EDITORIALS contractility by 50% in wild-type CFTR1 pigs, but this effect was not seen in airway smooth muscle from CFTR knockout pigs or wild-type CFTR1 mice, which served as an important negative control, as murine CFTR is not responsive to ivacaftor. What are the implications of these observations? First, the results may help explain the rapid and profound positive effect of ivacaftor on airway obstruction in patients with CF with gating mutations. Dramatic and sustained improvements in FEV1 have been observed in as few as 3 days after the initiation of ivacaftor therapy in patients with CF with the G551D CFTR gating mutation, suggesting that some of this benefit may result from reduced airway tone after restored CFTR function (12). Second, the effect of ivacaftor on CFTR function in airway smooth muscle raises the question of whether CFTR potentiation may have benefits in other reversible airway disorders, such as asthma and chronic obstructive lung disease. Although it is premature to advocate for the use of ivacaftor or other potentiators in these non-CF diseases based on the results of this study, the findings do provide tools and testable hypotheses to better understand whether CFTR is a relevant therapeutic target in non-CF airway disorders. The results also identify a potentially rapid biomarker of CFTR modulator bioactivity, examining airway reactivity in the context of CFTR modulator development. The availability of robust airway CFTR biomarkers has been a limitation to early-phase clinical trial conduct of CFTR modulators, particularly in patients with mild or preserved lung function. In addition, identifying novel biomarkers that are rapid readouts of CFTR activity will become crucial as additional CFTR modulators enter clinical trials, as physicians and patients will be reluctant to perform placebo-controlled trials that have prolonged periods off of efficacious CFTR modulator regimens. Finally, the results of this study help expand our understanding of CFTR in lung physiology. CFTR has been shown to be expressed in several nonepithelial cell types, but exactly how CFTR expression in nonepithelial cells contributes to disease has been more difficult to demonstrate. The results reported by Cook and colleagues provide provocative clues to CFTR function and dysfunction outside of epithelial compartments and relationships to established lung disease manifestations. n Author disclosures are available with the text of this article at www.atsjournals.org. John P. Clancy, M.D. Division of Pulmonary Medicine and

Department of Pediatrics Cincinnati Children’s Hospital Medical Center Cincinnati, Ohio

ORCID ID: 0000-0002-9695-097X (J.P.C.).

References 1. Rowe SM, Miller S, Sorscher EJ. Cystic fibrosis. N Engl J Med 2005; 352:1992–2001. 2. Kent BD, Lane SJ, van Beek EJ, Dodd JD, Costello RW, Tiddens HA. Asthma and cystic fibrosis: a tangled web. Pediatr Pulmonol 2014; 49:205–213. 3. Balfour-Lynn IM, Elborn JS. “CF asthma”: what is it and what do we do about it? Thorax 2002;57:742–748. 4. Cook DP, Rector MV, Bouzek DC, Michalski AS, Gansemer ND, Reznikov LR, Li X, Stroik MR, Ostedgaard LS, Abou Alaiwa MH, et al. Cystic fibrosis transmembrane conductance regulator in sarcoplasmic reticulum of airway smooth muscle: implications for airway contractility. Am J Respir Crit Care Med 2016;193:417–426. 5. Stoltz DA, Meyerholz DK, Pezzulo AA, Ramachandran S, Rogan MP, Davis GJ, Hanfland RA, Wohlford-Lenane C, Dohrn CL, Bartlett JA, et al. Cystic fibrosis pigs develop lung disease and exhibit defective bacterial eradication at birth. Sci Transl Med 2010;2:29ra31. 6. Hoegger MJ, Fischer AJ, McMenimen JD, Ostedgaard LS, Tucker AJ, Awadalla MA, Moninger TO, Michalski AS, Hoffman EA, Zabner J, et al. Impaired mucus detachment disrupts mucociliary transport in a piglet model of cystic fibrosis. Science 2014;345:818–822. 7. Stoltz DA, Meyerholz DK, Welsh MJ. Origins of cystic fibrosis lung disease. N Engl J Med 2015;372:351–362. 8. Meyerholz DK, Stoltz DA, Namati E, Ramachandran S, Pezzulo AA, Smith AR, Rector MV, Suter MJ, Kao S, McLennan G, et al. Loss of cystic fibrosis transmembrane conductance regulator function produces abnormalities in tracheal development in neonatal pigs and young children. Am J Respir Crit Care Med 2010;182:1251–1261. 9. Van Goor F, Hadida S, Grootenhuis PD, Burton B, Cao D, Neuberger T, Turnbull A, Singh A, Joubran J, Hazlewood A, et al. Rescue of CF airway epithelial cell function in vitro by a CFTR potentiator, VX-770. Proc Natl Acad Sci USA 2009;106:18825–18830. 10. Ramsey BW, Davies J, McElvaney NG, Tullis E, Bell SC, Dˇrev´ınek P, Griese M, McKone EF, Wainwright CE, Konstan MW, et al.; VX08770-102 Study Group. A CFTR potentiator in patients with cystic fibrosis and the G551D mutation. N Engl J Med 2011;365: 1663–1672. 11. Wainwright CE, Elborn JS, Ramsey BW, Marigowda G, Huang X, Cipolli M, Colombo C, Davies JC, De Boeck K, Flume PA, et al.; TRAFFIC Study Group; TRANSPORT Study Group. Lumacaftor-ivacaftor in patients with cystic fibrosis homozygous for Phe508del CFTR. N Engl J Med 2015;373: 220–231. 12. Accurso FJ, Rowe SM, Clancy JP, Boyle MP, Dunitz JM, Durie PR, Sagel SD, Hornick DB, Konstan MW, Donaldson SH, et al. Effect of VX-770 in persons with cystic fibrosis and the G551D-CFTR mutation. N Engl J Med 2010;363:1991–2003.

