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Allergic sensitization to inhaled antigens is increasingly common; however, the mechanisms remain poorly understood. Lung epithelial cells, once thought to be merely a passive barrier impeding allergen penetrance, have recently been shown to recognize allergens via expression of pattern recognition receptors (PRRs) and mount an innate immune response driven by the activation of the cytokine NF-кB. In their review, Lambrecht and Hammad discuss recent findings that describe epithelial cells as crucial in allergy inhalation outcomes ( J Allergy Clin Immunol 2014; 134(3): 499-507 ). Traditionally, allergic asthma has been characterized as a disease of the adaptive immune system, whereby lymphocytes overreact to harmless antigens and mount a type 2 immune response, subsequently causing the activation of effector cells like mast cells, basophils and eosinophils. Recently, research has been changing this view to accommodate the concept that cells of the innate immune system contribute signif...

Airway epithelial cells are an important part of the innate immune system in the lung. Not only do they establish mucociliary clearance, epithelial cells produce anti-microbial peptides, chemokines, and cytokines that recruit and activate other cell types and promote pathogen clearance. Recent studies emphasize the importance of epithelial derived cytokines in the promotion of Th2 immune responses, at least in part by conditioning local dendritic cells (DCs). Epithelial cells also from a barrier to the outside world comprised of airway surface liquids, mucus, and apical junctional complexes (AJC) that form between neighboring cells. In their recent review, Georas and Rezaee discuss why defective epithelial barrier function may be linked to Th2 polarization in asthma, and propose a rheostat model of barrier dysfunction that implicates the size of inhaled allergen particles as an important factor influencing adaptive immunity ( J Allergy Clin Immunol 2014; 134(3): 509-520 ).  Increa...