The bronchi are part of the respiratory system. Their function is to carry air from the outside to the inside of the lungs. They branch off from the trachea into several bronchi and bronchioles.

Fibroblasts are the most abundant cell type in the bronchi. Bronchial fibroblasts (BF) have a mesenchymal stem cell phenotype and their main function is to produce type III collagen, elastin and extracellular matrix proteoglycans. Bronchial fibroblasts play an important role in the repair and remodeling processes after injury. The controlled accumulation of fibroblasts at sites of inflammation is crucial for effective tissue repair after injury. Inadequate or excessive accumulation of fibroblasts can result in abnormal tissue function. For example, excessive fibroblast proliferation and collagen secretion that occurs due to bronchial subepithelial fibrosis can lead to airway obstruction and bronchial hyperreactivity.