Anthony J. Fischer

Impaired Mucus Detachment Disrupts Mucociliary Transport in a Piglet Model of Cystic Fibrosis

A breathtaking tale of sticky mucus Patients with cystic fibrosis have difficulty breathing because their airways are clogged with thick mucus. Does this mucus accumulate because there is a defect in the way it is produced? Or does it accumulate because of other disease features, such as dehydration or airway wall remodeling? Distinguishing between these possibilities is important for future drug development. In a study of piglets with cystic fibrosis, Hoegger et al. identify mucus production as the primary defect (see the Perspective by Wine). The airway glands of the piglets synthesized strands of mucus normally, but the strands were never released and stayed tethered to the gland ducts. Science, this issue p. 818; see also p. 730 Lung disease in pigs with cystic fibrosis is caused by aberrant tethering of mucus to the airway glands that produce it. [Also see Perspective by Wine] Lung disease in people with cystic fibrosis (CF) is initiated by defective host defense that predisposes airways to bacterial infection. Advanced CF is characterized by a deficit in mucociliary transport (MCT), a process that traps and propels bacteria out of the lungs, but whether this deficit occurs first or is secondary to airway remodeling has been unclear. To assess MCT, we tracked movement of radiodense microdisks in airways of newborn piglets with CF. Cholinergic stimulation, which elicits mucus secretion, substantially reduced microdisk movement. Impaired MCT was not due to periciliary liquid depletion; rather, CF submucosal glands secreted mucus strands that remained tethered to gland ducts. Inhibiting anion secretion in non-CF airways replicated CF abnormalities. Thus, impaired MCT is a primary defect in CF, suggesting that submucosal glands and tethered mucus may be targets for early CF treatment.

Innate Immune Functions of the Airway Epithelium

The epithelium of the respiratory tract forms a large surface area that maintains intimate contact with the environment. Through the act of breathing, this mucosal surface encounters an array of pathogens and toxic particulates. In response to these challenges many strategies have evolved to protect the host. These include the barrier functions of the epithelium, cough, mucociliary clearance, resident professional phagocytes, and the secretion of a number of proteins and peptides with host defense functions. Thus, the surface and submucosal gland epithelium of the conducting airways is a constitutive primary participant in innate immunity. In addition, this tissue may serve the function of a secondary amplifier of innate immune responses following neurohumoral input, stimulation with cytokines from cells such as alveolar macrophages, or engagement of pattern recognition receptors. Here, we provide an overview of the airway epitheliums role in pulmonary innate immunity, especially in the context of bacterial and viral infections, emphasizing findings from human cells and selected animal models. We also provide examples of human disease states caused by impaired epithelial defenses in the lung.

Assessing mucociliary transport of single particles in vivo shows variable speed and preference for the ventral trachea in newborn pigs

Significance Mucociliary transport (MCT) defends lungs by removing particulates, and defective MCT is hypothesized to contribute to the onset of lung diseases such as asthma, chronic bronchitis, and cystic fibrosis. However, testing those hypotheses has been limited by current MCT assays and mouse models of human disease. We developed an in vivo MCT assay in newborn pigs, which share physiological and anatomical features with humans. The X-ray–computed tomographic-based method provided high spatial and temporal resolution. We discovered that particles preferentially travel up the ventral airway surface. We also discovered substantial heterogeneity in rates of individual particle movement, indicating that MCT does not likely involve homogeneous mucus blankets. The granularity of the data may aid understanding of MCT and disease pathogenesis. Mucociliary transport (MCT) is an innate defense mechanism that removes particulates, noxious material, and microorganisms from the lung. Several airway diseases exhibit abnormal MCT, including asthma, chronic bronchitis, and cystic fibrosis. However, it remains uncertain whether MCT abnormalities contribute to the genesis of disease or whether they are secondary manifestations that may fuel disease progression. Limitations of current MCT assays and of current animal models of human disease have hindered progress in addressing these questions. Therefore, we developed an in vivo assay of MCT, and here we describe its use in newborn wild-type pigs. We studied pigs because they share many physiological, biochemical, and anatomical features with humans and can model several human diseases. We used X-ray multidetector-row–computed tomography to track movement of individual particles in the large airways of newborn pigs. Multidetector-row–computed tomography imaging provided high spatial and temporal resolution and registration of particle position to airway anatomy. We discovered that cilia orientation directs particles to the ventral tracheal surface. We also observed substantial heterogeneity in the rate of individual particle movement, and we speculate that variations in mucus properties may be responsible. The increased granularity of MCT data provided by this assay may provide an opportunity to better understand host defense mechanisms and the pathogenesis of airway disease.

