E-selectin–mediated leukocyte rolling. A total of 2 × 10⁶/mL WT and variant HL-60s were perfused over monolayers containing either E-selectin–expressing L/E cells (A,D) or IL-1β–stimulated HUVECs (B,E) at 1 dyne/cm². WT and ST3Gal-4^−/− mouse neutrophils were also perfused over L/E cells (C,F). Top panels present rolling and adherent cell density data 2 minutes after start of perfusion. Bottom panels present rolling velocity in the form of cumulative histogram plots. Median rolling velocity is indicated by straight line at 50% in the lower panels. Number in parentheses present “(number of independent experiments/total number of cells analyzed).” Rolling velocity was not measured when <5 cells rolled in a given run. † and ‡ denote statistically significance differences (P < .05) for rolling and adherent cell density, respectively. Here, † and ‡ are different with respect to all other treatments, except that treatments marked by † and ‡ in a given panel are not different from each other. HAE-1f, KPL-1, and 2PH1 are blocking mAbs against human E-selectin, human PSGL-1, and murine PSGL-1, respectively. Elimination of ST3Gal-4 activity has a more drastic effect on human, rather than murine, leukocyte rolling on E-selectin.