Three strains of influenza A virus (H3N2): interferon sensitivity in vitro and interferon production in volunteers

Early Induction of Cross-Reactive CD8+ T-Cell Responses in Tonsils After Live-Attenuated Influenza Vaccination in Children

BACKGROUND

Live-attenuated influenza vaccine (LAIV) was licensed for prophylaxis of children 2-17 years old in Europe in 2012 and is administered as a nasal spray. Live-attenuated influenza vaccine induces both mucosal and systemic antibodies and systemic T-cell responses. Tonsils are the lymph nodes serving the upper respiratory tract, acting as both induction and effector site for mucosal immunity.

METHODS

Here, we have studied the early tonsillar T-cell responses induced in children after LAIV. Thirty-nine children were immunized with trivalent LAIV (containing A/H1N1, A/H3N2, and B viruses) at days 3, 7, and 14 before tonsillectomy. Nonvaccinated controls were included for comparison. Tonsils and peripheral blood (pre- and postvaccination) were collected to study T-cell responses.

RESULTS

Tonsillar and systemic T-cell responses differed between influenza strains, and both were found against H3N2 and B viruses, whereas only systemic responses were observed against A/H1N1. A significant increase in cross-reactive tonsillar CD8+ T cells recognizing conserved epitopes from a broad range of seasonal and pandemic viruses occurred at day 14. Tonsillar T cells showed significant cytokine responses (Th1, Th2, and granulocyte-macrophage colony-stimulating factor).

CONCLUSIONS

Our findings support the use of LAIV in children to elicit broadly cross-reactive T cells, which are not induced by traditional inactivated influenza vaccines and may provide protection to novel virus strains.

Respiratory Barrier as a Safeguard and Regulator of Defense Against Influenza A Virus and Streptococcus pneumoniae

The primary function of the respiratory system of gas exchange renders it vulnerable to environmental pathogens that circulate in the air. Physical and cellular barriers of the respiratory tract mucosal surface utilize a variety of strategies to obstruct microbe entry. Physical barrier defenses including the surface fluid replete with antimicrobials, neutralizing immunoglobulins, mucus, and the epithelial cell layer with rapidly beating cilia form a near impenetrable wall that separates the external environment from the internal soft tissue of the host. Resident leukocytes, primarily of the innate immune branch, also maintain airway integrity by constant surveillance and the maintenance of homeostasis through the release of cytokines and growth factors. Unfortunately, pathogens such as influenza virus and Streptococcus pneumoniae require hosts for their replication and dissemination, and prey on the respiratory tract as an ideal environment causing severe damage to the host during their invasion. In this review, we outline the host-pathogen interactions during influenza and post-influenza bacterial pneumonia with a focus on inter- and intra-cellular crosstalk important in pulmonary immune responses.

Virus-virus interactions impact the population dynamics of influenza and the common cold

When multiple pathogens cocirculate this can lead to competitive or cooperative forms of pathogen–pathogen interactions. It is believed that such interactions occur among cold and flu viruses, perhaps through broad-acting immunity, resulting in interlinked epidemiological patterns of infection. However, to date, quantitative evidence has been limited. We analyzed a large collection of diagnostic reports collected over multiple years for 11 respiratory viruses. Our analyses provide strong statistical support for the existence of interactions among respiratory viruses. Using computer simulations, we found that very short-lived interferences may explain why common cold infections are less frequent during flu seasons. Improved understanding of how the epidemiology of viral infections is interlinked can help improve disease forecasting and evaluation of disease control interventions.

The human respiratory tract hosts a diverse community of cocirculating viruses that are responsible for acute respiratory infections. This shared niche provides the opportunity for virus–virus interactions which have the potential to affect individual infection risks and in turn influence dynamics of infection at population scales. However, quantitative evidence for interactions has lacked suitable data and appropriate analytical tools. Here, we expose and quantify interactions among respiratory viruses using bespoke analyses of infection time series at the population scale and coinfections at the individual host scale. We analyzed diagnostic data from 44,230 cases of respiratory illness that were tested for 11 taxonomically broad groups of respiratory viruses over 9 y. Key to our analyses was accounting for alternative drivers of correlated infection frequency, such as age and seasonal dependencies in infection risk, allowing us to obtain strong support for the existence of negative interactions between influenza and noninfluenza viruses and positive interactions among noninfluenza viruses. In mathematical simulations that mimic 2-pathogen dynamics, we show that transient immune-mediated interference can cause a relatively ubiquitous common cold-like virus to diminish during peak activity of a seasonal virus, supporting the potential role of innate immunity in driving the asynchronous circulation of influenza A and rhinovirus. These findings have important implications for understanding the linked epidemiological dynamics of viral respiratory infections, an important step towards improved accuracy of disease forecasting models and evaluation of disease control interventions.

Virus dynamics and phyloanatomy: Merging population dynamic and phylogenetic approaches

In evolutionary biology and epidemiology, phylodynamic methods are widely used to infer population biological characteristics, such as the rates of replication, death, migration, or, in the epidemiological context, pathogen spread. More recently, these methods have been used to elucidate the dynamics of viruses within their hosts. Especially the application of phylogeographic approaches has the potential to shed light on anatomical colonization pathways and the exchange of viruses between distinct anatomical compartments. We and others have termed this phyloanatomy. Here, we review the promise and challenges of phyloanatomy, and compare them to more classical virus dynamics and population genetic approaches. We argue that the extremely strong selection pressures that exist within the host may represent the main obstacle to reliable phyloanatomic analysis.

