Chemotaxis of granulocytes across bovine pulmonary artery intimal explants without endothelial cell injury

Emigration of granulocytes from vessel lumen to a site of injury is a hallmark of acute inflammation but whether this migration is necessarily associated with vascular damage is not clear. To follow the structural changes associated with granulocyte migration across an intact endothelial cell layer and to assess changes in vascular permeability, an in vitro technique was developed in which intimal explants were stripped from bovine pulmonary artery and mounted in chemotaxis chambers. All explants studied had granulocytes and trace amounts of 3H-water, 14C-sucrose and 125I-albumin in the upper well of the chambers. Experimental explants had zymosan-activated plasma in the lower well and control explants had either serum in the lower well or zymosan-activated plasma in the upper well. Explants were incubated at 37 degrees C for periods from 15 min to 3 hr. When the chemoattractant was added to the lower well, granulocytes migrated into the explants. Transmission and scanning electron microscopy showed an orderly sequence of granulocyte--endothelial interactions throughout which the two cell types maintained close opposition--granulocyte adherence to and exploration of the endothelial surface; penetration and migration through the interendothelial cell junction; reapposition and reformation of the luminal 'tight' junctions and finally passage of granulocytes through the endothelial basal lamina. After 60 min incubation, the majority of granulocytes seen in each section was through the endothelial cell layer and after 2 hr, they were through the basal lamina. Structural evidence of granulocyte or endothelial cell damage was not found at any of the times examined, neither was there any demonstrable increase in intimal permeability. In control explants, granulocyte migration was strikingly less frequent at 2 hr (approximately 10% of that seen towards the chemoattractant). Thus, granulocyte migration across an endothelial cell layer towards a chemoattractant is not necessarily associated with structural evidence of endothelial cell injury or increased vascular permeability.