Innate immunological function of TH2 cells in vivo

T cells are normally dependent on TCR stimulation to be activated. Guo and colleagues now show that memory type 2 helper T cells can respond to interleukin 33 elicited by helminth infection in an TCR-independent way to induce eosinophilic inflammation. Type 2 helper T cells (TH2 cells) produce interleukin 13 (IL-13) when stimulated by papain or house dust mite extract (HDM) and induce eosinophilic inflammation. This innate response is dependent on IL-33 but not T cell antigen receptors (TCRs). While type 2 innate lymphoid cells (ILC2 cells) are the dominant innate producers of IL-13 in naive mice, we found here that helminth-infected mice had more TH2 cells compared to uninfected mice, and thes e cells became major mediators of innate type 2 responses. TH2 cells made important contributions to HDM-induced antigen-nonspecific eosinophilic inflammation and protected mice recovering from infection with Ascaris suum against subsequent infection with the phylogenetically distant nematode Nippostrongylus brasiliensis. Our findings reveal a previously unappreciated role for effector TH2 cells during TCR-independent innate-like immune responses.