Influenza vaccine-mediated protection in older adults: Impact of influenza infection, cytomegalovirus serostatus and vaccine dosage

Age-related changes in T-cell function are associated with a loss of influenza vaccine efficacy in older adults. Both antibody and cell-mediated immunity plays a prominent role in protecting older adults, particularly against the serious complications of influenza. High dose (HD) influenza vaccines induce higher antibody titers in older adults compared to standard dose (SD) vaccines, yet its impact on T-cell memory is not clear. The aim of this study was to compare the antibody and T-cell responses in older adults randomized to receive HD or SD influenza vaccine as well as determine whether cytomegalovirus (CMV) serostatus affects the response to vaccination, and identify differences in the response to vaccination in those older adults who subsequently have an influenza infection. Older adults (≥65years) were enrolled (n=106) and randomized to receive SD or HD influenza vaccine. Blood was collected pre-vaccination, followed by 4, 10 and 20weeks post-vaccination. Serum antibody titers, as well as levels of inducible granzyme B (iGrB) and cytokines were measured in PBMCs challenged ex vivo with live influenza virus. Surveillance conducted during the influenza season identified those with laboratory confirmed influenza illness or infection. HD influenza vaccination induced a high antibody titer and IL-10 response, and a short-lived increase in Th1 responses (IFN-γ and iGrB) compared to SD vaccination in PBMCs challenged ex vivo with live influenza virus. Of the older adults who became infected with influenza, a high IL-10 and iGrB response in virus-challenged cells was observed post-infection (week 10 to 20), as well as IFN-γ and TNF-α at week 20. Additionally, CMV seropositive older adults had an impaired iGrB response to influenza virus-challenge, regardless of vaccine dose. This study illustrates that HD influenza vaccines have little impact on the development of functional T-cell memory in older adults. Furthermore, poor outcomes of influenza infection in older adults may be due to a strong IL-10 response to influenza following vaccination, and persistent CMV infection.

Single dose vaccination of the ASO3-adjuvanted A(H1N1)pdm09 monovalent vaccine in health care workers elicits homologous and cross-reactive cellular and humoral responses to H1N1 strains

Healthcare workers (HCW) were prioritized for vaccination during the 2009 influenza A(H1N1)pdm09 pandemic. We conducted a clinical trial in October 2009 where 237 HCWs were immunized with a AS03-adjuvanted A(H1N1)pdm09 monovalent vaccine. In the current study, we analyzed the homologous and cross-reactive H1N1 humoral responses using prototype vaccine strains dating back to 1977 by the haemagglutinin inhibition (HI), single radial hemolysis SRH), antibody secreting cell (ASC) and memory B cell (MBC) assays. The cellular responses were assessed by interferon-γ (IFN-γ) ELISPOT and by intracellular staining (ICS) for the Th1 cytokines IFN-γ, interleukin-2 (IL-2) and tumor necrosis factor-α (TNF-α). All assays were performed using blood samples obtained prior to (day 0) and 7, 14 and 21 d post-pandemic vaccination, except for ASC (day 7) and ICS (days 0 and 21). Vaccination elicited rapid HI, SRH and ASC responses against A(H1N1)pdm09 which cross reacted with seasonal H1N1 strains. MBC responses were detected against the homologous and seasonal H1N1 strains before vaccination and were boosted 2 weeks post-vaccination. An increase in cellular responses as determined by IFN-γ ELISPOT and ICS were observed 1–3 weeks after vaccination. Collectively, our data show that the AS03-adjuvanted A(H1N1)pdm09 vaccine induced rapid cellular and humoral responses against the vaccine strain and the response cross-reacted against prototype H1N1 strains dating back to 1977.

Connecting within-host dynamics to the rate of viral molecular evolution

Viruses evolve rapidly, providing a unique system for understanding the processes that influence rates of molecular evolution. Neutral theory posits that the evolutionary rate increases linearly with the mutation rate. The occurrence of deleterious mutations causes this relationship to break down at high mutation rates. Previous studies have identified this as an important phenomenon, particularly for RNA viruses which can mutate at rates near the extinction threshold. We propose that in addition to mutation dynamics, viral within-host dynamics can also affect the between-host evolutionary rate. We present an analytical model that predicts the neutral evolution rate for viruses as a function of both within-host parameters and deleterious mutations. To examine the effect of more detailed aspects of the virus life cycle, we also present a computational model that simulates acute virus evolution using target cell-limited dynamics. Using influenza A virus as a case study, we find that our simulation model can predict empirical rates of evolution better than a model lacking within-host details. The analytical model does not perform as well as the simulation model but shows how the within-host basic reproductive number influences evolutionary rates. These findings lend support to the idea that the mutation rate alone is not sufficient to predict the evolutionary rate in viruses, instead calling for improved models that account for viral within-host dynamics.

Validation of the wild-type influenza A human challenge model H1N1pdMIST: an A(H1N1)pdm09 dose-finding investigational new drug study

BACKGROUND

Healthy volunteer wild-type influenza challenge models offer a unique opportunity to evaluate multiple aspects of this important virus. Such studies have not been performed in the United States in more than a decade, limiting our capability to investigate this virus and develop countermeasures. We have completed the first ever wild-type influenza A challenge study under an Investigational New Drug application (IND). This dose-finding study will lead to further development of this model both for A(H1N1)pdm09 and other strains of influenza.

