Activated allergen-specific Th2 cells produce IL-4, IL-5, IL-9 and IL-13, which play a key role in the maintenance of allergen-specific IgE levels, eosinophilia, recruitment of inflammatory cells to inflamed tissues, production of mucus and decreased threshold of contraction of smooth muscles 5, 9. As a consequence of these events, the more severe clinical manifestations of allergy, such as chronic persistent asthma, allergic rhinitis, atopic dermatitis,

and in extreme cases, systemic anaphylactic reactions appear. Recently, Tyrosine Kinase Inhibitor Library concentration newly identified cytokines such as IL-25, IL-31 and IL-33 have been shown to participate in the Th2 response and inflammation 10–12. Additionally, other effector T-cell subsets can contribute to ongoing allergic reactions. Depending on the specific disease model and stage

of inflammation, Th1 cells can either exacerbate the effector phase, for example, by inducing apoptosis of the epithelium in asthma and atopic dermatitis 13, 14, or dampen allergic inflammation 15. Recently, it has been shown that IL-32 induced by IFN-γ and TNF-α is an essential player in keratinocytes apoptosis in atopic dermatitis, which leads to eczema formation 16. An increase in activation-induced cell death of high amounts of IFN-γ-producing Th1 cells, as determined by intracellular mTOR inhibitor staining and flow cytometry, also contributes to the predominant Th2 profile in atopic Methisazone diseases 17. It has also been demonstrated that neutralization of IL-17 and Th17-related functions in an experimental asthma model reduces neutrophilia,

while increasing eosinophil infiltration in the lung 18. In addition, recently, two new subsets of effector Th cells have been identified according to their cytokine signature, Th9 and Th22 cells. Although Th9 and Th22 cells’ potential contribution to allergic inflammation requires further investigations, Th9 cells may represent an IL-9- and IL-10-producing subset that lack suppressive function and promote tissue inflammation 19, while Th22 cells contribute to epidermal hyperplasia in inflammatory skin diseases 20, 21. In addition to the above-mentioned effector Th cell subsets, T cells with immunoregulatory properties exist and these are broadly referred as Treg. Other cell subsets with suppressive capacity include CD8+ T cells, γδ T cells, CD4−CD8− T cells, IL-10-producing B cells, IL-10-producing NK cells, IL-10-producing DC and some macrophage subsets 9, 22. The main role of all these cell subsets is to maintain integrity of the body through avoiding misguided or excessive immune responses that may result in harmful immune pathology, as well as to keep a state of tolerance to innocuous substances. Treg have the ability to control and modify the development of allergic diseases altering the ongoing sensitization and effector phases via several major pathways (Fig. 1).