The increased incidence of allergic disease seems to rely on many factors. Among them, the association between genetic variations of the immune response and environmental pressure by allergens, infectious agents and pollutants should be taken into consideration. In alternative to conventional treatments with corticosteroids and antihistaminics, nutraceuticals have been shown to act on allergic disease either during allergic sensitisation or on consolidated disease.
In this review, special emphasis is placed on the effects of dietary polyphenols on three major allergic diseases, namely atopic eczema, food allergy and asthma. Interference of polyphenols with T-helper 2 activation seems to be the main mechanism of their inhibitory effects on allergy development. Moreover, deficits of T-regulatory cells seem to play a pathogenic role in allergic disease and, therefore, these cells may represent a major target of polyphenol activity.
As described in the previous paragraphs, manipulation of mucosal tolerance still represents the best approach to prevent or treat allergic disorders. In fact, antigen-specific IT is the only treatment that can afford long-lasting protection against allergic disease after therapy is finished. However, IT has been shown to be very effective in the treatment of rhinitis and insect venom allergy but less beneficial in allergic asthma.
Just recently, evidence has been provided that increased proportions of Treg cells have been found in grass pollen allergics after IT and in IT-treated hay fever patients. This last evidence coupled to the ability of polyphenols to induce Treg cell activation may lead to the formulation of a combined therapy by IT and polyphenols for the treatment of those allergic diseases which are less responsive to IT treatment alone. Conclusively, maintenance of immune homoeostasis at mucosal levels via activation of Treg function seems to represent one of the major exploitable approaches for the therapy of human allergy.