NADPH Oxidase 1 Is Associated with Altered Host Survival and T Cell Phenotypes after Influenza A Virus Infection in Mice

The role of the reactive oxygen species-producing NADPH oxidase family of enzymes in the pathology of influenza A virus infection remains enigmatic. Previous reports implicated NADPH oxidase 2 in influenza A virus-induced inflammation. In contrast, NADPH oxidase 1 (Nox1) was reported to decrease inflammation in mice within 7 days post-influenza A virus infection. However, the effect of NADPH oxidase 1 on lethality and adaptive immunity after influenza A virus challenge has not been explored. Here we report improved survival and decreased morbidity in mice with catalytically inactive NADPH oxidase 1 (Nox1*/Y) compared with controls after challenge with A/PR/8/34 influenza A virus. While changes in lung inflammation were not obvious between Nox1*/Y and control mice, we observed alterations in the T cell response to influenza A virus by day 15 post-infection, including increased interleukin-7 receptor-expressing virus-specific CD8+ T cells in lungs and draining lymph nodes of Nox1*/Y, and increased cytokine-producing T cells in lungs and spleen. Furthermore, a greater percentage of conventional and interstitial dendritic cells from Nox1*/Y draining lymph nodes expressed the co-stimulatory ligand CD40 within 6 days post-infection. Results indicate that NADPH oxidase 1 modulates the innate and adaptive cellular immune response to influenza virus infection, while also playing a role in host survival. Results suggest that NADPH oxidase 1 inhibitors may be beneficial as adjunct therapeutics during acute influenza infection.

Increased Dietary Salt Intake Does Not Influence Influenza A Virus-Induced Disease Severity in Mice

Influenza viruses are pathogens of significant public health importance. The influence of nutritional status on severity of disease has become increasingly recognized. In particular, high dietary salt intake has been linked to cardiovascular disease, but the effects on infectious diseases have not been studied. This study investigated the impact on influenza-induced morbidity and mortality in mice fed isocaloric diets containing 10-fold increments of sodium by altering the salt levels. Following infection, despite higher levels of IFN-gamma cytokine in the lung as well as virus-neutralizing antibody in the serum of mice fed the lowest salt level, the amounts of dietary salt intake had no substantial impact on the disease severity or the ability to respond immunologically to the infection.

A Newly Emerged Swine-Origin Influenza A(H3N2) Variant Dampens Host Antiviral Immunity but Induces Potent Inflammasome Activation

We compared the innate immune response to a newly emerged swine-origin influenza A(H3N2) variant containing the M gene from 2009 pandemic influenza A(H1N1), termed "A(H3N2)vpM," to the immune responses to the 2010 swine-origin influenza A(H3N2) variant and seasonal influenza A(H3N2). Our results demonstrated that A(H3N2)vpM-induced myeloid dendritic cells secreted significantly lower levels of type I interferon (IFN) but produced significantly higher levels of proinflammatory cytokines and induced potent inflammasome activation. The reduction in antiviral immunity with increased inflammatory responses upon A(H3N2)vpM infection suggest that these viruses have the potential for increased disease severity in susceptible hosts.

NLRC5 interacts with RIG-I to induce a robust antiviral response against influenza virus infection

The NLR protein, NLRC5 is an important regulator of MHC class I gene expression, however, the role of NLRC5 in other innate immune responses is less well defined. In the present study, we report that NLRC5 binds RIG-I and that this interaction is critical for robust antiviral responses against influenza virus. Overexpression of NLRC5 in the human lung epithelial cell line, A549, and normal human bronchial epithelial cells resulted in impaired replication of influenza virus A/Puerto Rico/8/34 virus (PR8) and enhanced IFN-β expression. Influenza virus leads to induction of IFN-β that drives RIG-I and NLRC5 expression in host cells. Our results suggest that NLRC5 extends and stabilizes influenza virus induced RIG-I expression and delays expression of the viral inhibitor protein NS1. We show that NS1 binds to NLRC5 to suppress its function. Interaction domain mapping revealed that NLRC5 interacts with RIG-I via its N-terminal death domain and that NLRC5 enhanced antiviral activity in an leucine-rich repeat domain independent manner. Taken together, our findings identify a novel role for NLRC5 in RIG-I-mediated antiviral host responses against influenza virus infection, distinguished from the role of NLRC5 in MHC class I gene regulation.

