FDCs and S1PR2 cooperate to promote GC B cell clustering. (A) Distribution of B cells transduced with control (hCD4-vector) or S1PR2 encoding (S1pr2-hCD4) retroviral constructs 1 d after transfer to control (Ctrl)- or DTx-treated CD21-DTR chimera recipients. Splenic sections were stained to detect the transferred B cells (hCD4; brown) and endogenous B cells (B220; blue). Data are representative of three mice of each type analyzed in two experiments. (B and C) GC B cell location in mLNs of ROSA^DTR+CD21Cre⁺ mice reconstituted with S1pr2^−/− BM, immunized 8 d before with SRBC and control or DTx treated 2 d before analysis. (B) Flow cytometric analysis and numbers of GC B cells (IgD^lowFas⁺GL7⁺) in mLNs. Statistical analysis was performed with the two-tailed unpaired Student’s t test. n.s., not significant. (C) Sections of mLN stained for GL7 (blue) and IgD (brown). Bars: (A) 200 µm; (C, left) 400 µm; (C, right) 100 µm.