KINETICS OF LEUKOCYTE-INDUCED CHANGES IN ENDOTHELIAL BARRIER FUNCTION

1 Extravasation of polymorphonuclear leukocytes (PMN) and associated p lasma leakage are key events in the inflammatory process. The kinetics of PMN-induced changes in endothelial barrier function were studied b y means of confluent monolayers of bovine aorta or human umbilical vei n endothelial cells (EC), cultured on permeable membranes and mounted in a two-compartment diffusion chamber. The model permitted continuous measurement of transendothelial electrical resistance (TEER), and ana lysis of protein efflux and PMN migration across the EC monolayer. 2 T ransendothelial chemotactic stimulation (fMLP or LTB4) of PMN resting on EC in the upper compartment induced a prompt decline in TEER, follo wed by an increase in protein flux and transmigration of PMN. Adding t he chemoattractant together with PMN in the upper compartment provoked adhesion of PMN, fall in TEER and increase in protein permeability, b ut no transmigration of PMN, whereas inhibition of PMN adhesion to EC by pretreatment with anti-CD18 mAb prevented all responses to chemotac tic stimulation. 3 Chemoattractant-induced adhesion of PMN to the EC m onalayer induced a rapid rise in EC cytosolic free Ca2+, similar to th at obtained by direct stimulation of EC with histamine, indicating an active response of EC to PMN activation and adhesion. 4 In summary, co ntinuous recording of transendothelial electrical resistance in the in vitro model described permits rapid and sensitive analysis of leukocy te activation-induced effects on EC barrier function. The kinetics and specificity of the EC and PMN responses to chemoattractant stimulatio n suggest that activated PMN, via adhesion-dependent events, have a di rect effect on EC junctional integrity independent of whether transmig ration occurs or not.