Group 2 innate lymphoid cells license dendritic cells to potentiate memory TH2 cell responses

Memory TH2 cells are rapidly recruited to tissues after exposure to stimulatory ligands. McKenzie and colleagues demonstrate that ILC2s have an essential role in facilitating TH2 cell memory responses in lung, skin and gut. Rapid activation of memory CD4+ T helper 2 (TH2) cells during allergic inflammation requires their recruitment into the affected tissue. Here we demonstrate that group 2 innate lymphoid (ILC2) cells have a crucial role in memory TH2 cell responses, with targeted depletion of ILC2 cells profoundly impairing TH2 cell localization to the lungs and skin of sensitized mice after allergen re-challenge. ILC2-derived interleukin 13 (IL-13) is critical for eliciting production of the TH2 cell–attracting chemokine CCL17 by IRF4+CD11b+CD103− dendritic cells (DCs). Consequently, the sentinel function of DCs is contingent on ILC2 cells for the generation of an efficient memory TH2 cell response. These results elucidate a key innate mechanism in the regulation of the immune memory response to allergens.