Research Article

Neural Crest–Derived Pericytes Promote Egress of Mature Thymocytes at the Corticomedullary Junction

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Science  22 Apr 2010:
DOI: 10.1126/science.1188222


T cell egress from the thymus is essential for adaptive immunity, yet the requirements for and sites of egress are incompletely understood. Here, we show that transgenic expression of sphingosine-1-phosphate receptor-1 (S1P1) in immature thymocytes leads to their perivascular accumulation and premature release into circulation. Using an intravascular procedure to label emigrating cells, we find that mature thymocytes exit via blood vessels at the corticomedullary junction. By deleting sphingosine kinases in neural crest–derived pericytes, we provide evidence that these specialized vessel-ensheathing cells are a necessary S1P source for normal thymic egress. Lymphatic endothelial cell–derived S1P was not required. These studies identify the major thymic egress route and define a role for pericytes in promoting reverse transmigration of cells across blood vessel endothelium.