MZ B cell migration into follicles requires GRK2-dependent S1PR1 desensitization. (A) Flow cytometric analysis of splenic MZ B cells from WT and GRK2f/− Mb1-cre (KO) mice for S1PR1, CXCR5 and CXCR4. (B) Transwell migration of WT and KO MZ B cells to S1P, CXCL12, CXCL13 and S1PR1 agonist SEW2871. Three replicates were run for each group. Bars indicate mean (±SEM). (C) Flow cytometric detection of 5 min in vivo anti-CD19-PE labeled MZ B cells from WT, GRK2f/− Mb1-cre (KO) or GRK2+/− (Het) mice shown as a histogram overlay (left panel) and a summary of data from 4 experiments (WT n=28, KO n=15, Het n=13 mice) (center panel). Right panel shows a summary of data from 3 experiments for WT and GRK2\f/− Mb1-cre (KO) cells present in mixed BM chimeras (n= 8). Bars indicate mean (±SEM). (D) Flow cytometric detection of 5 min in vivo anti-CD19-PE labeled MZ B cells from WT, GRK2+/− (GRK2 het), S1PR1+/− (S1PR1 het) and GRK2+/− S1PR1+/− (GRK2/S1PR1 het/het) mice shown as a histogram overlay (left panel) and a summary of data from 5 mice (right panel). Bars indicate mean (±SEM). (E) Immunohistochemical localization of CD1dhi MZ B cells (blue) with respect to the MAdCAM1+ marginal sinus (brown) in spleen sections from GRK2+/+ Mb1-cre (WT) and GRK2f/− Mb1-cre (KO) mice. MZ, marginal zone. FO, follicle.