S1P1 blockade limits blood lymphocyte access to the LN parenchyma. WT mice were either treated or not with FTY-720 (36 hours) or SEW-2871 (8 hours) and injected intravenously with 10 millions of CMTMR labeled lymphocytes (red). (A) One hour later, LNs were harvested, sectioned in multiple slices, stained for PNAd (green) and Sytox63/nuclei (blue) and analyzed by confocal microscopy. The position of each individual cell is highlighted with a red dot. Arrowheads indicate HEVs in which transferred cells accumulate. (B) For each LN, densities of transferred cells inside and outside PNAd⁺ HEVs were calculated and presented as a ratio. Each symbol represents the averaged ratio calculated from all the imaged slices of a given LN. Data are representative of 3 different experiments (2 or 3 mice per experiment, minimum of 3 LNs per mouse).