. Ag-specific CD4+ T cells proliferate and evolve into memory CD4+ T cells efficiently, but the production of effector cytokines is seriously hampered during this phase. This decoupling of proliferation and effector cytokine production doesn’t appear in conjunction with increased suppression by regulatory T cells or decreased induction of transcription factors. Rather, GATA-3 and ROR-γt levels are elevated when compared with cells that have effector cytokine production. T-bet dominance over GATA-3 and ROR-γt decreases with the disarmament of effector cytokine production. Importantly, upon reinfection, these decoupled cells produce elevated levels of IFN-γ and were effective in virus eradication. These results provide a mechanism through altered T-bet dominance to dampen the cytokine storm without impeding the generation of memory T cells in influenza virus infection.

Sterilizing immunity is a unique immune status, which prevents effective virus infection into the host. It is different from the immunity that allows infection but with subsequent successful eradication of the virus. Pre-infection induces sterilizing immunity to homologous influenza virus challenge in ferret. In our antigen-specific experimental system, mice pre-infected with PR8 influenza virus through nasal route are likewise resistant to reinfection of the same strain of virus. The virus is cleared before establishment of effective infection. Intramuscular influenza virus injection confers protection against re-infection with facilitated virus clearance but not sterilizing immunity. Pre-infection and intramuscular injection generates comparable innate immunity and antibody response, but only pre-infection induces virus receptor reduction and efficient antigen-specific T cell response in the lungs. Pre-infection with nH1N1 influenza virus induces virus receptor reduction but not PR8-specific T cell immune response in the lungs and cannot prevent infection of PR8 influenza virus. Pre-infection with PR8 virus induced PR8-specific T cell response in the lungs but cannot prevent infection of nH1N1 virus either. These results reveal that antigen-specific T cell immunity is required for sterilizing immunity.

Some healthy individuals suffer from severe disease and even mortality with the same strain of influenza virus that causes self-limited illnesses in the majority of people. This fact exemplifies the importance of host factors in influenza disease manifestation. Our C3-HA transgenic mice express hemagglutinin (HA) as a self-antigen that is identical to the HA of PR8 influenza virus. Compared to wild type mice, C3-HA mice incurred severe disease with PR8, but not with HA-mismatched influenza virus. Self-HA in C3-HA mice altered the immune response to the infection and impaired clearance of the influenza virus. However, different mechanisms contribute for exacerbated disease in C3-HA mice with different level of HA. In C3-HALow mice, low-level self-HA modulated HA specific immunity upon infection with less clonotypic expansion, T-bet induction and effector cytokines IFN-γ and TNF-α production of both HA-specific CD4+ and CD8+ T cells on day 4- post infection. The T cell activation status contracted further on day 7- post infection. Impaired immunity resulted in delayed virus clearance leading to severe disease and death. In C3-HAHigh mice, high-level self-HA also modulated impaired immunity and virus clearance on day 4- post infection. In contrast to further reduction on day 7- post infection in C3-HALow mice, the HA specific T cell immunity was higher on day 7- than day 4- post infection in C3-HAHigh mice. The boosted HA specific immunity resulted in severe disease with autoimmunity as a predominant feature in pathology. Our animal model exemplified the complicated interaction between cross-reactive self-antigen and influenza virus with severe disease as the results of antigen level dependent distinct mechanisms.

Streptococcus pneumoniae often causes superinfection in influenza and exacerbates the disease with more severity and even mortality. In our influenza hemagglutinin (HA) antigen-specific transgenic mouse model, mice suffered from severe disease and died with increased virus titer and pathology in the lungs upon serotype-3 Streptococcus pneumoniae superinfection on day 4- post PR8 strain H1N1 influenza virus infection. Same dose viral or bacterial infection caused mild disease in control mice. Streptococcus pneumoniae supreinfection attenuated anti-influenza T cell immunity in the lungs. There was less clonotypic expansion, T-bet induction and effector cytokines IFN-γ and TNF-α production in HA-specific CD4+ T cells on day 2- and 3- post bacterial superinfection, with impaired viral clearance. Streptococcus pneumoniae strains with different combinations of bacterial neuraminidase (NA) demonstrated varied degrees of T cell immunity attenuation. Streptococcus pneumoniae with NA-B only was the most suppressive with up-regulated active TGF-β and down-regulated IFN-γ expression in HA-specific CD4+ T cells, followed by those with both NA-A and NA-B. Streptococcus pneumoniae with both NA-A and NA-B and inserted NA-C was least suppressive. With in vitro experiments, recombinant bacterial NA-A or NA-B augmented TGF-β and attenuated IFN-γ in HA-specific CD4+ T cells in overnight culture with PR8 virus. Recombinant bacterial NA-C mitigated TGF-β and increased IFN-γ in HA-specific CD4+ T cells. Our results demonestrates distinct immune alteration by different bacterial neuraminidases, which may play a significnt role of disease manifestation in influenza with bacterial superinfection.

