An essential function for the nuclear receptor RORγt in the generation of fetal lymphoid tissue inducer cells

Lymphoid tissue inducer (LTi) cells are associated with early development of lymph nodes and Peyer's patches. We show here that during fetal life the nuclear hormone receptor RORgammat is expressed exclusively in and is required for the generation of LTi cells. RORgammat(+) LTi cells provide essential factors, among which lymphotoxin-alpha(1)beta(2) is necessary but not sufficient for activation of the mesenchyma in lymph node and Peyer's patch anlagen. This early LTi cell-mediated activation of lymph node and Peyer's patch mesenchyma forms the necessary platform for the subsequent development of mature lymphoid tissues.