Long-Term Neuroinflammation Induced by Influenza A Virus Infection and the Impact on Hippocampal Neuron Morphology and Function.

Acute influenza infection has been reported to be associated with neurological symptoms. However, the long-term consequences of an infection with neurotropic and non-neurotropic influenza A virus (IAV) variants for the CNS remain elusive. We can show that spine loss in the hippocampus after infection with neurotropic H7N7 (rSC35M) and non-neurotropic H3N2 (maHK68) in female C57BL/6 mice persists well beyond the acute phase of the disease. Although spine number was significantly reduced at 30 d postinfection (dpi) with H7N7 or H3N2, full recovery could only be observed much later at 120 dpi. Infection with H1N1 virus, which was shown previously to affect spine number and hippocampus-dependent learning acutely, had no significant long-term effects. Spine loss was associated with an increase in the number of activated microglia, reduced long-term potentiation in the hippocampus, and impairment in spatial memory formation, indicating that IAV-associated inflammation induced functional and structural alterations in hippocampal networks. Transcriptome analyses revealed regulation of many inflammatory and neuron- and glia-specific genes in H3N2- and H7N7-infected mice at day 18 and in H7N7-infected mice at day 30 pi that related to the structural and functional alterations. Our data provide evidence that neuroinflammation induced by neurotropic H7N7 and infection of the lung with a non-neurotropic H3N2 IAV result in long-term impairments in the CNS. IAV infection in humans may therefore not only lead to short-term responses in infected organs, but may also trigger neuroinflammation and associated chronic alterations in the CNS.SIGNIFICANCE STATEMENT In the acute phase of influenza infection, neuroinflammation can lead to alterations in hippocampal neuronal morphology and cognitive deficits. The results of this study now also provide evidence that neuroinflammation induced by influenza A virus (IAV) infection can induce longer-lasting, virus-specific alterations in neuronal connectivity that are still detectable 1 month after infection and are associated with impairments in spatial memory formation. IAV infection in humans may therefore not only lead to short-term responses in infected organs, but may also trigger neuroinflammation and associated chronic alterations in the CNS.

TLR8 regulation of LILRA3 in monocytes is abrogated in human immunodeficiency virus infection and correlates to CD4 counts and virus loads.

BACKGROUND: LILRA3 is an immunostimulatory molecule which can conditionally induce the proliferation of cytotoxic cells. LILRA3 has a deletion genotype which is associated with multiple immune disorders. In this study, we wanted to analyze the regulation of LILRA3 and its significance in the context of HIV infection. RESULTS: We analyzed a panel of TLR agonists and found that ssRNA40, a TLR8 agonist, is a potent inducer of LILRA3 in healthy individuals. However, this regulation is much diminished in HIV. Comparison of TLR8 to TLR4 induction of LILRA3 indicated that LPS induces less LILRA3 than ssRNA40 among healthy controls, but not HIV patients. Levels of LILRA3 induction correlated to virus load and CD4 counts in untreated patients. Recombinant LILRA3 can induce a host of proinflammatory genes which include IL-6 and IL-1α, as well as alter the expression of MHC and costimulatory molecules in monocytes and B-cells. CONCLUSION: Our experiments point towards a beneficial role for LILRA3 in virus infections, especially in ssRNA viruses, like HIV, that engage TLR8. However, the potentially beneficial role of LILRA3 is abrogated during a HIV infection. We believe that more work has to be done to study the role of LILRA3 in infectious diseases and that there is a potential for exploring the use of LILRA3 in the treatment of virus infections.

Identification of specific residues in avian influenza A virus NS1 that enhance viral replication and pathogenicity in mammalian systems.