Th1 cells control their activity by producing regulatory IL-10. Here we report that Th1 cell-derived IL-10 facilitates their expansion and, in addition, augments Th1 cell production of IFN-γ, TNF-α and IL-2 during the early phase of influenza. In our antigen-specific mouse experimental system, influenza haemagglutinin-specific CD4(+) T cells respond to infection with the induction of T-bet, and produce both IFN-γ and IL-10. In the early phase of infection, an abundance of viral neuraminidase causes TGF-β activation of haemagglutinin-specific CD4(+) T cells. CD4(+) T-cell-derived IL-10 inhibits neuraminidase-driven TGF-β activation and counteracts the virus-mediated immune suppression. As the host eradicates the virus, neuraminidase activity wanes and IL-10 receptors are upregulated on CD4(+) T cells in the late phase of infection. IL-10 then suppresses immune activation and aids in recovery from infection and inflammation. These results reveal a previously unrecognized function of Th1 cell-derived IL-10 in vivo.

The immune system responds to influenza virus infection for eradication of the virus but the associated inflammation may cause tissue damage to the host. In our antigen-specific mouse system, naïve influenza hemagglutinin (HA)-specific CD4+ T cells adoptively transferred with infection respond with Th1 phenotype and produce IFN-γ. Some of them secrete IL-17 as well. Second batch HA specific CD4+ T cells, adoptively transferred on day 4 after infection and the first transfer, respond to the infection with Th17 phenotype. They produce IL-17 but not IFN-γ. Both the Th1 and Th17 cells are activated with similar levels of ZAP-70 phosphorylation and T-bet induction. For the Th17 cells, IFN-γ deficiency is associated with excessive ROR-γt induction and altered T-bet dominance. Th17 cells display surface LAG-3 expression, suppress T cell activation in vitro and decrease lung inflammation in vivo. The evolution of Th17 cells is augmented in IL-10 deficiency, with IL-10 knockout mice as the recipients transferred with IL-10 knockout HA specific CD4+ T cells. There is increased neuraminidase-mediated TGF-β activation in this IL-10 deficient environment. Viral neuraminidase mediated TGF-β activation in the first batch of HA specific CD4+ T cells facilitates the Th17 evolution of the 2nd batch of cells. The 6.5 T cell receptor (TCR) transgenic mice of monotonous HA specific TCR repertoire respond to influenza virus infection with Th17 deviation and demonstrate survival benefit. Consecutive waves of naïve HA specific T cells from the thymus in 6.5 mice may evolve with mechanisms similar to consecutive adoptive transfers. Evolution of protective Th17 immunity is facilitated by neuraminidase-mediated TGF-β activation.

Influenza virus infection causes mild and self-limiting illness in most of the healthy individuals, but some healthy people develops complications as a result of the infection and suffers from severe disease and eventually dies. Here we report that pre-existing matched antigens attenuate antigen-specific immunity to the infection. High virus load and associated increase of pathogenic innate response in the lungs exacerbates the disease. The C3-HAHigh and C3-HALow transgenic mice are with inherent expression of Hemagglutinin (HA) antigen from PR8 strain of H1N1 influenza virus. Compared to wild type mice, these mice suffered from severe disease and higher mortality upon infection of wild type PR8 virus but not upon infection of reverse genetically raised PR8 virus with replaced HA from H3N2 influenza virus. Adoptively transferred PR8 virus HA-specific 6.5 CD4+ and Clone-4 CD8+ T cells responded minimally to PR8 virus infection in C3-HA mice. There was less clonotypic expansion, T-bet induction and effector cytokines IFN-γ and TNF-α production of both 6.5 CD4+ and Clone-4 CD8+ T cells. Virus neutralizing antibodies were less as well. The attenuation was associated with increased LAG-3+ but not Foxp-3+ population of HA-specific T cells in the lungs. In contrast to the instigated weak antigen-specific immunity, PR8 virus infection caused neutrophils more efficient for inflammatory IL-6 secretion and robust bronchus infiltration in C3-HA mice. These results suggest that a host factor cross-reactive to the antigens of influenza virus may exacerbate the disease with similar attenuated antigen-specific adaptive immunity accompanied by augmented innate immunity to influenza virus infection.

