VEROTOXIN-1 PROMOTES LEUKOCYTE ADHESION TO CULTURED ENDOTHELIAL-CELLSUNDER PHYSIOLOGICAL FLOW CONDITIONS

Hemolytic uremic syndrome (HUS), which is the most common cause of acu te renal failure in infants and small children, is caused by verotoxin (VT)-producing Escherichia coli infection. Endothelial injury determi nes microvascular thrombosis and evidence is available from recent stu dies that suggests that leukocyte activation participates in endotheli al damage. We studied here the effect of VT-1 on leukocyte adhesion to vascular endothelium under physiologic flow conditions. Human umbilic al vein endothelial cells (HUVECs) were incubated for 24 hours with VT -1 (0.1, 1, and 10 pmol/L) and then exposed to a total leukocyte suspe nsion in a parallel plate flow chamber under laminar flow conditions ( 1.5 dynes/cm(2)). Adherent cells were counted by digital image process ing. Results showed that VT-1 dose-dependently increased the number of adhering leukocytes to HUVECs as compared with unstimulated cells. Th e adhesive response elicited by VT-1 was comparable to that of interle ukin-1 beta (IL-1 beta), one of the most potent inducers of endothelia l cell adhesiveness. Exposure of HUVECs to VT-1 did not affect the num ber of rolling leukocytes, which was similar to that of control values . To examine the role of adhesion molecules in VT-1-induced leukocyte adhesion, HUVECs were incubated with mouse monoclonal antibodies again st E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascula r cell adhesion molecule-1 (VCAM-1) before adhesion assay. Functional blocking of E-selectin, ICAM-1, and VCAM-1 on endothelial cells signif icantly inhibited VT-1-induced increase in leukocyte adhesion. In some experiments, before VT-1 incubation, HUVECs were pretreated for 24 ho urs with tumor necrosis factor alpha (TNF alpha: 100 U/mL), which is k nown to increase VT receptor expression on HUVECs. The number of adher ing leukocytes on HUVECs exposed to TNF alpha and VT-1 significantly i ncreased as compared with HUVECs incubated with VT-1 and TNF alpha alo ne. These results suggest that VT-1 modulates leukocyte-endothelium in teraction. thus increasing leukocyte adhesion and upregulating adhesiv e proteins on endothelial surface membrane. (C) 1995 by The American S ociety of Hematology.