Adverse role of influenza A virus-induced Nox1 in neutralizing antibody responses and survival against lethal viral challenge in mice. (P1407)

Highly pathogenic influenza viruses can elicit a severe cytokine storm, leading to acute lung injury (ALI), or in its more severe form, acute respiratory distress syndrome (ARDS). Reactive oxygen species (ROS) produced by NADPH Oxidase (Nox) enzymes of both the lung infiltrating cells and the lung epithelial tissue can contribute to lung injury directly or via inflammatory signaling pathways. Here, we present evidence that Nox1 expression is enhanced in vitro (A549 lung epithelial cells, 33-fold; THP-1 monocytic cells, 633-fold; HULEC lung endothelial cells, 27-fold) and in vivo (mouse lung tissue, 17-fold) in response to infection with influenza A virus. Notably, in A549 cells, Nox1 expression levels were enhanced by laboratory strains A/X31 (H3N2) and A/WSN/33 (H1N1), as well as A(H1N1)pdm09 clinical isolates (A/California/08/2009, A/Mexico/4108/2009, and A/Texas/15/2009) of influenza A virus. Nox1 induction was virus dose- and replication-dependent. However, Nox1-deficient mice had a higher survival rate (p=0.008) compared to wild-type controls in response to a lethal dose of A/PR8/1934 influenza. Improved survival of Nox1-deficient mice corresponded with increased (p=0.0006) flu-specific neutralizing antibody responses. These results suggest that therapeutic blockade of Nox1 deserves further attention as a possible adjunct therapy for influenza A-associated ALI/ARDS.

A novel quinazolin-derived reactive oxygen species-inhibitor suppresses influenza A virus-induced inflammatory mediators and leads to enhanced survival in mice (P4214)

Acute lung injury (ALI) and its more severe form acute respiratory distress (ARD) can result from infectious agents, including several strains of influenza A virus. Recent evidence suggests that excessive production of reactive oxygen species (ROS) is a major contributor to ALI caused by influenza. We evaluated the effects of TG6-44, a novel inhibitor of ROS production, in in vitro and in vivo models of influenza A virus infection. In vitro, using the monocytic cells (THP-1) and human PBMC infected with influenza A virus (X31), we found that TG6-44 treatment decreased virus-induced ROS and inflammatory markers in THP1 (IL6, IFNγ , MCP1, TNFα , MIP1β) and in PBMC (IL6, IL8, TNFα , MCP1). Also, in influenza A virus-infected THP1 cells, TG6-44 treatment led to a reduction in virus-induced cell death as evidenced by decreased Caspase3 activation, decreased proportion of Annexin V+/PI+ cells, and increased Bcl2 phosphorylation. Notably, TG6-44-treatment decreased the proportion of THP1 cells expressing viral nucleoprotein and delayed its translocation into the nucleus. Moreover, mice infected with a lethal dose of influenza A virus (PR8) and given TG6-44 had both reduced levels of virus-induced inflammatory markers in lungs and a higher survival rate compared to controls. Taken together, our results demonstrate anti-inflammatory and anti-infective effects of TG6-44, and suggest ROS-inhibitors as valuable adjunct therapeutics to reduce ALI/ARD caused by influenza A virus infection.

Protein energy malnutrition decreases immunity and increases susceptibility to influenza infection in mice

BACKGROUND

Protein energy malnutrition (PEM), a common cause of secondary immune deficiency in children, is associated with an increased risk of infections. Very few studies have addressed the relevance of PEM as a risk factor for influenza.

METHODS

We investigated the influence of PEM on susceptibility to, and immune responses following, influenza virus infection using isocaloric diets providing either adequate protein (AP; 18%) or very low protein (VLP; 2%) in a mouse model.

RESULTS

We found that mice maintained on the VLP diet, when compared to mice fed with the AP diet, exhibited more severe disease following influenza infection based on virus persistence, trafficking of inflammatory cell types to the lung tissue, and virus-induced mortality. Furthermore, groups of mice maintained on the VLP diet showed significantly lower virus-specific antibody response and a reduction in influenza nuclear protein-specific CD8(+) T cells compared with mice fed on the AP diet. Importantly, switching diets for the group maintained on the VLP diet to the AP diet improved virus clearance, as well as protective immunity to viral challenge.

