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Open Access Research

Analysis of the proteome of human airway epithelial secretions

Mehboob Ali13, Erik P Lillehoj2, Yongsung Park1, Yoshiyuki Kyo1 and K Chul Kim1*

Author Affiliations

1 Department of Physiology and Lung Center, Temple University School of Medicine, Philadelphia, PA, USA

2 Department of Pediatrics, University of Maryland School of Medicine, Baltimore, MD, USA

3 Department of Pharmacology and Experimental Therapeutics, Thomas Jefferson University, 1020 Locust Street, JAH 364, Philadelphia, PA 19107, USA

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Proteome Science 2011, 9:4  doi:10.1186/1477-5956-9-4

Published: 20 January 2011

Abstract

Background

Airway surface liquid, often referred to as mucus, is a thin layer of fluid covering the luminal surface that plays an important defensive role against foreign particles and chemicals entering the lungs. Airway mucus contains various macromolecules, the most abundant being mucin glycoproteins, which contribute to its defensive function. Airway epithelial cells cultured in vitro secrete mucins and nonmucin proteins from their apical surface that mimics mucus production in vivo. The current study was undertaken to identify the polypeptide constituents of human airway epithelial cell secretions to gain a better understanding of the protein composition of respiratory mucus.

Results

Fifty-five proteins were identified in the high molecular weight fraction of apical secretions collected from in vitro cultures of well-differentiated primary human airway epithelial cells and isolated under physiological conditions. Among these were MUC1, MUC4, MUC5B, and MUC16 mucins. By proteomic analysis, the nonmucin proteins could be classified as inflammatory, anti-inflammatory, anti-oxidative, and/or anti-microbial.

Conclusions

Because the majority of the nonmucin proteins possess molecular weights less than that selected for analysis, it is theoretically possible that they may associate with the high molecular weight and negatively charged mucins to form a highly ordered structural organization that is likely to be important for maintaining the proper defensive function of airway mucus.