Adhesion Molecules Regulating Human Leukocyte Attachment to Porcine Vascular Endothelium

Abstract

463 Xenograft rejection may partly be mediated by infiltration of the porcine organ by the recipient's leukocytes. In humans and mice, leukocyte recruitment to sites of inflammation involves a cascade of interactions between adhesion molecules and their ligands. We have therefore studied the role of adhesion molecules in human leukocyte binding to TNF-a stimulated porcine aortic endothelial cell (PAEC) monolayers. Activation of PAEC enhances surface expression of E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and L-selectin ligand as demonstrated by staining with human L-selectin/murine IgM fusion protein. In both binding assays and hydrodynamic flow chamber assays, human neutrophils and lymphocytes adhered to activated PAEC. E-selectin and L-selectin primarily mediated neutrophil adhesion under shear conditions, while E-selectin and the ß2 integrins promoted firm arrest. Under flow conditions, combined blockade of E-selectin, L-selectin, P-selectin glycoprotein ligand-1 (a hematopoietic P-selectin ligand) and ß2 integrins dramatically reduced neutrophil attachment to PAEC. L-selectin primarily mediated lymphocyte attachment under shear conditions, whileß2 integrin and VCAM-1/VLA-4 interactions mediated static lymphocyte adhesion. Combined blockade of ß2 integrins, VLA-4 (aß1 integrin), VCAM-1, and L-selectin essentially inhibited all lymphocyte binding to PAEC. These results demonstrate that interactions between porcine adhesion molecules and their human counterreceptors remain remarkably intact across species. Further, disrupting successive steps of the adhesion cascade, namely leukocyte capture, rolling, and stable arrest, could diminish infiltration of a transplanted porcine organ by the human recipient's leukocytes, thereby attenuating xenograft rejection.