Experimental studies on vein graft atherosclerosis (I). Histochemical studies using monoclonal antibodies for smooth...

Vein graft atherosclerosis characterized by smooth muscle cell proliferation has become the most serious cause of late graft failure. This study was designed to elucidate why marked histological differences occur in atherosclerotic changes between the vein graft and the artery. Fourteen rabbits underwent autonomous transplantation of femoral vein sections (10-12 mm in length) into femoral arteries on the same side. They were then kept on either commercial or 1% cholesterol diet. At 4, 8, 15 and 30 weeks after the operation, they were sacrificed and histochemical & immunocytochemical studies on atherosclerotic changes found in graft and arteries were carried out, using monoclonal antibodies for macrophages (RAM 11) and smooth muscle cells (HHF 35). Atherosclerotic lesions found in arteries of rabbits fed by cholesterol for more than 8 weeks were characterized with the accumulation of macrophage-derived foamy cells with fibrous caps. In contrast, the lesions found in the grafts of the same rabbits were occupied with proliferating smooth muscle cells and very few macrophages. Furthermore, in lesions of the vein grafts of rabbits fed cholesterol for 4 weeks, macrophages were rather frequently encountered in the bottom of the lesions and/or its medial layer, scattering and sometimes forming mass-lesions. These results may suggest structural differences in the vein with its thin and sparse internal elastic lamina and with its thin medial layer, allowing macrophages to pass easily through the elastic lamina and scatter into the media. This may be the reason why autonomous vein graft atherosclerosis is mainly composed of proliferated smooth muscle cells.