METHODS

Volunteers were admitted to an isolation unit at the National Institutes of Health Clinical Center for a minimum of 9 days. A reverse genetics, cell-based, Good Manufacturing Practice (GMP)-produced, wild-type A(H1N1)pdm09 virus was administered intranasally. Escalating doses were given until a dose was reached that produced disease in a minimum of 60% of volunteers.

RESULTS

An optimal dose of 10(7) tissue culture infectious dose 50 was reached that caused mild to moderate influenza disease in 69% of individuals with mean viral shedding for 4-5 days and significant rises in convalescent influenza antibody titers. Viral shedding preceded symptoms by 12-24 hours and terminated 2-3 days prior to symptom resolution, indicating that individuals may be infectious before symptom development. As expected, nasal congestion and rhinorrhea were most common, but interestingly, fever was observed in only 10% of individuals.

CONCLUSIONS

This study represents the first healthy volunteer influenza challenge model using a GMP-produced wild-type virus under an IND. This unique clinical research program will facilitate future studies of influenza pathogenesis, animal model validation, and the rapid, efficient, and cost-effective evaluation of efficacy of novel vaccines and therapeutics. Clinical Trials Registration.NCT01646138.

Towards multiscale modeling of influenza infection

Aided by recent advances in computational power, algorithms, and higher fidelity data, increasingly detailed theoretical models of infection with influenza A virus are being developed. We review single scale models as they describe influenza infection from intracellular to global scales, and, in particular, we consider those models that capture details specific to influenza and can be used to link different scales. We discuss the few multiscale models of influenza infection that have been developed in this emerging field. In addition to discussing modeling approaches, we also survey biological data on influenza infection and transmission that is relevant for constructing influenza infection models. We envision that, in the future, multiscale models that capitalize on technical advances in experimental biology and high performance computing could be used to describe the large spatial scale epidemiology of influenza infection, evolution of the virus, and transmission between hosts more accurately.

Respiratory viruses from hospitalized children with severe pneumonia in the Philippines

BACKGROUND

Pneumonia remains a leading cause of child death in developing countries. The viruses in severe pneumonia remain poorly defined.

METHODS

The study was conducted at the Eastern Visayas Regional Medical Center in Tacloban City, Philippines from May 2008 to May 2009. Patients aged 8 days to 13 years old who were admitted to the Department of Pediatrics with severe pneumonia were enrolled for the study. Upon admission, polymerase chain reaction was performed using nasopharyngeal swabs and blood cultures to detect respiratory viruses and bacteria, respectively.

RESULT

Among the 819 patients enrolled, at least one virus was detected in 501 cases (61.2%). In addition, 423 cases were positive for a single virus while bacteria were detected in the blood culture sample of 31 cases. The most commonly detected viruses were human rhinoviruses (n = 189), including types A (n = 103), B (n = 17), and C (n = 69), and respiratory syncytial virus (RSV) (n = 165). Novel viruses such as human metapneumovirus, human coronavirus NL63, human bocavirus, and human polyomaviruses WU and KI were also detected. There were 70 deaths, and one or more viruses were detected in 35 (50%) of these cases. Positivity only for influenza A virus (OR = 4.3, 95% CI = 1.3-14.6) was significantly associated with fatal outcome. From the blood culture, Burkholderia cepacia group (n = 9), Streptococcus pneumoniae (n = 4), Staphylococcus aureus (n = 4), Haemophilus influenzae (n = 1), and Salmonella C1 (n = 1) were also isolated.

CONCLUSION

Viruses were commonly detected in children with severe pneumonia in the Philippines. Hence, viral etiologies should be considered while developing better effective strategies to reduce child pneumonia-related deaths in developing countries.

The impact of host immune status on the within-host and population dynamics of antigenic immune escape

Antigenically evolving pathogens such as influenza viruses are difficult to control owing to their ability to evade host immunity by producing immune escape variants. Experimental studies have repeatedly demonstrated that viral immune escape variants emerge more often from immunized hosts than from naive hosts. This empirical relationship between host immune status and within-host immune escape is not fully understood theoretically, nor has its impact on antigenic evolution at the population level been evaluated. Here, we show that this relationship can be understood as a trade-off between the probability that a new antigenic variant is produced and the level of viraemia it reaches within a host. Scaling up this intra-host level trade-off to a simple population level model, we obtain a distribution for variant persistence times that is consistent with influenza A/H3N2 antigenic variant data. At the within-host level, our results show that target cell limitation, or a functional equivalent, provides a parsimonious explanation for how host immune status drives the generation of immune escape mutants. At the population level, our analysis also offers an alternative explanation for the observed tempo of antigenic evolution, namely that the production rate of immune escape variants is driven by the accumulation of herd immunity. Overall, our results suggest that disease control strategies should be further assessed by considering the impact that increased immunity--through vaccination--has on the production of new antigenic variants.

