Probiotics for the Airways: potential to improve epithelial and immune homeostasis DOI: 10.1111/all.13495 Abstract: Probiotics are live microorganisms that confer a health benefit on the host when applied in adequate amounts. The therapeutic effects of probiotics have been mostly studied in the gastrointestinal tract, but recent evidence points towards the potential of these bacteria to prevent and/or treat chronic airway diseases. In this review, possible mechanisms of action of probiotics in the airways are described, with a particular focus on their capacity to modulate the epithelial barrier function and their mode of interaction with the immune system. Indeed, probiotic bacteria, mostly lactobacilli, can promote the expression and regulation of tight junctions and adherence junctions, resulting in the restoration of a defective epithelial barrier.These bacteria interact with the epithelial barrier and immune cells through pattern recognition receptors, such as toll-like receptors, which upon activation can stimulate or suppress various immune responses. Finally, the clinical potential of probiotics to treat inflammatory diseases of the upper and lower respiratory tract, and the difference between their mode of application (e.g. oral or nasal) are discussed here. First Author: Katleen Martens, Msc Correspondence: Clinical Division of Otorhinolaryngology, Head and Neck Surgery All Authors: Katleen Martens, Msc; Benoit Pugin, PhD; Ilke De Boeck, Msc; Irina Spacova, PhD; Brecht Steelant, PhD; Sven F. Seys, PhD; Sarah Lebeer, PhD; Peter W. Hellings, PhD,MD