Enhancement of Respiratory Mucosal Antiviral Defenses by the Oxidation of Iodide

Recent reports postulate that the dual oxidase (DUOX) proteins function as part of a multicomponent oxidative pathway used by the respiratory mucosa to kill bacteria. The other components include epithelial ion transporters, which mediate the secretion of the oxidizable anion thiocyanate (SCN(-)) into airway surface liquid, and lactoperoxidase (LPO), which catalyzes the H(2)O(2)-dependent oxidation of the pseudohalide SCN(-) to yield the antimicrobial molecule hypothiocyanite (OSCN(-)). We hypothesized that this oxidative host defense system is also active against respiratory viruses. We evaluated the activity of oxidized LPO substrates against encapsidated and enveloped viruses. When tested for antiviral properties, the LPO-dependent production of OSCN(-) did not inactivate adenovirus or respiratory syncytial virus (RSV). However, substituting SCN(-) with the alternative LPO substrate iodide (I(-)) resulted in a marked reduction of both adenovirus transduction and RSV titer. Importantly, well-differentiated primary airway epithelia generated sufficient H(2)O(2) to inactivate adenovirus or RSV when LPO and I(-) were supplied. The administration of a single dose of 130 mg of oral potassium iodide to human subjects increased serum I(-) concentrations, and resulted in the accumulation of I(-) in upper airway secretions. These results suggest that the LPO/I(-)/H(2)O(2) system can contribute to airway antiviral defenses. Furthermore, the delivery of I(-) to the airway mucosa may augment innate antiviral immunity.

Tracheomalacia is associated with lower FEV1 and Pseudomonas acquisition in children with CF

Tracheomalacia (TM) occurs in approximately 1 in 2,100 children. Because the trachea develops abnormally in animal models of cystic fibrosis (CF), we hypothesized this may also occur in children with CF, increasing their risk of TM.

Differential diagnosis of chronic cough in children.

A cough is considered chronic when it lasts >4 weeks. Chronic cough can be from a variety of causes. This article provides a structured approach to evaluating the child with chronic cough. Beginning with the disturbing cough that is absent once asleep, consistent with the habit cough syndrome, the diagnostic criteria for 10 causes of chronic cough are discussed. Using a structured approach to the differential diagnosis, common and uncommon causes can be identified. Well-established causes of chronic cough, such as asthma, are likely to be well known to the reader, whereas more recently identified etiologies, such as protracted bacterial bronchitis, are presented in more detail. The differential value of flexible and rigid bronchoscopy and bronchoalveolar lavage for aiding in the differential diagnosis is included for those entities where their use is essential.

