@article {2422, title = {Thymic progenitor homing and lymphocyte homeostasis are linked via S1P-controlled expression of thymic P-selectin/CCL25}, journal = {Journal of Experimental Medicine}, volume = {206}, number = {4}, year = {2009}, note = {ISI Document Delivery No.: 444VXTimes Cited: 19Cited Reference Count: 55Gossens, Klaus Naus, Silvia Corbel, Stephane Y. Lin, Shujun Rossi, Fabio M. V. Kast, Joergen Ziltener, Hermann J.}, month = {Apr}, pages = {761-778}, type = {Article}, abstract = {Thymic T cell progenitor (TCP) importation is a periodic, gated event that is dependent on the expression of functional P-selectin ligands on TCPs. Occupancy of intrathymic TCP niches is believed to negatively regulate TCP importation, but the nature of this feedback mechanism is not yet resolved. We show that P-selectin and CCL25 are periodically expressed in the thymus and are essential parts of the thymic gate-keeping mechanism. Periodicity of thymic TCP receptivity and the size of the earliest intrathymic TCP pool were dependent on the presence of functional P-selectin ligand on TCPs. Furthermore, we show that the numbers of peripheral blood lymphocytes directly affected thymic P-selectin expression and TCP receptivity. We identified sphingosine-1-phosphate (S1P) as one feedback signal that could mediate influence of the peripheral lymphocyte pool on thymic TCP receptivity. Our findings suggest a model whereby thymic TCP importation is controlled by both early thymic niche occupancy and the peripheral lymphocyte pool via S1P.}, keywords = {ADULT-MOUSE, ENDOTHELIAL-CELLS, EPITHELIAL-CELLS, KAPPA-B, LIGAND PSGL-1, MICE, NECROSIS-FACTOR-ALPHA, P-SELECTIN, PLASMA SPHINGOSINE 1-PHOSPHATE, T-CELLS}, isbn = {0022-1007}, url = {://000266009600006}, author = {Gossens, K. and Naus, S. and Corbel, S. Y. and Lin, S. J. and Rossi, F. M. V. and Kast, J. and Ziltener, H. J.} }