Cutting edge: the chemokine receptor CXCR3 retains invariant NK T cells in the thymus.

The current model used to define T cell export from the thymus suggests that emigrating lymphocytes seed the peripheral organs as functionally mature cells. This model holds true for the majority of T cells exported from the thymus with the exception of invariant NK T (iNKT) cells. iNKT cells undergo lineage expansion after positive selection and acquire NK receptor expression once fully mature; yet, the majority of mature iNKT cells are retained in the thymus by an as of yet unidentified mechanism. In this study we demonstrate that mature iNKT cells are retained in the thymus by the chemokine receptor CXCR3. We propose that the expression of CXCR3 ligands in the thymic medullary epithelium promotes the chemotactic retention of mature iNKT thymocytes and prevents leakage of iNKT cells into the peripheral circulation.