aly peritoneal B cells show a comparable dependence on S1P for intestinal IgA production. WT (A) or aly (B) peritoneal B cells (5 × 10⁶ cells) were adoptively transferred into SCID mice, which were treated with vehicle only (□) or FTY720 (■) every 2 days. Two weeks after cell transfer, fecal extracts were collected for measurement of IgA levels by ELISA. Data are presented as means plus or minus SEM (n = 4). *P < .01; **P < .05.