Development and evolution of ROR?t plus cells in a microbe's world

The nuclear hormone receptor retinoid-related orphan receptor ?t (ROR?t) induces a pro-inflammatory program in lymphoid cells, culminating in the expression of interleukin-6 (IL-6), IL-17, IL-22, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor. During ontogeny, the first type of cells expressing ROR?t are lymphoid tissue inducer cells, a type of innate lymphoid cell (ILC) generated in mammalian fetuses to induce the development of lymph nodes and Peyers patches. After birth, ROR?t+ ILCs and ROR?t+ T cells are involved in the defense of epithelial surfaces against extracellular microbes and play an important role in the intestinal homeostasis with symbiotic microbiota. The development and evolution of ROR?t+ cells is intimately associated with the construction of a stable hostmicrobe interface.