Fig. 2.

S1P and lymphocyte trafficking. Lymphocytes in circulation have their S1P₁ mostly internalized due to the high S1P concentration. Upon entrance in secondary lymphoid organs where the S1P concentration is low, they gradually recover the surface expression of S1P₁ and regain ability to egress from the lymphoid organs toward S1P in circulation. FTY720 is phosphorylated by sphingosine kinase 2 and induces the internalization and subsequent degradation of S1P₁ and thereby inhibits the lymphocyte egress. Reproduced from Obinata and Hla (75) with permission.