The study of. Hung and colleagues takes us one step further in our quest to iden- .... cipal targets for RSV infection in human airways are apical ciliated epithelial ...
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of novel imaging and genetic tools has increased our ability to determine the cellular origin and functional contribution of the heterogenous group of cells that populate fibrotic lesions. The study of Hung and colleagues takes us one step further in our quest to identify lung stromal cell progenitors; these new findings, taken together with our collective knowledge of other mesenchymal cells, can help us rapidly learn more of the role of pericytes in pulmonary fibrosis, perhaps identifying novel therapeutic targets. Author disclosures are available with the text of this article at www.atsjournals.org.
Ivan O. Rosas, M.D. Division of Pulmonary and Critical Care Brigham and Women’s Hospital Boston Massachusetts and Harvard Medical School Boston Massachusetts Robert M. Kottman, M.D. Patricia J. Sime, M.D. Pulmonary and Critical Care Division University of Rochester Medical Center Rochester, New York References 1. Kriz W, Kaissling B, Le Hir M. Epithelial-mesenchymal transition (EMT) in kidney fibrosis: fact or fantasy? J Clin Invest 2011;121:468–474. 2. Tanjore H, Xu XC, Polosukhin VV, Degryse AL, Li B, Han W, Sherrill TP, Plieth D, Neilson EG, Blackwell TS, et al. Contribution of epithelial-derived fibroblasts to bleomycin-induced lung fibrosis. Am J Respir Crit Care Med 2009;180:657–665. 3. Kim KK, Kugler MC, Wolters PJ, Robillard L, Galvez MG, Brumwell AN, Sheppard D, Chapman HA. Alveolar epithelial cell mesenchymal transition develops in vivo during pulmonary fibrosis and is regulated by the extracellular matrix. Proc Natl Acad Sci USA 2006;103:13180–13185. 4. Rock JR, Barkauskas CE, Cronce MJ, Xue Y, Harris JR, Liang J, Noble PW, Hogan BL. Multiple stromal populations contribute to pulmonary fibrosis without evidence for epithelial to mesenchymal transition. Proc Natl Acad Sci USA 2011;108:E1475–E1483. 5. Chapman HA, Li X, Alexander JP, Brumwell A, Lorizio W, Tan K, Sonnenberg A, Wei Y, Vu TH. Integrin a6b4 identifies an adult distal lung epithelial population with regenerative potential in mice. J Clin Invest 2011;121:2855–2862. 6. Hashimoto N, Jin H, Liu T, Chensue SW, Phan SH. Bone marrow-derived progenitor cells in pulmonary fibrosis. J Clin Invest 2004;113:243–252.
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7. Andersson-Sjöland A, de Alba CG, Nihlberg K, Becerril C, Ramírez R, Pardo A, Westergren-Thorsson G, Selman M. Fibrocytes are a potential source of lung fibroblasts in idiopathic pulmonary fibrosis. Int J Biochem Cell Biol 2008;40:2129–2140. 8. Phillips RJ, Burdick MD, Hong K, Lutz MA, Murray LA, Xue YY, Belperio JA, Keane MP, Strieter RM. Circulating fibrocytes traffic to the lungs in response to CXCL12 and mediate fibrosis. J Clin Invest 2004;114:438–446. 9. Moeller A, Gilpin SE, Ask K, Cox G, Cook D, Gauldie J, Margetts PJ, Farkas L, Dobranowski J, Boylan C, et al. Circulating fibrocytes are an indicator of poor prognosis in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2009;179:588–594. 10. Hung C, Linn G, Chow Y-H, Kobayashi A, Mittelsteadt K, Altemeier WA, Gharib SA, Schnapp LM, Duffield JS. Role of lung pericytes and resident fibroblasts in the pathogenesis of pulmonary fibrosis. Am J Respir Crit Care Med 2013;188:820–830. 11. Campanholle G, Ligresti G, Gharib SA, Duffield JS. Cellular mechanisms of tissue fibrosis. 3. Novel mechanisms of kidney fibrosis. Am J Physiol Cell Physiol 2013;304:C591–C603. 12. Rajkumar VS, Howell K, Csiszar K, Denton CP, Black CM, Abraham DJ. Shared expression of phenotypic markers in systemic sclerosis indicates a convergence of pericytes and fibroblasts to a myofibroblast lineage in fibrosis. Arthritis Res Ther 2005;7:R1113–R1123. 