Mice deficient in S1P₁ have an impaired response to AMD3100-induced HPC mobilization. (A) PCR amplification of exon 2 and GAPDH from DNA isolated from the blood of poly I:poly C–treated S1P₁^fl/fl or Mx1Cre.S1P₁^fl/fl (S1P₁^−/−) mice. (B) RT-PCR amplification of S1P₁ and GAPDH mRNA isolated from the blood of poly I:poly C–treated S1P₁^fl/fl or Mx1Cre.S1P₁^fl/fl (S1P₁^−/−) mice. (C) H&E-stained sections of spleens isolated from S1P₁^fl/fl and S1P₁^−/− mice. Representative fields of view obtained using SPOT Version 4.6 software and a SPOT RTKE camera attached to an Olympus BX40 microscope with a PlanApo 2×/0.08 lens are shown. Original magnification was 20×. (D-E) S1P₁^−/− or S1P₁^fl/fl mice received AMD3100 or placebo. WBC counts (D) were performed on blood collected by cardiac puncture. CFUs (E) were enumerated using semisolid cultures, and the number of CFUs/mL was calculated using total WBCs. Each dot represents data from a single animal and the bar indicates the mean for the cohort. *P < .05 compared with controls in S1P₁^fl/fl mice; #P < .05 compared with AMD3100 in S1P₁^fl/fl mice. Pooled data collected as mice became available are shown.