Cytokine-induced increases in endothelial permeability occur after adhesion molecule expression

Transmigration of neutrophils (PMNs) through endothelial cell tight junctions is a critical stage in the tissue injury of ischemia-reperfusion (I/R). Although cytokines are released in I/R, it is unclear whether cytokines directly increase permeability or this phenomenon requires both expression of cell adhesion molecules and PMN adhesion-activation.

We exposed confluent monolayers of human umbilical vein endothelial cells to physiologic concentrations of interleukin-1 (10 pg/ml) and tumor necrosis factor-alpha (10 pg/ml) in the absence of PMNs. Tight junction permeability was quantified with both transendothelial electrical resistance and albumin flux, whereas expression of endothelial-leukocyte adhesion molecule-1 was measured by flow cytometry (t test p < 0.05).

Stimulation with tumor necrosis factor-alpha or interleukin-1 produced maximal transendothelial electrical resistance decreases at 12 hours with return to baseline at 24 hours. Increases in albumin flux began at 6 hours, with maximum effects at 24 hours. These changes occurred soon after maximal expression of endothelial-leukocyte adhesion molecule-1 at 4 hours.

Cytokines induced increases in both cell adhesion molecule expression and endothelial permeability. This sequence of events is consistent with direct cytokine effects on cytoarchitecture, because it occurred without the adhesion-activation of PMNs.