CONCLUSIONS

Our results highlight the impact of protein energy on immunity to influenza infection and suggest that balanced protein energy replenishment may be one strategy to boost immunity against influenza viral infections.

Rapid differentiation of monocytes into type I IFN-producing myeloid dendritic cells as an antiviral strategy against influenza virus infection

Myeloid dendritic cells (mDCs) have long been thought to function as classical APCs for T cell responses. However, we demonstrate that influenza viruses induce rapid differentiation of human monocytes into mDCs. Unlike the classic mDCs, the virus-induced mDCs failed to upregulate DC maturation markers and were unable to induce allogeneic lymphoproliferation. Virus-induced mDCs secreted little, if any, proinflammatory cytokines; however, they secreted a substantial amount of chemoattractants for monocytes (MCP-1 and IP-10). Interestingly, the differentiated mDCs secreted type I IFN and upregulated the expression of IFN-stimulated genes (tetherin, IFITM3, and viperin), as well as cytosolic viral RNA sensors (RIG-I and MDA5). Additionally, culture supernatants from virus-induced mDCs suppressed the replication of virus in vitro. Furthermore, depletion of monocytes in a mouse model of influenza infection caused significant reduction of lung mDC numbers, as well as type I IFN production in the lung. Consequently, increased lung virus titer and higher mortality were observed. Taken together, our results demonstrate that the host responds to influenza virus infection by initiating rapid differentiation of circulating monocytes into IFN-producing mDCs, which contribute to innate antiviral immune responses.

The 3' untranslated regions of influenza genomic sequences are 5'PPP-independent ligands for RIG-I

Retinoic acid inducible gene-I (RIG-I) is a key regulator of antiviral immunity. RIG-I is generally thought to be activated by ssRNA species containing a 5'-triphosphate (PPP) group or by unphosphorylated dsRNA up to ~300 bp in length. However, it is not yet clear how changes in the length, nucleotide sequence, secondary structure, and 5' end modification affect the abilities of these ligands to bind and activate RIG-I. To further investigate these parameters in the context of naturally occurring ligands, we examined RNA sequences derived from the 5' and 3' untranslated regions (UTR) of the influenza virus NS1 gene segment. As expected, RIG-I-dependent interferon-β (IFN-β) induction by sequences from the 5' UTR of the influenza cRNA or its complement (26 nt in length) required the presence of a 5'PPP group. In contrast, activation of RIG-I by the 3' UTR cRNA sequence or its complement (172 nt) exhibited only a partial 5'PPP-dependence, as capping the 5' end or treatment with CIP showed a modest reduction in RIG-I activation. Furthermore, induction of IFN-β by a smaller, U/A-rich region within the 3' UTR was completely 5'PPP-independent. Our findings demonstrated that RNA sequence, length, and secondary structure all contributed to whether or not the 5'PPP moiety is needed for interferon induction by RIG-I.

Influenza A virus neuraminidase protein enhances cell survival through interaction with carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) protein

The influenza virus neuraminidase (NA) protein primarily aids in the release of progeny virions from infected cells. Here, we demonstrate a novel role for NA in enhancing host cell survival by activating the Src/Akt signaling axis via an interaction with carcinoembryonic antigen-related cell adhesion molecule 6/cluster of differentiation 66c (C6). NA/C6 interaction leads to increased tyrosyl phosphorylation of Src, FAK, Akt, GSK3β, and Bcl-2, which affects cell survival, proliferation, migration, differentiation, and apoptosis. siRNA-mediated suppression of C6 resulted in a down-regulation of activated Src, FAK, and Akt, increased apoptosis, and reduced expression of viral proteins and viral titers in influenza virus-infected human lung adenocarcinoma epithelial and normal human bronchial epithelial cells. These findings indicate that influenza NA not only aids in the release of progeny virions, but also cell survival during viral replication.

