NEUTROPHIL ROLLING ALTERED BY INHIBITION OF L-SELECTIN SHEDDING IN-VITRO

THE L-selectin adhesion molecule is involved in guiding leukocytes to sites of inflammation(1). L-selectin is cleaved by an unusual proteoly tic activity at a membrane-proximal site resulting in rapid shedding f rom the cell surface(2-7). Although it has been demonstrated that L-se lectin mediates, in part, the early event of leukocyte rolling under h ydrodynamic flows(8-10), the contribution of shedding to L-selectin fu nction has remained unknown. Here we show that hydroxamic acid-based m etalloprotease inhibitors block L-selectin downregulation from the cel l surface of stimulated neutrophils, without affecting Mac-1 mobilizat ion or general neutrophil activation, and inhibit cleavage of L-select in in a cell-free system. Unexpectedly, the hydroxamic acid-based inhi bitors reduced neutrophil rolling velocity under hydrodynamic flow, re sulting in increased neutrophil accumulation. These results suggest th at L-selectin is cleaved in seconds-much faster than previously suspec ted-during the process of rolling under hydrodynamic flow, and that sh edding of L-selectin may contribute significantly to the velocity of l eukocyte rolling, L-selectin shedding during rolling interactions may be physiologically important for limiting leukocyte aggregation and ac cumulation at sites of inflammation.