Both ICAM-1- and VCAM-1-Integrin Interactions Are Important in Mediating Monocyte Adhesion to Human Saphenous Vein

Abstract

Atherosclerosis underlies late occlusion of human saphenous vein (HSV) coronary artery bypass grafts. Monocyte infiltration is implicated, but its mechanisms are unclear given that HSV normally expresses the ICAM-1 but not the VCAM-1 adhesion molecule. To define the mechanisms underlying monocyte adhesion, samples of HSV taken from coronary artery bypass graft patients were co-cultured with human monocytes and adherent monocytes were quantified by immunocytochemistry for CD68 on transverse sections. Pre-treatment of veins with anti-ICAM-1 antibodies reduced monocyte adhesion (monocytes/mm of section) from 7.2 ± 1.5 to 3.1 ± 0.7 (p < 0.05, n = 6), but the effect of anti-VCAM-1 was not significant (4.1 ± 0.7). Paradoxically, pre-treatment of monocytes with either anti-β₂-integrins, the counter-receptor of ICAM-1, or anti-α₄ integrins, the counter-receptor of VCAM-1, significantly reduced adhesion (1.8 ± 0.6 and 2.4 ± 0.7, respectively, p < 0.05). These results were clarified by immunocytochemistry, which confirmed that VCAM-1 expression was absent in harvested vein but was induced in the endothelium during co-culture. Consistent with this, when anti-ICAM-1 or anti-VCAM-1 was present throughout co-culture, either of them reduced adhesion (from 4.2 ± 0.9 to 2.3 ± 0.5 and 2.2 ± 0.4, respectively, p < 0.02, n = 8) and there was no further effect of adding both (2.0 ± 0.5). These results demonstrate that both ICAM-1/β₂ and VCAM-1/α₄ integrin interactions mediate monocyte adhesion to HSV, possibly as part of a common pathway. These experiments imply that either integrin might be targeted to reduce monocyte infiltration into HSV grafts.