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MUC5AC and MUC5B Mucins Increase in Cystic Fibrosis Airway Secretions during Pulmonary Exacerbation

¹ Department of Pulmonary Medicine, Philipps-University Marburg, Marburg, Germany; ² Department of Pediatrics, Justus-Liebig-University Giessen, Giessen, Germany; and ³ Department of Pediatrics, Wake Forest University Health Sciences, Winston-Salem, North Carolina

Correspondence and requests for reprints should be addressed to Markus O. Henke, M.D., Philipps-University Marburg, Department of Pulmonary Medicine, Baldingerstrasse 1, 35043 Marburg, Germany. E-mail: markus.henke{at}staff.uni-marburg.de

Rationale: Cystic fibrosis (CF) is believed to be associated with mucus hypersecretion; thus, the principal airway gel-forming mucins, MUC5AC and MUC5B, are also expected to be increased relative to non-CF secretions. However, we have shown that these mucins are decreased during stable CF disease.

Objectives: In this study, we determine if these mucins increase during a pulmonary exacerbation of CF.

Methods: Expectorated sputum was collected from 11 adults with CF during stable disease and then during a pulmonary exacerbation and from 12 healthy control subjects. MUC5AC and MUC5B proteins were measured by Western blot. DNA content was measured using microfluorimetry.

Results: MUC5AC protein increased by 908% and MUC5B by 59% (p < 0.05 for both) during an exacerbation compared with periods of stable disease. During stable disease, the vol/vol quantity of MUC5AC protein was 89% less than normal mucus, and the mucin-associated sugars, measured using a lectin binding assay, were 46% less compared with normal mucus. The concentration of DNA in CF sputum did not increase during an exacerbation.

Conclusions: During a CF exacerbation, concentration of secreted mucin increased to the amount found in mucus from normal subjects, suggesting that the capacity to secrete mucin in response to an infection or inflammatory stimulus is preserved in CF airways. This might help to protect the airway from injury.

Key Words: respiratory • mucus • hypersecretion • mucin • DNA

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Composition of sputum in cystic fibrosis (CF) during a pulmonary exacerbation compared with that of normal mucus provides information on the pathophysiological influence of recurrent airway inflammation on the progression of the lung destruction in CF. Mucin is the major component of mucus in healthy airways, and is responsible for protection of the epithelium. What This Study Adds to the Field In CF, mucin is decreased during stable disease but increases during a pulmonary exacerbation; however, it still does not exceed the concentration of normal, noninflamed airways.

 

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