Particularly in the context of Immunoglobulin E (IgE)-mediated allergy, Tregs inhibit the development of type 2 CD4+ T helper (Th2) cells and impair their cytokine production in response to allergens (3, 4) by a combination of soluble and cell-to-cell contact molecules such as interleukin (IL)-10 and IL-35, Transforming Growth Factor-beta (TGF-β), granzymes, T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1) or T cell immunoglobulin and mucin domain-containing Protein 3 (TIM3) (5, 6). Here, PDCD1 is linked to allergic disease.