Occlusion of saphenous vein grafts is a major problem after coronary a
rtery bypass grafting. Segments of occluded and suboccluded implanted
aortocoronary grafts were obtained during re-intervention bypass graft
ing in 47 patients yielding a total of 80 vein grafts. The grafts were
studied by immunohistochemistry for smooth muscle cells (alpha-SMC ac
tin), macrophages (HAM56), cell replication (PCNA, Ki-67) and transmis
sion and scanning electronmicroscopy (TEM, SEM). In 81% of the examine
d grafts the (sub)occlusion was due to a myo-intimal thickening and an
associated luminal accumulation of foam cells and mural thrombi. The
foam cells were constantly found at the luminal site of the myo-intima
l thickening and within the luminal part of adherent thrombi. Transmis
sion electronmicroscopy demonstrated phagocytosis of platelets and pla
telet fragments by the foam cells. A significant fraction of the foam
cells demonstrated nuclear immunoreactivity for Ki-67 and PCNA. The my
o-intimal thickening of the vein grafts was composed of smooth muscle
cells lying in a fibrous tissue matrix. The smooth muscle cells were s
urrounded by prominent basal lamina and showed ultrastructural feature
s of apoptosis. Our results support the hypothesis that phagocytosis o
f lipid rich platelets by monocytes set up a mechanism for foam cell f
ormation and replication in human saphenous vein grafts. The transform
ation of a smooth muscle cell rich myo-intimal thickening towards a fi
brous, cell poor intimal thickening could be induced by progressive sm
ooth muscle cell loss through apoptosis.