S1P1 receptor expression regulates emergence of NKT cells in peripheral tissues

The S1P(1) receptor, on the surface of lymphocytes and endothelial cells, regulates the unique trafficking behavior of certain lymphocyte populations. We have examined whether the S1P(1) receptor also dictates the distinctive tissue distribution of V alpha 14-J alpha 18 natural killer T (NKT) cells, whose trafficking pattern is not well understood. Mice (TCS1P(1)KO) were established with a conditional deletion of the S1P(1) receptor in thymocytes that included precursors of NKT cells. Within the thymus, NKT cells were found at normal or increased levels, indicating that S1P(1) receptor expression was dispensable for NKT cell development. However, substantially reduced numbers of NKT cells were detected in the peripheral tissues of the TCS1P(1)KO mice. Short-term S1P(1) deletion after NKT cells had established residence in the periphery did not substantially alter their distribution in tissues, except for a partial decrease in the spleen. FTY720, a S1P(1) receptor ligand that has potent effects on the trafficking of conventional T cells, did not alter the preexisting distribution of NKT cells within peripheral tissues of wild-type mice. Our results indicate that the S1P(1) receptor expression on NKT cells is dispensable for development within thymus but is essential for the establishment of their tissue residency in the periphery.