S1PR2 is important for Tfh cell retention in the GC. (A) Representative two-photon images of GCs. GFP+ S1pr2+/+ or GFP+ S1pr2V/V OT-II T cells (2 × 104 cells per head), S1pr2+/+ OT-II T cells (2 × 105 cells per head), and CFP+ Hy10 B cells (2 × 105 cells per head) were transferred to recipient mice. Explanted LNs were observed 7 or 8 d after s.c. immunization with HEL-OVA in alum. 1–3 d before imaging, 1.4–3.0 × 107 rhodamine-labeled polyclonal B cells were transferred for demarcation of the follicular regions. See also Videos 1 and 2. The images are 84 µm (left) and 96 µm (right) z-projections. Data are representative of two independent experiments with 8 (S1pr2+/+) and 5 (S1pr2V/V) recipient mice in total. (B) Cell tracking analysis of OT-II T cells that access the interface zone from the GC. GC surfaces were reconstructed from the CFP images in A. The tracks show migration paths of OT-II T cells that entered the interface zone from the GC and then left the interface zone to the GC (yellow) or FM (pink). The color brightness of the tracks is reduced on the parts submerged under the GC surfaces. The horizontal histogram shows the ratios of yellow tracks to pink tracks. Dots represent individual LNs used for the imaging analysis. 6–79 cells were tracked per LN. **, P < 0.01 (Student’s t test). (C) Cell tracking analysis data of OT-II T cells that access the interface zone from the FM. The tracks show migration paths of OT-II T cells that entered the interface zone from the FM and then left the interface zone to the FM (yellow) or GC (pink). The graph shows the ratios of yellow tracks to pink tracks. 12–98 cells were tracked per LN. Bars, 50 µm. Data are pooled from two independent experiments with 8 (S1pr2+/+) and 4 (S1pr2V/V) mice in total (B and C).