13. Göritz C, Dias DO, Tomilin N, Barbacid M, Shupliakov O, Frisén J. A pericyte origin of spinal cord scar tissue. Science 2011;333:238– 242. 14. Katare R, Riu F, Mitchell K, Gubernator M, Campagnolo P, Cui Y, Fortunato O, Avolio E, Cesselli D, Beltrami AP, et al. Transplantation of human pericyte progenitor cells improves the repair of infarcted heart through activation of an angiogenic program involving microRNA-132. Circ Res 2011;109:894–906. 15. Liu S, Agalliu D, Yu C, Fisher M. The role of pericytes in blood-brain barrier function and stroke. Curr Pharm Des 2012;18:3653–3662. 16. Phipps RP, Penney DP, Keng P, Quill H, Paxhia A, Derdak S, Felch ME. Characterization of two major populations of lung fibroblasts: distinguishing morphology and discordant display of Thy 1 and class II MHC. Am J Respir Cell Mol Biol 1989;1:65–74. 17. Humphreys BD, Lin SL, Kobayashi A, Hudson TE, Nowlin BT, Bonventre JV, Valerius MT, McMahon AP, Duffield JS. Fate tracing reveals the pericyte and not epithelial origin of myofibroblasts in kidney fibrosis. Am J Pathol 2010;176:85–97. 18. Lebleu VS, Taduri G, O’Connell J, Teng Y, Cooke VG, Woda C, Sugimoto H, Kalluri R. Origin and function of myofibroblasts in kidney fibrosis. Nat Med 2013;19:1047–1053. Copyright ª 2013 by the American Thoracic Society DOI: 10.1164/rccm.201308-1494ED
Modeling Respiratory Syncytial Virus Cytopathogenesis in the Human Airway Respiratory syncytial virus (RSV) is a worldwide cause of respiratory tract infections in young children, the elderly, and immune suppressed with hospitalizations from bronchiolitis around 30% and intensive care admission for ventilatory assistance approximately 2% (1–3). Despite our increasing understanding of RSV disease in humans, the mechanisms underlying disease remain rudimentary because most findings have been limited to animal models and continuous cell lines (4, 5). Although these studies have provided a number of important insights into RSV–host interactions, animal models, with the exception of chimpanzees, are semipermissive for RSV infection and do not reproduce the range of pathologies described in RSV-infected humans (6). Continuous cell lines, such as HEp-2 and A549 cells, have been used extensively to study RSV–host interactions; however, they inadequately reveal the complexities of RSV infection and the host cell response in the human respiratory tract. Therefore, the need for
models of RSV infection that elucidate RSV–host interactions is compelling. In this regard, the advent of technology to culture primary human airway epithelial cells and differentiate these cells into physiologically authentic pseudostratified airway epithelial cultures has provided a path forward. RSV is a descending infection that commences in the upper respiratory tract and progresses to the lower respiratory tract. The principal targets for RSV infection in human airways are apical ciliated epithelial cells (7–10). However, there is very little information about the cytopathogenesis of RSV in the nasal tract (8). There are a number of groups now exploiting fully differentiated primary normal human bronchial epithelial cells to study RSV–host interaction as these cells emulate aspects of airway epithelium morphology and physiology (11). In an earlier study by Villenave and colleagues, the authors described a model of RSV infection based
Editorials
on well-differentiated primary pediatric bronchial epithelial cells (WD-PBECs) that reproduced several hallmarks of RSV infection in infant lungs (9). In this issue of the Journal, Guo-Parke and colleagues of the same group (pp. 842–851) extend their earlier findings to describe a new model of RSV infection based on welldifferentiated primary pediatric nasal epithelial cells (WD-PNECs), and, importantly, compare WD-PNEC responses in parallel with those of WD-PBECs derived from the same subjects to explore RSV cytopathogenesis in upper and lower respiratory tract epithelia (12). These studies are