Fig. 1

Innate lymphoid cells development. Common lymphoid progenitors (CLPs) differentiate into common innate lymphoid progenitors (CILPs), which can give rise to natural killer precursors (NKP) and common helper innate lymphoid progenitors (CHILPs) [19]. By expressing the transcription factors (TF) T-bet and EOMES, NKP cells can develop into NK cells. In turn, CHILPs can differentiate into innate lymphoid cell precursors (ILCPs) or lymphoid tissue inducer precursors cells (LTiP) [20]. ILC1s, ILC2s and ILC3s originate from ILCPs upon expression of different transcription factors (grey boxes). Finally, LTiP can generate LTi cells. To distinguish ILC subtypes, a population negative for lineage markers of other immune cells should be identified first (e.g., CD3, CD4, CD8, CD14, CD15, CD16, CD19, CD20, CD33, CD34, CD203c, and FcɛRI). Next, NK cells can be defined as CD56⁺ CD94⁺ CD127⁻ whereas ILCs are CD94⁻ and CD127⁺. The specific subtypes can be distinguished based on their expression of CD117 and CD294, as ILC1s are CD117⁻ CD294⁻, ILC2 are CD117^± CD294⁺, and ILC3s and LTi cells are CD117⁺ CD294⁻ [21].