NIK-mediated signaling in non-B cells controls S1P-mediated peritoneal B-cell emigration of peritoneal B cells, but not their immigration. (A,B) Peritoneal B cells were isolated from WT mice, labeled with CFSE, and adoptively transferred via the intraperitoneal (i.p.) (A) or intravenous (i.v.) (B) routes into SCID mice. (C,D) Similarly, CFSE-labeled peritoneal WT B cells were transferred into aly mice from which peritoneal cells were removed 8 hours before transfer. The reconstituted mice were treated simultaneously with (right panels) or without (left panels) FTY720. After 12 hours, cells were isolated from the peritoneal cavity for the analysis of CFSE⁺ B220⁺ cells. Flow cytometric data are representative of 3 independent experiments and are presented as means plus or minus SEM (n = 3).