seminal, as they show that RSV-infected WD-PNEC cells replicate the hallmarks of RSV cytopathogenesis evident in WD-PBEC cells derived from the same subjects, and, importantly, aspects of RSV pathogenesis in infants. The relative ease of access to infant nasal epithelial cells paves the path forward to more robust studies of RSV pathogenesis in human airway epithelium derived from infants, and to assessing the therapeutic potential of pharmaceutical intervention against RSV in a physiologically authentic culture system. Several discussion points emerge from the principal findings of the study by Guo-Parke and colleagues (12), particularly as there was no obvious cytopathogenesis in either WD-PNEC or WD-PBEC cultures after RSV infection. This is pertinent as grossly damaged airway epithelium interspersed with intact RSV antigen–positive epithelium has been reported in several studies from pediatric airway tissues (7, 10, 13). RSV infection was shown to be localized to apical ciliated epithelial cells, but there was no detectable infection of goblet cells, findings consistent with previous publications and histology studies on lung tissues from infants infected with RSV (7, 9, 10, 14). Also, not all ciliated cells were infected with RSV, as there was evidence of noncontiguous or clumps of infected cells, a finding consistent with RSV infection in the lungs of infants (7, 10, 15). Together, these findings indicate that RSV infection is unlikely to be directly responsible for the destruction of airway epithelium in vivo. The host response to RSV infection in both WD-PNECs and WD-PBECs was indicated through chemokine expression of IL-6, chemokine (C-X-C motif) ligand (CXCL) 8, CXCL10, CXCL11, CCL5, and TNF-related apoptosis-inducing ligand (TRAIL) (12). These findings were also consistent with chemokine secretions in nasal aspirates and bronchoalveolar lavages from infants hospitalized with RSV infection (15). Interestingly, type III IFNs, in particular IL-29, were secreted from either WD-PNEC or WD-PBEC cultures after RSV infection, whereas there was no detectable type I IFN expression. This finding has implications for the purported role of RSV nonstructural (NS) protein governance of type I IFNs (IFNa/ IFNb) to facilitate RSV replication (16), but is consistent with previous publications reporting a predominance of type III IFNs after infection of primary epithelial cell cultures with RSV or influenza virus (8, 11, 17, 18). These findings suggest that type III, rather than type I, IFNs are the principal antiviral protagonists against RSV and influenza virus expressed during infection of airway epithelium. In conclusion, the recent study by Guo-Parke and colleagues describing a new model of RSV infection based on WD-PNECs and WD-PNECs (12) provides important insights into RSV interaction of airway epithelial cells derived from the upper and lower respiratory tracts in the same subject. This study is translational and timely because there is a need to develop new therapeutic strategies as countermeasures to RSV disease, as there is presently no safe and effective RSV vaccine and treatments are limited (16), particularly because nasal brushes are considerably easier to obtain than bronchial brushes in infants and young children. The findings from this study also provide the impetus and rationale that is needed to move forward with studies defining the host response in WD-PNECs derived from defined cohorts, for example, examining outcomes and host cell responses in patients with different clinical histories of severe or mild RSV disease, or different susceptibilities to severe RSV infection. Such studies can provide
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insights into the cellular and molecular basis of RSV pathogenesis in humans that have not been previously possible. Author disclosures are available with the text of this article at www.atsjournals.org.