Reassortment of their segmented genomes allows influenza A viruses (IAV) to gain new characteristics, which potentially enable them to cross the species barrier and infect new hosts. Improved replication was observed for reassortants of the strictly avian IAV A/FPV/Rostock/34 (FPV, H7N1) containing the NS segment from A/Goose/Guangdong/1/1996 (GD, H5N1), but not for reassortants containing the NS segment of A/Mallard/NL/12/2000 (MA, H7N3). The NS1 of GD and MA differ only in 8 aa positions. Here, we show that efficient replication of FPV-NSMA-derived mutants was linked to the presence of a single substitution (D74N) and more prominently to a triple substitution (P3S+R41K+D74N) in the NS1MA protein. The substitution(s) led to (i) increased virus titres, (ii) larger plaque sizes and (iii) increased levels and faster kinetics of viral mRNA and protein accumulation in mammalian cells. Interestingly, the NS1 substitutions did not affect viral growth characteristics in avian cells. Furthermore, we show that an FPV mutant with N74 in the NS1 (already possessing S3+K41) is able to replicate and cause disease in mice, demonstrating a key role of NS1 in the adaptation of avian IAV to mammalian hosts. Our data suggest that (i) adaptation to mammalian hosts does not necessarily compromise replication in the natural (avian) host and (ii) very few genetic changes may pave the way for zoonotic transmission. The study reinforces the need for close surveillance and characterization of circulating avian IAV to identify genetic signatures that indicate a potential risk for efficient transmission of avian strains to mammalian hosts.

RNAseq expression analysis of resistant and susceptible mice after influenza A virus infection identifies novel genes associated with virus replication and important for host resistance to infection.

BACKGROUND: The host response to influenza A infections is strongly influenced by host genetic factors. Animal models of genetically diverse mouse strains are well suited to identify host genes involved in severe pathology, viral replication and immune responses. Here, we have utilized a dual RNAseq approach that allowed us to investigate both viral and host gene expression in the same individual mouse after H1N1 infection. RESULTS: We performed a detailed expression analysis to identify (i) correlations between changes in expression of host and virus genes, (ii) host genes involved in viral replication, and (iii) genes showing differential expression between two mouse strains that strongly differ in resistance to influenza infections. These genes may be key players involved in regulating the differences in pathogenesis and host defense mechanisms after influenza A infections. Expression levels of influenza segments correlated well with the viral load and may thus be used as surrogates for conventional viral load measurements. Furthermore, we investigated the functional role of two genes, Reg3g and Irf7, in knock-out mice and found that deletion of the Irf7 gene renders the host highly susceptible to H1N1 infection. CONCLUSIONS: Using RNAseq analysis we identified novel genes important for viral replication or the host defense. This study adds further important knowledge to host-pathogen-interactions and suggests additional candidates that are crucial for host susceptibility or survival during influenza A infections.

Effects of aging on influenza virus infection dynamics.

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

Systems genetics of influenza A virus-infected mice identifies TRIM21 as a critical regulator of pulmonary innate immune response.

Tripartite motif 21 (TRIM21) is a cytosolic Fc receptor that targets antibody-bound, internalized pathogens for destruction. Apart from this intrinsic defense role, TRIM21 is implicated in autoimmune diseases, inflammation, and autophagy. Whether TRIM21 participates in host interactions with influenza A virus (IAV), however, is unknown. By computational modeling of body weight and lung transcriptome data from the BXD parents (C57BL/6 J (B6) and DBA/2 J (D2)) and 41 BXD mouse strains challenged by IAV, we reveal that a Trim21-associated gene network modulates the early host responses to IAV infection. Trim21 transcripts were significantly upregulated in infected mice of both B6 and D2 backgrounds. Its expression was significantly higher in infected D2 than in infected B6 early after infection and significantly correlated with body weight loss. We identified significant trans-eQTL on chromosome 14 that regulates Trim21 expression. Nr1d2 and Il3ra were among the strongest candidate genes. Pathway analysis found Trim21 to be involved in inflammation and immunity related pathways, such as inflammation signaling pathways (TNF, IL-17, and NF-κB), viral detection signaling pathways (NOD-like and RIG-I-like), influenza, and other respiratory viral infections. Knockdown of TRIM21 in human lung epithelial A549 cells significantly augmented IAV-induced expression of IFNB1, IFNL1, CCL5, CXCL10, and IFN-stimulated genes including DDX58 and IFIH1, among others. Our data suggest that a TRIM21-associated gene network is involved in several aspects of inflammation and viral detection mechanisms during IAV infection. We identify and validate TRIM21 as a critical regulator of innate immune responses to IAV in human lung epithelial cells.

