Chemosensory cells in the respiratory tract as crucial regulators of innate immune responses.
Monika I HollenhorstGabriela Krasteva-ChristPublished in: The Journal of physiology (2023)
During recent years chemosensory cells in extraoral tissues have been established as mediators for the detection and regulation of innate immune processes in response to pathogens. Under physiological conditions, chemosensory cells are present throughout the respiratory epithelium of the upper and lower airways as well as in the main olfactory epithelium. Additionally, they emerge in the alveolar region of the lung upon viral infections. Chemosensory cells in the upper and the lower airways detect signalling molecules from gram-positive and gram-negative bacteria as well as aeroallergens, and fungi. Upon stimulation they release multiple molecules, such as the transmitter acetylcholine (ACh), the cysteinyl leukotriene E4 (LTE 4 ), and the cytokine IL-25, which act autocrine and paracrine and thereby orchestrate the innate immune responses in the respiratory system. Activation of chemosensory cells stimulate various immune cells, e.g., innate lymphoid cells type 2, modulate the mucociliary clearance, and induce a protective neurogenic inflammation. This review compiles and discusses recent findings regarding chemosensory cell function in the respiratory tract. Abstract figure legend Chemosensory cells that are characterised by the expression of a functional bitter taste signalling cascade are widely expressed in tissues outside of taste buds in the tongue. In the respiratory system they are known under diverse names, microvillous cells in the main olfactory epithelium, solitary chemosensory cells in the upper airways, brush cells in the lower airways and tuft cells in the lung. In recent literature, some authors refer to these chemosensory cells generally as tuft cells, regardless of the organ they are expressed in. While little is known about the function of microvillous cells and lung tuft cells, a clear role for solitary chemosensory cells and brush cells in eliciting important innate immune functions after being stimulated with metabolites from pathogens has been established. This review discusses recent findings on the function of these chemosensory cells in the respiratory tract. This article is protected by copyright. All rights reserved.