Relevance of L-selectin shedding for leukocyte rolling in vivo

The velocity of rolling leukocytes is thought to be determined by the expre ssion of adhesion molecules and the prevailing wall shear stress. Here, we investigate whether rapid cleavage of L-selectin may be an additional physi ologic regulatory parameter of leukocyte rolling. A unique protease in the membrane of leukocytes cleaves L-selectin after activation, resulting in L- selectin shedding. The hydroxamic acid-based metalloprotease inhibitor KD-I X-73-4 completely prevented L-selectin shedding in vitro and significantly decreased the rolling velocity of leukocytes in untreated wild-type C57BL/6 mice from 55 to 35 mu m/s in vivo. When E-selectin was expressed on the en dothelium (tumor necrosis factor [TNF]-alpha treatment 2.5-3 h before the e xperiment), Polling velocity was 4 mu m/s and did not change after the appl ication of KD-IX-73-4. However, KD-IX-73-4 decreased mean rolling velocity by 29% from 23 to 16 mu m/s in E-selectin-deficient mice treated with TNF-a lpha. The reduction of velocity caused by KD-IX-73-4 was immediate (<5 s) a fter injection of KD-IX-73-4 as shown by a novel method using a local cathe ter. These results establish a role for L-selectin shedding in regulating l eukocyte rolling velocity in vivo.