Ralph A. Tripp, Ph.D. Department of Infectious Diseases University of Georgia Athens, Georgia References 1. Thorburn K, Eisenhut M, Riordan A. Mortality and morbidity of nosocomial respiratory syncytial virus (RSV) infection in ventilated children— a ten year perspective. Minerva Anestesiol 2012;78:782. 2. Deshpande SA, Northern V. The clinical and health economic burden of respiratory syncytial virus disease among children under 2 years of age in a defined geographical area. Arch Dis Child 2003;88:1065–1069. 3. Hon KL, Leung TF, Cheng WY, Ko NM, Tang WK, Wong WW, Yeung WH, Chan PK. Respiratory syncytial virus morbidity, premorbid factors, seasonality, and implications for prophylaxis. J Crit Care 2012;27:464–468. 4. Kao YJ, Piedra PA, Larsen GL, Colasurdo GN. Induction and regulation of nitric oxide synthase in airway epithelial cells by respiratory syncytial virus. Am J Respir Crit Care Med 2001;163:532–539. 5. Noah TL, Becker S. Respiratory syncytial virus-induced cytokine production by a human bronchial epithelial cell line. Am J Physiol 1993;265:L472–L478. 6. Bem RA, Domachowske JB, Rosenberg HF. Animal models of human respiratory syncytial virus disease. Am J Physiol Lung Cell Mol Physiol 2011;301:L148–L156. 7. Johnson JE, Gonzales RA, Olson SJ, Wright PF, Graham BS. The histopathology of fatal untreated human respiratory syncytial virus infection. Mod Pathol 2007;20:108–119. 8. Jewell NA, Cline T, Mertz SE, Smirnov SV, Flan˜o E, Schindler C, Grieves JL, Durbin RK, Kotenko SV, Durbin JE. Lambda interferon is the predominant interferon induced by influenza A virus infection in vivo. J Virol 2010;84:11515–11522. 9. Villenave R, Thavagnanam S, Sarlang S, Parker J, Douglas I, Skibinski G, Heaney LG, McKaigue JP, Coyle PV, Shields MD, et al. In vitro modeling of respiratory syncytial virus infection of pediatric bronchial epithelium, the primary target of infection in vivo. Proc Natl Acad Sci USA 2012;109: 5040–5045. 10. Welliver TP, Garofalo RP, Hosakote Y, Hintz KH, Avendano L, Sanchez K, Velozo L, Jafri H, Chavez-Bueno S, Ogra PL, et al. Severe human lower respiratory tract illness caused by respiratory syncytial virus and influenza virus is characterized by the absence of pulmonary cytotoxic lymphocyte responses. J Infect Dis 2007;195:1126–1136. 11. Okabayashi T, Kojima T, Masaki T, Yokota S, Imaizumi T, Tsutsumi H, Himi T, Fujii N, Sawada N. Type-III interferon, not type-I, is the predominant interferon induced by respiratory viruses in nasal epithelial cells. Virus Res 2011;160:360–366. 12. Guo-Parke H, Canning P, Douglas I, Villenave R, Heaney LG, Coyle PV, Lyons JD, Shields MD, Power UF. Relative respiratory syncytial virus cytopathogenesis in upper and lower respiratory tract epithelium. Am J Respir Crit Care Med 2013;188:842–851. 13. Wong JY, Rutman A, O’Callaghan C. Recovery of the ciliated epithelium following acute bronchiolitis in infancy. Thorax 2005;60:582–587. 14. Zhang L, Peeples ME, Boucher RC, Collins PL, Pickles RJ. Respiratory syncytial virus infection of human airway epithelial cells is polarized, specific to ciliated cells, and without obvious cytopathology. J Virol 2002;76:5654–5666. 15. Villenave R, Shields MD, Power UF. Respiratory syncytial virus interaction with human airway epithelium. Trends Microbiol 2013;21:238–244. 16. Oshansky CM, Zhang W, Moore E, Tripp RA. The host response and molecular pathogenesis associated with respiratory syncytial virus infection. Future Microbiol 2009;4:279–297. 17. Hsu AC, Barr I, Hansbro PM, Wark PA. Human influenza is more effective than avian influenza at antiviral suppression in airway cells. Am J Respir Cell Mol Biol 2011;44:906–913. 18. Ioannidis I, Ye F, McNally B, Willette M, Flan˜o E. Toll-like receptor expression and induction of type I and type III interferons in primary airway epithelial cells. J Virol 2013;87:3261–3270. Copyright ª 2013 by the American Thoracic Society DOI: 10.1164/rccm.201308-1491ED
