Transgenic mice have recently become an important model for the study of human atherosclerotic disease. This is an extremely important model, as cardiovascular disease is a leading cause of mortality in western society. Atherosclerosis involves occlusion of arteries by the formation of atherosclerotic plaques. Plaques are often composed of fibrin, platelets, endothelial cells, inflammatory cells, and smooth muscle cells. Occluded arteries are often opened via balloon angioplasty. Even after successful dilation, vessels can become reoccluded. Several mechanisms thought to be involved include thrombosis, smooth muscle proliferation, and extracellular matrix deposition. Thus, there are specific techniques used to assess this model. Histopathology is critical for examining the atherosclerotic plaques and the proposed mechanisms of their formation. Tissue preparation of vascular tissues includes sectioning the tissues longitudinally to assess intimal lesion development. Cross sections will enable wall thickness to be assessed. Special stains are employed to identify specific plaque components and to assess the integrity of the vessel walls. Routine histopath is performed with H&E staining. Van Gieson stains elastin fibers within the vessel wall. Oil red-O stains lipid and will allow one to visualize and measure the surface area of intimal lesions using a calibrated microscope.26 Gomori's stain is used to demonstrate muscle fibers, collagen, and nuclei in vessel walls. Individual cell types are often identified on H&E. Immunostaining can be used to detect specific cell types within the intima and specific cell types that comprise atherosclerotic plaques. The proliferation of smooth muscle cells and the resulting intimal thickening is a major component in the pathogenesis of atherosclerotic lesions and is thought to contribute to restenosis following balloon angioplasty. The proliferation of smooth muscle cells can be measured on H&E sections via autoradiography by counting labeled nuclei of cells. Cross-sectional areas of vessel intima can be obtained by tracing images on a digitizing pad and using special software to calculate the area.27

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