Innate lymphoid cells that produce type 2 cytokines (ILC2 cells) precede and are known to influence expansion of the adaptive CD4+ type 2 helper T cell (TH2 cell) responses. In Immunity, McKenzie and colleagues use two different ILC2 cell–deficient mouse strains to show that ILC2 cells contribute to the development of efficient TH2 responses to the parasitic worm Nippostrongylus brasiliensis in a manner dependent on major histocompatibility complex (MHC) class II. ILC2 cells express MHC class II and the costimulatory receptors CD80 and CD86, acquire and process antigen and can induce antigen-specific activation and proliferation of T cells with efficiency lower than that of CD11c+ dendritic cells but equivalent to that of plasmacytoid dendritic cells or naive B cells. The antigen-dependent crosstalk with T cells leads to the proliferation of ILC2 cells and secretion of type 2 cytokines in a manner dependent on the production of interleukin 2 (IL-2) from T cells. Human ILC2 cells express MHC class II and can also present antigen to T cells, which suggests a conserved mechanism.

Immunity 41, 283–295 (2014)