Increased iron sequestration in alveolar macrophages in chronic obstructive pulmonary disease

Free iron in lung can cause the generation of reactive oxygen species, an important factor in chronic obstructive pulmonary disease (COPD) pathogenesis. Iron accumulation has been implicated in oxidative stress in other diseases, such as Alzheimer’s and Parkinson’s diseases, but little is known about iron accumulation in COPD. We sought to determine if iron content and the expression of iron transport and/or storage genes in lung differ between controls and COPD subjects, and whether changes in these correlate with airway obstruction. Explanted lung tissue was obtained from transplant donors, GOLD 2–3 COPD subjects, and GOLD 4 lung transplant recipients, and bronchoalveolar lavage (BAL) cells were obtained from non-smokers, healthy smokers, and GOLD 1–3 COPD subjects. Iron-positive cells were quantified histologically, and the expression of iron uptake (transferrin and transferrin receptor), storage (ferritin) and export (ferroportin) genes was examined by real-time RT-PCR assay. Percentage of iron-positive cells and expression levels of iron metabolism genes were examined for correlations with airflow limitation indices (forced expiratory volume in the first second (FEV₁) and the ratio between FEV₁ and forced vital capacity (FEV₁/FVC)). The alveolar macrophage was identified as the predominant iron-positive cell type in lung tissues. Futhermore, the quantity of iron deposit and the percentage of iron positive macrophages were increased with COPD and emphysema severity. The mRNA expression of iron uptake and storage genes transferrin and ferritin were significantly increased in GOLD 4 COPD lungs compared to donors (6.9 and 3.22 fold increase, respectively). In BAL cells, the mRNA expression of transferrin, transferrin receptor and ferritin correlated with airway obstruction. These results support activation of an iron sequestration mechanism by alveolar macrophages in COPD, which we postulate is a protective mechanism against iron induced oxidative stress.

Chemosensory functions for pulmonary neuroendocrine cells

The mammalian airways are sensitive to inhaled stimuli, and airway diseases are characterized by hypersensitivity to volatile stimuli, such as perfumes, industrial solvents, and others. However, the identity and function of the cells in the airway that can sense volatile chemicals remain uncertain, particularly in humans. Here, we show that solitary pulmonary neuroendocrine cells (PNECs), which are morphologically distinct and physiologically undefined, might serve as chemosensory cells in human airways. This conclusion is based on our finding that some human PNECs expressed members of the olfactory receptor (OR) family in vivo and in primary cell culture, and are anatomically positioned in the airway epithelium to respond to inhaled volatile chemicals. Furthermore, apical exposure of primary-culture human airway epithelial cells to volatile chemicals decreased levels of serotonin in PNECs, and the led to the release of the neuropeptide calcitonin gene-related peptide (CGRP) to the basal medium. These data suggest that volatile stimulation of PNECs can lead to the secretion of factors that are capable of stimulating the corresponding receptors in the lung epithelium. We also found that the distribution of serotonin and neuropeptide receptors may change in chronic obstructive pulmonary disease, suggesting that increased PNEC-dependent chemoresponsiveness might contribute to the altered sensitivity to volatile stimuli in this disease. Together, these data indicate that human airway epithelia harbor specialized cells that respond to volatile chemical stimuli, and may help to explain clinical observations of odorant-induced airway reactions.

Reactive oxygen species induce antiviral innate immune response through IFN-λ regulation in human nasal epithelial cells

This study sought to explore the role of the IFN-related innate immune responses (IFN-β and IFN-λ) and of reactive oxygen species (ROS) after influenza A virus (IAV) infection for antiviral innate immune activity in normal human nasal epithelial (NHNE) cells that are highly exposed to IAV. Passage-2 NHNE cells were inoculated with the IAV WSN/33 for 1, 2, and 3 days to assess the capacity of IFN and the relationship between ROS generation and IFN-λ secretion for controlling IAV infection. Viral titers and IAV mRNA levels increased after infection. In concert with viral titers, we found that the generation of IFNs, such as IFN-β, IFN-λ1, and IFN-λ2/3, was induced after IAV infection until 3 days after infection. The induction of IFN-λ gene expression and protein secretion may be predominant after IAV infection. Similarly, we observed that intracellular ROS generation increased 60 minutes after IAV infection. Viral titers and mRNA levels of IAV were significantly higher in cases with scavenging ROS, in cases with an induced IFN-λ mRNA level, or where the secreted protein concentration of IFN-λ was attenuated after the suppression of ROS generation. Both mitochondrial and dual oxidase (Doux)2-generated ROS were correlated with IAV mRNA and viral titers. The inhibition of mitochondrial ROS generation and the knockdown of Duox2 gene expression highly increased IAV viral titers and decreased IFN-λ secretion. Our findings suggest that the production of ROS may be responsible for IFN-λ secretion to control IAV infection. Both mitochondria and Duox2 are possible sources of ROS generation, which is required to initiate an innate immune response in NHNE cells.