Immunization with live virus vaccine protects highly susceptible DBA/2J mice from lethal influenza A H1N1 infection.

BACKGROUND: The mouse represents an important model system to study the host response to influenza A infections and to evaluate new prevention or treatment strategies. We and others reported that the susceptibility to influenza A virus infections strongly varies among different inbred mouse strains. In particular, DBA/2J mice are highly susceptible to several influenza A subtypes, including human isolates and exhibit severe symptoms after infection with clinical isolates. FINDINGS: Upon intra-muscular immunization with live H1N1 influenza A virus (mouse-adapted PR8M, and 2009 pandemic human HA04), DBA/2J mice mounted virus-specific IgG responses and were protected against a subsequent lethal challenge. The immune response and rescue from death after immunization in DBA/2J was similar to those observed for C57BL/6J mice. CONCLUSIONS: DBA/2J mice represent a suitable mouse model to evaluate virulence and pathogenicity as well as immunization regimes against existing and newly emerging human influenza strains without the need for prior adaptation of the virus to the mouse.

Toxocara canis- and Toxocara cati-Induced Neurotoxocarosis Is Associated with Comprehensive Brain Transcriptomic Alterations.

Toxocara canis and Toxocara cati are globally occurring zoonotic roundworms of dogs and cats. Migration and persistence of Toxocara larvae in the central nervous system of paratenic hosts including humans may cause clinical signs of neurotoxocarosis (NT). As pathomechanisms of NT and host responses against Toxocara larvae are mostly unknown, whole-genome microarray transcription analysis was performed in cerebra and cerebella of experimentally infected C57Bl/6J mice as paratenic host model at days 14, 28, 70, 98, and 120 post-infection. Neuroinvasion of T. cati evoked 220 cerebral and 215 cerebellar differentially transcribed genes (DTGs), but no particular PANTHER (Protein ANalysis THrough Evolutionary Relationships) pathway was affected. In T. canis-infected mice, 1039 cerebral and 2073 cerebellar DTGs were identified. Statistically significant dysregulations occurred in various pathways, including cholesterol biosynthesis, apoptosis signaling, and the Slit/Robo mediated axon guidance as well as different pathways associated with the immune and defense response. Observed dysregulations of the cholesterol biosynthesis, as well as the Alzheimer disease-amyloid secretase pathway in conjunction with previous histopathological neurodegenerative findings, may promote the discussion of T. canis as a causative agent for dementia and/or Alzheimer's disease. Furthermore, results contribute to a deeper understanding of the largely unknown pathogenesis and host-parasite interactions during NT, and may provide the basis for prospective investigations evaluating pathogenic mechanisms or designing novel diagnostic and therapeutic approaches.

Murine CXCR3+CD27bright NK cells resemble the human CD56bright NK-cell population.

Human NK cells can be subdivided into CD56(dim) and CD56(bright) NK cells, which exhibit different phenotypical and functional characteristics. As murine NK cells lack CD56 or a distinct correlate, direct comparative studies of NK cells in mice and humans are limited. Although CD27 is currently proposed as a feasible subset marker in mice, we assume that the usage of this marker alone is insufficient. We rather investigated the expression of the chemokine receptor CXCR3 for its suitability for distinguishing murine NK-cell subsets with simultaneous consideration of CD27. Compared with CXCR3(-) NK cells, exerting stronger cytotoxic capability, CXCR3+ NK cells displayed an activated phenotype with a lower expression of Ly49 receptors, corresponding to human CD56(bright) NK cells. Also in common with human CD56(bright) NK cells, murine CXCR3+ NK cells exhibit prolific expansion as well as robust IFN-gamma, TNF-alpha and MIP-1alpha production. We additionally demonstrated changes in both CXCR3 and CD27 expression upon NK-cell activation. In summary, CXCR3 serves as an additional applicable marker for improved discrimination of functionally distinct murine NK-cell subsets that comply with those in humans.

