| Intercellular adhesion plays a pivotal role in numerous diverse biological processes that occur within the vasculature, ranging from inflammation to cancer metastasis. These cell-cell interactions must be highly specific in nature for proper regulation of the various physiological events. While the involvement of the adhesion molecule E-selectin on endothelial cells in these patho-physiological phenomena has been demonstrated, the kinetics and molecular constituents that govern these adhesive interactions under shear, as well as the influence of vascular cells such as platelets and red blood cells on these phenomena, remain to be fully characterized. Therefore, this study was undertaken to elucidate the mechanisms that mediate both leukocyte and tumor cell adhesion to endothelium under simulated physiological flow conditions.; This work provides functional evidence that glycosphingolipids constitute ligands for E-selectin but not P-selectin. Chinese hamster ovary (CHO) cells expressing E-selectin (CHO-E) or P-selectin (CHO-P) were perfused in a parallel plate flow chamber over α2,3-sialyl Lewis X (α2,3-sLex ) presented as the hexaosylceramide glycosphingolipid, as a model of neutrophil membrane glycolipid, adsorbed in a monolayer containing phosphatidylcholine and cholesterol. As monitored in real time by phase contrast microscopy, CHO-E cells tethered extensively and formed stronger adhesive interactions with α2,3-sLe x glycosphingolipid compared to CHO-P cells. Using a similar flow chamber/phase contrast microscopy technique, it was shown that tumor cell glycolipids on LS174T colon adenocarcinoma cells also participate in tumor cell adhesion to E-selectin on endothelial cells. Sialylated glycoproteins and a non-sialylated ligand also mediate E-selectin adhesion. The addition of platelets to the LS174T cell perfusions induced platelet-mediated secondary tumor cell tethering to endothelium, and the addition of red blood cells to the perfusions failed to eliminate secondary tethering.; To further characterize the binding of LS174T cells and THP-1 cells with platelets, cell suspensions were subjected to a uniform shear field using a cone-and-plate rheometer. The results indicate that hydrodynamic shear-induced collisions augment platelet-LS174T cell binding. It was also found that exogenous plasma proteins such as fibrinogen and von Willebrand factor may exert an inhibitory effect on adhesion under the appropriate conditions.; Collectively, these findings may provide insights for the rational development of novel therapeutics to effectively combat cellular processes such as inflammation and cancer metastasis. |