Long-term IL-33-producing epithelial progenitor cells in chronic obstructive lung disease

Chronic obstructive lung disease is characterized by persistent abnormalities in epithelial and immune cell function that are driven, at least in part, by infection. Analysis of parainfluenza virus infection in mice revealed an unexpected role for innate immune cells in IL-13-dependent chronic lung disease, but the upstream driver for the immune axis in this model and in humans with similar disease was undefined. We demonstrate here that lung levels of IL-33 are selectively increased in postviral mice with chronic obstructive lung disease and in humans with very severe chronic obstructive pulmonary disease (COPD). In the mouse model, IL-33/IL-33 receptor signaling was required for Il13 and mucin gene expression, and Il33 gene expression was localized to a virus-induced subset of airway serous cells and a constitutive subset of alveolar type 2 cells that are both linked conventionally to progenitor function. In humans with COPD, IL33 gene expression was also associated with IL13 and mucin gene expression, and IL33 induction was traceable to a subset of airway basal cells with increased capacities for pluripotency and ATP-regulated release of IL-33. Together, these findings provide a paradigm for the role of the innate immune system in chronic disease based on the influence of long-term epithelial progenitor cells programmed for excess IL-33 production.

High-throughput screening normalized to biological response: application to antiviral drug discovery

The process of conducting cell-based phenotypic screens can result in data sets from small libraries or portions of large libraries, making accurate hit picking from multiple data sets important for efficient drug discovery. Here, we describe a screen design and data analysis approach that allow for normalization not only between quadrants and plates but also between screens or batches in a robust, quantitative fashion, enabling hit selection from multiple data sets. We independently screened the MicroSource Spectrum and NCI Diversity Set II libraries using a cell-based phenotypic high-throughput screening (HTS) assay that uses an interferon-stimulated response element (ISRE)-driven luciferase-reporter assay to identify interferon (IFN) signal enhancers. Inclusion of a per-plate, per-quadrant IFN dose-response standard curve enabled conversion of ISRE activity to effective IFN concentrations. We identified 45 hits based on a combined z score ≥2.5 from the two libraries, and 25 of 35 available hits were validated in a compound concentration-response assay when tested using fresh compound. The results provide a basis for further analysis of chemical structure in relation to biological function. Together, the results establish an HTS method that can be extended to screening for any class of compounds that influence a quantifiable biological response for which a standard is available.

IL-13-induced airway mucus production is attenuated by MAPK13 inhibition

Increased mucus production is a common cause of morbidity and mortality in inflammatory airway diseases, including asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. However, the precise molecular mechanisms for pathogenic mucus production are largely undetermined. Accordingly, there are no specific and effective anti-mucus therapeutics. Here, we define a signaling pathway from chloride channel calcium-activated 1 (CLCA1) to MAPK13 that is responsible for IL-13-driven mucus production in human airway epithelial cells. The same pathway was also highly activated in the lungs of humans with excess mucus production due to COPD. We further validated the pathway by using structure-based drug design to develop a series of novel MAPK13 inhibitors with nanomolar potency that effectively reduced mucus production in human airway epithelial cells. These results uncover and validate a new pathway for regulating mucus production as well as a corresponding therapeutic approach to mucus overproduction in inflammatory airway diseases.