Influenza virus partially counteracts restriction imposed by tetherin/BST-2

Influenza virus infections lead to a burst of type I interferon (IFN) in the human respiratory tract, which most probably accounts for a rapid control of the virus. Although in mice, IFN-induced Mx1 factor mediates a major part of this response, the situation is less clear in humans. Interestingly, a recently identified IFN-induced cellular protein, tetherin (also known as CD317, BST-2, or HM1.24), exerts potent antiviral activity against a broad range of retroviruses, as well as several other enveloped viruses, by impeding the release of newly generated viral particles from the cell surface. Here we show that influenza virus belongs to the targets of this potent antiviral factor. Ectopic expression of tetherin strongly inhibited fully replicative influenza virus. In addition, depleting endogenous tetherin increased viral production of influenza virions, both in cells constitutively expressing tetherin and upon its induction by IFN. We further demonstrate, by biochemical and morphological means, that tetherin exerts its antiviral action by tethering newly budded viral particles, a mechanism similar to the one that operates against HIV-1. In addition, we determined that the magnitude of tetherin antiviral activity is comparable with or higher than the one of several previously identified anti-influenza cellular factors, such as MxA, ADAR1, ISG15, and viperin. Finally, we demonstrate that influenza virus reduces the impact of tetherin-mediated restriction on its replication by several mechanisms. First, the influenza virus NS1 protein impedes IFN-mediated tetherin induction. Second, influenza infection leads to a decrease of tetherin steady state levels, and the neuraminidase surface protein partly counteracts its activity. Overall, our study helps to delineate the intricate molecular battle taking place between influenza virus and its host cells.

In vitro analysis of virus particle subpopulations in candidate live-attenuated influenza vaccines distinguishes effective from ineffective vaccines

Two effective (vac+) and two ineffective (vac-) candidate live-attenuated influenza vaccines (LAIVs) derived from naturally selected genetically stable variants of A/TK/OR/71-delNS1[1-124] (H7N3) that differed only in the length and kind of amino acid residues at the C terminus of the nonstructural NS1 protein were analyzed for their content of particle subpopulations. These subpopulations included total physical particles (measured as hemagglutinating particles [HAPs]) with their subsumed biologically active particles of infectious virus (plaque-forming particles [PFPs]) and different classes of noninfectious virus, namely, interferon-inducing particles (IFPs), noninfectious cell-killing particles (niCKPs), and defective interfering particles (DIPs). The vac+ variants were distinguished from the vac- variants on the basis of their content of viral subpopulations by (i) the capacity to induce higher quantum yields of interferon (IFN), (ii) the generation of an unusual type of IFN-induction dose-response curve, (iii) the presence of IFPs that induce IFN more efficiently, (iv) reduced sensitivity to IFN action, and (v) elevated rates of PFP replication that resulted in larger plaques and higher PFP and HAP titers. These in vitro analyses provide a benchmark for the screening of candidate LAIVs and their potential as effective vaccines. Vaccine design may be improved by enhancement of attributes that are dominant in the effective (vac+) vaccines.

Sensitivity of rapid immunoassay for influenza A and B in the early phase of the disease

BACKGROUND

Immunochromatography (IC) tests are often used for the rapid diagnosis of influenza. Once influenza is diagnosed, an anti-influenza drug can be administered. Physicians claim, however, that they are not sufficiently sensitive, especially in the early phase of the disease. The aim of the present study was therefore to analyze the sensitivity of the IC test from the standpoint of virology.

METHODS

To evaluate the sensitivity of the IC test statistically, 736 nasopharyngeal specimens were subjected to the IC test and virus isolation (VI). The IC test (+) specimens were compared with VI (+) specimens in the early phase after fever onset. Amounts of the virus in IC(-)VI(+) specimens were compared with those in IC(+)VI(+) specimens on real-time reverse transcriptase-polymerase chain reaction. The isolated viruses from these specimens were subjected to the IC test at the same dose. The nucleotide sequences of NP genes were compared.

RESULTS

The IC test was less sensitive for diagnosis in the early phase of the disease. Amounts of virus were significantly lower in IC(-)VI(+) specimens than in IC(+)VI(+) specimens. No variations were observed in the isolated viruses.

CONCLUSIONS

The IC test is not sufficiently sensitive owing to the low amount of virus in the nasopharyngeal tract in the early phase of the disease. Influenza should be diagnosed on the basis of clinical symptoms within 1 day after the fever onset.

The relationship between encephalitis lethargica and influenza: a critical analysis

Since encephalitis lethargica's (EL) prevalence in the 1920s, epidemiologic and clinical debate has persisted over whether EL was caused by, potentiated by, or merely coincident with the Spanish influenza pandemic. Epidemiologic analyses generally suggest that the disorders were coincidental. Beginning in the 1970s, modern experiments on archival brain samples mainly failed to confirm a direct relationship between influenza and EL. These experimental studies have technical limitations, e.g., the appropriateness of antibodies, polymerase chain reaction (PCR) primers and controls, and the extreme paucity and age of available material. These factors render the case against influenza less decisive than currently perceived. Nevertheless, there is little direct evidence supporting influenza in the etiology of EL. Almost 100 years after the EL epidemic, its etiology remains enigmatic, raising the possibility of a recurrence of EL in a future influenza pandemic.