Multiplex profiling of inflammation-related bioactive lipid mediators in Toxocara canis- and Toxocara cati-induced neurotoxocarosis.

BACKGROUND: Somatic migration of Toxocara canis- and T. cati-larvae in humans may cause neurotoxocarosis (NT) when larvae accumulate and persist in the central nervous system (CNS). Host- or parasite-induced immunoregulatory processes contribute to the pathogenesis; however, detailed data on involvement of bioactive lipid mediators, e.g. oxylipins or eico-/docosanoids, which are involved in the complex molecular signalling network during infection and inflammation, are lacking. METHODOLOGY/PRINCIPAL FINDINGS: To elucidate if T. canis- and T. cati-induced NT affects the homeostasis of oxylipins during the course of infection, a comprehensive lipidomic profiling in brains (cerebra and cerebella) of experimentally infected C57BL/6J mice was conducted at six different time points post infection (pi) by liquid-chromatography coupled to electrospray tandem mass spectrometry (LC-ESI-MS/MS). Only minor changes were detected regarding pro-inflammatory prostaglandins (cyclooxygenase pathway). In contrast, a significant increase of metabolites resulting from lipoxygenase pathways was observed for both infection groups and brain regions, implicating a predominantly anti-inflammatory driven immune response. This observation was supported by a significantly increased 13-hydroxyoctadecadienoic acid (HODE)/9-HODE ratio during the subacute phase of infection, indicating an anti-inflammatory response to neuroinfection. Except for the specialised pro-resolving mediator (SPM) neuroprotectin D1 (NPD1), which was detected in mice infected with both pathogens during the subacute phase of infection, no other SPMs were detected. CONCLUSIONS/SIGNIFICANCE: The obtained results demonstrate the influence of Toxocara spp. on oxylipins as part of the immune response of the paratenic hosts. Furthermore, this study shows differences in the alteration of the oxylipin composition between T. canis- and T. cati-brain infection. Results contribute to a further understanding of the largely unknown pathogenesis and mechanisms of host-parasite interactions during NT.

New aspects of NK cell subset identification and inference of NK cells' regulatory capacity by assessing functional and genomic profiles.

Natural killer (NK) cells represent important early effector cells of the innate immune system. They can lyse virally infected and malignant cells without prior sensitization, making them important members of the first line of defense. In addition, they participate in the regulation of immune responses and hematopoiesis by producing various cytokines and chemokines. These different functional capacities can to some extent be assigned to distinct NK cell populations. In humans, CD56(dim) NK cells featuring strong cytotoxic capacity can be easily distinguished from CD56(bright) NK cells, which predominantly produce cytokines and exert only marginal cytotoxicity. Murine NK cells lack CD56 expression and no correlate marker enabling identification of functional subpopulations has been described. Here, we summarize and discuss human NK cell populations in greater detail in order to evaluate their regulatory capacity and to detect alternative and distinctive markers, e.g. CXCR3 and CD27, which are shared by both humans and mice.

Interleukin-21 differentially affects human natural killer cell subsets.