Self-cleavage of human CLCA1 protein by a novel internal metalloprotease domain controls calcium-activated chloride channel activation

The chloride channel calcium-activated (CLCA) family are secreted proteins that regulate both chloride transport and mucin expression, thus controlling the production of mucus in respiratory and other systems. Accordingly, human CLCA1 is a critical mediator of hypersecretory lung diseases, such as asthma, chronic obstructive pulmonary disease, and cystic fibrosis, that manifest mucus obstruction. Despite relevance to homeostasis and disease, the mechanism of CLCA1 function remains largely undefined. We address this void by showing that CLCA proteins contain a consensus proteolytic cleavage site recognized by a novel zincin metalloprotease domain located within the N terminus of CLCA itself. CLCA1 mutations that inhibit self-cleavage prevent activation of calcium-activated chloride channel (CaCC)-mediated chloride transport. CaCC activation requires cleavage to unmask the N-terminal fragment of CLCA1, which can independently gate CaCCs. Gating of CaCCs mediated by CLCA1 does not appear to involve proteolytic cleavage of the channel because a mutant N-terminal fragment deficient in proteolytic activity is able to induce currents comparable with that of the native fragment. These data provide both a mechanistic basis for CLCA1 self-cleavage and a novel mechanism for regulation of chloride channel activity specific to the mucosal interface.

Asthma as a chronic disease of the innate and adaptive immune systems responding to viruses and allergens

Research on the pathogenesis of asthma has traditionally concentrated on environmental stimuli, genetic susceptibilities, adaptive immune responses, and end-organ alterations (particularly in airway mucous cells and smooth muscle) as critical steps leading to disease. The focus of this cascade has been the response to allergic stimuli. An alternative scheme suggests that respiratory viruses and the consequent response of the innate immune system also drives the development of asthma as well as related inflammatory diseases. This conceptual shift raises the possibility that sentinel cells such as airway epithelial cells, DCs, NKT cells, innate lymphoid cells, and macrophages also represent critical components of asthma pathogenesis as well as new targets for therapeutic discovery. A particular challenge will be to understand and balance the innate as well as the adaptive immune responses to defend the host against acute infection as well as chronic inflammatory disease.

P-glycoprotein is a major determinant of norbuprenorphine brain exposure and antinociception

Norbuprenorphine is a major metabolite of buprenorphine and potent agonist of μ, δ, and κ opioid receptors. Compared with buprenorphine, norbuprenorphine causes minimal antinociception but greater respiratory depression. It is unknown whether the limited antinociception is caused by low efficacy or limited brain exposure. Norbuprenorphine is an in vitro substrate of the efflux transporter P-glycoprotein (Mdr1), but the role of P-glycoprotein in norbuprenorphine transport in vivo is unknown. This investigation tested the hypothesis that limited norbuprenorphine antinociception results from P-glycoprotein-mediated efflux and limited brain access. Human P-glycoprotein-mediated transport in vitro of buprenorphine, norbuprenorphine, and their respective glucuronide conjugates was assessed by using transfected cells. P-glycoprotein-mediated norbuprenorphine transport and consequences in vivo were assessed by using mdr1a(+/+) and mdr1a(-/-) mice. Antinociception was determined by hot-water tail-flick assay, and respiratory effects were determined by unrestrained whole-body plethysmography. Brain and plasma norbuprenorphine and norbuprenorphine-3-glucuronide were quantified by mass spectrometry. In vitro, the net P-glycoprotein-mediated efflux ratio for norbuprenorphine was nine, indicating significant efflux. In contrast, the efflux ratio for buprenorphine and the two glucuronide conjugates was unity, indicating absent transport. The norbuprenorphine brain/plasma concentration ratio was significantly greater in mdr1a(-/-) than mdr1a(+/+) mice. The magnitude and duration of norbuprenorphine antinociception were significantly increased in mdr1a(-/-) compared with mdr1a(+/+) mice, whereas the reduction in respiratory rate was similar. Results show that norbuprenorphine is an in vitro and in vivo substrate of P-glycoprotein. P-glycoprotein-mediated efflux influences brain access and antinociceptive, but not the respiratory, effects of norbuprenorphine.

