Nasal Immunity, Rhinitis, and Rhinosinusitis

The mucosal layer of the upper airways is continuously exposed to microbes, irritants, and pollutants to which it needs to defend itself. Apart from mechanical components such as mucous secretion and the epithelial barrier, innate and adaptive immune mechanisms involving dendritic cells, macrophages, and T and B cells aim to maintain the integrity of the mucosa. However, viral infections of the upper airways, allergen exposure, bacterial colonization, eventual mucosal invasion, and the release of bacterial products impact heavily on the mucosal layer, leading to chronic diseases such as allergic rhinitis, chronic rhinosinusitis, and nasal polyposis. The diseases manifest themselves at different levels: mucosal remodeling, eosinophilic and neutrophilic types of inflammation, and, finally, asthma comorbidity. The endotyping of chronic rhinosinusitis makes use of tissue biomarkers to identify the dominant T helper cell and cytokine pattern, as well as related inflammatory processes for the selection of therapeutic interventions and the prediction of the likelihood of comorbidity.