Fig. 1.

Development from interleukin (IL)-7Rα⁺ CD117^low Sca-1^low cells found in the fetal liver to lymphoid tissue inducer (LTi) cells in mouse. The fetal liver cells give rise to lymphoid cells including T, B, natural killer (NK) and dendritic cells and integrin α4β7-expressing LTi cells. Fetal LTi cells migrate to lymph node and spleen anlagen and intestine. In the intestine, LTi cells induce Peyer's patch formation. LTi cells differentiate into CD11c⁺ dencritic cells (DCs) in the presence of IL-3, tumour necrosis factor (TNF)-α and stem cell factor and into NK1·1⁺ cells in the presence of IL-15.