[Current techniques used for the diagnosis of respiratory virus infectious in intensive care units]

Plusieurs centaines de virus respiratoires différents peuvent être détectés chez les patients atteints d'une infection virale respiratoire et hospitalisés dans un service de réanimation : virus influenza, virus respiratoire syncytial, virus para-influenza, adénovirus, coronavirus, rhinovirus, entérovirus, métapneumovirus humain, bocavirus… La recherche de ces virus doit être effectuée sur un prélèvement nasal ou trachéobronchique, riche en cellules épithéliales. Chez les patients immunodéprimés, il faut ajouter un lavage bronchoalvéolaire pour rechercher le cytomégalovirus et les adénovirus. La mise en évidence d'antigènes viraux par immunofluorescence (IF) ou technique immunoenzymatique dans les cellules infectées est en théorie la méthode la plus simple et rapide à utiliser. Comme pour toutes les techniques de diagnostic, la qualité du prélèvement est un déterminant majeur de son efficacité. Cette méthode est malheureusement peu sensible dans les infections respiratoires chez l'adulte. La recherche virale en culture, compliquée et de réponse tardive, peut être utile dans ce cas en raison de son efficacité. Les méthodes PCR sont plus efficaces : elles peuvent identifier les virus non détectés par les techniques conventionnelles et elles augmentent l'isolement des virus classiques. Elles permettent aussi d'identifier les sous-types viraux, d'étudier par séquençage la variabilité génétique des souches et de quantifier la charge virale respiratoire. Les techniques multiplex recherchant plusieurs virus directement dans les prélèvements sont les plus adaptées au diagnostic en raison du nombre de virus à rechercher. Des méthodes PCR en temps réel, fournissant un résultat rapide, ont été récemment développées. La richesse en cellules et le transport du prélèvement sont moins critiques pour les recherches virales en PCR que pour les techniques conventionnelles d'IF et de culture. De plus, les acides nucléiques persistent plus longtemps que les virus infectieux, permettant ainsi un diagnostic plus tardif. Néanmoins, dans un laboratoire de virologie clinique où la rapidité, le coût modéré et la simplicité des techniques sont des exigences prioritaires, le meilleur choix est d'utiliser séquentiellement l'IF et les PCR multiplex. Le développement des outils de PCR multiplex en temps réel est la priorité majeure du futur.

Amelioration of influenza virus pathogenesis in chickens attributed to the enhanced interferon-inducing capacity of a virus with a truncated NS1 gene

Avian influenza virus (AIV) A/turkey/Oregon/71-SEPRL (TK/OR/71-SEPRL) (H7N3) encodes a full-length NS1 protein and is a weak inducer of interferon (IFN). A variant, TK/OR/71-delNS1 (H7N3), produces a truncated NS1 protein and is a strong inducer of IFN. These otherwise genetically related variants differ 20-fold in their capacities to induce IFN in primary chicken embryo cells but are similar in their sensitivities to the action of IFN. Furthermore, the weak IFN-inducing strain actively suppresses IFN induction in cells that are otherwise programmed to produce it. These phenotypic differences are attributed to the enhanced IFN-inducing capacity that characterizes type A influenza virus strains that produce defective NS1 protein. The pathogenesis of these two variants was evaluated in 1-day-old and 4-week-old chickens. The cell tropisms of both viruses were similar. However, the lesions in chickens produced by the weak IFN inducer were more severe and differed somewhat in character from those observed for the strong IFN inducer. Differences in lesions included the nature of inflammation, the rate of resolution of the infection, and the extent of viral replication and/or virus dissemination. The amelioration of pathogenesis is attributed to the higher levels of IFN produced by the variant encoding the truncated NS1 protein and the antiviral state subsequently induced by that IFN. The high titer of virus observed in kidney tissue ( approximately 10(9) 50% embryo lethal doses/g) from 1-day-old chickens infected intravenously by the weak IFN-inducing strain is attributed to the capacity of chicken kidney cells to activate the hemagglutinin fusion peptide along with their unresponsiveness to inducers of IFN as measured in vitro. Thus, the IFN-inducing capacity of AIV appears to be a significant factor in regulating the pathogenesis, virulence, and viral transmission of AIV in chickens. This suggests that the IFN-inducing and IFN induction suppression phenotypes of AIV should be considered when characterizing strains of influenza virus.

Kinetics of influenza A virus infection in humans

Currently, little is known about the viral kinetics of influenza A during infection within an individual. We utilize a series of mathematical models of increasing complexity, which incorporate target cell limitation and the innate interferon response, to examine influenza A virus kinetics in the upper respiratory tracts of experimentally infected adults. The models were fit to data from an experimental H1N1 influenza A/Hong Kong/123/77 infection and suggest that it is important to include the eclipse phase of the viral life cycle in viral dynamic models. Doing so, we estimate that after a delay of approximately 6 h, infected cells begin producing influenza virus and continue to do so for approximately 5 h. The average lifetime of infected cells is approximately 11 h, and the half-life of free infectious virus is approximately 3 h. We calculated the basic reproductive number, R(0), which indicated that a single infected cell could produce approximately 22 new productive infections. This suggests that antiviral treatments have a large hurdle to overcome in moderating symptoms and limiting infectiousness and that treatment has to be initiated as early as possible. For about 50% of patients, the curve of viral titer versus time has two peaks. This bimodal behavior can be explained by incorporating the antiviral effects of interferon into the model. Our model also compared well to an additional data set on viral titer after experimental infection and treatment with the neuraminidase inhibitor zanamivir, which suggests that such models may prove useful in estimating the efficacies of different antiviral therapies for influenza A infection.

