Pathway of leukocyte transendothelial migration across an in vitro human blood brain barrier model

Abstract

Leukocyte transendothelial migration (TEM) can occur at endothelial junctions (paracellular) or directly through the endothelial cell body (transcellular). Both pathways involve similar molecules but the factors governing the migratory pathway choice are unknown. Transcellular TEM may preferentially occur in vasculature where the junctions are complex and tight, such as the blood brain barrier (BBB). Therefore, to study the pathway of TEM at the BBB in vitro, we constructed a human BBB model by culturing human umbilical vein endothelial cells in astrocyte conditioned media supplemented with cAMP modulators. Our model exhibits >;5 fold greater barrier function as measured by transendothelial electrical resistance and permeability to FITC‐Dextran. We investigated the pathway of TEM using 3D confocal imaging of fixed immunostained cells. Despite enhanced barrier function, paracellular TEM predominated to the same extent as under standard conditions. Interestingly, directly activating the leukocytes with apical TNF or MCP‐1 (CCL2) increased the proportion of transcellular TEM equally under both standard and tight junction conditions. Thus, the route of TEM is not altered by the tightness of endothelial junctions under these conditions, but can be influenced by the activation state of the leukocytes. This research was supported by T32 Al07476 to RCW and RO1 HL046849 and R37 HL064774 to WAM.