COX-2–dependent angiogenesis is instrumental in supporting extrathymic T-cell development in the OM⁺ LN. Fetal liver cells from OM⁺ Ly5.1⁺ mice were injected in adult thymectomized irradiated COX-2^–/– mice and COX-2⁺ littermates. The number of CD4⁺CD8⁺ T cells per mesenteric LN (left panel) and the mean number of CD62L ligand⁺ HEVs per 100 × field (right panel) were assessed on day 90 after transplantation. There were 3 mice per group. *P < .001, COX-2^–/– mice versus COX-2⁺ littermates.