High throughput screening for small molecule enhancers of the interferon signaling pathway to drive next-generation antiviral drug discovery

Most of current strategies for antiviral therapeutics target the virus specifically and directly, but an alternative approach to drug discovery might be to enhance the immune response to a broad range of viruses. Based on clinical observation in humans and successful genetic strategies in experimental models, we reasoned that an improved interferon (IFN) signaling system might better protect against viral infection. Here we aimed to identify small molecular weight compounds that might mimic this beneficial effect and improve antiviral defense. Accordingly, we developed a cell-based high-throughput screening (HTS) assay to identify small molecules that enhance the IFN signaling pathway components. The assay is based on a phenotypic screen for increased IFN-stimulated response element (ISRE) activity in a fully automated and robust format (Z'>0.7). Application of this assay system to a library of 2240 compounds (including 2160 already approved or approvable drugs) led to the identification of 64 compounds with significant ISRE activity. From these, we chose the anthracycline antibiotic, idarubicin, for further validation and mechanism based on activity in the sub-µM range. We found that idarubicin action to increase ISRE activity was manifest by other members of this drug class and was independent of cytotoxic or topoisomerase inhibitory effects as well as endogenous IFN signaling or production. We also observed that this compound conferred a consequent increase in IFN-stimulated gene (ISG) expression and a significant antiviral effect using a similar dose-range in a cell-culture system inoculated with encephalomyocarditis virus (EMCV). The antiviral effect was also found at compound concentrations below the ones observed for cytotoxicity. Taken together, our results provide proof of concept for using activators of components of the IFN signaling pathway to improve IFN efficacy and antiviral immune defense as well as a validated HTS approach to identify small molecules that might achieve this therapeutic benefit.

Antiviral IFN-γ responses of monocytes at birth predict respiratory tract illness in the first year of life

Background

Viral respiratory tract infections are the leading cause of acute illness during infancy and are closely linked to chronic inflammatory airway diseases later in life. However, the determinants of susceptibility to acute respiratory tract infections still need to be defined.

Objective

We investigated whether the individual variation in antiviral response at birth determines the risk for acute respiratory tract illness in the first year of life.

Methods

We studied 82 children who were enrolled in a birth cohort study of inner-city children with at least 1 parent with allergy or asthma. We cultured cord blood monocytes and assessed IFNG and CCL5 mRNA production at 24 hours after inoculation with respiratory syncytial virus. We also monitored the frequency of acute respiratory tract illness at 3-month intervals and analyzed nasal lavage samples for respiratory tract viruses at the time of illness during the first year.

Results

Respiratory tract infection was reported for 88% of subjects, and respiratory tract viruses were recovered in 74% of symptomatic children. We observed a wide range of antiviral responses in cord blood monocytes across the population. Furthermore, a decrease in production of IFNG (but not CCL5) mRNA in response to respiratory syncytial virus infection of monocytes was associated with a significant increase in the frequency of upper respiratory tract infections (r = −0.42, P < .001) and the prevalence of ear and sinus infections, pneumonias, and respiratory-related hospitalizations.

Conclusion

Individual variations in the innate immune response to respiratory tract viruses are detectable even at birth, and these differences predict the susceptibility to acute respiratory tract illness during the first year of life.

Monitoring in vivo changes in lung microstructure with ³He MRI in Sendai virus-infected mice

Recently, a Sendai virus (SeV) model of chronic obstructive lung disease has demonstrated an innate immune response in mouse airways that exhibits similarities to the chronic airway inflammation in human chronic obstructive pulmonary disease (COPD) and asthma, but the effect on distal lung parenchyma has not been investigated. The aim of our study is to image the time course and regional distribution of mouse lung microstructural changes in vivo after SeV infection. (1)H and (3)He diffusion magnetic resonance imaging (MRI) were successfully performed on five groups of C57BL/6J mice. (1)H MR images provided precise anatomical localization and lung volume measurements. (3)He lung morphometry was implemented to image and quantify mouse lung geometric microstructural parameters at different time points after SeV infection. (1)H MR images detected the SeV-induced pulmonary inflammation in vivo; spatially resolved maps of acinar airway radius R, alveolar depth h, and mean linear intercept Lm were generated from (3)He diffusion images. The morphometric parameters R and Lm in the infected group were indistinguishable from PBS-treated mice at day 21, increased slightly at day 49, and were increased with statistical significance at day 77 (p = 0.02). Increases in R and Lm of infected mice imply that there is a modest increase in alveolar duct radius distal to airway inflammation, particularly in the lung periphery, indicating airspace enlargement after virus infection. Our results indicate that (3)He lung morphometry has good sensitivity in quantifying small microstructural changes in the mouse lung and that the Sendai mouse model has the potential to be a valid murine model of COPD.

