| Abstract: | Granulocyte recruitment during the acute inflammatory response is initiated by their rolling along the endothelial lining of postcapillary venules. To determine whether expression of L-selectin alone is sufficient for rolling, the murine pre-B lymphocytic cell line 300.19, which does not bind E- or P-selectin, was transfected with human L-selectin cDNA, which led to stable L-selectin expression at a level similar to that of blood lymphocytes. Fluorescent-labeled cells were infused retrogradely into a side branch of the superior mesenteric artery of anesthetized rats. In venules of the mesenteric membrane, leukocyte rolling occurs without intentional stimulation. On average, 17% +/- 6% of L-selectin transfectants rolled in the observed venules, while mock-transfected cells did not roll. Rolling of L-selectin transfectants began approximately 20 minutes after surgery and continued for at least 120 minutes. In contrast, HL-60 promyelocytes, which express sialyl-Lewis(x) tetrasaccharide (sLe(x)) but not L- selectin and that bind to E- and P-selectin in vitro, did not roll between 20 and 120 minutes, but some HL-60 cells rolled at very early (< 20 minutes) and late (> 2 hours) time points. Pretreatment with either of two function-blocking monoclonal antibodies recognizing the lectin domain of L-selectin completely blocked rolling of L-selectin transfectants and sharply reduced (by 70%) rolling of isolated human granulocytes. Taken together, these results show that L-selectin can mediate leukocyte rolling by virtue of its lectin activity. |
