Skip to main content
. Author manuscript; available in PMC: 2017 Jul 6.
Published in final edited form as: Annu Rev Physiol. 2016 Oct 21;79:67–91. doi: 10.1146/annurev-physiol-021014-071635

Figure 3.

Figure 3

The thymic egress strategy and microenvironmental distribution of S1P. Newly matured thymocytes exit thymic parenchyma into perivascular spaces. Double basement membrane, one located in ECs and the other in epithelial cells, forms the unique space. After migrating to the perivascular spaces, thymocytes exit into the blood by sensing the sharp S1P gradient at the thymic-vascular interface. Pericytes are proposed to provide S1P in the perivascular space to support the recruitment of thymocytes. The pericytic S1P transporter is not yet determined. ECs might also contribute to S1P distribution at the perivascular space by secreting S1P to the abluminal side of thymic vasculature. Conversely, LPP3 localizes toward the basolateral side of ECs and finely tunes S1P levels at the thymus-blood interface. LPP3 is also expressed in epithelial cells, which would highlight the perivascular S1P compartmentalization or gradients. Abbreviations: EC, endothelial cell; LPP3, lipid phosphate phosphatase 3; S1P, sphingosine 1-phosphate; SPNS2, spinster homolog 2.