Copyright © 2016 by the American Thoracic Society

Seeking an Accurate, Point-of-Contact Diagnostic Test for Bacterial Pneumonia In settings in which the availability of antibiotics and radiological facilities are limited, rapid and accurate identification of bacterial pneumonia has the potential to reduce the unnecessary use of antibiotics and save children’s lives. In resource-poor settings, the

Editorials

most widely used method for deciding which children with acute respiratory symptoms should receive early antibiotic therapy is the World Health Organization’s Pneumonia Diagnostic Criteria. This combination of surrogate clinical signs allows field workers to

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EDITORIALS Table 1. Wish List for Infection Diagnostics in the 2015 United Kingdom Review on Antimicrobial Resistance (5) Test

Comment

Rapid diagnostics to be used at home to indicate bacteria or viral infection Biomarker panels to distinguish whether patients admitted via accident and emergency for pneumonia have bacterial infections or not A bedside test that reliably excludes any infection A definitive test to confirm a viral infection Rapid tests to rule out bacteria or fungi in blood cultures Rapid categorization test for pathogens and resistance New tests that make use of technologies and platforms that are already being adopted widely in diagnostic laboratories Fast and frugal heuristics

rapidly treat the vast majority of cases of bacterial pneumonia, but these criteria result in many children with viral infections receiving unnecessary antibiotics. Where bacterial pneumonia is associated with high mortality, this is a reasonable compromise. However, the incidence of community-acquired pneumonia in children in resource-poor countries is falling. For example, for 2010, pneumonia incidence in these countries was 0.22 episodes per child-year, with 12% of cases progressing to severe episodes, for a decrease of more than 25% from the previous decade (1). As mortality falls, the limitations of the World Health Organization’s criteria become more important. For example, a recent systematic review found that the diagnostic performance of the signs approved by the World Health Organization (e.g., age-related fast breathing and lower chest wall indrawing) is poor (2). The review concluded that any revised decision tree based on symptoms alone is unlikely to result in a significant increase in diagnostic precision (2). In this issue of the Journal, the article by Valim and colleagues (pp. 448–459) is therefore a welcome attempt to address this important diagnostic gap (3). The researchers assessed the capacity of a wide range of plasma proteins to discriminate among bacterial, viral, and malarial infection in children presenting with pneumonia to a district hospital in Mozambique, where etiology was identified by bacterial microscopy and culture, viral polymerase chain reaction, chest radiograph, and white cell count. They found that a combination of haptoglobin, tumor necrosis factor receptor 2 or IL-19, and tissue inhibitor of metalloproteinases-1 showed promising 96% sensitivity and 86% specificity for bacterial pneumonia diagnosis. The strengths of this study are the use of an exploratory data set and a validation data set, recruitment in an appropriate resource-poor population, inclusion of healthy controls, and the potential for translation into a cheap diagnostic test. But more work remains to be done. For example, diagnostic specificity needs to be improved, and generalizability needs to be assessed in a separate population. Furthermore, the Gordian knot of what should be used as the gold standard for new point of care tests remains firmly tied. Indeed, a recent Lancet editorial concluded that there is no gold standard diagnostic test available for bacterial pneumonia and that 354

