IMMUNOCYTOCHEMICAL DETERMINATION OF CELL-TYPE AND PROLIFERATION RATE IN HUMAN VEIN GRAFT STENOSES

Purpose: Vascular reconstructions ate prone to fail as a result of the development of stenotic lesions, which have historically been attribu ted to myointimal hyperplasia. In animal models, these lesions are ass ociated with marked proliferative smooth muscle cell (SMC) response to vascular injury. However, recent studies using sensitive immunocytoch emical techniques in human lesions have generally failed to detect sig nificant cellular proliferation. To clarify the role of cellular proli feration in humans, we characterized the cellular composition and prol iferative index of 14 early infrainguinal vein graft stenoses. Methods : All infrainguinal vein grafts at our institution are prospectively e nrolled in a duplex surveillance protocol, the details of which have b een previously reported. Among 98 grafts placed within the last year, 11 patients were identified with 14 progressive, focal, high-grade les ions that met previously established threshold criteria for prophylact ic revision to prevent graft thrombosis. Lesions were first detected f rom 1 week to 7 months after surgery and were removed and replaced wit h segmental interposition grafts (1.5 to 10 months). Freshly excised l esions were placed in Methyl Carnoy's fixative, paraffin embedded, and serially sebioned. The cellular composition of each lesion was determ ined with cell-specific immunochemical reagents: or SMC actin, von Wil lebrand factor (endothelial cell), CD 68 (macrophage), and CD 45RB (mo nocyte). Actively proliferating cells were identified using antibody t o proliferating cell nuclear antigen (PCNA). The identity of PCNA-posi tive cells was determined by double-label immunocytochemical staining, and the proliferative index (PCNA-positive cells/total cells x 100) w as calculated by computer-assisted counts of representative gridded cr oss-sections of each lesion. Results: All excised lesions demonstrated marked thickening with severe luminal encroachment and were highly ce llular, with a predominance of alpha SMC actin+. Endothelial cells on the blood flow surface were present to a variable degree, and seven le sions exhibited striking numbers of macrophages and monocytes. The lat ter cell types were most abundant near microvessels in the deep neoint ima and adventitia. Active cellular proliferation was identified prima rily in SMCs, with a mean PCNA index of 1.34%. However, significant PC NA reactivity was not limited to SMCs, but was also identified in macr ophages and monocytes, particularly in lesions greater than 3 months o ld. Conclusions: Previous immunocytochemical studies of human coronary restenosis atherectomy specimens have generally detected low rates of cellular proliferation (0.5%), but these lesions may not truly repres ent myointimal hyperplasia, rather a mixture of atherosclerosis, throm bosis, and ''restenosis.'' In contrast, the present study of early hum an vein graft lesions detected by duplex surveillance indicates that s ignificant cellular proliferation occurs, although rates are lower tha n those obtained in animals such as the rat carotid injury model. In a ddition, although SMCs are the predominant proliferating cell type in human vein grafts, our identification of proliferating monocytes and m acrophages raises the question of the contribution of an inflammatory component to the development of human lesions. The present study repre sents the first report of PCNA determination in a series of human infr ainguinal vein grafting procedures.