Fig. 1.

Respiratory epithelial cells function as an “orchestrator” to initiate, coordinate, and respond to inhaled stimuli. 1: Respiratory epithelial cells form a physical and mechanical barrier to protect against respiratory stimuli. 2: Respiratory epithelial cells express receptors and ligands that interact with neighboring epithelial cells, respiratory immune cells, and inhaled stimuli such as respiratory pathogens. 3: Respiratory epithelial cells secrete soluble factors such as cytokines, chemokines, and antimicrobial peptides to contribute to respiratory host defense.