Fig. 7.

A model of LN development during the perinatal period. Migrating hemopoietic cells including LNi cells aggregate with LNo cells to form the LN anlage. In normal mice, the structure persists until after birth when it is colonized by mature lymphoid cells generated in the thymus and the bone marrow. In aly/aly mice, these structures degenerate near the end of pregnancy, so that there is no structure to be colonized by mature lymphoid cells after birth. In Il2rγ^−/−Rag2^−/− mice, these structures persist for a few days after birth, but, because of the complete absence of lymphoid cells, they degenerate within the first week after birth. In Il7r^−/− mice, these structures are maintained by the few lymphoid cells that exist in these mice; however, the size of the LNs remains small throughout life.