No detectable endothelial‐ or leukocyte‐derived L‐selectin ligand activity on the endothelium in inflamed cremaster muscle venules

L‐selectin is important in mediating leukocyte recruitment in inflammation. The role of L‐selectin was for long believed to be influenced by an inducible endothelial ligand; however, L‐selectin ligand activity was recently shown to be mediated by leukocytic P‐selectin glycoprotein ligand 1 (PSGL‐1). Still, it is unknown whether PSGL‐1 is deposited on the endothelium or whether leukocyte fragments or leukocytic uropods are presented on the venular surface. Moreover, it is unclear whether ligands for L‐selectin other than PSGL‐1 are present in inflammation. Overall, this has complicated understanding of the mechanisms that guide recruitment of inflammatory cells. Here, I used intravital microscopy on mouse cremaster muscle venules to show that L‐selectin influences leukocyte rolling in inflammation exclusively by mediating L‐selectin/PSGL‐1‐dependent, secondary capture to rolling and adherent leukocytes. I show that leukocyte primary capture in inflammation is mediated almost entirely by P‐selectin, whereas the capacity of E‐selectin to mediate capture appears to be minimal. In parallel, primary capture remaining after function inhibition of P‐selectin is not decreased by blockage or absence of L‐selectin. Rolling along the endothelium in venules following a number of inflammatory treatments was abolished by simultaneous blockage of P‐selectin, E‐selectin, and VCAM‐1, indicating that there is no additional adhesive pathway involving L‐selectin or any other molecule that can mediate leukocyte rolling in inflamed cremaster muscle venules in response to the used stimuli. Moreover, in vivo staining failed to detect any L‐selectin ligand activity on the endothelium. These data demonstrate that expression of L‐selectin on leukocytes is insufficient for mediating rolling and efficient recruitment of leukocytes in inflammation.