Alternatively activated macrophages and airway disease

Macrophages are the most abundant immune cell population in normal lung tissue and serve critical roles in innate and adaptive immune responses as well as the development of inflammatory airway disease. Studies in a mouse model of chronic obstructive lung disease and translational studies of humans with asthma and COPD have shown that a special subset of macrophages is required for disease progression. This subset is activated by an alternative pathway that depends on production of IL-4 and IL-13, in contrast to the classic pathway driven by interferon-γ. Recent and unexpected results indicate that alternatively activated macrophages (AAMs) can also become a major source of IL-13 production and, thereby, drive the increased mucus production and airway hyperreactivity that is characteristic of airway disease. Although the normal and abnormal functions of AAMs are still being defined, it is already apparent that markers of this immune cell subset can be useful to guide stratification and treatment of patients with chronic airway diseases. Here, we review basic and clinical research studies that highlight the importance of AAMs in the pathogenesis of asthma, COPD, and other chronic airway diseases.

Molecular heterogeneity in the choroid plexus epithelium: the 22-member γ-protocadherin family is differentially expressed, apically localized, and implicated in CSF regulation

The choroid plexus (CP) epithelium develops from the ependyma that lines the ventricular system, and plays a critical role in the development and function of the brain. In addition to being the primary site of CSF production, the CP maintains the blood-CSF barrier via apical tight junctions between epithelial cells. Here we show that the 22-member γ-protocadherin (γ-Pcdh) family of cell adhesion molecules, which we have implicated previously in synaptogenesis and neuronal survival, is highly expressed by both CP epithelial and ependymal cells, in which γ-Pcdh protein localization is, surprisingly, tightly restricted to the apical membrane. Multi-label immunostaining demonstrates that γ-Pcdhs are excluded from tight junctions, basolateral adherens junctions, and apical cilia tufts. RT-PCR analysis indicates that, as a whole, the CP expresses most members of the Pcdh-γ gene family. Immunostaining using novel monoclonal antibodies specific for single γ-Pcdh proteins shows that individual epithelial cells differ in their apically localized γ-Pcdh repertoire. Restricted mutation of the Pcdh-γ locus in the choroid plexus and ependyma leads to significant reductions in ventricular volume, without obvious disruptions of epithelial apical-basal polarity. Together, these results suggest an unsuspected role for the γ-Pcdhs in CSF production and demonstrate a surprising molecular heterogeneity in the CP epithelium.

Host epithelial-viral interactions as cause and cure for asthma

Research on the pathogenesis of asthma has concentrated on initial stimuli, genetic susceptibilities, adaptive immune responses, and end-organ alterations (particularly in airway mucous cells and smooth muscle) as critical steps leading to disease. Recent evidence indicates that the innate immune cell response to respiratory viruses also contributes to the development of inflammatory airway disease. We further develop this concept by raising the issue that the interaction between host airway epithelial cells and respiratory viruses is another aspect of innate immunity that is also a critical determinant of asthma. We also introduce a rationale for how antiviral performance at the epithelial cell level might be improved to prevent acute infectious illness and chronic inflammatory disease caused by respiratory viruses.

A New Electrospray Aerosol Generator with High Particle Transmission Efficiency

A new single-capillary electrospray (ES) aerosol generator has been developed for monodisperse particle production with maximal transmission efficiency. The new generator consists of both a spray chamber in a point-to-orifice-plate configuration and a charge reduction chamber that can hold up to 4 Nuclespot ionizers (Model P-2042, NRD Inc.). The 2 chambers are partitioned by an orifice plate. To optimize the particle transmission efficiency of the prototype, a systematic study was performed on the generator by varying the system setup and operation. Two key dimensions of the generator setup, the orifice diameter and the distance from the capillary tip to the orifice plate, were varied. Fluorescence analysis was applied to characterize the loss of ES-generated particles at different locations of the prototype. It was found that particle loss in the generator could be reduced by either increasing the orifice diameter or decreasing the distance between the capillary tip and the orifice plate. Increasing either the total radioactivity of the ionizers or the flowrate of the particle carrier gas also further decreased the particle loss in the system. The maximum particle transmission efficiency of 88.0% was obtained with the spray chamber fully opened to the charge reduction chamber, the capillary tip at the same level as the orifice plate, and 4 bipolar ionizers installed.