Reduce visits to the doctor, and thus reduce healthcare resource consumption Reduce healthcare resource consumption Reduce the empirical use of antimicrobials Reduce cost of looking for the cause of viral infections, the majority of which cannot be detected by existing technology Reducing time to conclude that a negative result is real and offering the chance to reduce the length of unnecessary antibiotic treatment Easier in samples from sterile sites than in samples from sites with potential pathogens and normal bacterial flora Easier to encourage wide adoption of such tests faster than those that rely on novel technologies Rules of thumb that integrate a small number of immediately available data sources to support a decision that is both satisfactory and sufficient

radiological diagnosis is, at best, silver or bronze (4). But these limitations are not insurmountable, and the study of Valim and colleagues (3) should be seen as an important first step in the development of a point-of-care test based on plasma proteins. Do these results have any relevance to diagnosis in resourcerich settings? It may be argued that current treatment based on clinical diagnosis and chest radiograph delivers appropriate therapy for many individuals. Unfortunately, similar to the World Health Organization criteria, current diagnostic pathways in resource-rich countries also result in unnecessary use of antibiotics for viral infections and the unnecessary use of broad-spectrum antibiotics for bacterial infections (5). For example, it is estimated that of 40 million people in the United States who are given antibiotics for respiratory indications, 27 million prescriptions are unnecessary (5). Because overprescribing of antibiotics is a major driver of increased prevalence of antimicrobial resistance, there is an urgent need in both resource-poor and resource-rich settings for more research into rapid diagnostic tools for bacterial pneumonia. The 2015 UK Government/Welcome Trust Review of Antimicrobial Resistance (5) provides a “wish list” for infection diagnostics (Table 1). It remains to be seen whether a combination of plasma proteins will make these wishes come true. n Author disclosures are available with the text of this article at www.atsjournals.org. Jonathan Grigg, M.D. Barts and the London School of Medicine and Dentistry Queen Mary University of London London, United Kingdom

ORCID ID: 0000-0003-3109-6028 (J.G.).

References 1. Rudan I, O’Brien KL, Nair H, Liu L, Theodoratou E, Qazi S, Lukšic´ I, Fischer Walker CL, Black RE, Campbell H. Child Health Epidemiology Reference Group (CHERG). Epidemiology and etiology of childhood pneumonia in 2010: estimates of incidence, severe morbidity,

American Journal of Respiratory and Critical Care Medicine Volume 193 Number 4 | February 15 2016

EDITORIALS mortality, underlying risk factors and causative pathogens for 192 countries. J Glob Health 2013;3:010401. 2. Rambaud-Althaus C, Althaus F, Genton B, D’Acremont V. Clinical features for diagnosis of pneumonia in children younger than 5 years: a systematic review and meta-analysis. Lancet Infect Dis 2015;15:439–450. 3. Valim C, Ahmad R, Lanaspa M, Tan Y, Acacio ´ S, Gillette MA, Almendinger KD, Milner DA Jr, Madrid L, Pelle´ K, et al. Responses to bacteria, virus, and malaria distinguish the etiology of pediatric clinical pneumonia. Am J Respir Crit Care Med 2016;193:448–459.

4. Qazi S, Were W. Improving diagnosis of childhood pneumonia. Lancet Infect Dis 2015;15:372–373. 5. O’Neill J. Rapid diagnostic: stopping unnecessary use of antibiotics. Review on antimicrobial resistance. [accessed 2015 Nov 3]. Available from: http://amr-review.org/sites/default/files/PaperRapid-Diagnostics-Stopping-Unnecessary-Prescription-LowRes.pdf