Infection of lung epithelial cells with pandemic 2009 A(H1N1) influenza viruses reveals isolate-specific differences in infectivity and host cellular responses

To better understand the early virus-host interactions of the pandemic 2009 A(H1N1) viruses in humans, we examined early host responses following infection of human epithelial cell cultures with three 2009 A(H1N1) viruses (A/California/08/2009, A/Mexico/4108/2009, and A/Texas/15/2009), or a seasonal H1N1 vaccine strain (A/Solomon Islands/3/2006). We report here that infection with pandemic A/California/08/2009 and A/Mexico/4108/2009 viruses resulted in differences in virus infectivity compared to either pandemic A/Texas/15/2009 or the seasonal H1N1 vaccine strain. In addition, IFN-β levels were decreased in cell cultures infected with either the A/California/08/2009 or the A/Mexico/4108/2009 virus. Furthermore, infection with A/California/08/2009 and A/Mexico/4108/2009 viruses resulted in lower expression of four key proinflammatory markers (IL-6, RANTES, IP-10, and MIP-1β) compared with infection with either A/Texas/15/2009 or A/Solomon Islands/3/2006. Taken together, our results demonstrate that 2009 A(H1N1) viruses isolated during the Spring wave induced varying degrees of early host antiviral and inflammatory responses in human respiratory epithelial cells, highlighting the strain-specific nature of these responses, which play a role in clinical disease.

Increased Myeloid Derived Suppressor Cell recruitment and skewed TH2 response during influenza A virus infection in the absence of TLR7. (49.21)

Influenza A virus (IAV) is recognized by the innate immune system through RNA sensing pattern recognition receptors. One such receptor, Toll like receptor 7 (TLR7), and its downstream adaptor MyD88, have been shown to play an important role in the adaptive immune response to IAV infection. We investigated the specific contribution of TLR7 on the innate immune response to IAV. C57/B6 (WT) and TLR7-gene knock-out (TLR7-/-) mice were inoculated intranasally with a sub-lethal dose of Influenza A/PR/8/34 virus (PR8). Lungs were collected on days 3, 5, and 7post-infection to characterize cellular infiltrates and determine viral titers. TLR7-/- mice displayed increased morbidity following infection, despite having similar lung viral titers to WT mice. By day 7 post-infection, TLR7-/- mice had increased numbers of MDSC, neutrophil, and dendritic cell recruited to the lungs. Furthermore, on day 10 post-infection, the CD4+ T-cells of TLR7-/- mice expressed significantly higher levels of IL-4 compared with those of WT mice. To investigate functional differences between WT and TLR7-/- MDSCs, we purified MDSCs from day 7 infected mice and co-cultured them with OT-2 T-cells in the presence of ovalbumin peptide. On day 3, we observed increased numbers of IL-10 producing OT-2 T-cells when cultured with TLR7-/- MDSCs. Taken together, we conclude that TLR7 plays an important role in modulating the magnitude and quality of MDSCs and TH1/TH2 polarization during IAV infection.

Protein energy malnutrition decreases immunity and increases susceptibility to influenza infection. (67.5)

Protein energy malnutrition (PEM), a common cause of secondary immune deficiency in children, is associated with an increased risk of infection. We investigated the influence of PEM on susceptibility and immune responses to influenza virus infection using a mouse model. Groups of weanling mice maintained on isocaloric diets providing varying levels of protein energy [18%/adequate protein (AP), 5%/low protein (LP), and 2%/very low protein (VLP)] were infected with either 2009 A(H1N1) or laboratory-adapted H1N1 virus and assessed for disease severity and immune responsiveness. We found that compared to mice fed with AP and LP diets, mice maintained on the VLP diet exhibited an increase in virus-induced mortality and morbidity. Mice maintained on the VLP diet demonstrated diminished IFNγ levels and increased virus titer and inflammatory cell types in lung tissue, compared with mice on higher protein content diets. Moreover, groups of mice maintained on the VLP diet showed a lower hemagglutination-inhibition antibody response and reduced total numbers of splenic NP-specific CD8+ T cells compared with mice on higher protein content diets. Following re-feeding of the VLP group with the AP diet, post-infection morbidity, mortality and virus titer were all improved. Our results highlight the impact of protein energy on immunity to influenza infection and suggest balanced protein energy replenishment may be one strategy to boost immunity against influenza viral infections.

Sirolimus enhances the magnitude and quality of viral-specific CD8+ T-cell responses to vaccinia virus vaccination in rhesus macaques

Sirolimus is a potent antiproliferative agent used clinically to prevent renal allograft rejection. However, little is known about the effects of maintenance immunosuppressive agents on the immune response to potentially protective vaccines. Here we show that sirolimus paradoxically increases the magnitude and quality of the CD8+ T-cell response to vaccinia vaccination in nonhuman primates, fostering more robust recall responses compared to untreated and tacrolimus-treated controls. Enhancement of both the central and effector memory compartments of the vaccinia-specific CD8+ T-cell response was observed. These data elucidate new mechanistic characteristics of sirolimus and suggest immune applications extending beyond its role as an immunosuppressant.

