Functional regulatory T cells and allergen immunotherapy

Purpose of review Burgeoning literature ascribing roles for regulatory T cells (Treg) in controlling clinical allergy frequently relies on phenotypic markers rather than functional suppression assays. This review examines evidence for functional Treg in controlling immune responses to allergen with particular focus on allergen-specific immunotherapy. Recent findings Over the last year, use of recently identified Treg markers has facilitated more precise delineation and isolation of Treg subtypes. Advanced flow cytometry allows better discrimination and tracking of effector T cells (Teff) and Treg in co-culture assays for Treg function. These approaches enable critical appraisal of the evidence for Treg mediation of the observed changes in immune reactivity to allergen accompanying immunotherapy. Recent studies suggest that different mechanisms of immune regulation may occur at different times of immunotherapy, with Treg playing a more important role early in treatment. Additionally, advanced imaging techniques reveal increased Treg numbers in allergen-exposed mucosal tissue after therapy consistent with an enhanced local functional role. Summary These findings support a mechanistic role for Treg early in allergen immunotherapy. Research is required to clarify the precise Treg subsets involved, their specificity and how their activity can be enhanced during immunotherapy by appropriate allergen form, optimal site of administration and use of adjuvants and adjunct therapies.