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Leukocyte-platelet aggregate adhesion and vascular permeability in intact microvessels: role of activated endothelial cells

Department of Physiology and Pharmacology, West Virginia University, Morgantown, West Virginia

Leukocyte-platelet aggregation and aggregate adhesion have been indicated as biomarkers of the severity of tissue injury during inflammation or ischemic reperfusion. The objective of this study is to investigate the mechanisms of the aggregate adhesion and quantitatively evaluate its relationship with microvessel permeability. A combined autologous blood perfusion with single microvessel perfusion technique was employed in rat mesenteric venular microvessels. The aggregate adhesion was induced by systemic application of TNF- plus local application of platelet-activating factor (PAF). Changes in permeability were determined by measurements of hydraulic conductivity (L_p) before and after aggregate adhesion in the same individually perfused microvessels. The compositions of the adherent aggregates were identified with fluorescent labeling and confocal imaging. In contrast to leukocyte adhesion as single cells resulting in no increase in microvessel permeability, aggregate adhesion induced prolonged increases in microvessel L_p (6.1 ± 0.9 times the control, n = 9) indicated by the initial L_p measurements after 3 h of blood perfusion, which is distinct from the transient L_p increase caused by PAF-induced endothelial activation in the absence of blood. Isoproteronol (Iso) attenuated aggregate adhesion-mediated L_p increases if applied after autologous blood perfusion and prevented the aggregate adhesion if the initial endothelial activation is inhibited by applying Iso before PAF administration but showed less effect on single leukocyte adhesion. This study demonstrated that leukocyte-platelet aggregate adhesion via a mechanism different from that of single leukocyte adhesion caused a prolonged increase in microvessel permeability. Our results also indicate that the initial activation of endothelial cells by PAF plays a crucial role in the initiation of leukocyte-platelet aggregate adhesion.

hydraulic conductivity; tumor necrosis factor-; platelet-activating factor

This article has been cited by other articles:

				Y. Jiang, K. Wen, X. Zhou, D. Schwegler-Berry, V. Castranova, and P. He Three-dimensional localization and quantification of PAF-induced gap formation in intact venular microvessels Am J Physiol Heart Circ Physiol, August 1, 2008; 295(2): H898 - H906. [Abstract] [Full Text] [PDF]