Pathogenic virus-specific T cells cause disease during treatment with the calcineurin inhibitor FK506: implications for transplantation

Pathogenic virus-specific T cells can inflict a cytokine storm and lethal disease even in immunosuppressive conditions.

Recently, several cases of fatal lymphocytic choriomeningitis virus (LCMV) infection occurred in transplant recipients being treated with the immunosuppressive calcineurin inhibitor FK506. These findings were surprising because LCMV is a noncytolytic virus. To understand how a noncytolytic virus can cause disease under conditions of immunosuppression, we used the mouse LCMV model and found that, similar to the observations in human transplant recipients, LCMV infection of FK506-treated mice resulted in a lethal disease characterized by viremia, lack of seroconversion, and minimal lymphocytic infiltrates in the tissues. However, despite the apparent absence of an antiviral immune response, this disease was orchestrated by virus-specific T cells. FK506 did not prevent the generation and proliferation of LCMV-specific T cells but instead altered their differentiation so that these effector T cells lost the ability to control virus but were still capable of mediating disease. These pathogenic T cells initiated a cytokine storm characterized by high levels of tumor necrosis factor (TNF) and interleukin 6 (IL-6), and depletion of T cells or blockade of these inflammatory cytokines prevented the lethal disease. Our study shows that inhibiting calcineurin can generate pathogenic T cells and indicates that T cell–mediated viral disease can occur even under conditions of immunosuppression. Furthermore, we identify a potential strategy (blockade of TNF and IL-6) for treatment of transplant recipients who have acute complications of viral infection.

5'PPP-RNA induced RIG-I activation inhibits drug-resistant avian H5N1 as well as 1918 and 2009 pandemic influenza virus replication

BACKGROUND

Emergence of drug-resistant strains of influenza viruses, including avian H5N1 with pandemic potential, 1918 and 2009 A/H1N1 pandemic viruses to currently used antiviral agents, neuraminidase inhibitors and M2 Ion channel blockers, underscores the importance of developing novel antiviral strategies. Activation of innate immune pathogen sensor Retinoic Acid Inducible Gene-I (RIG-I) has recently been shown to induce antiviral state.

RESULTS

In the present investigation, using real time RT-PCR, immunofluorescence, immunoblot, and plaque assay we show that 5'PPP-containing single stranded RNA (5'PPP-RNA), a ligand for the intracytoplasmic RNA sensor, RIG-I can be used as a prophylactic agent against known drug-resistant avian H5N1 and pandemic influenza viruses. 5'PPP-RNA treatment of human lung epithelial cells inhibited replication of drug-resistant avian H5N1 as well as 1918 and 2009 pandemic influenza viruses in a RIG-I and type 1 interferon dependant manner. Additionally, 5'PPP-RNA treatment also inhibited 2009 H1N1 viral replication in vivo in mice.

CONCLUSIONS

Our findings suggest that 5'PPP-RNA mediated activation of RIG-I can suppress replication of influenza viruses irrespective of their genetic make-up, pathogenicity, and drug-sensitivity status.

Anti-CD40 monoclonal antibody synergizes with CTLA4-Ig in promoting long-term graft survival in murine models of transplantation

Blockade of the CD40/CD154 signaling pathway using anti-CD154 Abs has shown promise in attenuating the alloimmune response and promoting long-term graft survival in murine model systems, although side effects observed in humans have hampered its progression through clinical trials. Appropriately designed anti-CD40 Abs may provide a suitable alternative. We investigated two isoforms of a novel monoclonal rat anti-mouse CD40 Ab (7E1) for characteristics and effects mirroring those of anti-CD154: 7E1-G1 (an IgG1 isotype); and 7E1-G2b (an IgG2b isotype). In vitro proliferation assays to measure the agonist properties of the two anti-CD40 Abs revealed similar responses when plate bound. However, when present as a soluble stimulus, 7E1-G1 but not 7E1-G2b led to proliferation. 7E1-G2b was as effective as anti-CD154 when administered in vivo in concert with CTLA4-Ig in promoting both allogeneic bone marrow chimerism and skin graft survival, whereas 7E1-G1 was not. The protection observed with 7E1-G2b was not due to depletion of CD40-bearing APCs. These data suggest that an appropriately designed anti-CD40 Ab can promote graft survival as well as anti-CD154, making 7E1-G2b an attractive substitute in mouse models of costimulation blockade-based tolerance regimens.

