Developing lymph nodes collect CD4(+)CD3(-) LT beta(+) cells that can differentiate to APC, NK cells, and follicular cells but not T or B cells

For a brief period during fetal lymph node organogenesis in mice, lymph node postcapillary high endothelial venules surprisingly express the Peyer's patch addressin MAdCAM-1. This expression allows initial seeding of this incipient structure by two unusual lymphocyte populations selectively expressing the Peyer's patch homing receptor integrin alpha 4 beta 7: CD4(+)CD3(-) oligolineage progenitors and TCR gamma delta(+) T cells. We show here that CD4(+)CD3(-) cells are lineage-restricted progenitors that express surface lymphotoxin-P (LTP) and the chemokine receptor BLR1 and that can become natural killer cells, dendritic antigen-presenting cells, and follicular cells of unknown outcome, but these cells do not become T or B lymphocytes. Since the necessity of lymphotoxin in lymphoid organ development has been shown, we propose that the novel subset of CD4(+) CD3(-)LT beta(+) fetal cells is instrumental in the development of lymphoid tissue architecture.