Pivotal roles of lymphatic endothelial cell layers in the permeability to hydrophilic substances through collecting lymph vessel walls: effects of inflammatory cytokines.

To address physiological and pathophysiological meanings of condensing effect of albumin in lymph through collecting lymph vessel walls, we established human lymphatic endothelial cells (LEC) and evaluated the size-dependent regulation of the permeability of such layers to hydrophilic substances. We also investigated the effects of tumor necrosis factor (TNF)-α or interleukin (IL)-1β on the permeability and on the morphology of human LEC. Significant amounts of 4 kDa dextran, but not 12 or 66 kDa dextran, passed through the layers. TNF-α or IL-1β induced significant increases in the permeability to 4 and 12 kDa dextrans. TNF-α or IL-1β also produced significant redistribution of the cytoskeletal F-actin in the LEC, which resulted in changes in their shape. Pretreatment with Y-27632, a Rho kinase inhibitor, or PD98059, an extracellular signal-regulated kinase (ERK) phosphorylation inhibitor, significantly abolished the TNF-α- or IL-1β-induced increases in the permeability of the layers to 4 and 12 kDa dextrans. Y-27632 and PD98059 significantly inhibited the changes in the F-actin distribution of the LEC produced by TNF-α or IL-1β. TNF-α or IL-1β caused significant increases in ERK 1/2 phosphorylation in the LEC, which were significantly inhibited by Y-27632 or PD98059. These findings suggest that the human LEC layer plays key roles in the transport of hydrophilic substances through collecting lymph vessel walls and that TNF-α or IL-1β significantly increases the permeability of the layers to 4 and 12 kDa dextrans via Rho kinase activation and the ERK 1/2 phosphorylation-mediated reorganization of F-actin in the LEC.