Interactions between the Bronchial Epithelium and Fibrocytes in the Pathogenesis of Airway Remodeling in Asthma

The histopathologic features of asthma include chronic airway inflammation, increased density of fibroblasts and myofibroblasts in the lamina propria and presence of structural abnormalities of the bronchial wall collectively referred to with the term "airway remodeling".The newly emerged population of fibroblasts and myofibroblasts contributes to airway remodeling by producing excessive amounts of collagenous and non-collagenous extracellular matrix components in the subepithelial zone and by expanding the mass of contractile cells in the bronchial wall.A substantial proportion of these mesenchymal cells in asthma exhibit the phenotypic and functional characteristic of fibrocytes, which represent a unique population of bone marrow-derived mesenchymal progenitors recruited to tissue sites from the circulation in response to injury or in chronic inflammatory conditions.Recent studies have demonstrated that the asthmatic bronchial epithelium is a major source of fibrocyte chemoattractants and growth factors.This review will focus on the novel observations suggesting that asthmatic epithelial cells may play a key role in the development and progression of airway remodeling by promoting the recruitment and local differentiation of fibrocytes.