Interleukin-21 (IL-21) is a cytokine with pleiotropic effects on various cell types including dendritic cells, B cells, T cells and natural killer (NK) cells. To evaluate if IL-21 affects human NK cell subpopulations in a similar fashion, functional studies were performed on CD56(dim) and CD56(bright) NK cells, both bearing IL-21 receptors at identical densities. Stimulation with IL-21 strongly induced proliferation of CD56(bright) NK cells and cytotoxicity against K562 target cells was preferentially augmented in CD56(dim) NK cells. In contrast, stimulation with IL-2 and IL-21 alone or in combination failed to induce interferon-gamma and tumour necrosis factor-alpha production in the two NK cell subsets. Intracellular analysis of signal transducer and activator of transcription (STAT) proteins revealed that IL-21 by itself induces phosphorylation of STAT1 and STAT3 in CD56(dim) NK cells, and to an even higher degree in CD56(bright) NK cells. In this CD56(bright) NK cell population alone, IL-2 weakly phosphorylated STAT1 and STAT3, which was further increased when cells were treated with the combination of both cytokines. In contrast, STAT5 was strongly phosphorylated only in CD56(bright) NK cells by low-dose IL-2, while IL-21 did not affect STAT5 at all. In summary, we present data indicating that the NK-cell-directed cytokines IL-2 and IL-21 not only affect functions in NK cell subpopulations differently but can also act additively.

Gene and protein characteristics reflect functional diversity of CD56dim and CD56bright NK cells.

Recent findings underline the role of NK cell subsets in regulating adaptive immunity. To define characteristics of NK cell subpopulations, purified CD56(dim) and CD56(bright) NK cells were analyzed by using gene chip arrays covering more than 39,000 transcripts. Gene profiling revealed resting NK cells to differ in respect to 473 transcripts with 176 exclusively expressed in CD56(dim) and 130 solely in CD56(bright) NK cells. Results were compared with array analyses using mRNA obtained from activated CD56(dim) and CD56(bright) NK cells. In this approach, NK cell receptors, cytolytic molecules, adhesion structures, and chemokine ligands showed differential expression patterns in the two subpopulations. These data were validated using FACS, RT-qPCR, or cytokine bead array (CBA) techniques. Cytokines produced by CD56(dim) and CD56(bright) NK cells were determined using a protein array covering 79 different bioactive mediators. GDNF, IGFBP-1, EGF, and TIMP-2 were detected in both subsets. In contrast, IGFBP-3 and IGF-1 were mainly produced by CD56(dim), while GM-CSF, TARC, and TGFbeta3 were expressed by CD56(bright) NK cells. In summary, we report new characteristic features of CD56(dim) and CD56(bright) NK cells, further underscoring that they represent independent populations with functionally diverse capabilities. The information on NK cells generated in this study will help to define corresponding NK cell populations in other species that lack CD56 expression on NK cells, such as mice. This will subsequently lead to the establishment of suitable animal models for detailed analysis of NK cell populations in vivo.

Deletion of Irf3 and Irf7 Genes in Mice Results in Altered Interferon Pathway Activation and Granulocyte-Dominated Inflammatory Responses to Influenza A Infection.

The interferon (IFN) pathway plays an essential role in the innate immune response following viral infections and subsequent shaping of adaptive immunity. Infections with influenza A viruses (IAV) activate the IFN pathway after the recognition of pathogen-specific molecular patterns by respective pattern recognition receptors. The IFN regulatory factors IRF3 and IRF7 are key players in the regulation of type I and III IFN genes. In this study, we analyzed the role of IRF3 and IRF7 for the host response to IAV infections in Irf3-/-, Irf7-/-, and Irf3-/-Irf7-/- knockout mice. While the absence of IRF3 had only a moderate impact on IFN expression, deletion of IRF7 completely abolished IFNα production after infection. In contrast, lack of both IRF3 and IRF7 resulted in the absence of both IFNα and IFNß after IAV infection. In addition, IAV infection of double knockout mice resulted in a strong increase of mortality associated with a massive influx of granulocytes in the lung and reduced activation of the adaptive immune response.

Microarray gene expression analysis reveals major differences between Toxocara canis and Toxocara cati neurotoxocarosis and involvement of T. canis in lipid biosynthetic processes.

