S1pr1 is a downstream effector molecule of KLF2 for PC egress. (A) PCA of bulk RNA-seq data from B1–8^hi integrin β7^hi or integrin β7^lo SPL PCs, or tamoxifen-treated B1–8^hi R26-creERT2 Klf2^+/+, or Klf2^fl/fl SPL PCs (n = 3). (B) Heatmap illustrating relative RNA expression of Itgb7, Itgam, Sell, Klf2, S1pr1, and Mki67 in the SPL PC populations indicated in A. (C) Representative FCM histograms showing surface S1pr1 expression (left) or its geometric mean fluorescence intensity (gMFI) (right) in SPL PC populations. n = 5 for Klf2^+/+ and n = 6 for Klf2^fl/fl. (D) Experimental design of adoptive co-transfer of B1–8^hi R26-creERT2 S1pr1^+/+ and S1pr1^fl/+ B cells. (E) Representative FCM histograms showing surface S1pr1 expression (left) or its gMFI (right) in SPL R26-creERT2 S1pr1^+/+ or S1pr1^fl/+ PCs after tamoxifen treatment (n = 4). (F) Representative FCM plots showing S1pr1^+/+ (CD45.1/1) or S1pr1^fl/+ (CD45.1/2) PCs (left), or the frequency of S1pr1^fl/+ PCs (right), in CD45.1⁺ SPL, blood, or BM PCs (n = 4). (G) Schematic illustration of the experimental protocol to induce Klf2 deletion and Klf2 or S1pr1 expression by FLEX-RV in adoptively transferred B1–8^hi R26-creERT2 Klf2^fl/fl B cells. (H) Representative FCM plots showing FLEX-RV-Klf2 or S1pr1-expressing PCs (CD45.1⁺ GFP⁺) in SPL, blood, or BM (left), or relative frequency of FLEX-RV–expressing PCs in blood or BM compared with SPL (right). n = 4 for Klf2^+/+ empty and Klf2^fl/fl S1pr1, n = 3 for Klf2^fl/fl empty and Klf2^fl/fl Klf2. Data in C, E, F, and H are representative of two independent experiments (n = 3 or 4 for C and n = 3 for E, F, and H, in the second experiment). Data were analyzed by two-tailed unpaired Student’s t test (C, left, E, and F), two-tailed paired Student’s t test (C, right), or one-way ANOVA followed by Tukey’s multiple comparisons test (F). *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001. PCs, plasma cells; SPL, spleen; BM, bone marrow.