Temporal and anatomic relationship between virus replication and cytokine gene expression after vaginal simian immunodeficiency virus infection

The current knowledge about early innate immune responses at mucosal sites of human immunodeficiency virus (HIV) entry is limited but likely to be important in the design of effective HIV vaccines against heterosexual transmission. This study examined the temporal and anatomic relationship between virus replication, lymphocyte depletion, and cytokine gene expression levels in mucosal and lymphoid tissues in a vaginal-transmission model of HIV in rhesus macaques. The results of the study show that the kinetics of cytokine gene expression levels in the acute phase of infection are positively correlated with virus replication in a tissue. Thus, cytokine responses after vaginal simian immunodeficiency virus (SIV) inoculation are earliest and strongest in mucosal tissues of the genital tract and lowest in systemic lymphoid tissues. Importantly, the early cytokine response was dominated by the induction of proinflammatory cytokines, while the induction of cytokines with antiviral activity, alpha/beta interferon, occurred too late to prevent virus replication and dissemination. Thus, the early cytokine response favors immune activation, resulting in the recruitment of potential target cells for SIV. Further, unique cytokine gene expression patterns were observed in distinct anatomic locations with a rapid and persistent inflammatory response in the gut that is consistent with the gut being the major site of early CD4 T-cell depletion in SIV infection.

Interferon induction and/or production and its suppression by influenza A viruses

Developmentally aged chicken embryo cells which hyperproduce interferon (IFN) when induced were used to quantify IFN production and its suppression by eight strains of type A influenza viruses (AIV). Over 90% of the IFN-inducing or IFN induction-suppressing activity of AIV populations resided in noninfectious particles. The IFN-inducer moiety of AIV appears to preexist in, or be generated by, virions termed IFN-inducing particles (IFP) and was detectable under conditions in which a single molecule of double-stranded RNA introduced into a cell via endocytosis induced IFN, whereas single-stranded RNA did not. Some AIV strains suppressed IFN production, an activity that resided in a noninfectious virion termed an IFN induction-suppressing particle (ISP). The ISP phenotype was dominant over the IFP phenotype. Strains of AIV varied 100-fold in their capacity to induce IFN. AIV genetically compromised in NS1 expression induced about 20 times more IFN than NS1-competent parental strains. UV irradiation further enhanced the IFN-inducing capacity of AIV up to 100-fold, converting ISP into IFP and IFP into more efficient IFP. AIV is known to prevent IFN induction and/or production by expressing NS1 from a small UV target (gene NS). Evidence is presented for an additional downregulator of IFN production, identified as a large UV target postulated to consist of AIV polymerase genes PB1 + PB2 + PA, through the ensuing action of their cap-snatching endonuclease on pre-IFN-mRNA. The products of both the small and large UV targets act in concert to regulate IFN induction and/or production. Knowledge of the IFP/ISP phenotype may be useful in the development of attenuated AIV strains that maximally induce cytokines favorable to the immune response.

Transcriptional analysis of human peripheral blood mononuclear cells after influenza immunization

Influenza A virus is a major cause of morbidity and mortality worldwide. There is a large knowledge base on the immune response to influenza. However, few studies have focused on global gene expression in immune cells after antigenic challenge. A better understanding of the host immune response is required for the development of more efficient means of prevention and treatment of influenza. In this study, global gene expression in peripheral blood mononuclear cells (PBMCs) after influenza immunization was analyzed. The differential gene expression in antigen-stimulated and non-stimulated PBMCs was determined by cDNA microarrays. To determine whether a specific gene profile was present during a proliferative memory cell response to influenza antigens, gene expression in response to PHA was compared with antigen-stimulated PBMCs. PHA induced the upregulation of 201 genes while influenza virus antigen upregulated more than triple that is 630 genes out of 1700 genes analyzed. Both influenza antigen and PHA commonly upregulated 138 genes. Interferon (IFN)-related genes were induced by influenza but not by PHA. The interferon-gamma induced protein precursor 10 (IP-10) was upregulated 27-fold while the interferon-induced 54 kDa protein exhibited a 13-fold increase. The following gene families were also selectively upregulated by influenza antigens: complement ligands and receptors, T cell activation genes, growth factors, genes related to antigen processing and inflammatory responses. With PHA, the genes TNF-R, CTSG, CD3 delta, C8B, CRF1 and CCR2 had higher expression compared with the viral antigen stimulation. Neutrophil defensins alpha-1 and two C-C chemokines, proteins MIP-1-beta and MIP-4, were among the genes upregulated by both PHA and influenza antigens. The results suggest that interferon-induced genes are one of the main transcriptional targets during the immune response to influenza virus.