Differential Gene Expression in Human Conducting Airway Surface Epithelia and Submucosal Glands

Human conducting airways contain two anatomically distinct epithelial cell compartments: surface epithelium and submucosal glands (SMG). Surface epithelial cells interface directly with the environment and function in pathogen detection, fluid and electrolyte transport, and mucus elevation. SMG secrete antimicrobial molecules and most of the airway surface fluid. Despite the unique functional roles of surface epithelia and SMG, little is known about the differences in gene expression and cellular metabolism that orchestrate the specialized functions of these epithelial compartments. To approach this problem, we performed large-scale transcript profiling using epithelial cell samples obtained by laser capture microdissection (LCM) of human bronchus specimens. We found that SMG expressed high levels of many transcripts encoding known or putative innate immune factors, including lactoferrin, zinc alpha-2 glycoprotein, and proline-rich protein 4. By contrast, surface epithelial cells expressed high levels of genes involved in basic nutrient catabolism, xenobiotic clearance, and ciliated structure assembly. Selected confirmation of differentially expressed genes in surface and SMG epithelia demonstrated the predictive power of this approach in identifying genes with localized tissue expression. To characterize metabolic differences between surface epithelial cells and SMG, immunostaining for a mitochondrial marker (isocitrate dehydrogenase) was performed. Because greater staining was observed in the surface compartment, we predict that these cells use significantly more energy than SMG cells. This study illustrates the power of LCM in defining the roles of specific anatomic features in airway biology and may be useful in examining how disease states alter transcriptional programs in the conducting airways.

Acute administration of ivacaftor to people with cystic fibrosis and a G551D-CFTR mutation reveals smooth muscle abnormalities

BACKGROUND Airflow obstruction is common in cystic fibrosis (CF), yet the underlying pathogenesis remains incompletely understood. People with CF often exhibit airway hyperresponsiveness, CF transmembrane conductance regulator (CFTR) is present in airway smooth muscle (ASM), and ASM from newborn CF pigs has increased contractile tone, suggesting that loss of CFTR causes a primary defect in ASM function. We hypothesized that restoring CFTR activity would decrease smooth muscle tone in people with CF. METHODS To increase or potentiate CFTR function, we administered ivacaftor to 12 adults with CF with the G551D-CFTR mutation; ivacaftor stimulates G551D-CFTR function. We studied people before and immediately after initiation of ivacaftor (48 hours) to minimize secondary consequences of CFTR restoration. We tested smooth muscle function by investigating spirometry, airway distensibility, and vascular tone. RESULTS Ivacaftor rapidly restored CFTR function, indicated by reduced sweat chloride concentration. Airflow obstruction and air trapping also improved. Airway distensibility increased in airways less than 4.5 mm but not in larger-sized airways. To assess smooth muscle function in a tissue outside the lung, we measured vascular pulse wave velocity (PWV) and augmentation index, which both decreased following CFTR potentiation. Finally, change in distensibility of <4.5-mm airways correlated with changes in PWV. CONCLUSIONS Acute CFTR potentiation provided a unique opportunity to investigate CFTR-dependent mechanisms of CF pathogenesis. The rapid effects of ivacaftor on airway distensibility and vascular tone suggest that CFTR dysfunction may directly cause increased smooth muscle tone in people with CF and that ivacaftor may relax smooth muscle. FUNDING This work was funded in part from an unrestricted grant from the Vertex Investigator-Initiated Studies Program.

Sonographic evidence of abnormal tracheal cartilage ring structure in cystic fibrosis.

Tracheal cartilage ring structural abnormalities have been reported in cystic fibrosis (CF) mice and pigs. Whether similar findings are present in humans with CF is unknown. We hypothesized that tracheal cartilage ring shape and size would be different in people with CF.

Bronchial Compression and Tracheosophageal Fistula Secondary to Prolonged Esophageal Foreign Body

Introduction: Foreign body ingestion is a common pediatric problem that can have a delayed presentation, as presented herein. Case Report: We present the case of a 15-year-old female who developed bronchial compression and an acquired tracheoesophageal fistula secondary to a longstanding esophageal foreign body. Discussion: There are several challenges in diagnosis and management of this unusual situation. We review the literature regarding prolonged retention of foreign bodies and the challenges in diagnosis in the developmentally disabled child. Conclusion: Providers must have a high suspicion for foreign bodies in the case of unusual symptoms present in children with neurodevelopmental delays.