ILC2s localize to the skin during an allergic response in vivo. An intraepidermal injection of HDM was given to an HDM-allergic individual, and 2 h later suction blisters were formed over the site of injection or on an uninjected area of skin. Fluid was extracted 26 h later, and flow cytometry was performed to analyze total cell (A) and ILC2 (B) accumulation expressed as percentage of cells within the plots (shown as numbers within each gated region). (C) Levels of IL-13, IL-5, and IL-4 within the blister fluid isolated from allergic (n = 5) and nonallergic donors (n = 3) were quantified 26 h after HDM administration into the skin. Statistical comparisons are made between cytokine levels from allergic and nonallergic donors. (D) Infiltration of ST2-expressing ILC2 into human skin 26 h after HDM or saline challenge (n = 4). (E) ILC2 (defined as Lin⁻CD45⁺IL-7Rα⁺ICOS⁺c-Kit⁺ cells) infiltration into the skin of C57BL/6 strain mice after subcutaneous administration of HDM allergen or PBS was measured using flow cytometry (n = 3–4). Data are representative of two independent experiments. *, P < 0.05; **, P < 0.01, unpaired Student’s t test (mean and SEM in C–E).