Functional replacement of the carboxy-terminal two-thirds of the influenza A virus NS1 protein with short heterologous dimerization domains

The NS1 protein of influenza A/WSN/33 virus is a 230-amino-acid-long protein which functions as an interferon alpha/beta (IFN-alpha/beta) antagonist by preventing the synthesis of IFN during viral infection. In tissue culture, the IFN inhibitory function of the NS1 protein has been mapped to the RNA binding domain, the first 73 amino acids. Nevertheless, influenza viruses expressing carboxy-terminally truncated NS1 proteins are attenuated in mice. Dimerization of the NS1 protein has previously been shown to be essential for its RNA binding activity. We have explored the ability of heterologous dimerization domains to functionally substitute in vivo for the carboxy-terminal domains of the NS1 protein. Recombinant influenza viruses were generated that expressed truncated NS1 proteins of 126 amino acids, fused to 28 or 24 amino acids derived from the dimerization domains of either the Saccharomyces cerevisiae PUT3 or the Drosophila melanogaster Ncd (DmNcd) proteins. These viruses regained virulence and lethality in mice. Moreover, a recombinant influenza virus expressing only the first 73 amino acids of the NS1 protein was able to replicate in mice lacking three IFN-regulated antiviral enzymes, PKR, RNaseL, and Mx, but not in wild-type (Mx-deficient) mice, suggesting that the attenuation was mainly due to an inability to inhibit the IFN system. Remarkably, a virus with an NS1 truncated at amino acid 73 but fused to the dimerization domain of DmNcd replicated and was also highly pathogenic in wild-type mice. These results suggest that the main biological function of the carboxy-terminal region of the NS1 protein of influenza A virus is the enhancement of its IFN antagonist properties by stabilizing the NS1 dimeric structure.

Tumor necrosis factor alpha exerts powerful anti-influenza virus effects in lung epithelial cells

Previous studies have associated influenza virus-induced expression of inflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha), with influenza pathogenesis in the human respiratory tract and have suggested that alpha and beta interferons are the first cytokines recruited to counteract such infection. However, we report here that TNF-alpha has powerful anti-influenza virus activity. When infected with influenza virus, cultured porcine lung epithelial cells expressed TNF-alpha in a dose-dependent manner. Expression of TNF-alpha was induced only by replicating virus. TNF-alpha showed strong antiviral activity against avian, swine, and human influenza viruses, and the antiviral effect of TNF-alpha was greater than that of gamma or alpha interferon. These findings suggest that TNF-alpha serves as the first line of defense against influenza virus infection in the natural host.

Cross-reactive, cell-mediated immunity and protection of chickens from lethal H5N1 influenza virus infection in Hong Kong poultry markets

In 1997, avian H5N1 influenza virus transmitted from chickens to humans resulted in 18 confirmed infections. Despite harboring lethal H5N1 influenza viruses, most chickens in the Hong Kong poultry markets showed no disease signs. At this time, H9N2 influenza viruses were cocirculating in the markets. We investigated the role of H9N2 influenza viruses in protecting chickens from lethal H5N1 influenza virus infections. Sera from chickens infected with an H9N2 influenza virus did not cross-react with an H5N1 influenza virus in neutralization or hemagglutination inhibition assays. Most chickens primed with an H9N2 influenza virus 3 to 70 days earlier survived the lethal challenge of an H5N1 influenza virus, but infected birds shed H5N1 influenza virus in their feces. Adoptive transfer of T lymphocytes or CD8(+) T cells from inbred chickens (B(2)/B(2)) infected with an H9N2 influenza virus to naive inbred chickens (B(2)/B(2)) protected them from lethal H5N1 influenza virus. In vitro cytotoxicity assays showed that T lymphocytes or CD8(+) T cells from chickens infected with an H9N2 influenza virus recognized target cells infected with either an H5N1 or H9N2 influenza virus in a dose-dependent manner. Our findings indicate that cross-reactive cellular immunity induced by H9N2 influenza viruses protected chickens from lethal infection with H5N1 influenza viruses in the Hong Kong markets in 1997 but permitted virus shedding in the feces. Our findings are the first to suggest that cross-reactive cellular immunity can change the outcome of avian influenza virus infection in birds in live markets and create a situation for the perpetuation of H5N1 influenza viruses.

Comparative susceptibility of respiratory viruses to recombinant interferons-alpha 2b and -beta

Intranasal recombinant interferon-alpha 2b (rIFN-alpha 2b) protects against natural colds due to rhinoviruses, but apparently not against those caused by viruses. Because rIFN-beta serine17 (rIFN-beta ser) appears less active than rIFN-alpha 2b in preventing natural rhinovirus colds, we compared the two IFNs in two in vitro assays against selected respiratory viruses. In a yield reduction assay, both IFNs had comparable activity against rhinovirus types 39 and 1A and coronavirus 229E, which were inhibited by 90% or more at IFN concentrations of 10(-11) to 10(-10) gram of protein/ml (approximately 2-20 IU/ml). Similar activities were observed with rIFN-beta ser against rhinoviruses isolated from clinical specimens. At concentrations of 10(-9) gram protein/ml, both IFNs inhibited the growth of influenza A and parainfluenza viruses, but not of adenovirus or respiratory syncytial virus in the cell culture systems tested. Thus, the different clinical protection conferred by rIFN-alpha 2b and rIFN-beta ser in studies of natural rhinovirus colds are not accounted for by differences in their in vitro activity against these viruses, and other explanations must be found.

