Group 2 innate lymphoid cells license dendritic cells to potentiate memory T helper 2 cell responses

Rapid memory CD4(+) T helper 2 (T(H)2) cell activation during allergic inflammation requires their recruitment into the affected tissue. Here we demonstrate that group 2 innate lymphoid cells (ILC2) play a critical role in memory T(H)2 cell responses, with targeted ILC2 depletion profoundly impairing T(H)2 cell localization to the lungs and skin of sensitized mice after allergen re-challenge. ILC2-derived interleukin-13 (IL-13) is critical for eliciting IRF4(+)CD11b(+)CD103(−) dendritic cells (DCs) to produce the T(H)2 cell-attracting chemokine CCL17. Consequently, the sentinel function of DCs is contingent on ILC2s for the generation of an efficient memory T(H)2 cell response. These results elucidate a key new innate mechanism in the regulation of the immune memory response to allergens.