Barrier function of airway tract epithelium

Ganesan, Shyamala; Comstock, Adam T; Sajjan, Uma S

The most prominent features of Clara cells are the membrane-bound electron dense secretory granules. Although these granules do not contain glycoprotein like in goblet cells, they secrete CC10 (or CCSP) protein which is used as a Clara cell marker. 26, 27 These cells also secrete surfactant proteins and antiproteinases that may protect bronchiolar epithelium. 28,29 Clara Impaired mucociliary clearance may also be a direct result of defective ciliary function as observed in patients with ciliary dyskinesia. Although these patients have normal secretion of mucus, it is not cleared due to defective ciliary beating. 67 On the other hand, in COPD patients the impaired mucociliary function may be due to a combination of excessive mucus production, increased viscosity of mucus due to acquired dysfunction of CFTR, and reduced ciliary beating. [68] [69] [70] It has been shown that respiratory epithelial cells exposed to cigarette smoke extract or condensate showed shorter and 70% fewer cilia compared control cells. 71 Although mice exposed to cigarette smoke showed slight increases in ciliary beat frequencies at 6 weeks and 3 mo, it was significantly reduced at 6 mo, and post-mortem examination revealed significant loss of tracheal ciliated cells. 72 Recently Yaghi et al. provided direct evidence of suppressed ciliary beating in nasal epithelium from COPD patients. 68 Such changes in number and function of cilia can significantly impair the mucociliary clearance function of airway epithelium.