A number of different phenotypes in the regulatory T cell population involved in allergy suppression have been postulated: “Tr1” cells, able of suppressing airway allergy through the action of IL-10; “Th3” cells, mainly acting through TGF-β (also secreting low levels of IL-10) and TGF-β dependent, which were shown to play a regulatory role at mucosal sites [58]; and FoxP3+ T cells which, though multiple mechanisms of action have been shown in vitro, it is unclear whether the same or different mechanisms are used in vivo (reviewed in [61]). This evidence concerns the gene IL10 and allergic respiratory disease.