The host immune system responds to influenza virus infection for eradication of the virus but the immune response associated inflammation causes tissue injury and damage to the host as well. In our antigen-specific mouse model system for influenza virus infection, influenza hemagglutinin antigen-specific CD4+ T cells responded to acute infection with Th1 effector phenotype. A significant proportion of them were also with concurrent expression of LAG-3, CTLA-4, GITR or CD25. Adoptive transfer of purified LAG-3 expressing hemagglutinin antigen-specific CD4+ T cells controlled lung inflammation with acute influenza virus infection, as represented by the activation of co-transferred influenza hemagglutinin antigen-specific CD8+ T cells. Control of the inflammation by LAG-3 expressing antigen-specific Th1 CD4+ T cells was not necessarily associated with impaired capacity of virus eradication. These results reveal, besides effector function for virus eradication, subsets of CD4+ T cells activated by acute influenza virus infection also acquired regulatory function to attenuate inflammation for reducing the damage to the host. These subsets of CD4+ T cells may be employed as the practical handle for management of severe influenza disease.

Pre-infection induces sterilizing immunity to homologous influenza virus challenge in ferret. In our antigen-specific experimental system, mice pre-infected with PR8 influenza virus through nasal route are likewise resistant to reinfection of the same strain of virus. The virus is cleared before establishment of effective infection. Intramuscular influenza virus injection confers protection against re-infection with facilitated virus clearance but not sterilizing immunity. Pre-infection and intramuscular injection generates comparable innate immunity and antibody response, but only pre-infection induces virus receptor reduction and antigen-specific T cell response in the lung. Pre-infection with nH1N1 influenza virus induces virus receptor reduction but not PR8 specific T cell immune response in the lung and cannot prevent infection with PR8 influenza virus. Pre-infection with PR8 virus induced PR8-specific T cell response in the lung but cannot prevent infection with nH1N1 virus either. Antigen specific T cell immunity is required for sterilizing immunity. We discuss the potential implications of these findings in vaccination strategy for effectual protection comparable to pre-infection.

The host immune system responds to influenza virus infection for eradication of the virus but the immune response associated inflammation causes tissue injury and damage to the host as well. Severe influenza with morbidity and mortality is commonly believed to be the result of overwhelming immune response. In addition to antiviral agent, adjuvant therapy with immune modulating agent is a reasonable approach for severe influenza and has been reported to be effective in clinical series. As the immunity is also critical for virus eradication and recovery, we investigated to try to define the appropriate window for immune modulation in our murine animal model of influenza virus infection. Rapamycin treatment in a wide dose range did not alter the clinical course of severe influenza. In combination with antiviral agent Oseltamivir, rapamycin failed to offer additional benefit beyond treatment with Oseltamivir alone. Oseltamivir barely rescued the mice from severe influenza if the treatment was delayed until 48 hours after infection. Rapamycin did not provide salvage effect in this scenario. In fact, rapamycin suppressed influenza antigen specific CD4+ T cell response and impaired the virus eradication capacity. The virus burden in the lung increased with intense neutrophil infiltration and hyaline deposition in the alveoli. In conclusion, rapamycin cannot be relied upon as a salvage measure in severe influenza with progressive illness under treatment with Oseltamivir. T cell immunity is suppressed but other arms of immunity are recruited with undesirable effect on the disease outcome.

Critical illnesses in pregnancy account for 0.11 to 0.89% of deliveries resulting in ICU admissions. The high rate of perinatal asphyxia in infants and high mortality rate in gravid patients supported a strategy of early delivery during the third trimester. The mortality rate of acute respiratory distress syndrome (ARDS) is high and varied from 15 to 72% among the studies. The present study reports the outcomes of early delivery within 48 hours after ICU admission in pregnant patients with ARDS.

Purpose The toll-like receptor 4 (TLR4) signaling pathway is involved in chronic inflammation and insulin resistance, which are associated with obesity and diabetes mellitus. In the present study, a model of high-fat diet (HFD) feeding of mice was used to investigate the role of TLR4 in overnutrition- and obesity-associated inflammation and infiltration of macrophages and microglia in the retina. Methods Wild-type C57BL/6 and TLR4 knockout (TLR4KO; B6.B10ScN-Tlr4(lps-del)/JthJ) mice were fed a HFD or control chow diet (CD) for 6 months. The TLR4 expression, the relative increase in macrophages/microglia (CD11b(+) and CD45(+) cells), the presence of markers of oxidative stress (gp91phox and malondialdehyde; MDA), and DNA damage (phosphorylated histone H2AX; γH2AX) were assessed by real-time PCR and immunofluorescence studies. Results The HFD for 6 months showed increased obesity, glucose intolerance, and insulin resistance in mice. Toll-like receptor 4 expression was found in vascular pericytes at the inner retina. Increased CD11b(+) and CD45(+) cells, phosphorylated NF-κB, interleukin-6, gp91phox, MDA, and γH2AX were observed in the retina of mice fed a HFD compared to CD counterparts. TLR4KO mice did not show the adverse effects of HFD. Conclusions Our results indicate that HFD-induced macrophage/microglial cell activation and retinal impairment were reduced in the absence of TLR4. The findings suggest that TLR4 is implicated in the pathogenesis of retinal diseases caused by metabolic disorders.

