Effects of sublingual immunotherapy on allergic inflammation: an update

The most common allergic diseases, and especially the respiratory disorders such as rhinitis and asthma, are closely related to the allergic inflammation elicited by the causative allergen. This makes inflammation the main target of anti-allergic therapies. Among the available treatments, allergen specific immunotherapy (AIT) has a patent effect on allergic inflammation, which persists also after its discontinuation, and is the only therapy able to modify the natural history of allergy. The traditional, subcutaneous route of administration was demonstrated to modify the allergen presentation by dendritic cells (DCs) that in turn correct the phenotype of allergen-specific T cells, switching from the Th2-type response, typical of allergic inflammation and characterized by the production of IL-4, IL-5, IL-13, IL-17, and IL-32 cytokines to a Th1-type response. This immune deviation is related to an increased IFN-gamma and IL-2 production as well as to the anergy of Th2 or to tolerance, the latter being related to the generation of allergen-specific T regulatory (Treg) cells, which produce cytokines such as IL-10 and TGF-beta. Anti-inflammatory mechanisms observed during sublingual AIT with high allergen doses proved to be similar to subcutaneous immunotherapy. Data obtained from biopsies clearly indicate that the pathophysiology of the oral mucosa, with particular importance for mucosal DCs, plays a crucial role in inducing tolerance to the administered allergen.