Antiviral chemotherapy and prophylaxis of viral respiratory disease

Respiratory viruses continue to be major causes of morbidity and mortality. Currently available chemotherapy is limited to oral amantadine for uncomplicated influenza A and aerosolized ribavirin for respiratory syncytial virus (RSV) infections. Amantadine is also efficacious for chemoprophylaxis of influenza A virus infections. Rimantadine has similar clinical efficacy and is better tolerated than amantadine. Aerosolized ribavirin may be useful in the treatment of serious respiratory illness caused by viruses other than RSV. Intranasal application of interferon is effective in interrupting the spread of rhinovirus colds in families, but chronic use is limited by nasal toxicity. Several newer agents and approaches for chemoprophylaxis and therapy are at different stages of clinical investigation. Combinations of antiviral agents may offer the best therapeutic advantage but have not been adequately tested in man. As additional drugs become available and uses expand for the currently available agents, rapid viral diagnosis will assume an increasingly important role in their optimal use.

Antiviral Chemotherapyand Prophylaxis of Viral Respiratory Disease

Several antiviral agents are currently available for the treatment and prophylaxis of viral respiratory disease. These include oral amantadine for influenza A and aerosolized ribavirin for respiratory syncytial virus infections. Additional agents, such as rimantadine and intranasal interferons, and newer approaches, including thе use of combination chemotherapy, offer promise for the improved management of viral respiratory tract infections.

Interferon response in normal and Aleutian disease virus-infected mink

Studies were done to determine whether differences in interferon production are responsible for the resistance of pastel mink to Aleutian disease. The abilities of normal pastel and sapphire mink to produce interferon when inoculated with either Newcastle disease virus or a synthetic polyribonucleotide, poly (I):poly (C), were identical, even to the production of a novel, acid-labile interferon. The resistance of pastel mink to Aleutian disease did not correlate with interferon production, because neither sapphire nor pastel mink produced detectable amounts of interferon when infected with either the Pullman strain of Aleutian disease virus (ADV) or the highly virulent Utah I strain. Sapphire mink infected with the Pullman strain responded normally to poly (I):poly (C) early in the course of the disease, but interferon production was impaired late, when the mink were hypergammaglobulinemic and had renal, vascular, and hepatic lesions. These data suggest that ADV Pullman neither stimulates nor interferes with interferon production in infected mink and may represent a mechanism whereby ADV can more readily establish infection.

Combined interferon-alpha 2, rimantadine hydrochloride, and ribavirin inhibition of influenza virus replication in vitro

Recombinant DNA-produced human interferon-alpha 2 inhibited the replication of influenza A and B viruses in primary rhesus monkey kidney cells (RMK). Human interferon-alpha 2 interacted additively or synergistically with rimantadine hydrochloride or ribavirin in reducing the yield of clinical isolates of either H3N2 or H1N1 subtype influenza A viruses. The combination of human interferon-alpha 2 and ribavirin also inhibited the replication of an influenza B virus to a greater extent than either single agent. In addition to drug concentration, the virus inoculum and duration of culture were important variables in determining the degree of inhibition. Single drugs or combinations did not significantly inhibit the growth of uninfected RMK cells, which indicated that the observed interactions with respect to antiviral activity were not due to cell cytotoxicity.

Influenza vaccination and theophylline pharmacokinetics in patients with chronic obstructive lung disease

Total Theophylline clearance rate was measured before and 24 hours after standard influenza vaccination in seven men with stable chronic obstructive lung disease. In four, total theophylline clearance rate was also measured 48 hours after vaccine administration. There was no significant change in the clearance rate after either time interval. These results do not support recent recommendations to monitor serum theophylline concentrations or reduce theophylline dosage during the 48-hour period following influenza vaccination. Nevertheless, pending further studies, patients maintained on a regimen of theophylline preparations should be followed clinically for theophylline toxicity for the first several days after receiving influenza vaccine.

Susceptibility of influenza viruses to interferon and to poly(I) . Poly(C) determined by the plaque reduction method

Susceptibility of eight strains of influenza A and B viruses to interferon and to poly(I) . poly(C) were determined by the plaque reduction method. All strains tested were slightly less susceptible than vesicular stomatitis virus (VSV) in an established line of canine kidney (MDCK) cells. The 50% plaque depression doses (PD50) of poly(I) . poly(C) for influenza A and B viruses were as high as 3.0- to 4.5-fold and 6- to 18-fold that for VSV, respectively. The amounts of interferon required to inhibit plaque formation of influenza A and B viruses by 50% were 3.0-6.2 and 7.3-15.2 units/ml, respectively. The ratio of PD50 of poly(I) . poly(C) for each strain of influenza viruses tested to that for VSV in chick embryo cells was almost the same as in MDCK cells. Furthermore, in chick embryo cells, the strains of influenza virus tested were demonstrated to be much more susceptible to poly(I) . poly(C) than both Newcastle disease virus and vaccinia virus. It is suggested that influenza viruses may be relatively susceptible to interferon and to poly(I) . poly(C).

Skin reactions to interferon inoculations are reduced but not abolished by purification

The skin reactions to partially-purified fibroblast-derived (HulFN-beta) and leucocyte-derived (HulFN-alpha) interferons and to HulFN-alpha of increasing purity were studied in normal volunteers. Reactions consisted of an immediate flare followed by a dense well-circumscribed erythema maximal at 4-8 hours. HulFN-beta caused significantly larger reactions than HulFN-alpha of approximately the same purity. Immediate flare reactions occurred even to the most pure preparation tested but the late reactions were significantly reduced. Experiments suggested that the early reactions to impure HulFN-alpha were in part mediated by local histamine release and late reactions in part by local prostaglandin synthesis. This suggests that interferon itself may not be the cause of general symptoms during a virus illness.