Equal expression of S1P1 by peritoneal B1 and B2 B cells. (A) Quantitative RT-PCR analysis for S1P receptors was performed using RNA isolated from sorted splenic B (□), peritoneal B1 (▨), and B2 (▪) B cells. The relative quantity of specific mRNA was expressed as a ratio to GAPDH. The data are expressed as mean ± SD from 4 mice. (B) S1P1 expression in B1a and B1b cells was determined by quantitative RT-PCR analysis. (C) Flow cytometric analysis was performed to characterize B1a, B1b, and B2 B cells in the PerC of mice treated with FTY720. The data are representative of 3 independent experiments.