The development of LTi cells

Lymphoid tissue inducer (LTi) cells are programmed by the mammalian fetus to induce the development of lymph nodes and Peyer's patches. LTi cells share a pro-inflammatory profile with Th17 cells, as well as their requirement for the transcription factor RORγt. We discuss here the latest data on the fetal and post-natal development of LTi cells, and their relationship with the larger family of innate lymphoid cells (ILCs). We suggest that the re-programming of RORγt in a subset of common lymphoid progenitors allowed mammals to develop lymphoid organs before birth, whereas other vertebrates only develop such organs in response to infection or injury.

► LTi cells develop a ‘pro-inflammatory’ program similar to Th17 cells. ► Peripheral tissues induce terminal differentiation of LTi cells. ► The programming of RORγt in fetal development: key to mammalian lymphoid tissues? ► Adult LTi cells may have developed since the advent of vertebrates.