Toxocara canis and Toxocara cati are globally occurring intestinal nematodes of dogs and cats with a high zoonotic potential. Migrating larvae in the CNS of paratenic hosts, including humans, may cause neurotoxocarosis resulting in a variety of neurological symptoms. Toxocara canis exhibits a stronger affinity to the CNS than T. cati, causing more severe neurological symptoms in the mouse model. Pathomechanisms of neurotoxocarosis as well as host responses towards the respective parasite are mostly unknown. Therefore, the aim of this study was to characterise the pathogenesis at a transcriptional level using whole genome microarray expression analysis and identify differences and similarities between T. canis- and T. cati-infected brains. Microarray analysis was conducted in cerebra and cerebella of infected C57Bl/6J mice 42daysp.i. revealing more differentially transcribed genes for T. canis- than T. cati-infected brains. In cerebra and cerebella of T. canis-infected mice, a total of 2304 and 1954 differentially transcribed genes, respectively, were identified whereas 113 and 760 differentially transcribed genes were determined in cerebra and cerebella of T. cati-infected mice. Functional annotation analysis revealed major differences in host responses in terms of significantly enriched biological modules. Up-regulated genes were mainly associated with the terms "immune and defence response", "sensory perception" as well as "behaviour/taxis" retrieved from the Gene Ontology database. These observations indicate a strong immune response in both infection groups with T. cati-infected brains revealing less severe reactions. Down-regulated genes in T. canis-infected cerebra and cerebella revealed a significant enrichment for the Gene Ontology term "lipid/cholesterol biosynthetic process". Cholesterol is a highly abundant and important component in the brain, representing several functions. Disturbances of synthesis as well as concentration changes may lead to dysfunction in signal transduction and neurodegenerative disease. Overall, only a minor overlap of differentially transcribed genes was observed between the two infection groups in both brain parts. Most genes are regulated individually in each infection group, supporting the evident differences of both roundworm species observed in the paratenic host in previous studies. In summary the present study underlines the differences in pathogenicity of T. canis and T. cati. It furthermore provides a comprehensive basis for future analyses over the course of infection as well as functional tests to identify gene regulatory circuits that are crucial for pathogenesis of neurotoxocarosis. The results of this study provide a promising foundation for further specific research to evaluate the particular pathogenetic mechanisms and to identify possible therapeutic targets.

Hematological parameters in the early phase of influenza A virus infection in differentially susceptible inbred mouse strains.

BACKGROUND: Hematological parameters have not received much attention in small animal models of infection, particularly at very early time points. We therefore studied changes in leukocyte and thrombocyte numbers in a mouse model of influenza A virus (IAV) infection, including measurements within the first 24 h after infection, and also assessing effects, if any, of the infection/anesthesia procedure on these parameters. METHODS: DBA/2J and C57BL/6J mice (n = 5-8 per observation) were evaluated in a time course experiment of IAV infection, focusing on early time points. After anesthesia with ketamine/xylazine, a suspension of 2 × 10(3) focus forming units of the mouse-adapted IAV strain A/Puerto Rico/8/1934 (H1N1) in 20 µl sterile PBS, or 20 µl sterile PBS only ("mock treatment"), were instilled intranasally. Weight loss was assessed daily, and eight common hematological parameters and viral hemagglutinin (HA) mRNA expression were determined after 6, 12, 18, 24, 48 and 120 h. RESULTS: Hematological differences between the strains were apparent even in untreated mice. Infection-dependent changes, in particular increased granulocyte and decreased lymphocyte counts, were first detectable after 18 h in DBA/2J, were fully manifest in both strains at 48 h, and were usually more pronounced in the DBA/2J mice. In this strain, relative granulocyte and lymphocyte counts and the granulocyte/lymphocyte ratio correlated with viral HA mRNA expression and weight loss. In C57BL/6J, hematological parameters did not correlate with weight loss, but HA mRNA expression correlated weakly with total leukocyte counts, granulocyte/lymphocyte ratio, relative and absolute granulocyte counts, and relative lymphocyte counts. Significant changes due to mock treatment were mild and were detected only in C57BL/6J. CONCLUSION: This study underscores the value of hematological parameters in monitoring disease evolution in the early phase of IAV infection, and likely other pathogens. The hematological response to infection may differ significantly among inbred mouse strains.

