Role of S1P₁ in T- and B-cell trafficking to SLOs. (A-B) Thymocytes from S1P₁^+/ or S1P₁^–/– FL chimeras were differentially labeled with TRITC or CFSE, mixed, and adoptively transferred into WT mice (n = 6 mice/time-point). After 2.5 hours (A) or 20 hours (B), PBL, SLOs, and BM were harvested and single-cell suspensions were stained for CD4 and CD8α and analyzed by FACS for the presence of TRITC⁺ and CFSE⁺ SP T cells. (C-D) Differentially labeled splenocytes from S1P₁^+/ and S1P₁^–/– FL chimeras were adoptively transferred into WT mice (n = 4 mice/time-point).After 2.5 hours (C) and 20 hours (D), PBL, single-cell suspensions from SLOs, and BM were stained for B220 and analyzed by FACS for the presence of TRITC⁺ and CFSE⁺ B cells. Data are shown as total number of homed cells per million injected. Error bars indicate SEM. *P < .05; **P < .01.