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Abstract

To date, much of the adhesion work in the liver has been restricted to sinusoids and postsinusoidal venules. However, selectins have been localized on the portal (presinusoidal) venules and these vessels have been shown to be important in metastasis of tumors. The purpose of this study was to characterize the leukocyte-endothelial interactions within the 3 compartments of the hepatic microvasculature under baseline conditions and in response to tumor necrosis factor α (TNF-α). Mice deficient in P-selectin or both E- and P-selectin were compared with wild-type (C57Bl/6, wild type) mice. Animals were injected with murine TNF-α (15 μg/kg intraperitoneally [IP]) and the liver was examined by fluorescence intravital microscopy 4 hours later. Under baseline conditions, leukocyte flux in the portal venules was 1.42 ± 0.42 cells/min. Leukocyte flux in the portal venules of wild-type mice increased 8-fold in response to 4 hours of TNF-α stimulation. This was reduced by 50% in the P-selectin–deficient mice but was not reduced further by either the addition of an E-selectin antibody (9A9, 100 μg intravenously [IV]) to these mice or in mice deficient in both E- and P-selectin. In P-selectin–deficient mice, the addition of an antibody against α4 -integrin (R1-2, 75 μg IP) reduced rolling to baseline. But in the E- and P-double-selectin–deficient mice the addition of an antibody against L-selectin (Mel 14, 3 μg/kg IV) had no effect on TNF-α–induced recruitment. Similar responses were seen in the central venules, however, in the sinusoids the increased number of stationary leukocytes seen in response to 4 hours of TNF-α stimulation in the wild-type mice was not reduced in P-selectin–deficient mice with or without the α4 -integrin antibody. These data suggest that leukocytes can use α4 -integrin independent of the selectins in the venules. Within the sinusoids, however, inhibition of E-selectin, P-selectin, and α4 -integrin was insufficient to reduce leukocyte recruitment.