Sequential contribution of L- and P-selectin to leukocyte rolling in vivo.

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Abstract
Leukocyte recruitment into inflammatory sites is initiated by a reversible transient adhesive contact with the endothelium called leukocyte rolling, which is thought to be mediated by the selectin family of adhesion molecules. Selectin-mediated rolling precedes inflammatory cell emigration, which is significantly impaired in both P- and L-selectin gene-deficient mice. We report here that approximately 13% of all leukocytes passing venules of the cremaster muscle of wild-type mice roll along the endothelium at < 20 min after surgical dissection. Rolling leukocyte flux fraction reaches a maximum of 28% at 40-60 min and returns to 13% at 80-120 min. In P-selectin-deficient mice, rolling is absent initially and reaches 5% at 80-120 min. Rolling flux fraction in L-selectin-deficient mice is similar to wild type initially and declines to 5% at 80-120 min. In both wild-type and L-selectin-deficient mice, initial leukocyte rolling (0-60 min) is completely blocked by the P-selectin monoclonal antibody (mAb) RB40.34, but unaffected by L-selectin mAb MEL-14. Conversely, rolling at later time points (60-120 min) is inhibited by mAb MEL-14 but not by mAb RB40.34. After treatment with tumor necrosis factor (TNF)-alpha for 2 h, approximately 24% of all passing leukocytes roll in cremaster venules of wild-type and P-selectin gene-deficient mice. Rolling in TNF-alpha-treated mice is unaffected by P-selectin mAb or E-selectin mAb 10E9.6. By contrast, rolling in TNF-alpha-treated P-selectin-deficient mice is completely blocked by L-selectin mAb. These data show that P-selectin is important during the initial induction of leukocyte rolling after tissue trauma. At later time points and in TNF-alpha-treated preparations, rolling is largely L-selectin dependent. Under the conditions tested, we are unable to find evidence for involvement of E-selectin in leukocyte rolling in mice.