Polarization of adherent leukocytes. In vivo imaging using high-speed high-resolution multichannel fluorescence intravital videomicroscopy of αLβ2 integrin (blue), PSGL-1 (red), and the granulocyte marker Gr-1 (green) expressed on the leukocyte surface in tumor necrosis factor-α (TNF-α) inflamed venules. The majority of leukocytes migrates laterally in inflamed venules. These migrating leukocytes exhibit marked clustering of PSGL-1 at the trailing edge. The large PSGL-1 cluster may contribute to leukocyte recruitment through leukocyte-leukocyte secondary tethers. In contrast, the expression of αLβ2 is relatively homogenous on the leukocyte surface. Reproduced with permission from Nature Publishing Group.⁹⁰