Bronchial epithelial cells are cells that line the respiratory tract, specifically the bronchi, which are the larger airways in the lungs. These cells play a critical role in protecting the lungs from harmful substances and pathogens by producing mucus, which helps to trap and remove foreign particles. They also play a role in regulating the immune response in the lungs and maintaining the integrity of the respiratory tract. Research on bronchial epithelial cells is important for understanding respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and lung cancer, as well as for developing new therapies and treatments for these conditions.