Nasal Defensive Proteins: Distribution and a Biological Function

There are various defensive mechanisms in upper respiratory tract mucosal linings such as mechanical and functional barriers. The mechanical barrier of sinonasal mucosa consists of mucus, motile cilia, and respiratory epithelial cells linked by adhesion complexes that include tight junctions. On the other hand, the functional barrier in sinonasal mucosa is dynamic and more complex, being equipped with innate and acquired immune response among resident cells on the epithelia and immunocompetent cells in sinonasal submucosa. Importantly, various types of nasal defensive proteins in human nasal mucosa are responsible for exerting those defensive mechanisms. Those proteins are essential for a defense system against various invading pathogens such as bacteria and viruses and modulate allergic or infective chronic inflammations as well. Those proteins derived from epithelial cells or recruited inflammatory cells are also one of the important key players in the pathogenesis of rhinosinusitis and allergic rhinitis at the epithelial linings of nasal cavity and paranasal sinuses. Those defensive proteins could be classified from constitutional and functional aspects such as surfactants, mucins, antimicrobial peptides, and inflammatory cell-derived enzymes. More widely considered, chemokines, cytokines, and various antibodies can be dealt with as defensive proteins, to provoke cellular interactions against microbial infections or pathogenesis of sinonasal persistent inflammations. In this chapter, the general concept of various types of nasal defensive proteins and its function is introduced, as we focus on surfactants, mucins, and antimicrobial peptides.