Modeling Influenza Virus Infection: A Roadmap for Influenza Research.

Influenza A virus (IAV) infection represents a global threat causing seasonal outbreaks and pandemics. Additionally, secondary bacterial infections, caused mainly by Streptococcus pneumoniae, are one of the main complications and responsible for the enhanced morbidity and mortality associated with IAV infections. In spite of the significant advances in our knowledge of IAV infections, holistic comprehension of the interplay between IAV and the host immune response (IR) remains largely fragmented. During the last decade, mathematical modeling has been instrumental to explain and quantify IAV dynamics. In this paper, we review not only the state of the art of mathematical models of IAV infection but also the methodologies exploited for parameter estimation. We focus on the adaptive IR control of IAV infection and the possible mechanisms that could promote a secondary bacterial coinfection. To exemplify IAV dynamics and identifiability issues, a mathematical model to explain the interactions between adaptive IR and IAV infection is considered. Furthermore, in this paper we propose a roadmap for future influenza research. The development of a mathematical modeling framework with a secondary bacterial coinfection, immunosenescence, host genetic factors and responsiveness to vaccination will be pivotal to advance IAV infection understanding and treatment optimization.

Modulation of Ly49 D expression after allogeneic bone marrow transplantation and functional consequences.

Ly49 antigens, interacting with MHC class I molecules, enable NK cells to distinguish "self" from "non-self". Here, we investigated the activating receptor Ly49 D after allogeneic bone marrow transplantation (BMT). After transplantation of B6 bone marrow (BM) into BALB/c recipients we observed a significant reduction of Ly49 D+ NK cells and a decreased density of expression. We found a nonstochastic distribution of Ly49 D with Ly49 G2. In contrast to reduced coexpression with Ly49 A, a constant rate of Ly49 G2 on Ly49 D+ NK cells was observed in allogeneic chimeras. Cytotoxicity was reduced during the first two months after BMT After this time allogeneic chimeras showed tolerance against host-specific targets. We conclude that NK cells are able to shape their Lys49 repertoire fitting to a new environment after allogeneic BMT. This alteration seems to depend on the presence of new corresponding MHC class I molecules resulting in downregulation of respective receptors on donor cells. Analysing coexpression of Ly49 D and Ly49 G2, we found a relationship between these two receptors, showing a distinct effect after allogeneic BMT. Functional data indicate that a time of reduced NK cell cytotoxicity after BMT is followed by in vitro tolerance of allogeneic chimeras.

Systems biology and systems genetics - novel innovative approaches to study host-pathogen interactions during influenza infection.

Influenza represents a serious threat to public health with thousands of deaths each year. A deeper understanding of the host-pathogen interactions is urgently needed to evaluate individual and population risks for severe influenza disease and to identify new therapeutic targets. Here, we review recent progress in large scale omics technologies, systems genetics as well as new mathematical and computational developments that are now in place to apply a systems biology approach for a comprehensive description of the multidimensional host response to influenza infection. In addition, we describe how results from experimental animal models can be translated to humans, and we discuss some of the future challenges ahead.

Cellular changes in blood indicate severe respiratory disease during influenza infections in mice.

Influenza A infection is a serious threat to human and animal health. Many of the biological mechanisms of the host-pathogen-interactions are still not well understood and reliable biomarkers indicating the course of the disease are missing. The mouse is a valuable model system enabling us to study the local inflammatory host response and the influence on blood parameters under controlled circumstances. Here, we compared the lung and peripheral changes after PR8 (H1N1) influenza A virus infection in C57BL/6J and DBA/2J mice using virus variants of different pathogenicity resulting in non-lethal and lethal disease. We monitored hematological and immunological parameters revealing that the granulocyte to lymphocyte ratio in the blood represents an early indicator of severe disease progression already two days after influenza A infection in mice. These findings might be relevant to optimize early diagnostic options of severe influenza disease and to monitor successful therapeutic treatment in humans.