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Just What Are the Mucous Secretions of Cystic Fibrosis?

University of Mississippi Medical Center Jackson, Mississippi

To the Editor:

Dr. Henke and his colleagues (1) have visually and quantitatively demonstrated the impressive contribution that DNA makes to the sputum of patients with cystic fibrosis (CF), as well as the surprising paucity of immunostained mucins. Indeed, the authors noted that there appeared to be more DNA than mucin in CF sputum.

Earlier studies employing classic biochemical assays to characterize sputum from patients with CF, patients with bronchiectasis, and intubated patients were reviewed by Köhler (2). One such study showed that CF sputum had 5-fold greater levels of DNA than bronchiectasis sputum (3). However, DNA was no more than 4% of the sputum solids (ash plus DNA, carbohydrate, protein, and lipids) in CF sputum, and 1.6% in bronchiectactic sputum. In these samples, proteins were the dominant component of the sputum, being 52% of the solids in CF sputum and 39% in the bronchiectatic sputum. Total carbohydrates were little different between CF and bronchiectasis. Thus, one interpretation was that the quantity of glycoconjugates, ostensibly mucins, were similar in the two states, but that exudates added leukocyte nuclear DNA and serum protein to the CF sputum.

Do the findings of Henke and colleagues (1) indicate a shift in the pathogenesis of CF sputum over the last four decades, or perhaps a change in airway biology due to altered treatment modalities?

It may be time to repeat the classic biochemical assays on CF sputum to verify that CF sputum has indeed changed with contemporary therapy. Alternatively, if contemporary CF sputum has the same carbohydrate, protein, and lipid content as was the case forty years ago, it may be that immunoassay of CF sputum is not effective, either because of altered epitopes or because of the presence of an unrecognized interference.

Footnotes

Conflict of Interest Statement: T.M.D. has no declared conflicts of interest.

References

1. Henke MO, Renner A, Huber RM, Seeds MC, Rubin BK. MUC5AC and MUC5B mucins are decreased in cystic fibrosis airway secretions. Am J Respir Cell Mol Biol 2004;31:86–91.[Abstract/Free Full Text]
2. Köhler H. Das normale bronchialsekret. Z Tuberk Erkr Thoraxorg 1968;129:261–274.[Medline]
3. Matthews LW, Spector S, Lemm J, Potter JL. Studies on pulmonary secretions: I. The overall chemical composition of pulmonary secretions from patients with cystic fibrosis, bronchiectasis and laryngectomy. Am Rev Respir Dis 1963;88:199–204.[Medline]

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