2.4 Allergic Rhinitis
Allergic rhinitis (AR) has a similar inflammatory process to that of asthma. In allergic individuals, many Th2 cells infiltrate the nasal mucosa and release cytokines (e.g. IL-4, IL-5 and IL-13) that promote IgE production by plasma cells. Avoiding contact with allergens is the safest treatment, but it does not usually achieve satisfactory results.4444 Although anti-histamines and corticosteroids can significantly relieve related symptoms, such treatments must be taken repeatedly throughout the lives of allergic individuals.44,45 Immunotherapy administered through subcutaneous injection or sublingual administration of allergens induces immune tolerance, but continuous treatment is again required, which is expensive and can potentially lead to allergic reactions.46
Generally, large-scale production and release of inflammatory cells, including eosinophils and ROS and their metabolites, plays a vital role in the pathogenesis of allergic inflammatory airway diseases.47,48 As an endogenous anti-oxidant protein, Trx1 has strong anti-oxidative stress effects. Thus, administration of exogenous Trx1 can inhibit airway hyper responsiveness induced by specific allergens via the inhibition of eosinophil accumulation in the airway of mouse models with asthma.22,23 Quercetin has been suggested as a dietary supplement for improving the clinical symptoms of allergic diseases such as AR, but its precise mechanisms of action remain unclear. Nevertheless, Trx1 levels in the nasal mucosa are known to significantly increase after oral administration of quercetin; moreover, the frequency of nasal allergy-like symptoms, such as sneezing and nasal rubbing, are significantly reduced.49 These changes provide insights into the possible mechanism through which quercetin has favourable effects on AR.