Th1 cells control their activity by producing regulatory IL-10. Here we report that Th1 cell-derived IL-10 facilitates their expansion and in addition, augments Th1 cell production of IFN-γ, TNF-α, and IL-2 during the early phase of influenza. In our antigen-specific mouse experimental system, influenza hemagglutinin-specific CD4+ T cells respond to infection with the induction of T-bet, and produce both IFN-γ and IL-10. In the early phase of infection, an abundance of viral neuraminidase causes TGF-β activation of hemagglutinin-specific CD4+ T cells. CD4+ T cell-derived IL-10 inhibits neuraminidase-driven TGF-β activation and counteracts the virus-mediated immune suppression. As the host eradicates the virus, neuraminidase activity wanes and IL-10 receptors are up-regulated on CD4+ T cells in the late phase of infection. IL-10 then suppresses immune activation and aids in recovery from infection and inflammation. These results reveal a previously unrecognized function of Th1 cell-derived IL-10 in vivo.

Overwhelming inflammation with cytokine storm has been postulated as a major cause of severe influenza disease in human. In our influenza Ag- specific mouse experimental system, we discovered a Th17 deviation of CD4+ T cell response with resultant attenuation of inflammation in the late phase of influenza infection. Naïve hemagglutinin (HA)-specific CD4+ T cells respond to acute influenza virus infection with Th1 phenotype. In the presence of antigen specific Th1 CD4+ T cells, naïve CD4+ T cells adoptively transferred 4 days after the acute infection are activated with deviation to the Th17 phenotype. The second batch of naïve HA-specific CD4+ T cells is activated in an environment enriched with Th1 cytokines and active TGF-β. They proliferate, secrete IL-17 but not IFN-γ and express LAG-3 on the cell surface. They can suppress T cell activation in vitro and decrease lung inflammation in vivo. The 6.5 mice, with monotonous TCR repertoire responsive to influenza HA, reveal a Th17 deviated CD4+ T cell response and significant survival benefit in influenza virus infection. Consecutive waves of naïve CD4+ T cells from the thymus in 6.5 mice are probably activated as subsequent batches of naïve CD4+ T cells, with Th17 deviation which attenuates the inflammation in late phase of influenza virus infection.

Influenza virus invades the host while the host immune response defends to clear the virus. These responses may result in excessive inflammation with tissue injury, which is as detrimental as the invasiveness of the virus. Here we demonstrate a biphasic immune regulation by the host T cell cytokine interleukin-10. During the early phase of infection, viral neuraminidase increases with multiplication of the virus. The abundance of neuraminidase mediates a robust release of the suppressive cytokine TGF-β. Host interleukin-10 interacts with neuraminidase, counteracts the release of TGF-β, and supports the antiviral immunity. Neuraminidase activity wanes with eradication of the virus. In the late phase of the infection, interleukin-10 preferentially binds to up-regulated interleukin-10 receptors and attenuates the immune responses to avoid immune-mediated damage to the host.

IL-10 is regarded as an anti-inflammatory cytokine which prevents damage from immunopathology with exacerbated immune responses. However, severe lung inflammation in fatal human influenza is accompanied with increased levels of IL-10 as well as other pro-inflammatory cytokines. This information raises questions regarding the role IL-10 plays in inflammation associated with acute influenza. We found that IL-10 was produced by CD4+ T cells in synchronization with pro-inflammatory cytokines during an acute influenza virus infection in mice. IL-10 supplementation during the acute phase increased inflammation leading to death, while IL-10 knockout mice displayed decreased lung inflammation and survival benefits. In the absence of IL-10, influenza-specific CD4+ T cells divided less and produced less pro-inflammatory cytokines despite unaffected Th1 polarity, no increase of regulatory T cell populations, and no alteration in the kinetics of viral eradication. Influenza-specific CD4+ T cell derived IL-10 was more important than IL-10 from other sources for the detrimental effect. In this context of acute influenza in mice, IL-10 also impeded the release of mature TGF-β with decreased neuraminidase-mediated desialylation of host immune cells. The abundance of neuraminidase may contribute to the pro-inflammatory role of IL-10 we demonstrated in this context of acute influenza virus infection.