Molecular biology of olfactory mucus

Abstract

Olfactory mucus is nasal mucus that covers the olfactory mucosa located in the uppermost part of the nasal cavity. It is secreted by the Bowman’s glands in the olfactory mucosa. Several functions of olfactory mucus have been postulated, including protection of olfactory nerve tissue, prevention of pathogen invasion into the intracranial space through the nasal cavity, and olfactory perception. Recent advances in molecular biological techniques have permitted insightful analyses of olfactory mucus. In relation to pathology, in experimental animals, degeneration of Bowman’s glands is strongly spatially correlated with age-related degeneration of the olfactory neuroepithelium. Chronic rhinosinusitis is frequently associated with olfactory dysfunction, and the concentration of inflammatory mediators in the olfactory cleft mucus of patients with chronic rhinosinusitis is elevated than in control patients, suggesting roles in pathogenesis. Human olfactory mucus can metabolize odorants, and some of these metabolites have been shown to affect odor perception. This metabolic function is decreased in patients with idiopathic olfactory dysfunction and may be involved in the pathophysiology of olfactory dysfunction. The composition of olfactory mucus differs from that of respiratory mucus, containing high concentrations of lipocalin 15, a lipocalin family member thought to be involved in substance transport. Since there is a correlation between lipocalin 15 distribution in the human olfactory mucosa and that in olfactory receptor neurons, it may be possible to estimate the number of olfactory receptor neurons by quantifying lipocalin 15 in the olfactory mucus. Because olfactory mucus can be sampled minimally invasively in clinical practice, it is hoped that olfactory mucus analyses will lead to the development of objective tests of human olfactory function and new treatments that complement olfactory mucus function.