FDCs cooperate with S1pr2 to promote Gα13-dependent confinement of mLN GC B cells. (A–F) CD21-DTR or control mice were reconstituted with BCL2-tg (A and B), S1pr2^−/− (C and D), or Gna13 KO (f/f mb1-cre; E and F) BM. Chimeras were treated with 100 ng DTx i.p., and 16–20 h later the frequency of GC B cells in mLNs and lymph was analyzed by FACS (A, C, and E) or mLNs were analyzed immunohistochemically (B, D, and F) for the presence of GC B cells (GL7, top) or FDCs (CD35, bottom). Bars, 100 µm. The GC dispersal index was calculated within individual follicles by analyzing the area of the follicle with intermixing of GL7 and IgD stains (see Materials and methods and Fig. S1). A, C, and E are pooled data from two, four, and two independent experiments, respectively, with two to four mice per group in each experiment. Images in B, D, and F are representative of two, three, and two mice of each type, respectively. In dot plots in A, C, and E, dots indicate individual mice and lines indicate means. In dot plots in B, D, and F, dots indicate the GC dispersal index within an individual follicle and lines indicate means. **, P < 0.01, unpaired two-tailed Student’s t test.