RIG-I activation inhibits ebolavirus replication

Hemorrhagic fever viruses are associated with rapidly progressing severe disease with high case fatality, making them of public health and biothreat importance. Effective antivirals are not available for most of the members of this diverse group of viruses. A broad spectrum strategy for antiviral development would be very advantageous. Perhaps the most challenging target would be the highly immunosuppressive filoviruses, ebolavirus and marburgvirus, associated with aerosol infectivity and case fatalities in the 80-90% range. Here we report that activation of evolutionarily conserved cytosolic viral nucleic acid sensor, RIG-I can cause severe inhibition of ebolavirus replication. These findings indicate that RIG-I-based therapies may provide an attractive approach for antivirals against Ebola hemorrhagic fever, and possibly other HF viruses.

mTOR regulates memory CD8 T-cell differentiation

Memory CD8 T cells are a critical component of protective immunity and inducing effective memory T cell responses is a major goal of vaccines against chronic infections and tumors 1-3. Considerable effort has gone into designing vaccine regimens that will increase the magnitude of the memory response but there has been minimal emphasis on developing strategies to improve the functional qualities of memory T cells 4. In this study we show that mTOR, the mammalian target of rapamycin 5, is a major regulator of memory CD8 T cell differentiation and in contrast to what we expected the mTOR specific inhibitor rapamycin, an immunosuppressive drug, had surprising immunostimulatory effects on the generation of memory CD8 T cells. Treatment of mice with rapamycin following acute lymphocytic choriomeningitis virus (LCMV) infection enhanced not only the quantity but also the quality of virus specific CD8 T cells. Similar effects were seen after immunization of mice with a non-replicating VLP based vaccine. In addition, rapamycin treatment also enhanced memory T cell responses in non-human primates following vaccination with MVA (modified vaccinia virus - Ankara). Rapamycin was effective during both the expansion and contraction phases of the T cell response; during the expansion phase it increased the number of memory precursors and during the contraction phase (effector to memory transition) it accelerated the memory T cell differentiation program. Experiments using RNAi to inhibit mTOR, raptor or FKBP12 expression in antigen specific CD8 T cells showed that mTOR acts intrinsically through the mTORC1 pathway to regulate memory T cell differentiation. Thus, these studies identify a molecular pathway regulating memory formation and provide an effective strategy for improving the functional qualities of vaccine or infection induced memory T cells.

Early control of H5N1 influenza virus replication by the type I interferon response in mice

Widespread distribution of highly pathogenic avian H5N1 influenza viruses in domesticated and wild birds continues to pose a threat to public health, as interspecies transmission of virus has resulted in increasing numbers of human disease cases. Although the pathogenic mechanism(s) of H5N1 influenza viruses has not been fully elucidated, it has been suggested that the ability to evade host innate responses, such as the type I interferon response, may contribute to the virulence of these viruses in mammals. We investigated the role that type I interferons (alpha/beta interferon [IFN-alpha/beta]) might play in H5N1 pathogenicity in vivo, by comparing the kinetics and outcomes of H5N1 virus infection in IFN-alpha/beta receptor (IFN-alpha/betaR)-deficient and SvEv129 wild-type mice using two avian influenza A viruses isolated from humans, A/Hong Kong/483/97 (HK/483) and A/Hong Kong/486/97 (HK/486), which exhibit high and low lethality in mice, respectively. IFN-alpha/betaR-deficient mice experienced significantly more weight loss and more rapid time to death than did wild-type mice. HK/486 virus caused a systemic infection similar to that with HK/483 virus in IFN-alpha/betaR-deficient mice, suggesting a role for IFN-alpha/beta in controlling the systemic spread of this H5N1 virus. HK/483 virus replicated more efficiently than HK/486 virus both in vivo and in vitro. However, replication of both viruses was significantly reduced following pretreatment with IFN-alpha/beta. These results suggest a role for the IFN-alpha/beta response in the control of H5N1 virus replication both in vivo and in vitro, and as such it may provide some degree of protection to the host in the early stages of infection.