Epithelial EGF receptor signaling mediates airway hyperreactivity and remodeling in a mouse model of chronic asthma

Increases in the epidermal growth factor receptor (EGFR) have been associated with the severity of airway thickening in chronic asthmatic subjects, and EGFR signaling is induced by asthma-related cytokines and inflammation. The goal of this study was to determine the role of EGFR signaling in a chronic allergic model of asthma and specifically in epithelial cells, which are increasingly recognized as playing an important role in asthma. EGFR activation was assessed in mice treated with intranasal house dust mite (HDM) for 3 wk. EGFR signaling was inhibited in mice treated with HDM for 6 wk, by using either the drug erlotinib or a genetic approach that utilizes transgenic mice expressing a mutant dominant negative epidermal growth factor receptor in the lung epithelium (EGFR-M mice). Airway hyperreactivity (AHR) was assessed by use of a flexiVent system after increasing doses of nebulized methacholine. Airway smooth muscle (ASM) thickening was measured by morphometric analysis. Sensitization to HDM (IgG and IgE), inflammatory cells, and goblet cell changes were also assessed. Increased EGFR activation was detected in HDM-treated mice, including in bronchiolar epithelial cells. In mice exposed to HDM for 6 wk, AHR and ASM thickening were reduced after erlotinib treatment and in EGFR-M mice. Sensitization to HDM and inflammatory cell counts were similar in all groups, except neutrophil counts, which were lower in the EGFR-M mice. Goblet cell metaplasia with HDM treatment was reduced by erlotinib, but not in EGFR-M transgenic mice. This study demonstrates that EGFR signaling, especially in the airway epithelium, plays an important role in mediating AHR and remodeling in a chronic allergic asthma model.

Cutting edge: CD49d+ neutrophils induce FcepsilonRI expression on lung dendritic cells in a mouse model of postviral asthma

The increasing prevalence of atopy and asthma remains unexplained but may be due to infection with respiratory viruses. In support of this hypothesis, we showed that experimental asthma after viral infection in mice depended on type I IFN-driven upregulation of FcεRI on conventional dendritic cells (cDCs) in the lung. In this article, we demonstrate that FcεRI expression on lung cDCs depends on an unexpected activity of a CD49d(+) subset of polymorphonuclear neutrophils (PMNs) that are found in the lungs of wild-type C57BL6 but not mice deficient in type I IFNR. Expression of FcεRI depends in part on a CD11b-dependent interaction between PMNs and cDCs. This study demonstrates a PMN-cDC interaction in the lung that is necessary for the ability of viral infection to induce atopic disease.

Detection of respiratory viruses and the associated chemokine responses in serious acute respiratory illness

BACKGROUND

A specific diagnosis of a lower respiratory viral infection is often difficult despite frequent clinical suspicion. This low diagnostic yield may be improved by use of sensitive detection methods and biomarkers.

METHODS

The prevalence, clinical predictors and inflammatory mediator profile of respiratory viral infection in serious acute respiratory illness were investigated. Sequential bronchoalveolar lavage (BAL) fluids from all patients hospitalised with acute respiratory illness over 12 months (n=283) were tested for the presence of 17 respiratory viruses by multiplex PCR assay and for newly discovered respiratory viruses (bocavirus, WU and KI polyomaviruses) by single-target PCR. BAL samples also underwent conventional testing (direct immunoflorescence and viral culture) for respiratory virus at the clinician's discretion. 27 inflammatory mediators were measured in a subset of the patients (n=64) using a multiplex immunoassay.

RESULTS

39 respiratory viruses were detected in 37 (13.1% of total) patients by molecular testing, including rhinovirus (n=13), influenza virus (n=8), respiratory syncytial virus (n=6), human metapneumovirus (n=3), coronavirus NL63 (n=2), parainfluenza virus (n=2), adenovirus (n=1) and newly discovered viruses (n=4). Molecular methods were 3.8-fold more sensitive than conventional methods. Clinical characteristics alone were insufficient to separate patients with and without respiratory virus. The presence of respiratory virus was associated with increased levels of interferon gamma-inducible protein 10 (IP-10) (p<0.001) and eotaxin-1 (p=0.017) in BAL.

CONCLUSIONS

Respiratory viruses can be found in patients with serious acute respiratory illness by use of PCR assays more frequently than previously appreciated. IP-10 may be a useful biomarker for respiratory viral infection.