Abstract
Cystic fibrosis (CF) is a life-shortening disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene1. Although bacterial lung infection and the resulting inflammation cause most of the morbidity and mortality, how the loss of CFTR function first disrupts airway host defence has remained uncertain2,3,4,5,6. To investigate the abnormalities that impair elimination when a bacterium lands on the pristine surface of a newborn CF airway, we interrogated the viability of individual bacteria immobilized on solid grids and placed onto the airway surface. As a model, we studied CF pigs, which spontaneously develop hallmark features of CF lung disease7,8. At birth, their lungs lack infection and inflammation, but have a reduced ability to eradicate bacteria8. Here we show that in newborn wild-type pigs, the thin layer of airway surface liquid (ASL) rapidly kills bacteria in vivo, when removed from the lung and in primary epithelial cultures. Lack of CFTR reduces bacterial killing. We found that the ASL pH was more acidic in CF pigs, and reducing pH inhibited the antimicrobial activity of ASL. Reducing ASL pH diminished bacterial killing in wild-type pigs, and, conversely, increasing ASL pH rescued killing in CF pigs. These results directly link the initial host defence defect to the loss of CFTR, an anion channel that facilitates HCO3− transport9,10,11,12,13. Without CFTR, airway epithelial HCO3− secretion is defective, the ASL pH falls and inhibits antimicrobial function, and thereby impairs the killing of bacteria that enter the newborn lung. These findings suggest that increasing ASL pH might prevent the initial infection in patients with CF, and that assaying bacterial killing could report on the benefit of therapeutic interventions.
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Data deposits
Microarray data have been deposited in the Gene Expression Omnibus under accession numbers GSE36906 and GSE21071.
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Acknowledgements
We thank J. Bartlett, X. Chamling, J.-H. Chen, L. Durairaj, N. Gansemer, E. Hornick, P. Hughes, P. Ludwig, T. Mayhew, K. Mohn, L. Ostedgaard, M. Rector, L. Reznikov, L. Schneider, A. Shelton, T. Starner, P. Tan, A. Tucker, A. Walimbe and T. Yahr for assistance and/or discussion. This work was supported by the National Institutes of Health (NIH; HL51670, HL091842, HL102288) and the Cystic Fibrosis Foundation. D.A.S. was supported by AI076671 and Gilead Sciences Research Scholars Program in Cystic Fibrosis. H.P.H. was supported by Program Grant (RGP001612009-C) of the Human Frontier Science Program. M.J.W. is a Howard Hughes Medical Institute investigator.
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A.A.P., X.X.T., M.J.H., M.H.A.A., S.R., D.A.S., P.B.M., M.J.W. and J.Z. designed studies. A.A.P., X.X.T., M.J.H., M.H.A.A., S.R., T.O.M., P.H.K., C.L.W.-L., H.P.H., M.v.E., B.B., A.R.H. and D.A.S. performed experiments. A.A.P., X.X.T., M.J.H., M.H.A.A., S.R., D.A.S., P.B.M., M.J.W. and J.Z. wrote the manuscript.
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M.J.W. was co-founder of Exemplar Genetics, a company licensing materials and technology related to this work.
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Pezzulo, A., Tang, X., Hoegger, M. et al. Reduced airway surface pH impairs bacterial killing in the porcine cystic fibrosis lung. Nature 487, 109–113 (2012). https://doi.org/10.1038/nature11130
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DOI: https://doi.org/10.1038/nature11130
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