Copyright © 2016 by the American Thoracic Society

Mucking around in the Genome: MUC5B in Idiopathic Pulmonary Fibrosis Ever since a strong association was identified between a MUC5B gene promoter variant and idiopathic pulmonary fibrosis (IPF) (1), and subsequently validated in eight independent cohorts (2), there has been a major scientific push to explore the biological meaning of the MUC5B gene and protein in IPF. The dominant questions remain whether and how this mucin product renders individuals susceptible to IPF and (perhaps antithetically) why it is associated with a better prognosis. Before we assemble some new pieces of this equally large and exciting puzzle, including two research letters published in this issue of the Journal by Conti and colleagues (pp. 462–464) and Nakano and colleagues (pp. 464–466), it is important to remind ourselves that association between genetic variants and disease is not the same as a causation, even when the association is as solid and reproducible as the one between MUC5B variants and IPF (2, 3). The human genome is, after all, composed of 3.2 billion pairs of nucleotides, of which approximately 4 million nucleotides contain polymorphisms in a given individual. Of the 4 million, only z13,000 of them are located within exomes (the protein-coding portion of the genome) and exist as singlenucleotide polymorphisms (SNPs), and less than 5% are predicted to affect protein function. This means that each exome in an individual could theoretically carry up to one thousand SNPs that are potentially harmful and be of pathogenic relevance. It seems intuitive that if a genetic variant is more common in the general population, it is less likely to have clinical and/or biological significance (other than perhaps increasing disease susceptibility); in contrast, the less common the variant, the more likely its clinical significance. The interested reader is referred to an excellent review article on challenges interpreting medical applications of genome-wide association study discoveries (4). Now where does the association of MUC5B with IPF fit into this? In the initial report about the association between MUC5B and IPF, the minor allele of the SNP rs35705950 in the MUC5B promoter was present in 34 and 38% of subjects with familial and sporadic IPF, respectively, compared with only 9% among controls (1). This allele, when homozygous, conferred impressive odds of disease of 20.8 for familial interstitial pneumonia and 21.8 for IPF. The MUC5B promoter variant results in enhanced MUC5B protein expression, in both subjects with IPF as well as unaffected individuals with at least one copy of the minor allele (1). Although MUC5B was found in microscopic honeycomb regions of IPF lungs, it is also found in bronchi and proximal Editorials

bronchioles in both IPF and control subjects (1, 5). This finding suggests that in the absence of MUC5B genetic variants, other environmental and/or genetic factors likely cause MUC5B secretion into the airways. Somewhat antithetically, the MUC5B genetic variant is also associated with slower progression and better survival of patients with IPF (6), although subjects may be more symptomatic with cough (7). In this issue of the journal, two research letters now take us a step further in exploring the implications of MUC5B variants in human lungs. In the first, Conti and colleagues describe the expression of MUC5B and MUC5AC in distal airways and honeycomb lesions (2). Evaluating a well-characterized set of surgical lung biopsies from 23 patients with IPF, 18 with idiopathic nonspecific interstitial pneumonia (NSIP), 15 with NSIP associated with scleroderma, and normal lung tissue from smoker and nonsmoker controls, the authors characterized expression patterns. In IPF distal airways, the proportion of MUC5B1 cells was more than twofold higher compared with control, idiopathic, and scleroderma-associated NSIP. Importantly, the proportion of MUC5B1 cells in honeycomb cysts was similar to control airways, suggesting that epithelial makeup of honeycomb cysts may be similar to normal airways. MUC5B expression was similar among controls, scleroderma NSIP, and idiopathic NSIP In the distal airways. In contrast, the proportion of MUC5AC1 epithelial cells in IPF distal airways was similar to controls, whereas both idiopathic and scleroderma NSIP distal airways had markedly fewer numbers of MUC5AC-positive cells. These novel observations implicate the distal airways as the predominant source of MUC5B expression in IPF. This is an interesting report that seems to confirm the prior observations of Seibold and colleagues (1). Perhaps the biggest limitation of the work by Conti and colleagues is the absence of correlation between MUC5B expression and the MUC5B allele status. Thus, although their observations suggest dysregulation in the production and homeostasis of airway mucins and provide further evidence of the association between MUC5B and IPF, the study lacks definitive evidence that the MUC5B minor allele is responsible for the difference in mucin expression. The second research letter by Nakano and colleagues (3) seemingly picks up where Conti and colleagues leave off. In this work, the authors focus their efforts on the MUC5B rs35705950 SNP and show, for the first time, that the minor T allele enhances MUC5B expression in IPF lungs. In a series of elegant 355