Impact of NADPH Oxidase Inhibition on Influenza A Virus-induced Inflammation (134.80)

Activation of innate immunity pathways in susceptible cell types is critical for host defense against influenza-A viruses (IAV). Based on studies signifying a role for NOX1 in inflammation, we hypothesized that IAV of seasonal and pandemic potential may induce different isoforms of NOX enzymes in the respiratory tract, and that attenuation of virus strain-specific NOX enzymes can be exploited to prevent and/or treat severity of disease. Using three respiratory tract-relevant cell lines (epithelial/A549, endothelial/HULEC, and monoctytic/THP1) and three strains of IAV (H1N1/PR8, H3N2/X31, H1N1/WSN), we found significant upregulation of NOX1 in all three cell lines (e.g.-A549: PR8/55 fold; X31/35 fold; WSN/12,250 fold). Furthermore, in contrast to the epithelial cell line showing NOX1 expression by 4h with peak levels at 16h, the monocytic cell line showed delayed (8h) and sustained (48h) levels of NOX1. Interestingly, inhibition of NOX-isoforms in IAV-infected epithelial cells by diphenyleneiodonium (DPI), at a concentration (25μM), which did not impact cell death, showed significant decrease (75%) in virus triggered NOX1 levels. In addition, NOX-inhibition led to significant decrease in virus-induced chemokines (MCP1, MIP3, MIP1β, RANTES, and IP10) and proinflammatory cytokines (IL1α, IL6, IL8, and TNFα). Furthermore, decline in NOX1 correlated with a modest increase in viral NS1. Taken together, in addition to showing definitive evidence for upregulation of NOX1 in response to subtypes of IAV, our results strongly support a role for NOX1 in IAV-driven inflammation.

TGF-beta upregulation drives tertiary lymphoid organ formation and kidney dysfunction in calcineurin A-alpha heterozygous mice

Calcineurin is an important intracellular signaling molecule which can be inhibited by cyclosporin resulting in immune suppression and nephrotoxicity. Previously, we reported that homozygous loss of the alpha isoform of calcineurin impairs kidney development and function and mimics many features of cyclosporin nephrotoxicity. However, early lethality of null mice prevented further study of renal changes. Alternatively, we examined aged heterozygous (CnAalpha(+/-)) mice. In addition to renal dysfunction and inflammation, we find that CnAalpha(+/-) mice spontaneously develop tertiary lymphoid aggregates in the kidney, small intestine, liver, and lung. Lymphoid aggregates contain both T cells and B cells and exhibited organization suggestive of tertiary lymphoid organs (TLOs). Kidney function and TLO formation were highly correlated suggesting that this process may contribute to nephrotoxicity. Consistent with previous findings, transforming growth factor (TGF)-beta is significantly increased in CnAalpha(+/-) mice. Neutralization of TGF-beta attenuated TLO formation and improved kidney function. In conclusion, we report that haploinsufficiency of CnAalpha causes uregulation of TGF-beta which contributes to chronic inflammation and formation of TLOs. While the process that leads to TLOs formation in transplant allografts is unknown, TLOs are associated with poor clinical prognosis. This study suggests that calcineurin inhibition itself may lead to TLO formation and that TGF-beta may be a novel therapeutic target.

PD-1-dependent mechanisms maintain peripheral tolerance of donor-reactive CD8+ T cells to transplanted tissue

Peripheral mechanisms of self-tolerance often depend on the quiescent state of the immune system. To what degree such mechanisms can be engaged in the enhancement of allograft survival is unclear. To examine the role of the PD-1 pathway in the maintenance of graft survival following blockade of costimulatory pathways, we used a single-Ag mismatch model of graft rejection where we could track the donor-specific cells as they developed endogenously and emerged from the thymus. We found that graft-specific T cells arising under physiologic developmental conditions at low frequency were actively deleted at the time of transplantation under combined CD28/CD40L blockade. However, this deletion was incomplete, and donor-specific cells that failed to undergo deletion up-regulated expression of PD-1. Furthermore, blockade of PD-1 signaling on these cells via in vivo treatment with anti-PD-1 mAb resulted in rapid expansion of donor-specific T cells and graft loss. These results suggest that the PD-1 pathway was engaged in the continued regulation of the low-frequency graft-specific immune response and thus in maintenance of graft survival.