Figure 1. Development and differences of fetal and adult LTi cells.

In the fetal stage, LTi cells are developed from their progenitors in the fetal liver. LTi progenitor cells are featured by their high expression of integrin α₄β₇, IL-7Rα and RORγt. Other molecules such as CCR6, TRANCE and CXCR5 are also expressed by these progenitors. The progenitor cells then migrate to other organs such as fetal spleen, small intestine and thymus, where they further mature and start to express lymphtoxin α₁β₂ (LTα₁β₂) and IL-22. In the adult stage, LTi cells (or LTi-like cells) are developed from the progenitors in the bone marrow. These progenitors still express high levels of integrin α₄β₇ and IL-7Rα, but relatively low levels of RORγt. Gene expression in mature adult LTi-like cells are very similar to that in fetal LTi cells, except that adult LTi cells additionally express OX40L and CD30L.